004
FXUS02 KWBC 221831
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 PM EST MON DEC 22 2025
VALID 12Z THU DEC 25 2025 - 12Z MON DEC 29 2025
...AN ATMOSPHERIC RIVER WILL CONTINUE TO BRING HEAVY TO
SIGNIFICANT RAINFALL TO PARTS OF CALIFORNIA THROUGH ABOUT
THURSDAY...
..OVERVIEW
A QUITE AMPLIFIED AND WARMING UPPER RIDGE WILL SHIFT THROUGH THE
EAST-CENTRAL U.S. LATE THIS WEEK, AS DEEP TROUGHING OFF THE WEST
COAST SHIFTS INLAND BY THE WEEKEND TO FINALLY BRING AN END TO THE
ATMOSPHERIC RIVER (AR) IMPACTING CALIFORNIA. HEAVY TO SIGNIFICANT
RAINFALL THOUGH WILL CONTINUE THROUGH AT LEAST THURSDAY/CHRISTMAS
DAY FOR SOUTHERN CALIFORNIA WITH RAINFALL COVERAGE AND INTENSITY
WEAKENING BY FRIDAY AND ESPECIALLY THE WEEKEND. WEST COAST ACTIVITY
WILL ALSO CONTINUE, IN MODERATED FORM, FOR THE INTERMOUNTAIN WEST
AND ROCKIES. ACROSS THE MIDDLE PART OF THE NATION, THE BIG STORY
WILL BE UNSEASONABLE WARMTH AND POSSIBLE RECORD WARM TEMPERATURES
FROM THE SOUTHWEST INTO THE PLAINS AND EAST-CENTRAL STATES. THE
COLDER NORTHERN TIER MAY SEE PLOWABLE SNOW CHANCES FROM THE UPPER
GREAT LAKES TO THE NORTHEAST AS SHORTWAVES AND FRONTAL SYSTEMS PASS
THROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE GUIDANCE SHOWS GOOD AGREEMENT IN THE BEGINNING OF THE PERIOD,
BUT UNCERTAINTY REALLY GROWS BY THE WEEKEND, ESPECIALLY AS IT
PERTAINS TO THE EVOLUTION OF THE TROUGH AS IT MOVES INTO THE WEST.
MODELS GENERALLY SHOW THIS TROUGH TO SPLIT, SENDING A DEEPENED
SHORTWAVE INTO THE NORTH- CENTRAL U.S. AND CUTOFF ENERGY/CLOSED LOW
DEVELOPMENT OVER THE SOUTHWEST. BY SUNDAY, THE GFS IS FASTER WITH
THE NORTHERN STREAM SHORTWAVE WHICH ALLOWS FOR A QUICKER CUTOFF OF
THE UPPER LOW AND IT HOLDS A VERY STRONG LOW OVER CALIFORNIA INTO
EARLY NEXT WEEK. THERE MAY BE SLIGHTLY BETTER CONSENSUS (WITH
SUPPORT FROM THE ECMWF AND CMC AND ENSEMBLE MEANS) FOR SOMETHING A
BIT SLOWER, ALLOWING FOR A LATER AND MORE WESTWARD UPPER LOW OVER
THE EASTERN PACIFIC. THE AI GUIDANCE IS MIXED, WITH SOME SUPPORT
FOR THE GFS AS WELL. SO WITH UNCERTAINTY HIGH AND ALL SOLUTIONS
STILL IN PLAY, OPTED TO STICK FAIRLY CLOSE TO WPC CONTINUITY AND
THE ENSEMBLE MEANS FOR THE LATER PERIOD FORECAST. BASED ON
CONTINUITY THOUGH, MODELS HAVE TRENDED QUITE A BIT STRONGER WITH A
SURFACE LOW THROUGH THE GREAT LAKES AND NORTHEAST IN WHAT SEEMS TO
BE A TREND TOWARDS A MORE AMPLIFIED PATTERN OVERALL MID TO LATE
PERIOD. THE 13Z NBM SERVED AS A GOOD STARTING POINT FOR THE MEDIUM
RANGE SENSIBLE WEATHER GRIDS, WITH MINIMAL EDITING NEEDED GIVEN
HIGH UNCERTAINTY IN THE DETAILS.
