432
FXUS02 KWBC 191903
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 PM EST FRI DEC 19 2025
VALID 12Z MON DEC 22 2025 - 12Z FRI DEC 26 2025
...A SERIES OF ATMOSPHERIC RIVERS WITH ADDITIONAL ROUNDS OF HEAVY
RAINFALL TO IMPACT THE WEST COAST THROUGH THE PERIOD...
..OVERVIEW
UPPER RIDGING WILL WORK OVER THE INTERIOR WEST AND CENTRAL U.S.
EARLY NEXT WEEK, STRENGTHENING INTO MIDWEEK WITH A SOUTH-CENTRAL
U.S. UPPER HIGH SETTING UP IN RESPONSE TO DEEPENING EASTERN PACIFIC
UPPER TROUGHING. IN THIS IMPACTFUL PATTERN, ONSHORE FLOW WILL
CONTINUE TO DIRECT ATMOSPHERIC RIVERS (ARS) TOWARDS THE WEST COAST,
WITH HEAVY PRECIPITATION AFFECTING CALIFORNIA IN PARTICULAR, WITH
PRECIPITATION PUSHING INTO THE INTERMOUNTAIN WEST/ROCKIES AS WELL.
TEMPERATURE- WISE, UNSEASONABLY TO POTENTIALLY SOME RECORD-BREAKING
WARM TEMPERATURES ARE FORECAST ACROSS THE SOUTHWEST AND PORTIONS
OF THE PLAINS, THOUGH THE NORTHERN TIER CAN EXPECT MODESTLY COLDER
PERIODS WITH SHORTWAVES AND FRONTAL SYSTEMS MOVING THROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AGREEMENT ACROSS THE CONUS REMAINS IN GOOD AGREEMENT, AT
LEAST SYNOPTICALLY. THERE ARE SOME MINOR/LESS IMPACTFUL DIFFERENCES
IN TROUGH AND FRONTAL TIMING ACROSS THE CENTRAL TO EASTERN U.S.
EARLY WEEK. THE MOST UNCERTAIN AND IMPACTFUL PART OF THE PATTERN IS
WITH TROUGHING THAT DEEPENS OFF THE EASTERN PACIFIC AS IT MOVES
TOWARDS CALIFORNIA AND POSSIBLY ONSHORE BY NEXT FRIDAY. THE MODELS
DO AGREE THAT THIS WILL OCCUR, BUT THE DETAILS OF ENERGIES WITHIN
THE TROUGH AND VORT MAXES TOWARDS THE COAST WILL CREATE
CONSIDERABLE IMPACTS TO SENSIBLE WEATHER ASPECTS. THERE CONTINUES
TO BE A SIGNAL FOR A COUPLE OF ARS DURING THE PERIOD AND HEAVY
RAINFALL SHIFTING SOUTHWARD ALONG THE CALIFORNIA COAST WITH TIME,
BUT THERE IS SOME DISTRIBUTION/EXACT AMOUNTS UNCERTAINTY. BY NEXT
FRIDAY, SOME MORE IMPACTFUL TIMING DIFFERENCES EMERGE, WITH THE GFS
AND ENSEMBLE MEANS (AND SOME AI GUIDANCE) SHOWING A SLOWER/DEEPER
TROUGH/UPPER LOW OFF THE COAST, AND THE CMC SUGGESTING THE TROUGH
MOVES INLAND BY THEN. THE DETERMINISTIC ECMWF WAS SLOWER THAN THE
CMC BUT A BIT FASTER THAN THE GFS/CONSENSUS.
THE WPC FORECAST WAS ABLE TO UTILIZE A FULLY DETERMINISTIC MODEL
BLEND FOR DAYS 3-5. FOR 6 AND 7, DID INCORPORATE MORE ENSEMBLE
MEANS TO HELP MITIGATE THE SMALLER SCALE DIFFERENCES AND MAINTAIN
CONSISTENCY WITH THE PREVIOUS WPC FORECAST UNTIL A CLEARER TREND
EMERGES.
