957
FXUS02 KWBC 271925
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
225 PM EST SAT DEC 27 2025
VALID 12Z TUE DEC 30 2025 - 12Z SAT JAN 03 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 UPDATED 00/06Z MODEL GUIDANCE REMAINS GENERALLY WELL CLUSTERED
THROUGH THE EARLY PART OF THE MEDIUM RANGE PERIOD (NEXT TUESDAY-
THURSDAY). AN AMPLIFIED UPPER-LEVEL PATTERN IS INDICATED WITH A
DEEP UPPER-LOW/ACCOMPANYING STRONG SURFACE LOW OVER SOUTHEASTERN
CANADA WITHIN A BROAD UPPER-TROUGH OVER THE CENTRAL TO EASTERN
U.S., AND AN AMPLIFYING RIDGE MOVING EASTWARD OVER THE WESTERN U.S.
A COMPOSITE BLEND OF THE 06Z GFS AND 00Z ECMWF/CMC WAS USED WITH
GOOD CONTINUITY FROM THE PRIOR WPC FORECAST. THERE IS SOME
UNCERTAINTY WITH REGARDS TO AN OCCLUDED SYSTEM OVER THE SUBTROPICAL
PACIFIC THAT COULD BRING SOME PRECIPITATION TO SOUTHERN CALIFORNIA
AND THE SOUTHWESTERN U.S., AS WELL AS WITH AN UPPER-WAVE BRINGING
LIGHT PRECIPITATION CHANCES TO THE SOUTH- CENTRAL U.S., BUT THE
VARYING SOLUTIONS MAKE IT HARD TO PLACE MUCH CONFIDENCE IN EITHER
AT THIS TIME RANGE. THEN, BY LATER NEXT WEEK AND INTO THE WEEKEND,
UNCERTAINTY INCREASES RAPIDLY WITH RESPECT TO THE PATTERN EVOLUTION
OVER THE WESTERN TO CENTRAL U.S. AS AN UPPER-TROUGH APPROACHES THE
WEST COAST AND THE RIDGE BEGINS TO FLATTEN. WHILE ALL GUIDANCE
GENERALLY TENDS TO AGREE ON A FLATTENING RIDGE, THERE IS
SIGNIFICANT DIVERGENCE WITH RESPECT TO HOW DEEP THE UPPER-TROUGH
WILL DIG ALONG THE WEST COAST, AS WELL AS, NOT SURPRISINGLY, WITH
UNPREDICTABLE EMBEDDED WAVES BEGINNING TO PASS THROUGH THE WEST
TOWARDS THE PLAINS WITHIN THE FLATTENING FLOW. FOR EXAMPLE, THE
ECMWF/ECENS MEAN WOULD FAVOR WIDESPREAD, POTENTIALLY HEAVY
PRECIPITATION ACROSS MUCH OF THE WEST, ESPECIALLY ALONG THE WEST
COAST, WHILE THE CMC AND GFS/GEFS MEAN SHOW SIGNIFICANTLY LESS, IF
ANY, FOR MUCH OF THE REGION. FOR NOW, USED A MODEL BLEND FEATURING
60 TO THEN 70% OF THE GEFS/ECENS MEANS GIVEN THE LARGER SPREAD IN
THE DETERMINISTIC GUIDANCE, AND DID NOT INCLUDE ANY OF THE 12Z CMC
AS IT WAS AN OUTLIER IN DEVELOPING A DEEPENING LOW OVER THE SOUTH-
CENTRAL U.S. THE NBM ALSO REPRESENTED A GOOD COMPROMISE SOLUTION
AMONGST THE GUIDANCE FOR QPF, WITH BROAD PRECIPITATION CHANCES AS
INDICATED BY THE ECMWF/ECENS MEAN, BUT WITH LOWER AMOUNTS GIVEN THE
UNCERTAINTY. PRECIPITATION CHANCES ALSO VARY SIGNIFICANTLY OVER
THE SOUTHEASTERN U.S. WITH POTENTIAL GULF RETURN FLOW ALONG A
QUASI- STATIONARY BOUNDARY. BROAD, LIGHT PRECIPITATION CHANCES AS
INDICATED BY THE NBM REFLECT A GOOD COMPROMISE HERE FOR NOW AS
WELL.
..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.
WHILE UNCERTAINTY WITH REGARDS TO THE SPECIFICS REMAINS, THERE ARE
INDICATIONS FROM AT LEAST SOME OF THE MODEL GUIDANCE THAT HEAVY
RAINFALL WILL RETURN TO SOUTHERN CALIFORNIA WITH HEAVY SNOW IN THE
SIERRA NEXT THURSDAY/FRIDAY, WITH EXPANDING PRECIPITATION CHANCES
MORE BROADLY ACROSS MUCH OF THE WEST. MOIST GULF RETURN FLOW ALONG
A FRONTAL BOUNDARY ACROSS THE SOUTHEAST MAY BRING INCREASING
PRECIPITATION CHANCES NEXT WEEKEND, THOUGH WITH SIGNIFICANT
UNCERTAINTY ON COVERAGE AND AMOUNTS HERE AS WELL.
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. CONDITIONS MAY ALSO REACH LOCALLY DANGEROUS COLD
LEVELS ACROSS PORTIONS OF THE CENTRAL GULF COAST AND INTO THE
SOUTHEAST TUESDAY-WEDNESDAY WITH MORNING WIND CHILLS INTO THE 20S
AND POSSIBLY TEENS. MEANWHILE, HIGHS WELL INTO THE 60S AND 70S WILL
LIKELY CONTINUE FOR MUCH OF THE SOUTHERN PLAINS.
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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