173
FXUS02 KWBC 021945
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 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 THE 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 ON THE RAIN MAY BE
ATTRIBUTED TO THE UNCERTAINTY ON THE TIMING AND AMPLITUDE OF THE
TROUGH/UPPER LOW EJECTING ACROSS NORTHERN MEXICO TOWARD TEXAS THIS
WEEKEND. 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 AIR ALOFT 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 DOWN 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. HOWEVER, GIVEN THE UNCERTAINTY ON HOW
THE UPPER TROUGH ACROSS NORTHERN MEXICO WILL BE LIFTED AND EJECTED
INTO TEXAS THIS WEEKEND, THERE IS A POSSIBILITY FOR A BAND OF HEAVY
RAIN TO SET UP SOMEWHERE ACROSS EASTERN TEXAS THIS WEEKEND IF THE
UPPER TROUGH EVOLVES BETWEEN THE ECMWF AND GFS SCENARIOS. THE HEAVY
RAIN AXIS MAY THEN TRAIL SOUTHWEST TOWARD THE WESTERN GULF COAST
AND TAP ADDITIONAL MOISTURE FROM THE GULF NEXT MONDAY.
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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