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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