705
FXUS02 KWBC 281958
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EST SUN DEC 28 2025
VALID 12Z WED DEC 31 2025 - 12Z SUN JAN 04 2026
..OVERVIEW
AN AMPLIFIED UPPER LEVEL PATTERN IS EXPECTED TO BE IN PLACE ACROSS
THE CONTINENTAL U.S. TO START THE FORECAST PERIOD WEDNESDAY, WITH
AN UPPER RIDGE SITUATED OVER THE WEST COAST REGION AND A BROAD
UPPER TROUGH EAST OF THE MISSISSIPPI RIVER. THIS REMAINS THE CASE
GOING INTO THURSDAY, WITH A REINFORCING COLD FRONT ACROSS THE EAST,
AND THE UPPER RIDGE MOVES INLAND ACROSS THE INTERMOUNTAIN WEST AND
ROCKIES. THE RIDGE THEN BREAKS DOWN SOME AS A COUPLE OF PACIFIC
STORM SYSTEMS REACH THE WEST COAST. AS A RESULT, RAIN AND MOUNTAIN
SNOW MAKES A RETURN BY THE END OF THE WEEK ACROSS THE WEST, AND
LAKE EFFECT SNOW WILL BE COMMON DOWNWIND OF THE GREAT LAKES WITH
BELOW AVERAGE TEMPERATURES FROM THE NORTHERN PLAINS TO THE
NORTHEAST STATES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST MODEL GUIDANCE REMAINS WELL CLUSTERED MID- TO LATE WEEK
PARTICULARLY ON THE OVERALL PATTERN. GUIDANCE CONTINUES TO
INDICATE AN AMPLIFIED PATTERN FEATURING AN UPPER-LOW/ACCOMPANYING
DEEP SURFACE LOW OVER SOUTHEASTERN CANADA WITHIN BROADER TROUGHING
OVER THE CENTRAL TO EASTERN U.S., WITH AN UPPER- RIDGE OVER THE
WESTERN U.S. THIS ALLOWED FOR A COMPOSITE BLEND OF THE 06Z GFS AND
00Z ECMWF/CMC FOR THE FIRST PART OF THE UPDATED WPC FORECAST. SOME
ADJUSTMENTS WERE STILL NECESSARY TO THE NBM TO RAISE QPF FOR
FAVORABLE LAKE-EFFECT ZONES OF THE GREAT LAKES (PARTICULARLY THE
LOWER GREAT LAKES) AS WELL AS UPSLOPE PORTIONS OF THE APPALACHIANS
GIVEN AN EXPECTED CLIPPER SYSTEM AND POST-FRONTAL WEST-
NORTHWESTERLY FLOW PATTERN. ONE INTERESTING FEATURE OF NOTE WHICH
ALSO TIES INTO INCREASING UNCERTAINTY HEADING INTO THE WEEKEND IS
RETROGRADING UPPER-ENERGY DURING THE SHORT-RANGE PERIOD THAT MERGES
WITH AN OCCLUDED SYSTEM OVER THE SUBTROPICAL PACIFIC APPROACHING
CALIFORNIA BY MID-WEEK. THE NBM AND OTHER GUIDANCE HAVE TRENDED
MUCH WETTER ACROSS CALIFORNIA AND INTO THE GREAT BASIN/THE
SOUTHWEST AS A RESULT, AND THE UPDATED QPF FORECAST WAS INCREASED
TO REFLECT THIS. AS ALREADY NOTED AND HAS BEEN THE CASE FOR SEVERAL
FORECAST CYCLES, UNCERTAINTY WITH THE EVOLUTION OF THE PATTERN
OVER THE WEST INCREASES AS GUIDANCE DIFFERS AS THE UPPER- FLOW
BEGINS TO FLATTEN. THE GFS/ECMWF AND THEIR RESPECTIVE MEANS HAVE
COME INTO BETTER AGREEMENT ON THE TIMING AND AMPLITUDE OF AN UPPER-
TROUGH APPROACHING THE WEST COAST, AND THE NBM AND OTHER GUIDANCE
AT LEAST HAVE FOLLOWED A SIMILAR, WETTER TREND WITH EMBEDDED WAVES
IN THE FLOW AS WELL AS THE APPROACHING TROUGH. HOWEVER, THE UPDATED
WPC FORECAST STILL RELIED ON AN ENSEMBLE MEAN CONTRIBUTION FROM
THE ECENS AND THE GEFS OF 50% BY THE END OF THE PERIOD TO HANDLE
MORE SUBTLE DIFFERENCES. THE CMC DIFFERED SIGNIFICANTLY FROM THIS
GUIDANCE DEPICTING A FASTER UPPER-TROUGH AND ASSOCIATED STRONG
CLIPPER-LIKE SYSTEM SO IT WAS NOT INCLUDED. GUIDANCE ALSO CONTINUES
TO INDICATE THE POTENTIAL FOR UPPER-ENERGY TO INTERACT WITH A
QUASI-STATIONARY BOUNDARY ACROSS THE SOUTHEAST WITH POTENTIAL
SURFACE LOW ORGANIZATION NEXT WEEKEND. THE CONTRIBUTIONS FROM THE
ENSEMBLE MEANS FOR THE UPDATED FORECAST AND THE NBM FOR QPF REMAIN
A GOOD COMPROMISE SOLUTION FOR NOW.
