363
FXUS02 KWBC 301900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST SAT NOV 30 2024
VALID 12Z TUE DEC 03 2024 - 12Z SAT DEC 07 2024
...ARCTIC COLD IN THE CENTRAL AND EASTERN U.S. EXPECTED TO BE
REINFORCED LATER NEXT WEEK...
...SIGNIFICANT SYNOPTIC/LAKE-EFFECT SNOWS CONTINUE FOR THE GREAT
LAKES ESPECIALLY MIDWEEK...
..OVERVIEW
AN ANCHORING MEAN UPPER TROUGH WILL ENCOMPASS MUCH OF THE CENTRAL
TO EASTERN UNITED STATES NEXT WEEK, WITH ONLY A VERY GRADUAL SHIFT
EAST OVER TIME. WEST TO NORTHWEST WINDS UNDER THIS PATTERN WILL
FAVORABLE FOR LONG-DURATION LAKE-EFFECT AND TERRAIN-FOCUSED SNOWS
FROM THE GREAT LAKES TO THE INTERIOR NORTHEAST. SOME SNOWFALL
ACCUMULATIONS WILL BE SIGNIFICANT IN FAVORED LOCATIONS ON THE DOWNWIND
SIDE OF THE GREAT LAKES. THE PERIODICALLY REINFORCED TROUGH ALOFT
AND COLD SURFACE HIGH PRESSURE ORIGINALLY STEMMING FROM THE ARCTIC
WILL CAUSE CONTINUED COLDER THAN AVERAGE TEMPERATURES MIGRATING FAR
SOUTHWARD ACROSS CENTRAL AND EASTERN PARTS OF THE COUNTRY. A TEMPORARY
MODERATION APPEARS AROUND MIDWEEK BEFORE THE NEXT COLD SURGE ARRIVES
LATE WEEK. MEANWHILE, MODERATE RETURN FLOW FROM THE GULF OF MEXICO
WILL BRING ENHANCED RAINFALL CHANCES FROM TEXAS THROUGH THE
CENTRAL GULF COAST STATES. MEANWHILE, BENIGN WEATHER AND GRADUALLY
WARMING TEMPERATURES ARE FORECAST FOR MUCH OF THE WEST, ALBEIT WITH
ENHANCED SHOWERS BEST ABLE TO REACH THE PACIFIC NORTHWEST NEXT
WEEKEND WITH CLOSER PACIFIC SYSTEM APPROACH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES SHOW GOOD AGREEMENT TO BEGIN THE MEDIUM-
RANGE PERIOD ON THE COMING TUESDAY, WITH THE EASTERN HALF OF THE
COUNTRY UNDER THE GRIP OF POLAR AIR. UNCERTAINTY GRADUALLY GROWS
TOWARD THE END OF NEXT WEEK IN TERMS OF HOW FAST THE NEXT POLAR AIR
MASS FROM CANADA WILL SURGE SOUTH AND EAST ACROSS THE CENTRAL AND
EASTERN U.S., AND HOW FAST THE GULF MOISTURE WILL RETURN AND THEN
REACH FARTHER INLAND INTO THE SOUTH THROUGH THE END OF NEXT WEEK.
THERE APPEARS TO BE A GRADUAL MODEL CONSENSUS TO ACCELERATE THE
SOUTHWARD SURGE OF THE NEXT POLAR AIR REINFORCEMENT LATER NEXT
WEEK, WHICH WOULD AFFECT THE TIMING AND INTENSITY OF A CLIPPER LOW
PRESSURE SYSTEM FORECAST TO CROSS THE GREAT LAKES MIDWEEK. THE
SPEED OF THIS NEXT POLAR SURGE WILL AFFECT HOW FAR INLAND THE
RETURN MOISTURE WILL BE CARRIED INLAND ACROSS THE GULF COAST
STATES. A FASTER SOUTHWARD SURGE OF THE COLD AIR COULD MEAN A
FARTHER EAST-NORTHEAST PROGRESSION OF THE RAINFALL INTO THE SOUTH
LATER NEXT WEEK. THE POSITION AND THE SPEED OF EJECTION OF A
CLOSED LOW OVER THE SOUTHWEST MIDWEEK WILL ALSO HAVE A CONTROLLING
FACTOR FOR THE PRECIPITATION DISTRIBUTION ACROSS THE SOUTH. THE
ECMWF TENDS TO SLOW THE SPEED OF PROGRESSION OF THE RAINFALL INTO
THE GULF COAST STATES BEGINNING MIDWEEK WHILE A FASTER PROGRESSION
IS INDICATED BY THE GFS AND CMC.
