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Probabilistic MOS Guidance for Hazards

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					   Probabilistic MOS Guidance
           for Hazards



Meteorological Development Lab
September 2008
                      Background
• MDL is producing probabilistic guidance (EKDMOS) for
  T, Td, MaxT, MinT, QPF from NCEP's GEFS.
• Output is grids that define probability distribution of
  weather element.
• Technique
   – Regression applied to NCEP ensemble means.
   – KDE, normal kernel, mean and standard deviation from
     regression.
   – Spread Adjustment.
• Can these techniques be applied to high impact
  weather?
   – If so, we could generate probability distributions of impact
     variables.
   – Customers/partners could set their own thresholds.
                    Strategy
• Choose predictands that
  – Relate closely to NWS W/W/A
  – Have a quasi-normal distribution
• Combination of gridded guidance and
  appropriate WFO tools could help W/W/A
  generation.
  – Including Graphical Hazardous Weather Outlook
• Candidates
  – Wind Chill Temperature (WCH)
  – Heat Index (HDX)
         Wind Chill Temperature
• Directly relates to
   –   Extreme Cold Watch
   –   Extreme Cold Warning
   –   Wind Chill Watch
   –   Wind Chill Warning
• Wind Chill is defined as a function of
  Temperature and Wind Speed in NWSI 10-513.
• Range of values
   – Will limit development sample to a range of useful
     values.
   – Chart in NWSI 10-513 suggests T<= 40F and
     WindSpd >= 5 mph. SR SOOs suggest T<=50F.
                   Heat Index
• Directly relates to
   – Excessive Heat Watch
   – Excessive Heat Warning
   – Heat Advisory.
• Heat Index is defined as a function of
  Temperature and RH in NWSI 10-515. Two
  adjustments are provided as well.
• Range of values
   – Will limit development sample to a range of useful
     values.
   – Chart in NWSI 10-515 suggests T>= 85F.

				
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