How Does Radar Estimate Rainfall Verifying Tornado Warnings by tyndale


									N a t i o n a l W e a t h e r S e r v i c e Q u a d C i t i e s I A/ I L

                                                                                                            V ol. 3, Is s u e 2 , Fa ll 2006

INSIDE THIS ISSUE:              How Does Radar Estimate Rainfall?
                                Jeff Zogg
How Does Radar Es- 1
timate Rainfall?
                                The National Weather Service
                                (NWS) uses radar to detect the
                                location and intensity of various
Verifying Tornado          1    atmospheric phenomena includ-
Warnings                        ing thunderstorms, rain and
                                snow. You may have also no-
                                ticed that radar can also provide
Looking Ahead: El          3    rainfall estimates (i.e., amounts).
Niño and the Winter             How does radar do that? Con-
                                tinue reading to find out.
                                First, rainfall amounts are di-
Quad Cities Forecast 4          rectly related to rainfall rates.
Office Achieves Top             Specifically, the rainfall amount
                                is given by the average rainfall
Score for Upper Air             rate multiplied by duration over
                                which the rate was measured.
COOP Observations          5    For example, an average rainfall
                                rate of 0.50 inches over 3 hours
Needed                          would produce a rainfall amount
                                of 1.50 inches. The same con-
Reminders for Snow         5    cept is used with weather radar.       Recent example of storm total precipitation from our web-
Season                                                                 page (
                                Rainfall rate and drop size
New Climate Web            5
                                                                      in the air and (3) the average      Any change in the drop diameter
Services From NWS               The rainfall rate (R) is dependent
                                upon three things: (1) the drop       drop fall speed. The rainfall       will increase the rainfall rate by
Quad Cities                                                           rate is most sensitive to
                                diameter, (2) the number of drops
                                                                      changes in the drop diameter.       (continued on page 2)
Probability of a          7
White Christmas
                                Verifying Tornado Warnings
Winter Road Condi-        8     Steve Kuhl
tions References
                                Did you know that the National        occurred, the warning is consid-    fied to be correct. A FAR of
                                Weather Service issues tornado        ered a “hit” and is included in     zero is a perfect score, and a
                                warnings on a county basis and        what is called the Probability of   low FAR indicates that only a
                                keeps verification statistics for     Detection (POD) database. If a      few false alarm warnings were
Weather Home Compan-            these warnings? Whenever a            tornado warning is issued and a     issued.
ion is a semiannual publi-      NWS office, including your Quad       tornado does not occur, the
cation of the National          Cities Weather Forecast Office        warning is considered a “miss”
                                (WFO), issues a tornado warning,      and is included in a False Alarm    In addition to POD and FAR,
Weather Service office in                                                                                 warning lead times are also
                                employees work to identify            Rate (FAR) database. A POD
the Quad Cities. Contact                                                                                  tracked. The lead time for a
                                whether or not the tornado actu-      of 1 is a perfect score, and a
information can be found        ally occurred. If a tornado warn-     high POD means that most tor-
on page 8.                      ing is issued and verified to have    nado warnings issued were veri-     (continued on page 3)
Page 2                                                                                                            Volume 3, Issue 2

                             How Does Radar Estimate Rainfall?
                             (continued from page 1)

                                                                                                    underway to develop accurate Z-R
                                                                                                    values for other precipitation
                                                                                                    types such as snow.