..WEATHER/HAZARDS HIGHLIGHTS
EASTERN PACIFIC AMPLIFIED UPPER TROUGHING AND SYSTEM GENESIS WILL
WORK TOWARD THE WEST COAST WITH LEAD DEEP ONSHORE FLOW CONTINUING
TO DIRECT PACIFIC MOISTURE INTO THE WEST COAST INTO LATE THIS WEEK
WITH CONSIDERABLE FLOOD IMPACTS EXPECTED, ESPECIALLY FOR PARTS OF
SOUTHERN CALIFORNIA OVER THE CHRISTMAS PERIOD. THIS IMPACTFUL EVENT
WILL STEADILY LOSE INFLUENCE BY FRIDAY AND ESPECIALLY INTO THE
WEEKEND AS THE SURFACE LOW/FRONTAL SYSTEM WORKS INLAND WITH UPPER
TROUGH PROGRESSION. MARGINAL AND EMBEDDED SLIGHT RISK ERO THREATS
CONTINUE TO BE DEPICTED FOR THURSDAY/FRIDAY, FROM CENTRAL TO
SOUTHERN CALIFORNIA AND THE SOUTHERN GREAT BASIN. HIGHER ELEVATIONS
OF THE SIERRA SHOULD SEE AN EXTENDED HEAVY SNOW EVENT. TO THE
NORTH, THE PACIFIC NORTHWEST CAN ALSO EXPECT ORGANIZED
PRECIPITATION THIS WEEK, BUT WITH LESSER AMOUNTS. ADDITIONALLY,
MOISTURE IS FORECAST TO SPILL OVER THE CASCADES TO THE
INTERMOUNTAIN WEST AND NORTHERN/CENTRAL ROCKIES TO PRODUCE HEAVY
SNOW AT HIGHER ELEVATIONS. SOME PRECIPITATION MAY CONTINUE ACROSS
PARTS OF THE SOUTHWEST INTO NEXT WEEK, BUT HIGHLY DEPENDENT ON
EVOLUTION OF THE LINGERING CUTOFF LOW NEAR/OFF CALIFORNIA.
ELSEWHERE, LEADING SHALLOW SHORTWAVES MOVING THROUGH THE NORTHERN
TIER AND ASSOCIATED SURFACE SYSTEM REFLECTION AND POSSIBLE FLOW
AMPLIFICATION WITH THE DIGGING OF NORTHERN STREAM UPPER TROUGHING
INTO THE LOWER 48 MAY BRING GENERALLY LIGHT PRECIPITATION FROM THE
NORTH-CENTRAL U.S. TO THE GREAT LAKES AND OHIO VALLEY AND
NORTHEAST. THIS MAY INCLUDE CHANCES FOR SOME ENHANCED SNOWS WITH
MAIN FOCUS FROM THE UPPER GREAT LAKES TO INCREASINGLY SOUTHWARD
ACROSS THE NORTHEAST TO MONITOR.
TEMPERATURES WILL CONTINUE TO BE ANOMALOUSLY WARM FROM THE CENTRAL
TO EAST-CENTRAL U.S. THURSDAY TO SATURDAY. DAYTIME HIGHS 25-30+
DEGREES ABOVE NORMAL MAY SET DAYTIME AND WARM MORNING LOW RECORDS.
THE AIRMASS MOVES EAST WITH TIME, MODERATING AS IT REACHES THE EAST
ON SUNDAY. AN AMPLIFIED SHORTWAVE INTO THE NORTHEAST WILL BRING
TEMPERATURES BACK BELOW NORMAL BY NEXT MONDAY. OUT WEST,
TEMPERATURES SHOULD MODERATE TOWARDS NORMAL THIS WEEKEND, WITH
ANOTHER WARMUP POSSIBLE EARLY NEXT WEEK AS UPPER RIDGING BUILDS IN.
SANTORELLI/SCHICHTEL
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