516
FXUS02 KWBC 311932
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EST WED DEC 31 2025
VALID 12Z SAT JAN 03 2026 - 12Z WED JAN 07 2026
..OVERVIEW
BROAD CYCLONIC FLOW ALOFT WILL BE IN PLACE ACROSS THE GREAT LAKES
REGION AND THE NORTHEAST OVER THE WEEKEND, AND THEN THE TROUGH
BECOMES A LITTLE LESS AMPLIFIED AS THE DEEP LOW OVER CENTRAL CANADA
LIFTS OUT SOME TO THE NORTH. ACROSS THE SOUTHERN TIER STATES, A
WAVE OF LOW PRESSURE LOOKS TO DEVELOP ALONG A FRONTAL BOUNDARY AND
BRING RAINFALL CHANCES ACROSS THE SOUTHEAST U.S. INTO SATURDAY.
MEANWHILE, AN UPPER-LEVEL RIDGE WILL INITIALLY BE IN PLACE ACROSS
THE INTERMOUNTAIN WEST, REACHING THE PLAINS BY EARLY NEXT WEEK WITH
WIDESPREAD ABOVE AVERAGE TEMPERATURES. ROUNDS OF RAIN AND MOUNTAIN
SNOW WILL BE COMMONPLACE ACROSS THE WEST COAST STATES FOR THE
WEEKEND AND GOING INTO NEXT WEEK AS SHORTWAVES AND ONSHORE FLOW
AFFECT THE REGION. ADDITIONALLY, ANOTHER COUPLE OF CLIPPER SYSTEMS
WILL CROSS THE UPPER MIDWEST AND GREAT LAKES INTO EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS IN GOOD SYNOPTIC SCALE AGREEMENT WITH THE
GENERAL PATTERN ACROSS THE LOWER 48 GOING INTO THE WEEKEND. A QUICK
MOVING SHORTWAVE WILL CAUSE CYCLOGENESIS ALONG A FRONTAL BOUNDARY
IN THE SOUTHEAST SATURDAY AND MOVE INTO THE WESTERN ATLANTIC. BROAD
TROUGHING IS ALSO FORECAST FARTHER NORTH OVER THE GREAT LAKES TO
NORTHEAST THAT WILL HAVE MORE STAYING POWER, THOUGH SHOULD
GRADUALLY LIFT NEXT WEEK. CMC RUNS HAVE BEEN MORE SHALLOW/OFF WITH
THIS TROUGH. MEANWHILE, THE RIDGE AXIS OVER THE INTERMOUNTAIN WEST
SATURDAY SHOWS GOOD AGREEMENT IN SHIFTING AND EXPANDING EAST TO THE
PLAINS BY SUNDAY-MONDAY. THIS COULD ALL BE HANDLED WELL WITH A
MULTI-MODEL BLEND FOR THE FORECAST.
THE MOST UNCERTAIN ASPECT OF THE FORECAST IS THE TROUGH PATTERN
ACROSS THE EASTERN PACIFIC TO WESTERN U.S., INITIALLY WITH
SHORTWAVE TIMING AND PLACEMENT BUT EVENTUALLY WITH THE BROADER
PATTERN AS NEXT WEEK PROGRESSES. WITH THE 00Z/06Z MODEL CYCLE,
THERE WAS NOTABLE SPREAD BY TUESDAY-WEDNESDAY REGARDING THE
POSITION OF SOUTHERN STREAM TROUGHING/A POTENTIAL CLOSED LOW MOVING
INTO/TOWARD CALIFORNIA. THE CMC AND AIFS WERE ON THE PROGRESSIVE
SIDE WITH THIS FEATURE. MEANWHILE THE 06Z GFS IN PARTICULAR WAS
MUCH FARTHER NORTHWEST IN THE PACIFIC, WHILE THE ECMWF AND AI-GFS
WERE IN BETWEEN. IN THE NEWER 12Z MODEL CYCLE, MODELS ARE MORE
AGREEABLE WITH A PROGRESSIVE TROUGH/LOW, WITH THE BULK OF AI AND
DYNAMICAL GUIDANCE SHIFTING THAT WAY. THE 12Z ECMWF DOES SEEM
WEAKER THAN CONSENSUS WITH THE ENERGY BY NEXT WEDNESDAY THOUGH. THE
STREAM SEPARATION AND POSSIBLE NORTHERN STREAM SHORTWAVES ALSO
MAKE A DIFFERENCE WITH THE PATTERN ACROSS THE CENTRAL U.S. WITH
LOW/FRONTAL PLACEMENT AND TEMPERATURES. OVERALL, THE WPC FORECAST
USED INCREASING PROPORTIONS OF THE ENSEMBLE MEANS AS THE PERIOD
PROGRESSED TO MITIGATE INDIVIDUAL MODEL DIFFERENCES, WITH AN
OVERALL TREND TOWARD A FASTER WESTERN TROUGH.