 ...the radar does not
                                                                                                    Radar rainfall estimates
directly measure
(drop size, distribu-
                                                                                                    The NWS Doppler radar estimates
tion or fall speed)                                                                            the rainfall intensity each time it
measures the energy                                                                                 scans the sky. The radar then uses
returned from a pre-                                                                                the rainfall intensity-amount rela-
                                                                                                    tionship mentioned earlier to esti-
cipitation target...                                                                                mate the actual amount of rainfall
                                                                                                    that fell. Although the NWS Dop-
                                                                                                    pler radar provides 1- and 3-hour
                                                                                                    rainfall estimates by default, the
                             Example of a new NWS experimental precipitation analysis               radar operator can specify other
                             product that is based on radar data. It is available on the            durations as needed.
                             web at:
                                                                                                    Two common sources of error
                                                                                                    exist in rainfall estimates. One is
                             the third power, or cubed. For    sensitive to drop diameter. Any      when hail is present. Hail tends to
                             example, if the drop diameter     change in drop diameter will         reflect much higher amounts of
                             doubles, then the rainfall rate   increase the reflectivity by the     energy back to the radar, leading
                             will increase by a factor of 8.   sixth power. For example, if         to inflated Z and R values. In
                             That is, 23 = 8. Thus, you can    the drop size doubles, then the      addition, wet snow can also lead
                             see that changes in the drop      reflectivity will increase by a      to inflated Z and R values because
                             diameter will lead to much        factor of 64. That is, 26 = 64.      it also reflects higher than average
For More information         larger changes in the rainfall    Thus, you can see that reflectiv-    amounts of energy back to the
On the Web:                  rate.                             ity is very sensitive to changes     radar. The wet snow error is
                                                               in drop diameter.                    sometimes called the “bright
                                                                                                    band” error because it appears on
                             Target reflectivity and the                                            the radar screen as relatively
Radar equation and re-       radar equation                    Reflectivity-rainfall rela-
flectivity (NWS) --                                                                                 higher Z values, when compared
                                                               tionships                            to the surrounding lower Z values
                             Unfortunately, the radar does                                          associated with solely liquid pre-
courses/dloc/topic3/                                                                                cipitation.
                             not directly measure any of       Research has provided us with
                             the above three items. In-        equations that show the rela-
Section2.html                stead, it measures the energy     tionship between reflectivity        Conclusions
                             returned from a precipitation     (Z) and rainfall rate (R). These
Radar equation and re-       target. A precipitation target    equations are called Z-R rela-
                             can include a rain drop, snow-    tionships. Weather radar then        Even though the radar can provide
flectivity (American Mete-                                                                          us with rainfall estimates, real-
                             flake or hail stone. The NWS      uses these equations to estimate
orological Society) --       then uses the radar equation      R. Various Z-R relationships         time rainfall and weather observa-
http://                      which expresses the relation-     exist. Different relationships       tions that cooperative observers
amsglos-                     ship between the returned         are appropriate for different        and spotters give us are still ex-         energy and reflectivity of a      atmospheric conditions. For          tremely valuable. We use the
glossary/search?             precipitation target. Since all   example, some Z-R relation-          rainfall measurements to check
p=1&query=radar+equation     the terms of the radar equation   ships are better for non-tropical    the accuracy of the radar rainfall
                             except reflectivity are usually   showers and thunderstorms            estimates. If we notice that the
                             known, the reflectivity can be    while others are better for tropi-   rainfall estimates are too high or
                             determined.                       cal environments. The radar          too low then we can make adjust-
                                                               operator must make sure that         ments. Also, we can adjust the
                                                               the radar is using the appropri-     radar rainfall estimates in areas
                             Reflectivity (Z) depends on       ate Z-R relationship for the         where observers report hail. It is
                             two characteristics of liquid     given conditions. If the Z-R         important that we receive all of
                             precipitation: (1) the number     relationship is not appropriate      this information as quickly as
                             of drops and (2) the drop di-     then the rainfall estimates may      possible so that we improve our
                             ameter. Reflectivity is most      not be accurate. Research is         services.
Weather Home Companion                                                                                                            Page 3

Looking Ahead: El Niño and the Winter
Barbara Mayes
Despite the cold start to fall, the   Niño is forecast to persist through   the globe might seem far away,        ...The NWS is fore-
National Weather Service’s            the winter and into at least the      the effects of the warmer ocean       casting a better-
Climate Prediction Center is          early spring.                         are far-reaching. Weather pat-        than-usual chance
forecasting a better-than-usual                                             terns across most of the U.S.
chance for a mild winter this                                               change during an El Niño, bring-      for a mild winter
year across most of the Plains        What is El Niño?                      ing a higher-than-usual chance for    this year…
and upper Mississippi River                                                 the southeastern U.S. to stay cool
valley. The winter forecast is        The hallmark of El Niño is            and the northern and western U.S.
based on many factors, but one        warmer-than-normal sea surface        to stay warm through the winter.
major contributing factor is the      temperatures in the tropical Pa-
developing El Niño. The El            cific Ocean. While that part of       (continued on page 4)

