976   
FXUS21 KWNC 031920  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST DECEMBER 03 2024  
  
SYNOPSIS: A TRANSITIONAL MID-LEVEL HEIGHT PATTERN IS FORECAST ACROSS THE U.S.   
DURING WEEK-2 MAKING FOR A LOWER CONFIDENCE HAZARDS OUTLOOK. INITIAL MID-LEVEL   
LOW PRESSURE OVER THE EASTERN CONTIGUOUS U.S. (CONUS) FAVORS PERIODIC WAVES OF   
SURFACE LOW PRESSURE MOVING THROUGH THE EAST EARLY IN THE PERIOD, BUT THERE IS   
LARGE MODEL SPREAD REGARDING THE TRACK AND COLD AIR AVAILABILITY. BY THE SECOND   
HALF OF THE PERIOD, MID-LEVEL HEIGHTS ARE FORECAST TO INCREASE (DECREASE)   
ACROSS THE EAST (WEST), WITH ENHANCED ONSHORE FLOW BECOMING MORE LIKELY ACROSS   
THE WEST COAST OF THE CONUS.  
  
HAZARDS  
  
SLIGHT RISK OF HEAVY PRECIPITATION ACROSS MUCH OF THE EASTERN SEABOARD,   
SOUTHEAST, AND LOWER MISSISSIPPI VALLEY, WED-FRI, DEC 11-13.  
  
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY,   
GREAT LAKES, INTERIOR NORTHEAST, AND APPALACHIANS, WED-FRI, DEC 11-13.  
  
SLIGHT RISK OF HIGH WINDS ACROSS PORTIONS OF THE NORTHERN ROCKIES AND PLAINS,   
UPPER MISSISSIPPI VALLEY, GREAT LAKES, OHIO VALLEY, AND NORTHEAST, WED-FRI, DEC   
11-13.  
  
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE SOUTHERN   
PLAINS AND LOWER MISSISSIPPI VALLEY, WED-THU, DEC 11-12.  
  
DETAILED SUMMARY  
  
FOR FRIDAY DECEMBER 06 - TUESDAY DECEMBER 10:   
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
  
FOR WEDNESDAY DECEMBER 11 - TUESDAY DECEMBER 17: MULTIPLE AREAS OF SURFACE LOW   
PRESSURE ARE FORECAST TO TRACK ACROSS THE EASTERN CONUS DURING THE WEEK-2   
PERIOD, BUT MODELS CONTINUE TO BE INCONSISTENT WITH VARYING SOLUTIONS REGARDING   
THE INTERACTION BETWEEN NORTHERN AND SOUTHERN STREAM ENERGY, WHICH WILL   
ULTIMATELY DICTATE THE STRENGTH OF THESE SYSTEMS AS WELL AS THE AMOUNT OF COLD   
AIR AVAILABLE. THE NORTH ATLANTIC OSCILLATION IS FORECAST TO TRANSITION FROM   
NEGATIVE TO POSITIVE AROUND THIS TIME, WHICH CAN SOMETIMES LEAD TO A MORE   
AMPLIFIED STORM IN THE EAST. THE 0Z ECENS AND GEFS INDICATE A SURFACE LOW   
MOVING ACROSS THE GREAT LAKES AT THE OUTSET OF WEEK-2, WITH MANY RELATED   
IMPACTS BEGINNING PRIOR TO THE START OF THE PERIOD. AS THIS SYSTEM LIFTS OUT,   
ADDITIONAL SOUTHERN STREAM ENERGY IS FORECAST TO PUSH NORTHWARD. THE 0Z AND 6Z   
DETERMINISTIC GFS RUNS DEPICT ENOUGH COLD AIR IN THE WAKE OF THE FIRST SYSTEM   
TO RESULT IN A COLDER AND SNOWIER SOLUTION ACROSS THE INTERIOR NORTHEAST AND   
APPALACHIANS. HOWEVER, THE 0Z ECMWF IS CONSIDERABLY WARMER AND THE 12Z GFS LESS   
AMPLIFIED, FURTHER ILLUSTRATING THE WIDE RANGE OF OUTCOMES. THE ECENS   
PROBABILISTIC EXTREMES TOOL (PET) DEPICTS AT LEAST A 20 PERCENT CHANCE 3-DAY   
PRECIPITATION TOTALS EXCEED THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH   
ACROSS THE PARTS OF THE SOUTHEAST AND THE NORTHEASTERN COAST. WHILE THE GEFS   
PET IS NOT AS ROBUST, THE UNCALIBRATED 6Z GEFS IS NOTICEABLY WETTER THAN THE 0Z   
GEFS, PARTICULARLY ACROSS NEW ENGLAND. THEREFORE, A SLIGHT RISK FOR HEAVY   
PRECIPITATION IS HIGHLIGHTED ALONG THE EASTERN SEABOARD, EXTENDING BACK THROUGH   
PARTS OF THE SOUTHEAST AND LOWER MISSISSIPPI VALLEY, DEC 11-13, TO ACCOUNT FOR   
THE POTENTIAL INCREASE IN MOISTURE.   
  
