107
FXUS02 KWBC 021900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST MON DEC 2 2024
VALID 12Z THU DEC 05 2024 - 12Z MON DEC 09 2024
...ANOTHER BLAST OF ARCTIC AIR TO BRING MORE HEAVY LAKE-
EFFECT/ENHANCED SNOWS AND POSSIBLY SNOW SQUALLS NEAR THE GREAT
LAKES, HIGH WINDS AND ARCTIC COLD INTO THE CENTRAL AND EASTERN U.S...
...RETURN MOIST FROM THE GULF OF MEXICO COULD BRING ENHANCED
RAINFALL ACROSS THE WESTERN TO CENTRAL GULF COAST STATES LATE THIS
WEEK...
..OVERVIEW
A SYNOPTIC PATTERN THAT FAVORS UPPER-LEVEL TROUGHING OVER THE EASTERN
PART OF THE NORTH AMERICAN CONTINENT WILL SUPPORT ADDITIONAL
OUTBREAKS OF ARCTIC AIR INTO THE EASTERN TWO-THIRDS OF THE U.S. THE
RUSH OF ARCTIC AIR BEHIND AN INTENSIFYING ALBERTA CLIPPER WILL
FAVOR ANOTHER OUTBREAK OF HEAVY LAKE-EFFECT SNOW ACROSS THE GREAT
LAKES THROUGH THURSDAY ALONG WITH THE POSSIBILITY OF SNOW SQUALLS
AND HIGH WINDS. 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 THROUGH THE
WEEKEND INTO NEXT MONDAY WITH UNCERTAINTY ON THE TIMING AND INLAND
EXTENT OF THE RAIN. 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.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE TODAY CONTINUES WITH A GENERAL TREND FOR THE ARCTIC AIR TO
RUSH IN FASTER BEHIND THE INTENSIFYING ALBERTA CLIPPER SYSTEM THAT
IS FORECAST TO TRACK EAST THROUGH THE NORTHEAST ON THURSDAY.
GUIDANCE ALSO SHOWS A FASTER SOUTHWARD PLUNGE OF THE ARCTIC HIGH
AND THE ASSOCIATED ARCTIC AIR MASS INTO THE PLAINS. FOCUS WILL THEN
SHIFT TO THE GULF COAST WHERE THERE IS A NOTICEABLE DIFFERENCE
BETWEEN THE ECMWF AND GFS SOLUTIONS ON TIMING AND INLAND EXTENT OF
THE MOISTURE RETURNING FROM THE GULF OF MEXICO INTO THE WESTERN
GULF COAST STATES. THE ECMWF TENDS TO HOLD BACK THE INLAND PROGRESS
OF THE RAIN WHILE GFS IS MORE AGGRESSIVE. THE CMC IS IN BETWEEN
THESE EXTREMES. THE UNCERTAINTY MAY BE ATTRIBUTED TO THE
UNCERTAINTY ON THE TIMING AND AMPLITUDE OF THE TROUGH/UPPER LOW
EJECTING ACROSS NORTHERN MEXICO TOWARD TEXAS. 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 ITS WAY
ACROSS THE NORTHWEST/WEST.
ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED
FROM A COMPOSITE BLEND OF 40% FROM THE 00Z ECMWF/EC MEAN, 40% FROM
THE 06Z GFS/GEFS, AND 20% FROM THE 00Z CMC/CMC MEAN, TRANSITIONING
TO INCLUDE MORE OF THEIR RESPECTIVE ENSEMBLE MEANS STARTING NEXT
WEEKEND AMID STEADILY GROWING EMBEDDED SYSTEM FORECAST AND
CONTINUITY VARIANCES. THIS BLEND YIELDED A SOLUTION RATHER
COMPATIBLE WITH THE PREVIOUS WPC MEDIUM-RANGE PACKAGE. THE SLOWER
ECMWF SOLUTIONS WITH THE QPF ACROSS THE WESTERN GULF COAST REGION
WERE PREFERRED LATE IN THE FORECAST PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
ANOTHER OUTBREAK OF HEAVY LAKE-EFFECT SNOW IS LIKELY ACROSS THE
GREAT LAKES BEHIND AN INTENSIFYING CLIPPER LOW PRESSURE SYSTEM
ON THURSDAY. INFLUX OF COLDER THICKNESS BEHIND THE SYSTEM IS ALSO
RAISING THE POSSIBILITY OF SNOW SQUALLS DOWNWIND FROM THE GREAT
LAKES, AS WELL AS HIGH WINDS ACROSS A WIDER DOMAIN INTO THE OHIO
VALLEY, APPALACHIANS, AND ACROSS THE MID-ATLANTIC. LOCALLY VERY
HEAVY SNOW ACCUMULATIONS WILL BE POSSIBLE IN FAVORED DOWNWIND
LOCATIONS, AND TRAVEL CONDITIONS WILL LIKELY BE HAZARDOUS,
ESPECIALLY ON THURSDAY. 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 RETURNING FROM THE GULF WILL RESULT IN DAILY
RAIN CHANCES ALONG THE WESTERN 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.
KONG/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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