A CONSENSUS BLEND OF DETERMINISTIC AND ENSEMBLE MEANS FROM 40%
OF THE 00Z ECMWF/EC MEAN, 40% OF THE 06Z GFS/GEFS, AND 20% OF THE
00Z CMC/CMC MEAN WAS USED TO COMPOSED TODAY'S WPC MEDIUM-RANGE
FORECASTS. THE 00Z GFS APPEARS TOO SLOW WITH THE NEXT SURGE OF
POLAR AIR INTO THE CENTRAL AND EASTERN U.S. LATER NEXT WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
A HIGHLY FAVORABLE PATTERN FOR LAKE-EFFECT SNOW WILL PERSIST OVER
THE GREAT LAKES WELL INTO NEXT WEEK. A CLIPPER LOW PRESSURE SYSTEM
WILL LIKELY ENHANCE THE AMOUNTS AND EXPAND THE COVERAGE OF THE
SNOWFALL THROUGH THE GREAT LAKES AND LATER INTO INTERIOR NEW
ENGLAND WEDNESDAY AND THURSDAY. EXACT SNOW AXES AND LOCAL
INTENSITIES WILL DEPEND ON REINFORCING SYSTEM PASSAGES WITH WIND
DIRECTIONS THAT COULD VARY FROM NORTHWEST TO WEST DAY TO DAY, BUT
SOME AREAS DOWNWIND OF THE LAKES WILL SEE SIGNIFICANT
ACCUMULATIONS, LIKELY CAUSING TRAVEL DISRUPTIONS TO INCLUDE I-90
BETWEEN CLEVELAND AND BUFFALO AND I-81 NORTH OF SYRACUSE.
SHORTWAVES AND FRONTAL SYSTEMS MAY ALSO SUPPORT PERIODS WITH
ADDITIONAL LIGHT TO MODERATE SNOWS THAT COULD COVER A BROADER AREA
FROM THE NORTH-CENTRAL APPALACHIANS THROUGH FAVORED TERRAIN OF THE
NORTHEAST.
MUCH OF THE REST OF THE COUNTRY CAN EXPECT MAINLY DRY CONDITIONS
NEXT WEEK, BUT THERE ARE EXCEPTIONS. RETURN FLOW OF MOIST AIR FROM
THE GULF OF MEXICO COULD START TO COME INTO THE WESTERN GULF COAST
REGION BY EARLY NEXT WEEK TO FUEL SOME ENHANCED RAINFALL. THIS
LOOKS TO BE GRADUAL TO SPREAD ACROSS THE CENTRAL GULF COAST REGION
THROUGH MID-LATER NEXT WEEK. AT THIS POINT, THERE APPEARS TO BE
ENOUGH MODEL CONSENSUS TO INTRODUCE A MARGINAL EXCESSIVE RAINFALL
RISK FROM EASTERN TEXAS INTO CENTRAL LOUISIANA FOR DAY 5 (12Z WED -
12Z THU) AHEAD OF A WARM FRONT LIFTING NORTH FROM THE GULF COAST
WHERE UPPER-LEVEL DYNAMICS ARE FORECAST TO BE THE STRONGEST.
MEANWHILE, INITIAL UPPER RIDGING WILL KEEP THE WEST MAINLY DRY,
BUT ENHANCED PRECIPITATION CHANCES WILL GRADUALLY INCREASE FOR THE
PACIFIC NORTHWEST BY NEXT WEEKEND PENDING VARIANCE WITH
EXTENT/TIMING OF PACIFIC SYSTEM APPROACH.
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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