Verifying Tornado Warnings
(continued from page 1)

tornado warning is considered         occurred in the 36 county service      As the Meteorologist in Charge of
to be the time between when           area in which WFO Quad Cities          WFO Quad Cities, I am ex-
the warning is issued and when        has warning responsibility. The        tremely proud of the warning
the tornado actually occurs in        actual verification statistics for     service our office provided to the
the warned location.                  WFO Quad Cities was a Probabil-        citizens of eastern Iowa, western,
                                      ity of Detection of 84% and a False    Illinois, and northeastern Mis-
                                      Alarm Rate of 59%. Both these          souri during the 2006 severe
The 2006 NWS Probability of           scores exceeded the national NWS       weather season. It is my sincere
Detection goal for tornado            goals set for the year. Addition-      pledge to you that we will remain
warnings across the nation was        ally, the 2006 NWS national aver-      vigilant and continue to safeguard
to be correct 76% of the time,        age tornado warning lead time goal     our public from the threat of se-
and the False Alarm Rate goal         was 13 minutes. WFO Quad Cities        vere weather in the years to come.
for these warnings was 75%.           tornado warning lead time was 21
During the 2006 severe weather        minutes, which exceeded the na-
season, 31 confirmed tornadoes        tional goal by 8 minutes.                                                   ...Both of these
                                                                                                                  scores (POD and
                                                                                                                  FAR for NWS Quad
                                                                                                                  Cities office) ex-
                                                                                                                  ceeded the national
                                                                                                                  NWS goals set for
                                                                                                                  the year...
Page 4                                                                                                       Volume 3, Issue 2

                         Looking Ahead: El Niño and the Winter
                         (continued from page 3)

                         Rainfall patterns also change,
                         mostly in the southern states
                         and along the West Coast. In
                         the Quad Cities forecast area,
                         El Niño winters do tend to be
                         warmer than normal, with no
                         clear trend in the amount of

                         What does the winter fore-
                         cast mean?

                         Climate predictions are made
Average Annual           in terms of chances of depart-
                         ing from average conditions.
Snowfall*                Climate forecasts can’t tell
                         what the day-to-day weather
                         will be, but they can use infor-
Dubuque:        42.8     mation based on ocean tem-           since El Niño does not tend to      Climate forecasts are available
Cedar Rapids:   28.8     peratures and global flow pat-       change the climatology of pre-      at the national scale
                         terns to determine parts of the      cipitation in the winter in the     ( and
Moline:         33.8     U.S. where changes from usual        area. The winter outlook is not     locally (
                         conditions may occur. In this        able to tell how snowy the
Burlington:     29.1                                                                              climate/calendar_outlook.php?
                         case, the winter outlook calls       winter might be, because snow-      wfo=dvn).
                         for a higher-than-average            fall depends not only on tem-
                         chance that temperatures will        perature and precipitation but
* Source: NCDC Cli-
                         be above normal this winter in       also development of storm           The Local 3-Month Tempera-
mate Normals 1971-       the Quad Cities forecast area.       systems, which cannot be fore-      ture Outlooks are a new way to
2000                     The precipitation outlook calls      cast months in advance.             look at how the climate fore-
                         for equal chances of being wet,                                          casts can affect temperatures at
                         near normal, or dry this winter,                                         individual points in the area.

                          Quad Cities Forecast Office Achieves
Average Winter Sea-
son Temperature*          Top Score for Upper Air
                          John Hasse
Dubuque:        20.9      The Quad Cities National            These weather parameters are        received is a “snapshot” of the
Cedar Rapids:   22.2      Weather Service Forecast Of-        sent to an office computer          atmospheric conditions, and used
                          fice, is one of nearly 100 of-      through a radio transmitter         in supercomputers for improving
Moline:         24.8      fices across the nation that        housed in the radiosonde pack-      forecasts and warnings. Because
Burlington:     26.3      launches weather balloons           age. Balloons are usually filled    this data is so important, your
                          every day throughout the year.      with hydrogen gas (the lightest     NWS personnel launch balloons
                          In fact, the balloons are re-       element), and typically will rise   in all types of weather (except
*Source: NCDC Climate     leased twice a day, at 6 am and     to a height of around 20 miles      during lightning, of course).
                          6 pm CDT or 5 am and 5 pm           before bursting. A parachute
Normals 1971-2000 for     CST. A radiosonde                   attached to the radiosonde
meteorological winter—    (instrument package) attached       brings the “train” safely back to   History
Dec, Jan and Feb.         to the balloon, records tempera-    earth. Only about 20% of the
                          ture, relative humidity, pres-      “sondes” are found and sent
                                                                                                  Upper air observations started as
                          sure, wind direction and wind       back to the National Recondi-
                                                                                                  early as 1749 in Europe with the
                          speed. When winds aloft are         tioning Center in Kansas City,
                          also retrieved, the radiosonde is   Missouri. There, they are re-
                          then known as a “rawinsonde”.       built and used again. The data      (continued on page 6)
Weather Home Companion                                                                                                          Page 5

