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Hail Powerpoint - Oneonta

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					                         Hail




Large hail is not a killer, but does considerable damage
Falling from 20,000 feet or higher, large hailstones pack quite a punch!
Large hail does significant damage to cars.
Terminal Fall Velocity
Average annual number of days with hail
This is the biggest
hailstone known.
It fell at a town
called Aurora, NE
on June 22, 2003.
The Aurora hailstone was 7 inches in diameter. Imagine that falling
                on your head from 20,000 feet up!
This is the previous record-holder, the Coffeyville hailstone with
             some props (egg, hand) for comparison.
The Coffeyville hailstone cut into sections. Notice the layers
     This stone fell on Coffeyville, KS on Sept 3, 1970.
The rings are caused by different growth regimes. Clear ice is
 deposited slowly and contains few air bubbles. Cloudy ice
 occurswhen water freezes quickly, trapping the air bubbles.
Hail is often categorized by its size in relation to everyday objects
Marble




  Sizes of hail and the everyday objects used as adjectives
        (e.g., baseball-sized hail is 2.75” in diameter)
Oneonta hail, June 15, 2009.
   This is marble-sized
Those are small pine cones for comparison.
A schematic supercell radar echo with a hook echo.
Tornadic thunderstorms often also have large hail.
     The hailfall area is close to the tornado.
         Ingredients for Hail Growth

 In a basic sense, 3 Main “ingredients” are required:

1. Adequate updraft to keep hailstone aloft for an
   appropriate amount of time, -10 to -30C

    2. Sufficient supercooled water near the
       hailstone to enable growth during transit
       through an updraft

   3. A piece of ice or snow (embryo) for it to grow
       upon
Vertical cross section of a supercell hailstorm.
                Forecasting Hail

Deep, Moist Convection (DMC) has 3
  Ingredients:
1. Sufficiently deep low level moisture
2. Steep lapse rates (related to instability)
3. Sufficient lifting from LCL to LFC

   Once DMC identified as possibility, look
  for hail signal
       Hail Ingredients Provided DMC Possible


1. Strong
   updrafts
   necessary but
   not sufficient
 High CAPE in
  hail growth
  zones
      Hail Ingredients Provided DMC Possible


2. Storm scale
   winds:
   Speed/Direct-
   ional shear
   important
Wet-bulb Zero (WBZ): This is the level where evaporative cooling reduces a parcel
temperature to 0C. It correlates well with large hail when the altitude of the WBZ is
between 2200 meters and 2800 meters.

If the WBZ is higher than 2800 meters, hailstones must fall through a large layer which
is above 0C and usually do not reach the ground in frozen form.

If the WBZ is lower than 2200 meters, the lower atmosphere is relatively cold and stable
so the large updrafts needed for hail formation don’t exist.

The exception to the above guidelines is when the ground level is significantly above
sea level. That usually reduces the thickness of the low-level warm layer and hail
becomes more common. This is the reason for the hail maximum in the High Plains and
especially east of the Colorado Rockies.

Source: A World of Weather by Lee Grenci and Jon Nese (2001)
Example of Skew-T Log P determination of WBZ
WBZ   729 mb 2788m
               SHIP - Sig. Hail Parm.
             Strengths                                Weaknesses
• Based on large number of soundings    • Only forecasts SIG Category, not
and is simple to calculate              actual hail size
                                        (values > 1 favorable for SIG)
•High POD of SIG HAIL (>90%)            •Conditional on >0.75” hail
                                        “going to occur”
•Statistically separates SIG from NON •Based on SFCOA MUCAPE, thus may
SIG hail                                exhibit noise at times
                                        • Again, dependent upon accurate
• Widely available: (Mesoanalysis page, thermodynamic profile forecast
SFCOA, NMAP, NSHARP)                    • Will instability be realized? Forcing is
                                        not parameterized

SHIP = MUCAPE * MUMR * 7-5LR * 500T* 0-6 SHR / Constant
                  MUMR = Mixing Ratio of Most Unstable Parcel

				
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posted:3/29/2013
language:English
pages:33