..WEATHER/HAZARDS HIGHLIGHTS
THE BIGGEST STORY DURING THE PERIOD WILL FOCUS OUT WEST WITH
AMPLIFYING UPPER TROUGHING AND SYSTEM GENESIS WORKING TOWARD THE
WEST COAST AND PERSISTENT LEAD ONSHORE FLOW DIRECTING PACIFIC
MOISTURE INTO THE WEST COAST THROUGH NEXT WEEK. HIGH MOISTURE
ANOMALIES EXPECTED WITH ATMOSPHERIC RIVERS IMPACTING
NORTHERN/CENTRAL CALIFORNIA EARLY IN THE WEEK AND EVENTUALLY
CENTRAL/SOUTHERN CALIFORNIA THROUGH CHRISTMAS EVE/CHRISTMAS.
AN AR IS FORECAST TO TAKE AIM AT NORTHERN CALIFORNIA DURING THE
SHORT RANGE PERIOD INTO SUNDAY, CONTINUING WELL INTO NEXT WEEK,
SETTING UP A CONTINUED WET PERIOD FOR PARTICULARLY CALIFORNIA
DURING THE UPCOMING BUSY HOLIDAY WEEK. THE GUIDANCE SIGNAL IS
GROWING IN SUPPORT OF A RENEWED DEEP MOISTURE FEED MONDAY AND
TUESDAY FOR NORTHERN-CENTRAL CALIFORNIA, WITH HIGH RAIN RATES (1+
INCH PER 3 HOURS) AND AREAL AVERAGED RAINFALL OF 3"+ TOWARD COASTAL
AREAS AND 5"+ TOWARDS THE SIERRA NEVADA. WPC EXCESSIVE RAINFALL
OUTLOOK MARGINAL RISK THREAT AREAS WITH EMBEDDED SLIGHT RISK AREAS
CONTINUE FOR BOTH DAYS AS PRECIPITATION MAY PROVE SLOW TO SHIFT
FROM AREAS ALREADY WITH WET CONDITIONS. BY ABOUT MIDWEEK, SOME
CONNECTION TO TROPICAL PACIFIC MOISTURE IS LIKELY TO STREAM IN AND
MAY INCREASINGLY IMPACT SOUTHERN CALIFORNIA AS A SURFACE LOW
APPROACHES THE COAST. HIGHER ELEVATIONS OF THE SIERRA SHOULD SEE AN
EXTENDED HEAVY SNOW EVENT. TO THE NORTH, THE PACIFIC NORTHWEST CAN
ALSO EXPECT ORGANIZED PRECIPITATION INTO EARLY NEXT WEEK, BUT WITH
LESSER AMOUNTS AND INTENSITIES. ADDITIONALLY, MOISTURE IS FORECAST
TO SPILL OVER THE CASCADES AND INTO THE INTERMOUNTAIN WEST AND
NORTHERN/CENTRAL ROCKIES NEXT WEEK TO PRODUCE HEAVY SNOW AT HIGHER
ELEVATIONS.
SHALLOW SHORTWAVES MOVING THROUGH THE NORTHERN TIER AND ASSOCIATED
SURFACE SYSTEM REFLECTION FOCUS WILL BRING LIGHT PRECIPITATION
ACROSS THE NORTH-CENTRAL AND NORTHEASTERN U.S. THROUGH THE EARLY
PART OF NEXT WEEK, INCLUDING SOME LIGHT SNOWS. FARTHER SOUTH, SOME
WEAK TO MODERATE GULF MOISTURE MAY STREAM INTO TRAILING FRONTAL
SYSTEMS ACROSS THE SOUTH AND EAST-CENTRAL U.S. AND LEAD TO
PRECIPITATION (MOSTLY RAIN) CHANCES ACROSS THE LOWER MISSISSIPPI,
TENNESSEE, AND OHIO VALLEYS FOR EARLY TO MID NEXT WEEK.
WARMER THAN AVERAGE TEMPERATURES ARE FORECAST ACROSS THE INTERIOR
WEST AND CENTRAL U.S. THROUGH MUCH OF THE PERIOD. THE HIGHEST
ANOMALIES WILL LIKELY BE ACROSS THE INTERIOR WEST INTO THE PLAINS,
WITH WIDESPREAD TEMPERATURE ANOMALIES UPWARDS TO 20-30 DEGREES
ABOVE NORMAL. HIGHS INTO THE 80S ACROSS PARTS OF THE SOUTHWEST TO
TEXAS COULD SET DAILY RECORDS. UNSEASONABLE WARMTH IS LIKELY TO
SPREAD EAST ACROSS THE MID-LATITUDES TO THE MISSISSIPPI, OHIO, AND
TENNESSEE VALLEYS OVER THE CHRISTMAS HOLIDAY PERIOD.
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
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