238
FXUS02 KWBC 280715
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
215 AM EST SUN DEC 28 2025
VALID 12Z WED DEC 31 2025 - 12Z SUN JAN 4 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 COAST REGION, 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 DETERMINISTIC MODEL GUIDANCE INDICATES SOLID OVERALL
AGREEMENT WITH THE SYNOPTIC PATTERN THROUGH THURSDAY, AND A
GENERAL BLEND OF THE GUIDANCE SUFFICES FOR FRONTS AND PRESSURES.
THE BEST AGREEMENT IS NOTED ACROSS THE EASTERN U.S. WITH THE BROAD
UPPER LEVEL TROUGH PATTERN IN PLACE. MORE QUESTION MARKS ARISE
WITH THE EVENTUAL FLATTENING OF THE WESTERN U.S. RIDGE AS PACIFIC
SHORTWAVE ENERGY FROM BOTH THE SUBTROPICS AND THE NORTHEAST PACIFIC
MOVES TOWARDS THE WEST COAST TOWARDS THE END OF THE WEEK AND BEYOND.
WHILE OVERALL GUIDANCE REMAINS IN DECENTLY GOOD AGREEMENT FOR THE
EASTERN HALF OF THE COUNTRY, MODEL SPREAD DETERIORATES
SUBSTANTIALLY FROM THE ROCKIES TO THE WEST COAST. THIS INCLUDES
NOTEWORTHY DIFFERENCES BETWEEN THE OPERATIONAL GFS/ECMWF AND THEIR
RESPECTIVE ENSEMBLE MEANS AND AI MODELS, WITH NO CLEAR PREFERENCE
BY SATURDAY AS THE MODELS ARE STRUGGLING WITH THE PATTERN CHANGE
ACROSS THE WEST. THIS LEAD TO ENSEMBLE MEANS ACCOUNTING FOR ABOUT
70% OF THE FRONTS/PRESSURES FORECAST BY NEXT SUNDAY. IN TERMS OF
THE NBM, QPF/POPS VALUES CONTINUE TO BE RAISED NEAR THE GREAT
LAKES/OHIO VALLEY THROUGH THE END OF THE WEEK WITH A LIKELY LOW
BIAS IN THE NBM ACROSS THIS REGION.
..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 THROUGH WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE
GOVERNS THE WEATHER PATTERN ACROSS THE MAJORITY OF THE COUNTRY. A
WEAKENING OCCLUDED LOW PRESSURE SYSTEM FROM THE SUBTROPICS WILL
HEAD IN THE GENERAL DIRECTION OF SOUTHERN CALIFORNIA, AND BRING
LIGHT TO PERHAPS MODERATE RAINFALL BETWEEN 00Z-12Z THURSDAY, BUT
MODEL GUIDANCE SUGGESTS THE MORE IMPACTFUL RAINFALL DOESN'T ARRIVE
UNTIL AFTER 12Z THURSDAY. AFTER THAT, A MODEST SURGE OF MOISTURE
FROM THE PACIFIC INCREASES RAINFALL COVERAGE ACROSS THE TRANSVERSE
RANGES OF SOUTHERN CALIFORNIA AND ALSO THE PENINSULAR RANGE, AND A
MARGINAL RISK AREA HAS BEEN ADDED HERE FOR THE NEW DAY 5/THURSDAY
EXCESSIVE RAINFALL OUTLOOK. MODERATE TO HEAVY SNOW IS ALSO PROBABLE
FOR THE SIERRA NEXT THURSDAY/FRIDAY, WITH EXPANDING PRECIPITATION
CHANCES MORE BROADLY ACROSS MUCH OF THE WEST, ALTHOUGH MODEL
SOLUTIONS STILL DIFFER QUITE A BIT REGARDING SPECIFICS. MOIST
RETURN FLOW ALONG A FRONTAL BOUNDARY ACROSS THE SOUTHEAST MAY BRING
INCREASING RAINFALL CHANCES NEXT WEEKEND, THOUGH WITH SIGNIFICANT
UNCERTAINTY ON COVERAGE AND AMOUNTS HERE AS WELL.
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.
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.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page