..WEATHER/HAZARDS HIGHLIGHTS
LAKE EFFECT SNOW IS EXPECTED FROM MICHIGAN TO UPSTATE NEW YORK
WITH STRONG COLD AIR ADVECTION ACROSS THE GREAT LAKES THROUGH
THURSDAY. SOME HEAVY ACCUMULATIONS ARE LIKELY OVER THE COURSE OF
TUESDAY THROUGH THURSDAY, PARTICULARLY ACROSS PORTIONS OF UPSTATE
NEW YORK WHERE 1-2 FEET IS WELL WITHIN THE REALM OF POSSIBILITY,
AND SOME ADDITIONAL SNOW IS LIKELY GOING INTO FRIDAY AS WELL. SOME
UPSLOPE SNOWS ARE ALSO LIKELY ACROSS THE CENTRAL APPALACHIANS, AND
LIGHT SNOW FROM A CLIPPER TYPE SYSTEM IS EXPECTED FROM THE MIDWEST
TO THE OHIO VALLEY. THIS SYSTEM WILL REINFORCE THE COLD AIRMASS
THAT WILL ALREADY BE IN PLACE, BUT PROBABLY NOT COLD ENOUGH TO
ESTABLISH MANY RECORD LOWS.
IN TERMS OF HEAVY RAINFALL PROSPECTS, MOST OF THE COUNTRY SHOULD
BE DEVOID OF THAT AS SURFACE HIGH PRESSURE GOVERNS THE WEATHER
PATTERN ACROSS A MAJORITY OF THE COUNTRY. HOWEVER, A WEAKENING
OCCLUDED LOW PRESSURE SYSTEM FROM THE SUBTROPICS WILL HEAD IN THE
GENERAL DIRECTION OF SOUTHERN CALIFORNIA BRINGING A MODEST SURGE OF
MOISTURE FROM THE PACIFIC. THIS WILL INCREASE RAINFALL CHANCES
PARTICULARLY ACROSS THE TRANSVERSE RANGES OF SOUTHERN CALIFORNIA
AND ALSO THE PENINSULAR RANGE MID-WEEK, AND MARGINAL RISKS ARE
INCLUDED FOR THE DAY 4 AND 5 EXCESSIVE RAINFALL OUTLOOKS AS THIS
AREA REMAINS SENSITIVE GIVEN RECENT HEAVY RAINS. THE RISK FOR HEAVY
RAINFALL WILL EXPAND NORTHWARD TO COASTAL NORTHERN CALIFORNIA BY
THURSDAY/FRIDAY, AND HEAVY SNOWFALL IS ALSO EXPECTED FOR THE SIERRA
NEVADA AS PRECIPITATION CHANCES EXPAND MORE BROADLY ACROSS THE
WEST. SOME MODERATE SNOWS WILL BE POSSIBLE FOR THE INTERIOR
MOUNTAINS. MOIST RETURN FLOW ALONG A FRONTAL BOUNDARY ACROSS THE
SOUTHEAST MAY BRING INCREASING RAINFALL CHANCES NEXT WEEKEND,
THOUGH SIGNIFICANT UNCERTAINTY REMAINS WITH RESPECT TO BOTH
COVERAGE AND AMOUNTS.
A TEMPERATURE DICHOTOMY WILL CONTINUE TO EXIST ACROSS THE COUNTRY
FOR THE MIDDLE TO END OF THE WEEK WITH BELOW AVERAGE TEMPERATURES
FROM THE NORTHERN PLAINS TO THE MID-ATLANTIC/NORTHEAST, AND ABOVE
AVERAGE ACROSS MUCH OF THE WEST AND WESTERN HIGH PLAINS TO THE
WESTERN GULF COAST. THE COLDEST CONDITIONS ARE EXPECTED TO RESIDE
ACROSS THE UPPER MIDWEST, WHERE HIGHS FROM 0 TO 15 DEGREES WILL BE
COMMONPLACE ON THURSDAY WITH THE RENEWED SURGE OF ARCTIC AIR.
FREEZING TEMPERATURES WILL ALSO BE A CONCERN FOR SENSITIVE
VEGETATION ACROSS PORTIONS OF THE GULF COAST AND NORTHERN FLORIDA
WEDNESDAY AND THURSDAY MORNINGS. MEANWHILE, HIGHS WELL INTO THE 60S
AND 70S WILL LIKELY CONTINUE FOR MUCH OF THE SOUTHERN PLAINS AS
THIS AREA SHOULD REMAIN SOUTH OF THE JET STREAM.
PUTNAM/HAMRICK
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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