                               COOP NEWS

 COOP Observations Needed
 Bill Elliott

 To our Cooperative Ob-              ways of radio, across the state.      these agencies receive data real
 servers around the Daven-                                                 time.
 port Weather Office area:
                                     Secondly, all of the data, precipi-
 We need your observa-               tation, snow measurements, and        We know you are taking the
 tions.                              temperatures you record are           observations during the early
                                     needed for maps that are sent to      morning hours each day, now
 Yes, we do get your monthly         the world several times a day.        we ask that you please call us
 forms, and we like how they         Each of the parameters listed, is     daily with your vital reports.      ...Our goal is to get
                                     accumulated for every reporting       We answer the phones 24/7 and
 look and that they are on time,
                                     site in the U.S. and maps gener-      look forward to hearing from
                                                                                                               every COOP Ob-
 but we need to hear from you
 every day. Our goal is to get       ated from your data are sent to       you any time between the hours      server to call us, or
 every COOP Observer to call         every radio and TV station            of 6 AM and 8 AM. If you            in some other way
                                     across the U.S. and around the        can’t call us during those
 us, or in some other way get
                                     world. What a great way to get        hours, we still need your report.
                                                                                                               get your observa-
 your observation to us in real
 time.                               the credit you deserve.               If you prefer not to call us at     tion to us in real
                                                                           our 800 number, we can ar-          time...
                                                                           range for you to report by com-
 There are several reasons we        Thirdly, the data you provide are     puter or a toll free phone num-
 would like to do this, and there    important inputs into computer        ber data collection system.
 are several reasons you might       models and products that are          Precipitation calls are needed
 want to help get your observa-      developed by several national         for both rain and snowfall
 tions to us on a real time basis.   agencies on a daily and monthly       amounts, from Illinois and
                                     basis. For example, the National      Iowa. If you have any ques-
                                     Drought Monitor and the North         tions, please call Mike Zenner,
 The first and most important        Central River Forecast Center         Terry Simmons, or Bill Elliott
 reason is an increased demand       count on real-time precipitation
 for real time data. Your report                                           at 563-386-3976.
                                     reports to develop flood guid-
 would make the daily state          ance for all of the rivers across
 summary of observations that        the Midwest, and to determine         We look forward to hearing
 goes out to the rest of the world   the onset and end of droughts,        from you!
 at 815 AM every day of the          identify precipitation patterns,
 year. Some of these summaries       and evaluate soil moisture. It is
 are read verbatim over the air-     of the utmost importance that

 Reminders for Snow Season
 Reports of snow fall and snow       important for snow measure-                inner measuring tube of
 depth are in great demand each      ments to be taken in a consistent          the eight-inch manual rain
 winter. The prime users of          manner.                                    gauge. This allows the
 snow measurements are                                                          frozen precipitation to fall
 schools, businesses, highway                                                   into the overflow can for
 and road departments, insur-        Each season before the first               more accurate water
 ance agents, actuaries, media,      snow, Cooperative observers                equivalent measurements
 meteorologists, hydrologists,       should review instructions for
                                     measuring snow and prepare            2.   Check the gauge to ensure
 climate researchers and many
 others. Because demand for          gages and snowboards.
                                                                           (continued on page 6)
 snow information is high, it is     1. Remove the funnel and
Page 6                                                                                                          Volume 3, Issue 2