A SLIGHT RISK OF HEAVY SNOW IS ALSO HIGHLIGHTED ACROSS PORTIONS OF THE UPPER   
MISSISSIPPI VALLEY, GREAT LAKES, AND INTERIOR NORTHEAST, AND APPALACHIANS. THIS   
IS MORE UNCERTAIN, AND IS TIED TO THE POTENTIAL FOR SYNOPTIC SNOW ACROSS THE   
UPPER MIDWEST ASSOCIATED WITH THE FIRST SYSTEM AT THE OUTSET OF THE PERIOD, AND   
ACROSS THE INTERIOR NORTHEAST AND APPALACHIANS WITH THE SECOND SYSTEM SHOULD   
ENOUGH COLD AIR WORK IN. FINALLY, EITHER SYSTEM HAS THE POTENTIAL TO INDUCE   
LAKE EFFECT SNOW IN ITS WAKE DEPENDING ON ITS AMPLITUDE AS IT MOVES INTO   
SOUTHEASTERN CANADA, WITH A MORE AMPLIFIED SYSTEM ALSO FAVORING A STRONGER   
NORTHWESTERLY FLOW JUSTIFYING A SLIGHT RISK FOR HIGH WINDS. THIS HIGH WIND RISK   
IS EXTENDED BACK THROUGH THE NORTHERN ROCKIES AND PLAINS GIVEN A TIGHT PRESSURE   
GRADIENT IN THE GEFS AND CMCE AND A SYNOPTIC PATTERN SUPPORTIVE OF INCREASED   
DOWNSLOPE FLOW. DETERMINISTIC SOLUTIONS FROM THE ECMWF AND GFS CONTINUE TO   
INDICATE AN ACTIVE NORTHERN STREAM THROUGH THE END OF WEEK-2. HOWEVER,   
ENSEMBLES DEPICT A TREND TOWARD MORE RIDGING AND WARMER TEMPERATURES IN THE   
EAST BY MID-DECEMBER REDUCING CONFIDENCE IN THE SNOWFALL POTENTIAL. WARMER AIR   
AND RAINFALL COULD TRIGGER FLOODING CONCERNS DUE TO SNOW MELT, PARTICULARLY ON   
THE EASTERN SIDES OF LAKES ERIE AND ONTARIO.   
  
