070
FXUS02 KWNH 270704
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 AM EST SAT DEC 27 2025
VALID 12Z TUE DEC 30 2025 - 12Z SAT JAN 3 2026
..OVERVIEW
AN AMPLIFIED UPPER LEVEL PATTERN IS EXPECTED TO BE IN PLACE ACROSS
THE CONTINENTAL U.S. TO START THE FORECAST PERIOD TUESDAY, WITH AN
UPPER RIDGE SITUATED OVER THE WEST COAST REGION AND A BROAD UPPER
TROUGH EAST OF THE MISSISSIPPI RIVER, WITH A STRONG LOW PRESSURE
SYSTEM EXITING THE NORTHEAST. THIS REMAINS THE CASE GOING INTO THE
LATTER HALF OF THE WEEK, WITH A REINFORCING COLD FRONT ACROSS THE
EAST, AND THE UPPER RIDGE MOVES INLAND ACROSS THE INTERMOUNTAIN
WEST AND ROCKIES. RAIN AND MOUNTAIN SNOW MAKES A RETURN BY THURSDAY
ACROSS THE WEST COAST REGION AS TWO SEPARATE SYSTEMS FROM THE
PACIFIC AFFECT THE REGION, AND LAKE EFFECT SNOW WILL BE COMMON
DOWNWIND OF THE GREAT LAKES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST DETERMINISTIC MODEL GUIDANCE INDICATES SOLID OVERALL
AGREEMENT WITH THE SYNOPTIC PATTERN THROUGH WEDNESDAY, AND A
GENERAL BLEND OF THE GUIDANCE SUFFICES FOR FRONTS AND PRESSURES.
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. 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 AT ODDS WITH EACH
OTHER. THIS LEAD TO ENSEMBLE MEANS ACCOUNTING FOR ABOUT 2/3RDS OF
THE FRONTS/PRESSURES FORECAST BY THAT TIME. IN TERMS OF THE NBM,
QPF VALUES WERE RAISED NEAR THE GREAT LAKES/OHIO VALLEY, AND ALSO
ACROSS SOUTHERN CALIFORNIA WITH THE NEXT ROUND OF RAINFALL
APPROACHING THE REGION THURSDAY MORNING.
..WEATHER/HAZARDS HIGHLIGHTS
LAKE EFFECT SNOW IS EXPECTED IN THE WAKE OF THE STRONG DEPARTING
LOW PRESSURE SYSTEM, WHICH WILL BE ENTERING SOUTHEASTERN CANADA BY
TUESDAY MORNING. A FEW DAYS OF COLD AIR ADVECTION ACROSS THE GREAT
LAKES THROUGH THE REMAINDER OF NEXT WEEK WILL LIKELY RESULT IN SOME
HEAVY ACCUMULATIONS, PARTICULARLY ACROSS PORTIONS OF UPSTATE NEW
YORK WHERE 1-2 FEET IS WELL WITHIN THE REALM OF POSSIBILITY. 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, SO NO EXCESSIVE RAINFALL AREAS ARE
CURRENTLY WARRANTED NATIONWIDE FOR BOTH TUESDAY AND WEDNESDAY. RAIN
AND MOUNTAIN SNOW BECOME MORE WIDESPREAD ACROSS THE WEST BY FRIDAY
INTO SATURDAY.
A TEMPERATURE DICHOTOMY WILL CONTINUE TO EXIST ACROSS THE COUNTRY
NEXT WEEK WITH BELOW AVERAGE TEMPERATURES FROM THE NORTHERN PLAINS
TO THE EAST COAST, 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 IN THE 0S AND LOW TEENS ALONG WITH SUBZERO OVERNIGHT LOWS
WILL
BE COMMONPLACE, ESPECIALLY 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.
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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