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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page