945
FXUS02 KWBC 020659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST MON DEC 2 2024
VALID 12Z THU DEC 05 2024 - 12Z MON DEC 09 2024
...ANOTHER BLAST OF ARCTIC COLD TROUGH THE CENTRAL AND EASTERN
U.S. LATER THIS WEEK...
..HEAVY GREAT LAKE EFFECT SNOWS TO CONTINUE THROUGH THURSDAY
..OVERVIEW
UPPER LEVEL TROUGHING SETTLED OVER THE CENTRAL AND EASTERN U.S.
WILL DOMINATE THE WEATHER PATTERN THROUGH THIS WEEK INTO NEXT
WEEKEND, AND WEATHER SYSTEMS WILL BE DRIVEN BY SHORTWAVE TROUGHS
ROTATING AROUND THE BROAD UPPER LEVEL TROUGH. A COUPLE COLD FRONTS
WILL PUSH SOUTH ACROSS THE EASTERN TWO-THIRDS OF THE NATION THIS
WEEK AND WILL BRING ANOTHER BLAST OF COLD ARCTIC AIR. THIS PATTERN
WILL ALSO FAVOR LAKE EFFECT SNOW IN THE GREAT LAKES, BUT THE
HEAVIEST SHOULD COME TO AN END MID TO LATER THIS WEEK. ELSEWHERE,
HIGH PRESSURE WILL PERSIST IN THE INTERIOR WEST BEFORE A FRONTAL
SYSTEM WORKS THROUGH NEXT WEEKEND. MODERATE RAINS WILL FOCUS OVER
THE PACIFIC NORTHWEST LATER THIS WEEK, WITH SNOW CHANCES SPREADING
INLAND ACROSS ESPECIALLY FAVORED TERRAIN FROM CASCADES THROUGH THE
NORTHWEST AND NORTHERN ROCKIES NEXT WEEKEND WITH SYSTEM/COLDER
FLOW PROGRESSION. MEANWHILE, MOIST RETURN FLOW FROM THE GULF WILL
SUPPORT DAILY ENHANCED RAIN CHANCES SET TO SPREAD FROM THE WESTERN
TO CENTRAL GULF COAST STATES AND PARTS OF THE SOUTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE STILL SHOWS FAIRLY GOOD AGREEMENT THROUGH MUCH OF THE
PERIOD ON THE OVERALL LARGE SCALE FLOW, ALBEIT IN A PATTERN WITH
CLOSER TO AVERAGE OVERALL PREDICTABILITY GIVEN INCREASING EMBEDDED
SYSTEM FORECAST SPREAD THROUGH NEXT WEEKEND. CONFIDENCE IS ABOVE
NORMAL WITH RESPECT TO A MAIN COLD FRONT THROUGH THE EAST LATE THIS
WEEK, USHERING IN ANOTHER ROUND OF ARCTIC AIR FOR PARTS OF THE
NORTHERN PLAINS, MIDWEST, AND INTO THE EAST. THE NEXT SHORTWAVE
INTO THE NORTH-CENTRAL U.S. ON FRIDAY SHOULD BE WEAKER, BUT DOES
SHOW SOME UNCERTAINTY IN TERMS OF TIMING. OUT WEST, THE GUIDANCE
SHOWS THE UPPER RIDGE SHIFTING EAST NEXT WEEKEND TO USHER IN A MORE
COOL AND UNSETTLED PATTERN WITH SOME LINGERING UNCERTAINTY IN THE
TIMING OF A MAIN/WAVY COLD FRONT TO WORK OVER THE NORTHWEST/WEST.
ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED
FROM A COMPOSITE BLEND OF BEST CLUSTERED GUIDANCE OF THE 18 UTC
GFS AND 12 UTC ECMWF/CANADIAN ALONG WITH COMPATIBLE 01 UTC NATIONAL
BLEND OF MODELS AND WPC CONTINUITY FOR THURSDAY/FRIDAY. THIS
SOLUTION ALSO HAS STRONG MULTI-CENTER ENSEMBLE SUPPORT AND
FAVORABLE TRENDS FROM NEWER 00 UTC GUIDANCE INCLUDING A NOW MORE
IN LINE 00 UTC UKMET. MANUAL ADJUSTMENTS TO GUIDANCE WAS APPLIED
TO MORE STRONGLY EMPHASIZE GREAT LAKES SNOW POTENTIAL LINGERING
THIS PERIOD GIVEN FAVORABLE SUPPORT. LATER OPTED TO SWITCH
DETERMINISTIC MODEL PREFERENCES IN THE BLEND TO THEIR RESPECTIVE
GEFS/ECMWF/CANADIAN ENSEMBLE MEANS STARTING NEXT WEEKEND AMID
STEADILY GROWING EMBEDDED SYSTEM FORECAST AND CONTINUITY VARIANCES.
