651
FXUS02 KWBC 162000
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EST TUE DEC 16 2025
VALID 12Z FRI DEC 19 2025 - 12Z TUE DEC 23 2025
...ADDITIONAL ROUNDS OF HEAVY PRECIPITATION LIKELY FOR THE WEST
COAST...
..OVERVIEW
AFTER A TROUGH PUSHES THROUGH THE EASTERN U.S. ON FRIDAY, THE
UPPER FLOW WILL BECOME QUASI-ZONAL ACROSS THE LOWER 48. BROAD
SHALLOW TROUGHING IS FORECAST TO PUSH THROUGH THE NORTHERN TIER
OVER THE WEEKEND, AND THEN BROAD AND STRENGTHENING RIDGING WILL
AFFECT THE INTERIOR WEST TO CENTRAL U.S. INTO EARLY NEXT WEEK. THIS
FLOW PATTERN WILL CONTINUE TO BRING A SERIES OF ATMOSPHERIC RIVERS
(ARS) AND HEAVY PRECIPITATION TO THE PACIFIC NORTHWEST INTO
NORTHERN CALIFORNIA, WITH SOME PRECIPITATION PUSHING INTO THE
INTERMOUNTAIN WEST/ROCKIES AS WELL. TEMPERATURE-WISE, THE FLAT FLOW
WILL ALLOW FOR ABOVE AVERAGE TO RECORD-BREAKING WARM TEMPERATURES
FOR MOST OF THE CONUS AS ASTRONOMICAL WINTER BEGINS, THOUGH THE
NORTHERN TIER CAN EXPECT COLDER PERIODS WITH SHORTWAVES MOVING
THROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS IN VERY GOOD AGREEMENT ON THE LARGE SCALE,
WITH A MULTI-MODEL BLEND FAVORING THE ECMWF AND GFS SERVING AS A
GOOD STARTING POINT FOR THE FIRST HALF OF THE PERIOD. AFTER
SATURDAY, SOME TIMING AND AMPLITUDE QUESTIONS ARISE WITH INDIVIDUAL
SYSTEMS WITHIN THE OVERALL FLAT FLOW. BROAD TROUGHING ACROSS THE
NORTH-CENTRAL U.S. SATURDAY PUSHING EAST INTO SUNDAY WITH SURFACE
LOW PRESSURE NEAR THE U.S./CANADIAN BORDER MOSTLY SHOWS GOOD
CONSENSUS, EXCEPT THAT CMC RUNS CONTINUE TO HAVE LESS TROUGHING
WITH THIS FEATURE COMPARED TO THE EC/GFS/AI RUNS. THEN THERE IS
GOOD AGREEMENT FOR RIDGING TO BUILD ACROSS THE ROCKIES TO PLAINS
WHILE NORTHEAST PACIFIC TROUGHING DEEPENS. THIS WILL PROVIDE MEAN
SOUTHWESTERLY FLOW INTO CALIFORNIA AND THE NORTHWEST FOR ADDITIONAL
AR POTENTIAL. THE DETAILS OF THE EXACT AXIS/ORIENTATION/PLACEMENT
FOR THESE ARS WILL BE IMPACTFUL, BUT ARE STILL UNCERTAIN. OVERALL,
USED SOME ENSEMBLE MEANS TOWARD THE LATTER PART OF THE PERIOD TO
TEMPER INDIVIDUAL MODEL DIFFERENCES. THE NBM SERVED AS A GOOD
STARTING POINT FOR THE SENSIBLE WEATHER GRIDS.