A COLD FRONT IS FORECAST TO DROP SOUTHWARD THROUGH THE SOUTHERN PLAINS AND   
LOWER MISSISSIPPI VALLEY AT THE OUTSET OF WEEK-2. MODELS AND PETS GENERALLY   
DEPICT ELEVATED PROBABILITIES FOR MINIMUM TEMPERATURES DIPPING INTO THE 30S DEG   
F AS FAR SOUTH AS PARTS OF COASTAL TEXAS AND LOUISIANA, WITH HIGHER CHANCES OF   
SUBFREEZING TEMPERATURES ACROSS NORTHERN AND WESTERN TEXAS. AS A RESULT, A   
SLIGHT RISK FOR MUCH BELOW NORMAL TEMPERATURES IS HIGHLIGHTED ACROSS THE AREA,   
DEC 11-12. THIS IS FORECAST TO BE A QUICK SHOT OF COLD AIR WITH MODERATION   
FORECAST BY THE MIDDLE OF WEEK-2. WHILE AGRICULTURAL IMPACTS SHOULD BE MINIMAL,   
INCREASED CONCERN IS RELATED TO ELEVATED HEATING DEMANDS ANTICIPATED DURING   
THIS TIMEFRAME.   
  
THE 0Z ECENS AND GEFS DEPICT RIDGING ACROSS THE WEST AT THE START OF WEEK-2,   
WITH THE FEATURE QUICKLY WEAKENING BY THE MIDDLE OF THE PERIOD. THE ECENS   
CONTINUES TO DEPICT TROUGHING DEVELOPING IN ITS PLACE BY THE END OF THE PERIOD,   
WITH INCREASING AGREEMENT FROM THE GEFS AND CMCE COMPARED TO YESTERDAY. THE   
TREND TOWARD LOWER HEIGHTS WOULD BE SUPPORTIVE OF INCREASING ONSHORE FLOW   
ACROSS THE WEST COAST AND THIS IS REFLECTED IN THE INTEGRATED VAPOR TRANSPORT   
TOOL DERIVED FROM BOTH MODELS. THE GEFS PET DEPICTS PARTS OF THE PACIFIC   
NORTHWEST HAVING AT LEAST A 20 PERCENT CHANCE 3-DAY PRECIPITATION TOTALS EXCEED   
THE 85TH CLIMATOLOGICAL PERCENTILE AND 1-INCH THROUGHOUT THE PERIOD, WITH THE   
ECENS FOCUSING THESE ENHANCED PROBABILITIES FURTHER SOUTH ACROSS PORTIONS OF   
NORTHERN AND CENTRAL CALIFORNIA STARTING IN THE MIDDLE OF WEEK-2. GIVEN THE   
DIFFERING MODEL SOLUTIONS AND THE HIGHEST POTENTIAL BEING DURING THE SECOND   
HALF OF WEEK-2, NO RELATED HAZARDS ARE DEPICTED ACROSS THE WEST AT THIS TIME.   
HOWEVER, INCREASING CHANCES OF COASTAL RAIN AND HIGH ELEVATION SNOW ARE   
POSSIBLE ACROSS THE PACIFIC NORTHWEST SOUTHWARD THROUGH PARTS OF CALIFORNIA,   
ESPECIALLY LATER IN THE PERIOD. IF MODEL AGREEMENT IMPROVES, HAZARDS MAY BE   
INTRODUCED OVER PARTS OF THE WEST IN FUTURE OUTLOOKS.  
  
RIDGING RETROGRADING TO THE SOUTH OF ALASKA DURING WEEK-2 FAVORS THE AXIS OF   
STRONGEST ONSHORE FLOW SHIFTING AWAY FROM SOUTHEAST ALASKA DECREASING THE HEAVY   
PRECIPITATION POTENTIAL RELATIVE TO THE WEEK-1 PERIOD. ALTHOUGH SOME ENHANCED   
PRECIPITATION IS STILL POSSIBLE ACROSS SOUTHEAST ALASKA AT THE OUTSET OF THE   
PERIOD, HAZARDS THRESHOLDS ARE NOT FORECAST TO BE REACHED. HIGH PROBABILITIES   
FOR ABOVE-NORMAL TEMPERATURES ARE PREDICTED ACROSS ALASKA FOR WEEK-2.  
  
FORECASTER: THOMAS COLLOW   
  
  
 
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