253
FXUS02 KWBC 171910
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
210 PM EST WED DEC 17 2025
VALID 12Z SAT DEC 20 2025 - 12Z WED DEC 24 2025
...ADDITIONAL ROUNDS OF HEAVY PRECIPITATION LIKELY FOR THE WEST
COAST...
..OVERVIEW
A SHALLOW UPPER TROUGH IS LIKELY TO MOVE ACROSS THE CENTRAL AND
EASTERN U.S. OVER THE WEEKEND WITHIN RELATIVELY ZONAL FLOW.
UPSTREAM, LOW AMPLITUDE RIDGING IS FORECAST TO MOVE THROUGH THE
INTERIOR WEST AND CENTRAL U.S. EARLY NEXT WEEK, STRENGTHENING INTO
THE MIDDLE OF NEXT WEEK WITH A SOUTH-CENTRAL U.S. UPPER HIGH
SETTING UP IN RESPONSE TO DEEPENING EASTERN PACIFIC TROUGHING.
ONSHORE FLOW WILL CONTINUE TO DIRECT ATMOSPHERIC RIVERS (ARS)
TOWARDS THE WEST COAST, CAUSING HEAVY PRECIPITATION TO NORTHERN
CALIFORNIA IN PARTICULAR, WITH SOME PRECIPITATION PUSHING INTO THE
INTERMOUNTAIN WEST/ROCKIES AS WELL. TEMPERATURE-WISE, UNSEASONABLY
TO POTENTIALLY RECORD-BREAKING WARM TEMPERATURES ARE FORECAST
ACROSS THE SOUTHWEST AND PORTIONS OF THE PLAINS, THOUGH THE
NORTHERN TIER CAN EXPECT COLDER PERIODS WITH SHORTWAVES MOVING
THROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT ON THE LARGE SCALE
PATTERN THROUGH THIS WEEKEND INTO NEXT WEEK. SOME UNCERTAINTY
REMAINS IN THE SMALLER SCALE DETAILS, WITH MODELS SHOWING SOME
TIMING DIFFERENCES WITH SHORTWAVES MOVING ALONG THE NORTHERN TIER
OF THE NATION. THE UKMET SEEMS TO BE A LITTLE FASTER THAN THE
GENERAL CONSENSUS WHILE THE ECMWF IS A LITTLE SLOWER. ADDITIONALLY,
THERE IS UNCERTAINTY WITH THE DEPTH AND POSITIONING OF THE
DEVELOPING TROUGH/UPPER LOW OVER THE EASTERN PACIFIC MID-NEXT WEEK.
THE 06Z GFS SEEMED TO BE A BIT OF AN OUTLIER WITH A CLOSED LOW
FORMING MUCH FARTHER SOUTH THAN THE CMC/ECMWF AND ENSEMBLE MEANS
SUGGEST, BUT THE 12Z RUN HAS COME IN MUCH CLOSER TO THE OTHER
SOLUTIONS.
GIVEN GOOD AGREEMENT, A GENERAL DETERMINISTIC MODEL BLEND WAS USED
AS THE STARTING POINT FOR WPC'S AFTERNOON FORECAST BLEND. ENSEMBLE
MEANS FROM THE GEFS AND ECENS WERE ADDED IN INCREASING AMOUNTS
EARLY NEXT WEEK TO HELP SMOOTH OUT MODEL DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
PERSISTENT ONSHORE FLOW WILL DIRECT PACIFIC MOISTURE INTO THE WEST
COAST THROUGH THE WEEKEND AND INTO NEXT WEEK, WITH THE HIGHEST
MOISTURE ANOMALIES EXPECTED WITH ATMOSPHERIC RIVERS IMPACTING
NORTHERN CALIFORNIA. THE DAY 4/SATURDAY EXCESSIVE RAINFALL OUTLOOK
CONTINUES TO HIGHLIGHT MOST OF NORTHERN CALIFORNIA WITH A MARGINAL
RISK FOR ISOLATED FLOODING. BY SUNDAY, THE NEXT ATMOSPHERIC RIVER
WILL ARRIVE, BRINGING HEAVY PRECIPITATION WITH HIGH RAIN RATES (1+
INCH PER 3 HRS) TO NORTHERN CALIFORNIA AND PROMPTING A SLIGHT RISK
OF EXCESSIVE RAINFALL IN THE DAY 5/SUNDAY ERO. SOME PRECIPITATION
IS ALSO POSSIBLE FARTHER NORTH INTO THE PACIFIC NORTHWEST, BUT WITH
LESSER AMOUNTS AND INTENSITIES. ADDITIONAL ROUNDS OF MODERATE TO
HEAVY PRECIPITATION ARE LIKELY ON MONDAY AND TUESDAY AS WELL. FOR
THESE EVENTS, MOISTURE IS FORECAST TO SPILL OVER INTO THE
INTERMOUNTAIN WEST AND NORTHERN/CENTRAL ROCKIES, WHICH COULD
PRODUCE HEAVY SNOW AT HIGHER ELEVATIONS WITH SUFFICIENTLY COLD
TEMPERATURES.
SHALLOW SHORTWAVES MOVING THROUGH THE NORTHERN TIER COULD BRING
LIGHT PRECIPITATION ACROSS THE NORTH-CENTRAL AND NORTHEASTERN U.S.
THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK, INCLUDING SOME LIGHT
SNOW. FARTHER SOUTH, SOME WEAK TO MODERATE GULF MOISTURE MAY STREAM
INTO 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 OVER THE WEEKEND INTO
EARLY 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
MOST DAYS, WITH TEMPERATURES AS MUCH AS 20-30 DEGREES ABOVE NORMAL.
HIGHS IN THE 70S AND 80S ACROSS THE SOUTHWEST TO TEXAS COULD SET
DAILY RECORDS. MEANWHILE, THE NORTHERN TIER IS FORECAST TO SEE
SHOTS OF COLD AIR WITH SHORTWAVES AND COLD SURFACE HIGHS BEHIND
COLD FRONTS. BELOW ZERO LOWS ARE POSSIBLE IN PORTIONS OF NORTH
DAKOTA AND MINNESOTA, WHILE HIGHS COULD BE PERIODICALLY BELOW
AVERAGE AS WELL. THE EASTERN U.S. CAN EXPECT MORE TRANSIENT ABOVE
AND BELOW AVERAGE TEMPERATURES AS FRONTS PASS THROUGH.
DOLAN/TATE
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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