                         Reminders for Snow Season
                         (Continued from page 5)

                                                              When reporting solid pre-
                              there are no leaks. Take
                              appropriate action if leaks     cipitation:
                              are found.                                                            More complete information and
                         3.   Put a snowboard(s) out and      1.   Measure and record snow-         specific instructions on how and
                              mark the location(s) with a          fall (snow, ice pellets) since   where to measure snowfall and
                              flag or some other indicator         the previous snowfall obser-     winter precipitation, as well as
                              so boards can be found after         vation.                          obtaining water equivalent, can
                              a new snow-                     2.   Determine the depth of           be found on the web at the NWS
 Snow stick meas-             fall. Snowboards should be                                            Cooperative Observer website:
                                                                   snow on the ground at the
 uring record snow-           located in open locations            normal observation time.
 fall in Davenport in         (not under trees, or near       3.   Measure and record the 
                              other obstructions).
 December 2000.                                                    water equivalent of snow-        snowguid.htm.
                                                                   fall since the previous day's

                         Quad Cities Forecast Office Achieves
                         Top Score for Upper Air
                         (continued from page 4)

                         use of a kite to carry aloft a                                              radiosondes were flown. And
                         thermometer. With the ad-                                                   in 1937, the U.S. Weather
                         vent of hot air and hydrogen                                                Bureau established a net-
                         balloons in the 1780’s, sci-                                                work of upper air stations,
                         entists actually ascended                                                   which the National Weather
                         aloft, taking with them                                                     Service continues to this day.
                         weather instruments. As you
                         might imagine, this proved
                         to be very dangerous work.
                         In the meantime, the use of                                                 NWS Quad Cities named
          Ranked #1      kites in observing the upper                                                the best upper air site in
         in the Nation   atmosphere continued, and                                                   the nation in August
                         by the end of the 1800’s, kite                                              2006
         August 2006     observation stations were
                         established in Europe and in
                                                                                                     To help improve data qual-
                         the United States. The kites
                                                                                                     ity, quantity, and availability,
                         carried aloft meteorological
                                                                                                     an equation is used to rank
                         instruments or
                                                                                                     upper air station perform-
                         “meteorographs” that re-
                                                                                                     ance at NWS offices across
                         corded relative humidity,
                                                                                                     the nation. In August 2006,
                         temperature and pressure on
                                                                                                     the NWS Quad Cities had
                         a clockwork driven chart
                         recorder. However, a major     Inflating weather balloon inside upper air the highest ranking upper air
                                                                                                     performance in the nation
...The upper air pro-    drawback to using kites was building at NWS Quad Cities.
                                                                                                     with a score of 299.89 out of
                         that they could only reach an
gram is one of many      altitude of a couple of miles.         not be analyzed until the plane      300! The upper air program
                                                                                                 is one of many in the office
in the office where                                             landed. The lack of kites and
                                                                                                 where we strive for excellence,
                                                                airplanes to achieve high alti-
we strive for excel-     The advent of airplanes carrying       tudes, operate in any weather    helping to bring better forecasts
lence...                 weather instruments from about         conditions, and provide real-    and warnings to the public, using
                         1925 to World War II, meant the        time data helped create the need a proven method that started
                         demise of kite observations. Yet,      for radio transmission of upper- more than 200 years ago.
                         airplanes could not be flown in        air data. In the early 1930’s,
                         bad weather and the data could         the first radio-meteorographs or
Weather Home Companion                                                                                                             Page 7

 New Climate Web Services from NWS
 Quad Cities                                                                                                    Example of Informa-
 Ray Wolf
                                                                                                                tion Available from
 Much has happened in the last two years with the     This new web page is the vehicle with which we
 distribution of climate information and Coop data.   share virtually all climate-related information.          Data/Records:
 Most notable is the addition of new climate prod-    Note the tabs on top of the graphic below, which
 ucts on the web:                                     are used to navigate from topic to topic. Highlights            from some of the tabs/topics are described below.         Probability of
                                                                                                                Snowdepth > 1 Inch
                                                                                                                on Chirstmas Day

                                                                                                               This graphic can be
                                                                                                               found under “local cli-
                                                                                                               mate studies”

