654
FXUS02 KWBC 311901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 PM EST TUE DEC 31 2024
VALID 12Z FRI JAN 03 2025 - 12Z TUE JAN 07 2025
...BROAD CHANCES FOR IMPACTFUL WINTRY WEATHER ACROSS THE NORTH-
CENTRAL U.S. TO MID-MISSISSIPPI AND OHIO VALLEYS TO THE EAST COAST
OVER THE WEEKEND INTO EARLY NEXT WEEK...
..OVERVIEW
AS THE MEDIUM RANGE PERIOD BEGINS FRIDAY, BROAD TROUGHING WILL BE
IN PLACE ACROSS THE EAST, ALLOWING FOR ANOTHER COUPLE OF DAYS OF
LAKE EFFECT AND TERRAIN-ENHANCED CENTRAL APPALACHIANS SNOW.
MEANWHILE UPPER RIDGING WILL AMPLIFY OVER THE WEST FOR WARMER
TEMPERATURES WHILE A MODERATE ATMOSPHERIC RIVER WILL PROVIDE SOME
MODEST TO LOCALLY HEAVY PRECIPITATION OVER THE NORTHWEST/NORTHERN
CALIFORNIA CONTINUING INTO FRIDAY AHEAD OF AN EASTERN PACIFIC
TROUGH. THIS TROUGH IS FORECAST TO MOVE INLAND AND TOWARD THE
CENTRAL U.S. OVER THE WEEKEND, WHICH WILL SUPPORT A DEVELOPING LOW
PRESSURE SYSTEM OVER THE PLAINS AND EAST-CENTRAL U.S. EARLY NEXT
WEEK. MOISTURE ACCOMPANYING THIS LOW COULD LEAD TO HEAVY RAINFALL
CURRENTLY EXPECTED IN THE TENNESSEE VALLEY ON SUNDAY, WHILE COLD
TEMPERATURES IN PLACE FARTHER NORTH MAY PRODUCE A BROAD AREA OF
POSSIBLY IMPACTFUL SNOW ACCUMULATIONS IN THE NORTH-CENTRAL PLAINS
TO MID- MISSISSIPPI VALLEY AND OHIO VALLEY THIS WEEKEND, WITH
INCREASING CONCERNS FOR ICE IN THE TRANSITION ZONE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS AGREEABLE IN SHOWING A WEST UPPER RIDGE AND
EAST UPPER TROUGH LATE THIS WEEK. THE TIMING OF EASTERN PACIFIC
TROUGHING MOVING INTO THE WEST AND THEN CENTRAL U.S. AND DEVELOPING
SURFACE LOW PRESSURE SHOWS MUCH MORE MODEL VARIABILITY AND
UNCERTAINTY, HOWEVER. THROUGH THE NEW 12Z GUIDANCE FOR TODAY (WHICH
ALL CAME IN AFTER THE FORECAST GENERATION TIME), THE GFS IS THE
MOST SUPPRESSED AND FARTHEST SOUTH WITH THIS SYSTEM, WHILE THE CMC
AND ECMWF ARE FARTHER NORTH. COMPARED TO GUIDANCE A DAY OR SO AGO
THOUGH, THERE DOES SEEM TO BE A SLIGHT SOUTHERN TREND IN HEAVY
SNOW/ICE AXES SO THIS IS WORTH MONITORING AND MAYBE NOT COMPLETELY
DISCOUNTING THE GFS AT THIS POINT. ENSEMBLE MEANS ARE GENERALLY IN
THE MIDDLE AT THIS POINT AND NOT AS EXTREME AS THEIR DETERMINISTIC
COUNTERPARTS, WHICH FURTHER EMPHASES THE UNCERTAINTY NOT ONLY IN
NORTH-SOUTH PLACEMENT OF THE LOW TRACK BUT ALSO WITH THE TIMING. AT
THIS POINT, THE WPC BLEND, WHICH USED THE OLDER 00Z/06Z RUNS,
TRENDED TOWARDS A GENERAL MODEL BLEND WITH INCREASING ENSEMBLE MEAN
INFLUENCE IN AN ATTEMPT TO MITIGATE UNCERTAINTY WITH THIS SYSTEM.
