195   
FXUS21 KWNC 051906  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 05 2024  
  
SYNOPSIS: A POTENTIAL SURFACE LOW ACROSS THE EASTERN CONTIGUOUS U.S. (CONUS)   
AND ASSOCIATED IMPACTS NOW LOOK TO OCCUR DURING THE WEEK-1 PERIOD ALLOWING ALL   
RELATED HAZARDS TO BE REMOVED FROM THE NORTHEAST AND GREAT LAKES IN THE UPDATED   
OUTLOOK. FOLLOWING A QUICK SHOT OF COLD AIR BEHIND THIS SYSTEM, A WARMING TREND   
IS LIKELY ACROSS MUCH OF THE EAST DURING WEEK-2. MID-LEVEL LOW PRESSURE IS   
FORECAST ACROSS THE WEST COAST OF THE CONUS FAVORING A MORE ACTIVE PATTERN IN   
THE WEST, WITH INCREASED CHANCES FOR HEAVY COASTAL RAIN AND HIGH ELEVATION   
HEAVY SNOW.   
  
HAZARDS  
  
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND   
THE NORTHERN HALF OF CALIFORNIA, FRI-MON, DEC 13-16.  
  
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE CASCADES, KLAMATH, AND SIERRA   
NEVADAS, FRI-MON, DEC 13-16.  
  
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN AND CENTRAL ROCKIES,   
FRI-MON, DEC 13-16.  
  
SLIGHT RISK OF HIGH WINDS ACROSS MUCH OF THE NORTHWESTERN QUADRANT OF THE CONUS   
EXTENDING INTO THE NORTHERN AND CENTRAL PLAINS, FRI-MON, DEC 13-16.  
  
DETAILED SUMMARY  
  
FOR SUNDAY DECEMBER 08 - THURSDAY DECEMBER 12:   
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
  
FOR FRIDAY DECEMBER 13 - THURSDAY DECEMBER 19: MODELS CONTINUE TO INDICATE AN   
AREA OF SURFACE LOW PRESSURE LEADING TO INCREASED CHANCES OF HAZARDOUS RAIN OR   
SNOW ACROSS PARTS OF THE NORTHEAST DEPENDING ON THE AMOUNT OF NORTHERN STREAM   
INTERACTION. HOWEVER, THIS IS FORECAST TO OCCUR WITHIN THE WEEK-1 TIME PERIOD,   
WITH SURFACE HIGH PRESSURE ARRIVING OVER THE EAST BY THE START OF WEEK-2,   
SUPPORTING THE REMOVAL OF THE RELATED PRECIPITATION, SNOW, AND WIND HAZARDS   
PREVIOUSLY POSTED ACROSS THE NORTHEAST AND GREAT LAKES. WHILE SOME COLD AIR IS   
LIKELY ON THE BACKSIDE OF THIS SYSTEM, A WARMING TREND IS LIKELY ACROSS THE   
EAST DURING WEEK-2, AND THIS COULD RAISE FLOODING CONCERNS ALONG PARTS OF THE   
GREAT LAKES, PARTICULARLY ERIE AND ONTARIO, DUE TO EXPECTED SNOWMELT. RETURN   
FLOW IS ALSO FORECAST TO INCREASE ON THE BACKSIDE OF THE SURFACE HIGH ACROSS   
THE EAST-CENTRAL CONUS. THE ECENS PROBABILISTIC EXTREMES TOOL (PET) DEPICTS   
PARTS OF THE MIDDLE AND LOWER MISSISSIPPI AND TENNESSEE VALLEYS HAVING AT LEAST   
A 20 PERCENT CHANCE 3-DAY PRECIPITATION TOTALS EXCEED THE 85TH CLIMATOLOGICAL   
PERCENTILE AND 1-INCH IN THE MIDDLE OF THE PERIOD. HOWEVER, THE GEFS PET DOES   
NOT INDICATE A SUBSTANTIAL SIGNAL, AND A RELATED PRECIPITATION HAZARD IS NOT   
POSTED AT THIS TIME.  
  
THE 0Z ECENS AND GEFS ARE IN GOOD AGREEMENT REGARDING TROUGHING ALONG THE WEST   
COAST OF THE CONUS DURING WEEK-2, WHICH IS SUPPORTIVE OF INCREASED ONSHORE FLOW   
ACROSS THE WEST COAST. HOWEVER, COMPARED TO YESTERDAY, THE INTEGRATED VAPOR   
TRANSPORT (IVT) TOOLS ARE LESS ROBUST AND THE PROBABILITIES FOR HAZARDOUS   
PRECIPITATION IN THE PETS ARE MARGINAL AT BEST. THE ECENS AND GEFS PETS   
CONTINUE TO DEPICT PARTS OF THE WEST COAST HAVING AT LEAST A 20 PERCENT CHANCE   
3-DAY PRECIPITATION TOTALS EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH   
THROUGH THE MIDDLE OF THE PERIOD. TO MAINTAIN CONTINUITY WITH YESTERDAY, A   
SLIGHT RISK OF HEAVY PRECIPITATION REMAINS POSTED ACROSS PORTIONS OF THE   
PACIFIC NORTHWEST EXTENDING SOUTHWARD INTO THE NORTHERN HALF OF CALIFORNIA, DEC   
13-16. AN ACCOMPANYING SLIGHT RISK OF HEAVY SNOW IS ALSO POSTED ACROSS THE   
CASCADES, KLAMATH, SIERRA NEVADAS, AND THE NORTHERN AND CENTRAL ROCKIES,   
SUPPORTED BY THE GEFS SNOW WATER EQUIVALENT (SWE) PET WHICH DEPICTS AT LEAST A   
20 PERCENT CHANCE SWE EXCEEDS THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH,   
AND THE UNCALIBRATED ECMWF PROBABILITIES INDICATING ELEVATED CHANCES FOR DAILY   
SNOWFALL TOTALS GREATER THAN 6 INCHES OVER PARTS OF THE HIGHLIGHTED AREAS. A   
BROAD SLIGHT RISK OF HIGH WINDS IS ALSO HIGHLIGHTED DEC 13-16 ACROSS MUCH OF   
THE NORTHWESTERN QUADRANT OF THE CONUS EXTENDING INTO THE GREAT PLAINS, WITH   
THE STRONGEST SIGNALS FOR WIND SPEEDS GREATER THAN 25-MPH BEING ALONG THE   
IMMEDIATE WEST COAST AND ALSO ACROSS THE HIGH PLAINS TIED TO INCREASED   
DOWNSLOPE FLOW. PROBABILITIES FOR WIND SPEEDS EXCEEDING THE 85TH CLIMATOLOGICAL   
PERCENTILE ARE ELEVATED IN THE GEFS AND ECENS PETS ACROSS THE INTERMOUNTAIN   
REGION, SUGGESTIVE OF AN INCREASED HIGH WIND RISK IN THESE AREAS AS WELL.  
  
RIDGING IS GENERALLY FORECAST ACROSS ALASKA DURING WEEK-2. ALTHOUGH SOME   
ENHANCED PRECIPITATION IS STILL POSSIBLE OVER SOUTHERN ALASKA, HAZARDS   
THRESHOLDS ARE NOT FORECAST TO BE REACHED. HIGH PROBABILITIES FOR ABOVE-NORMAL   
TEMPERATURES ARE PREDICTED ACROSS MOST OF ALASKA FOR WEEK-2.  
  
FORECASTER: THOMAS COLLOW   
  
  
 
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