  Observed Weather                                     tion includes pie charts of the probability distribu-
                                                                                                               A closer look at a re-
                                                       tion of temperatures given the CPC outlook.
                                                                                                               gional graphic, shows
  The Observed Weather tab provides access to
                                                                                                               the probabilities of a
  current and archived ASOS-based climate prod-        Local Data/Records
  ucts including the Daily Climate Report, the F6                                                              White Christmas in the
  monthly summary, Record Reports, Monthly                                                                     local area, based on
  Climate Summaries, and the Regional and State        The Local Data/Records tab contains a wealth of         climatology.
  Temp/Precip Tables. When a product is selected,      information including graphs of actual and normal
  the location and timeframe menus update show-        temperature, precipitation and snowfall for the
  ing what information is available. For example,      current and past years, local Storm Data reports,       Probabilities for indi-
  the F6 database goes back 5 years and the Daily      area freeze dates and probabilities, snow cover
                                                       analyses, extreme event web pages, local climate        vidual cities are avail-
  Climate Report goes back three months. Note
  also links to the SPC and NCDC storm report          studies conducted by our office, and much more.         able. Here are some
  archives in the bottom left corner. This informa-    We have several additional local studies underway       examples:
  tion is available for several decades prior.         which will be posted to this page upon their com-
                                                       pletion. One project nearing completion is on the
                                                       changes in local severe weather climatology             ∗ Dubuque:     53 %
  Climate Prediction                                   (tornado and hail days) based on El Nino – La
                                                       Nina.                                                   ∗ Cedar Rapids: 47 %
  The Climate Prediction tab contains links to the                                                             ∗ Moline:      37 %
  Climate Prediction Center outlooks from week 2       NowData                                                 ∗ Burlington:  30 %
  through 1 year, plus El Nino-La Nina informa-
  tion, and the new Local Three-Month Tempera-
  ture Outlooks (L3MTO). The L3MTO combines            The NOWData tab (NOAA’s Online Weather
  CPC long range outlooks and coop climate data        Data) is a real-time portal to the Coop observer
  and converts the temperature forecast from a         (Continued on page 8)
  large scale down to a single point. This informa-
 NWS Quad Cities
 9050 Harrison Street
 Davenport, IA 52806

Weather Home Companion

NWS Quad Cities
                                New Climate Web Services
9050 Harrison Street
Davenport, IA 52806
                                from NWS Quad Cities
Phone:                          (continued from page 7)
(563) 386-3976                                                                                           Winter Road Conditions
                                and ASOS data for the current      impacts are occurring. You will
                                year and previous year. You        also find access to the National
On the web:                     can select from a number of        Drought Monitor on this page.          menu options to get normals,                                       Illinois: 1-800-452-IDOT
Editor: David Sheets            daily and monthly records,                                         (4368)
                                monthly averages, daily data,      The Drought Monitor is produced
                                and more for all these sites.      weekly and assigns a rating to                                              drought areas based on a combi- netcond.html
                                Since data is available daily,
                                you can see the value of report-   nation of standard objective
Contributors:                                                      drought indices plus local input
Bill Elliott, Hydro-            ing your Coop data each day.
                                                                   from a broad range of government      Iowa: 1-800-288-1047 or
meteorological Technician                                          agencies associated with water
John Haase, Meteorologist                                                                                511
                                Drought information services       resources. We provide the local
Intern                          have increased beginning in        input for eastern Iowa, northwest
Steve Kuhl, Meteorologist-in-   2005. From the left menu on        Illinois, and extreme northeast
Charge                          the main web page                  Missouri through our interactions
Barb Mayes, Forecaster          (, select          with the Corps of Engineers,          Missouri: 1-800-222-6400
David Sheets, Forecaster        Drought Status under Current       USGS, State Cooperative Exten-
Terry Simmons, Data                                                                            
                                Conditions. This links to a        sion Services, and USDA. This is
Acquisition Program Manager     page which contains a local        another area where daily Coop         itions/WinterRoadCondition
Ray Wolf, Science Operations    drought statement when moder-      observer data is extremely help-      s.htm
Officer                         ate or greater drought condi-      ful, if not critically important in
Jeff Zogg, Hydrology Program    tions cover a large part of our    meeting our mission.
Manager                         area and/or significant drought

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