..WEATHER/HAZARDS HIGHLIGHTS
AN ACTIVE WEATHER PATTERN DEVELOPS ALONG THE WEST COAST IN TIME
FOR THE WEEKEND AS A ORGANIZED LOW PRESSURE SYSTEM LIFTS
NORTHEASTWARD TOWARD THE PACIFIC NORTHWEST, WITH ITS COLD FRONT
REACHING THE CALIFORNIA COAST. A SOUTHWEST TO NORTHEAST ORIENTED
ATMOSPHERIC RIVER WILL AFFECT NORTHERN CALIFORNIA JUST AHEAD OF THE
FRONT, WITH HIGH MOISTURE ANOMALIES SPREADING INTO SOUTHERN
CALIFORNIA AS WELL ON SATURDAY. ANOTHER MOISTURE SURGE IS LIKELY ON
SUNDAY ACROSS CALIFORNIA. COASTAL REGIONS AND THE SIERRA NEVADA
FOOTHILLS CAN EXPECT THE HIGHEST RAIN TOTALS. MARGINAL RISKS REMAIN
IN PLACE FOR THESE AREAS IN BOTH THE DAY 4/SATURDAY AND DAY
5/SUNDAY EROS, EXPANDED SOUTHWARD INTO THE TRANSVERSE RANGES OF
SOCAL GIVEN THEIR ONGOING SENSITIVITY TO HEAVY RAIN DUE TO RECENT
(AND SHORT RANGE) HEAVY RAIN EVENTS AS WELL AS BURN SCARS IN THE
REGION. HEAVY SNOW IS LIKELY FOR THE HIGHER TERRAIN OF THE SIERRA.
MORE MODEST PRECIPITATION AMOUNTS ARE EXPECTED FARTHER NORTH IN THE
PACIFIC NORTHWEST AND FARTHER EAST INTO THE INTERMOUNTAIN WEST.
PRECIPITATION IS FORECAST TO CONTINUE INTO MONDAY-TUESDAY ACROSS
THE WEST, BUT WITH INCREASING UNCERTAINTY IN THE DETAILS DUE TO
MODEL DIFFERENCES.
ELSEWHERE ACROSS THE COUNTRY, AN AREA OF LOW PRESSURE IS EXPECTED
TO EXIT THE SOUTHEAST COAST ON SATURDAY. THIS QUICK-MOVING SYSTEM
WILL PRODUCE A CORRIDOR OF MODERATE RAINFALL AND SOME THUNDERSTORMS
FROM MISSISSIPPI EASTWARD TO THE COASTAL CAROLINAS, FOLLOWED BY
DRIER WEATHER ON SUNDAY. FARTHER NORTH, AFTER SOME LINGERING LAKE
EFFECT SNOW INTO SATURDAY, A SERIES OF CLIPPER SYSTEMS ARE FORECAST
TO TRACK FROM THE UPPER MIDWEST TO THE GREAT LAKES AND THEN NEW
ENGLAND DURING THE PERIOD. THESE RELATIVELY WEAK SYSTEMS COULD
PRODUCE A SWATH OF MAINLY LIGHT SNOW AND PERHAPS SOME MIXED WINTRY
PRECIPITATION ALONG THE SOUTHERN PORTION OF ITS TRACK. THE
POTENTIAL CLIPPER TUESDAY-WEDNESDAY AND LAKE EFFECT/UPSLOPE
SNOWFALL IN THE APPALACHIANS BEHIND IT SHOW THE MOST MODEL
UNCERTAINTY.
TEMPERATURES ARE LIKELY TO BE WARMER THAN AVERAGE ACROSS A WIDE
EXPANSE OF THE COUNTRY THIS WEEKEND INTO THE MIDDLE OF NEXT WEEK,
ESPECIALLY FROM THE ROCKIES TO THE CENTRAL AND SOUTHERN PLAINS.
HIGHS COULD BE 15 TO 25 DEGREES ABOVE AVERAGE FROM NORTHERN TEXAS
TO NEBRASKA, WITH LOWER 60S REACHING AS FAR NORTH AS NEBRASKA
SUNDAY INTO MONDAY. DAILY RECORDS FOR WARM LOWS AND HIGHS COULD BE
SET ACROSS THE INTERMOUNTAIN WEST AND PLAINS. THE EXCEPTION TO THE
MILD CONDITIONS WILL BE FROM THE GREAT LAKES TO THE NORTHEAST AS
THIS REGION REMAINS UNDER THE GENERAL INFLUENCE OF AN UPPER TROUGH
AND NORTH OF THE JET STREAM. HIGHS SHOULD BE 5 TO 15 DEGREES BELOW
AVERAGE, WITH THE COLDEST READINGS ACROSS MAINE.
TATE/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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