LATEST 00 UTC DETERMINISTIC MODEL GUIDANCE ALSO REMAINS LESS THAN
STELLAR WITH RUN TO RUN CONTINUITY WITH EMBEDDED SYSTEMS AT THESE
LONGER TIME FRAMES.
..WEATHER/HAZARDS HIGHLIGHTS
LAKE EFFECT SNOW IS FORECAST TO CONTINUE THIS WEEK AS A CLIPPER
LOW PRESSURE SYSTEM MOVES ACROSS THE REGION WEDNESDAY AND THURSDAY
FOLLOWED BY STRONG WEST-NORTHWESTERLY WINDS. SIGNIFICANT SNOW
ACCUMULATIONS WILL BE POSSIBLE IN FAVORED DOWNWIND LOCATIONS, AND
TRAVEL CONDITIONS WILL LIKELY BE HAZARDOUS, ESPECIALLY EARLIER IN
THE PERIOD. SNOW WILL ALSO BE POSSIBLE ELSEWHERE IN THE NORTHEAST
AS THE CLIPPER SYSTEM MOVES THROUGH, ESPECIALLY IN THE HIGHER
TERRAIN OF THE APPALACHIANS. CONDITIONS SHOULD IMPROVE BRIEFLY LATE
THIS WEEK, BUT ANOTHER LOW PRESSURE SYSTEM WILL BRING ANOTHER
CHANCE FOR WINTRY PRECIPITATION TO THE REGION NEXT WEEKEND.
THE REST OF THE NATION WILL BE MAINLY DRY THIS WEEK WITH A COUPLE
EXCEPTIONS. MOIST RETURN FLOW FROM THE GULF WILL RESULT IN DAILY
RAIN CHANCES ALONG THE GULF COAST AND INTO PORTIONS OF THE SOUTH.
WHILE THERE WILL LIKELY BE SOME INSTABILITY TO SUPPORT LOCALLY
HEAVIER DOWNPOURS, NO THREAT AREAS ARE DEPICTED IN THE WPC
EXCESSIVE RAINFALL OUTLOOK. ANY RISK OF HEAVY RAINFALL WILL
DECREASE THROUGH THE END OF THE WEEK AS INSTABILITY DECREASES AND
PRECIPITATION BECOMES MORE SPREAD OUT ACROSS THE GULF COAST REGION
AS FRONTS MOVE THROUGH. PRECIPITATION CHANCES WILL ALSO RETURN TO
THE NORTHWEST BY NEXT WEEKEND AS A PACIFIC FRONTAL SYSTEM
APPROACHES AND WORKS STEADILY INLAND. THIS WILL ACT TO PRODUCE A
MORE COOLER AND UNSETTLED AIRMASS ACROSS MUCH OF THE WEST, WITH
MODERATE RAINS OVER THE PACIFIC NORTHWEST AND SOME TERRAIN
ENHANCING SNOWS INLAND ACROSS THE NORTHWEST AND NORTHERN ROCKIES.
TEMPERATURES WILL DROP BELOW NORMAL FOR PARTS OF THE NORTH-CENTRAL
TO EASTERN U.S. THIS WEEK AS A COLD FRONT USHERS IN ANOTHER BLAST
OF ARCTIC AIR. DAYTIME HIGHS FROM THE UPPER MIDWEST INTO THE EAST
COULD BE 10-20 DEGREES BELOW NORMAL. ELSEWHERE, TEMPERATURES WILL
BE MILD FOR THIS TIME OF YEAR, GENERALLY NEAR TO SLIGHTLY ABOVE
AVERAGE WITH THIS MILDER AIR GRADUALLY EXPANDING EAST WITH TIME.
SCHICHTEL
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC MEDIUM
RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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