THIS GENERALLY IS CONSISTENT WITH PREVIOUS WPC FORECASTS AS WELL.
REGARDLESS, THERE IS AN INCREASING SIGNAL FROM ALL OF THE GUIDANCE
FOR A POSSIBLY IMPACTFUL SYSTEM WITH WINTRY WEATHER. ELSEWHERE
ACROSS THE CONUS, THE GUIDANCE SHOWS SUFFICIENT AGREEMENT WITH
OTHER LESS IMPACTFUL SYSTEMS AND THE GENERAL MODEL BLEND SEE, IT IS
MOSTLY A PRECIPITATION TYPE UNCERTAINTY. MED TO WORK WELL AS A
GOOD STARTING POINT.
..WEATHER/HAZARDS HIGHLIGHTS
LAKE EFFECT SNOW IS LIKELY INTO FRIDAY-SATURDAY WITH COLD AND
BRISK FLOW ACROSS THE GREAT LAKES. FAVORED AREAS COULD SEE HEAVY
SNOW AMOUNTS PILING UP, ESPECIALLY EAST OF LAKE ONTARIO.
ADDITIONALLY, SHORTWAVE ENERGY AND A COLD FRONT MAY PRODUCE LIGHT
SNOW IN THE OHIO VALLEY WITH TERRAIN ENHANCEMENT OF TOTALS IN THE
CENTRAL APPALACHIANS ON FRIDAY. FARTHER SOUTH, PARTS OF THE
WESTERN/CENTRAL GULF COAST COULD SEE PERIODS OF LIGHT RAIN.
AHEAD OF THE EASTERN PACIFIC UPPER TROUGH, MOISTURE IN THE FORM OF
A WEAK TO MODERATE ATMOSPHERIC RIVER WILL BE DIRECTED INTO THE
PACIFIC NORTHWEST TO NORTHERN CALIFORNIA, LIKELY PEAKING THURSDAY
NIGHT INTO FRIDAY MORNING. A MARGINAL RISK HAS BEEN CONTINUED FOR
THE DAY 4/FRIDAY ERO. THIS IS LIKELY A LOW END MARGINAL RISK BUT
THESE AREAS MAY BE MORE SENSITIVE THAN NORMAL DUE TO WET ANTECEDENT
CONDITIONS. RAIN RATES COULD BE HALF AN INCH TO AN INCH PER HOUR
EARLY FRIDAY. MODEST PRECIPITATION INCLUDING HIGHER ELEVATION SNOW
IS LIKELY INTO THE INTERMOUNTAIN WEST AND NORTHERN/CENTRAL ROCKIES.
ADDITIONAL ROUNDS OF LIGHT TO MODERATE PRECIPITATION ARE POSSIBLE
IN THE NORTHWEST INTO THE WEEKEND.
AS THE UPPER TROUGH MOVES INTO THE CENTRAL U.S., SURFACE LOW
PRESSURE IS FORECAST TO DEVELOP OVER THE SOUTHERN PLAINS OVER THE
WEEKEND. WHILE THE DETAILS REMAIN NEBULOUS, PRECIPITATION CHANCES
LOOK TO INCREASE GENERALLY ACROSS THE PLAINS AND MISSISSIPPI VALLEY
SATURDAY AND STRETCHING FARTHER INTO THE EAST-CENTRAL U.S. SUNDAY-
MONDAY AS THE LOW MOVES EAST. THIS PRECIPITATION WOULD BE SNOW IN
THE NORTHERN HALF OR SO OF THE U.S. GIVEN THE COLD TEMPERATURES,
WITH RAIN IN THE SOUTH. MODEL GUIDANCE CONTINUES TO SHOW A
RELATIVELY BROAD REGION WHERE THERE MAY BE A TRANSITION ZONE OF
SLEET AND/OR FREEZING RAIN IN BETWEEN THE RAIN AND SNOW, AND SOME
LOCATIONS COULD TRANSITION BETWEEN MULTIPLE PRECIPITATION TYPES.
