110
FXUS21 KWNC 021921
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 02 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 PORTIONS OF THE SOUTHERN PLAINS,
LOWER MISSISSIPPI AND TENNESSEE VALLEYS, AND THE SOUTHEAST, TUE-THU, DEC 10-12.
SLIGHT RISK OF HEAVY SNOW ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY,
GREAT LAKES, AND INTERIOR NORTHEAST, TUE-THU, DEC 10-12.
SLIGHT RISK OF HIGH WINDS ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY,
GREAT LAKES, OHIO VALLEY, AND NORTHEAST, TUE-THU, DEC 10-12.
DETAILED SUMMARY
FOR THURSDAY DECEMBER 05 - MONDAY DECEMBER 09:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY DECEMBER 10 - MONDAY DECEMBER 16: AT THE OUTSET OF WEEK-2,
ANOMALOUS TROUGHING IS FORECAST ACROSS THE EASTERN THIRD OF THE CONUS. AN AREA
OF SURFACE LOW PRESSURE IS FORECAST TO TRACK THROUGH THE EAST, HOWEVER, MODELS
SHOW LITTLE CONSISTENTLY IN REGARDS TO THE INTERACTION BETWEEN THE NORTHERN AND
SOUTHERN STREAMS. THE 0Z ECENS DEPICTS A MORE ACTIVE SOUTHERN STREAM AND ITS
CORRESPONDING 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 SOUTHERN PLAINS, LOWER MISSISSIPPI AND TENNESSEE
VALLEYS, AND SOUTHEAST SUPPORTING A SLIGHT RISK OF HEAVY PRECIPITATION OVER
THESE AREAS, 12/10-12/12. THE 0Z GEFS ALONG WITH SEVERAL RECENT DETERMINISTIC
GFS RUNS ARE MORE PROGRESSIVE AND DEPICT HIGHER CHANCES FOR HEAVY PRECIPITATION
OVER PARTS OF THESE AREAS OCCURRING PRIOR TO THE START OF WEEK-2.
AS THE SURFACE LOW TRACKS ACROSS THE GREAT LAKES, THIS MOISTURE IS PROJECTED TO
EXTEND NORTHWARD, BUT THE AMOUNT OF COLD AIR AVAILABLE IS UNCERTAIN. AN AREA OF
HEAVY SNOW CANNOT BE RULED OUT ON THE NORTHWESTERN SIDE OF THE SURFACE LOW,
WITH WARMER TEMPERATURES AND RAIN LIKELY TO THE EAST. HOWEVER, A MORE AMPLIFIED
SYSTEM COULD RESULT IN A WINTRY MIX ACROSS PARTS OF THE INTERIOR NORTHEAST IF
SOUTHERN STREAM ENERGY ARRIVES WITH COLD AIR REMAINING AT THE SURFACE. GIVEN
THE UNCERTAINTY, A SLIGHT RISK FOR HEAVY SNOW IS HIGHLIGHTED ACROSS THE UPPER
MISSISSIPPI VALLEY, GREAT LAKES, AND INTERIOR NORTHEAST, 12/10-12/12, ALTHOUGH
SNOW IS UNLIKELY ACROSS THE ENTIRE HIGHLIGHTED REGION. WARMER AIR AND RAINFALL
COULD TRIGGER FLOODING CONCERNS DUE TO SNOW MELT, PARTICULARLY ON THE EASTERN
SIDES OF LAKES ERIE AND ONTARIO. A MORE AMPLIFIED SYSTEM WOULD FAVOR ENHANCED
NORTHWESTERLY FLOW ON ITS BACKSIDE SUPPORTING A BROAD SLIGHT RISK OF HIGH WINDS
ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY, GREAT LAKES, OHIO VALLEY, AND
NORTHEAST, DEC 10-12. THIS COULD ALSO TRIGGER ADDITIONAL LAKE EFFECT SNOW
BANDS. 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. THEREFORE NO HAZARDS ARE
INDICATED BEYOND DAY-10.
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 IS
QUITE ROBUST WITH TROUGHING DEVELOPING IN ITS PLACE BY THE END OF THE PERIOD,
BUT THE GEFS MAINTAINS A MORE ZONAL MID-LEVEL HEIGHT PATTERN, WITH MORE
PERSISTENT RIDGING OFF THE WEST COAST IN THE 0Z CMCE. THE TREND TOWARD LOWER
HEIGHTS IN THE ECENS AND GEFS 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 DURING THE MIDDLE OF THE PERIOD,
WITH THE ECENS FOCUSING THESE ENHANCED PROBABILITIES FURTHER SOUTH ACROSS
PORTIONS OF NORTHERN AND CENTRAL CALIFORNIA DUE TO THE MORE ROBUST TROUGHING.
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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