THERE IS INCREASING CONCERN THAT THIS COULD BE PARTICULARLY
IMPACTFUL AND SIGNIFICANT IN SOME LOCATIONS (BUT THOSE LOCATIONS
REMAIN HIGHLY UNCERTAIN STILL). THE CENTRAL PLAINS INTO MIDDLE
MISSISSIPPI VALLEY TO PERHAPS THE TENNESSEE AND/OR LOWER OHIO
VALLEY APPEARS MOST LIKELY FOR TRANSITIONING PRECIPITATION TYPES AT
THIS POINT. THE WINTER WEATHER OUTLOOK DEPICTS A LARGE AREA OF
10-50+% PROBABILITIES OF "PLOWABLE" SNOW/SLEET FROM THE NORTH-
CENTRAL PLAINS EASTWARD ACROSS THE MIDDLE MISSISSIPPI VALLEY AND
OHIO VALLEY THIS WEEKEND. SOME WINTRY WEATHER MAY PUSH INTO THE
MID- ATLANTIC INTO PARTS OF THE NORTHEAST BY MONDAY, BUT WITH LOW
CONFIDENCE IN THE AMOUNTS. HEAVY RAIN AND THUNDERSTORMS IN THE WARM
SECTOR COULD ALSO BE HAZARDOUS WITH THIS SYSTEM, CURRENTLY
FORECAST TO PEAK IN THE TENNESSEE VALLEY ON SUNDAY. KEEP AN EYE ON
FUTURE FORECASTS AS DETAILS ARE LIKELY TO CHANGE.
GENERALLY, THE MEAN UPPER RIDGE OVER THE WEST WILL PROMOTE ABOVE
NORMAL TEMPERATURES FROM THE GREAT BASIN AND SOUTHWEST TO THE
SOUTHERN PLAINS LATE WEEK INTO THE WEEKEND. HIGHS WILL REACH WELL
INTO THE 70S IN THE DESERT SOUTHWEST, AND TEMPERATURES COULD WARM
INTO THE LOW 80S IN SOUTHERN TEXAS BY NEXT WEEKEND. THESE AREAS ARE
FORECAST TO MODERATE CLOSER TO NORMAL EARLY NEXT WEEK, PERHAPS
REACHING BELOW AVERAGE IN TEXAS. MEANWHILE THE MEAN TROUGH IN THE
CENTRAL/EASTERN U.S. WILL LEAD TO COOLER THAN NORMAL TEMPERATURES
FROM THE CENTRAL U.S. INTO THE MIDWEST TO EASTERN SEABOARD, WITH
MULTIPLE RESURGENCES OF COLD AIR. THE NORTHERN PLAINS ARE FORECAST
TO SEE THE MOST ANOMALOUS TEMPERATURES THROUGH THE WEEKEND, AROUND
10-20F BELOW NORMAL FOR HIGHS AND AROUND 5-15F BELOW NORMAL FOR
LOWS. THIS TRANSLATES TO HIGHS NOT REACHING OR BARELY REACHING 0F
AND LOWS BETWEEN -10F AND -20F IN SOME AREAS. THIS SHOULD NOT BE
RECORD BREAKING COLD, AS DAILY RECORDS THERE FOR THIS TIME OF YEAR
ARE GENERALLY IN THE -30S AND COLDER (LOW MINS) AND AROUND -20F FOR
LOW MAXES. HOWEVER, THE COLD COULD STILL BE HAZARDOUS AS WIND
CHILL VALUES MAY DIP BELOW -20F TO -30F.
SANTORELLI/TATE
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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