..WEATHER/HAZARDS HIGHLIGHTS
AN AR IS EXPECTED TO BE ONGOING AS THE PERIOD BEGINS FRIDAY INTO
PORTIONS OF OREGON, GRADUALLY DRIFTING SOUTHWARD INTO NORTHERN
CALIFORNIA AND WEAKENING. MAINTAINED A LOW END SLIGHT RISK ON DAY
4/FRIDAY WITHIN THE BROADER MARGINAL NEAR THE OR/CA BORDER GIVEN
THE POTENTIAL FOR 3-5 INCHES OF RAIN (NOT TOO UNCOMMON FOR THIS
AREA). THIS AREA HAS GENERALLY BEEN DRY LATELY (MUCH DRIER THAN
FARTHER NORTH) BUT DOES RECEIVE SOME PRECIPITATION IN THE SHORT
RANGE. THEN BY SATURDAY, LINGERING PRECIPITATION IS POSSIBLE ACROSS
NORTHERN CALIFORNIA, WITH POTENTIAL RENEWAL OF PRECIPITATION
SATURDAY NIGHT AS ANOTHER AR APPROACHES. WILL SHOW A MARGINAL RISK
IN MUCH OF NORTHERN CALIFORNIA FOR ISOLATED FLOODING. BY SUNDAY THE
NEXT AR IS FORECAST TO ARRIVE IN EARNEST ACROSS NORTHERN
CALIFORNIA AND SOUTHERN OREGON, WHICH COULD CONTINUE INTO MONDAY.
FOR THESE EVENTS, MOISTURE IS FORECAST TO SPILL OVER INTO THE
INTERMOUNTAIN WEST AND NORTHERN/CENTRAL ROCKIES, WHICH COULD
PRODUCE HEAVY SNOW IN HIGHER ELEVATION AREAS WITH SUFFICIENTLY COLD
TEMPERATURES.
THE UPPER TROUGH MOVING THROUGH THE NORTHEAST FRIDAY WILL PUSH A
FRONTAL SYSTEM THROUGH THE REGION. STRONG SOUTHERLY WINDS WILL
BRING IN AMPLE AND ANOMALOUS MOISTURE AHEAD OF THE FRONT FOR SOME
BRIEF HEAVY RAIN. NEGATIVES FOR ANY FLOODING WILL BE THE QUICK
MOVEMENT OF THE RAIN, TOTALS MAYBE ONLY REACHING OVER AN INCH IN
ISOLATED AREAS, AND LACK OF INSTABILITY. REGARDLESS, MAINTAINED A
LOW END MARGINAL RISK FOR PORTIONS OF NEW ENGLAND GIVEN THE
ANOMALOUSLY HIGH MOISTURE, STRONG UPPER LEVEL SUPPORT, AND FROZEN
GROUND WITH SOME SNOW COVER THAT COULD INCREASE RUNOFF POTENTIAL.
SOME LAKE EFFECT SNOW IS LIKELY BEHIND THE MAIN SYSTEM, AND SHALLOW
SHORTWAVES MOVING THROUGH THE NORTHERN TIER COULD BRING LIGHT
PRECIPITATION ACROSS THE NORTH-CENTRAL AND NORTHEASTERN U.S.
THROUGH THE WEEKEND. LIGHT TO MODERATE PRECIPITATION (MOSTLY RAIN)
MAY GET RENEWED ACROSS THE SOUTH AND EAST-CENTRAL U.S. OVER THE
WEEKEND, THOUGH WITH THE DETAILS UNCERTAIN.
WARMER THAN AVERAGE TEMPERATURES ARE FORECAST ACROSS THE INTERIOR
WESTERN AND CENTRAL U.S. THROUGH MUCH OF THE PERIOD. THE HIGHEST
ANOMALIES WILL LIKELY BE ACROSS THE PLAINS MOST DAYS, WITH
TEMPERATURES AS MUCH AS 20-30 DEGREES ABOVE NORMAL. ON FRIDAY HIGHS
IN THE 60S SHOULD EXPAND INTO WESTERN NEBRASKA AND SOUTH DAKOTA,
AND BY SATURDAY TEMPERATURES IN MUCH OF TEXAS SHOULD REACH THE
UPPER 70S TO LOW 80S. ON FRIDAY AND SATURDAY, RECORD HIGH
TEMPERATURES ARE FORECAST FROM CALIFORNIA ACROSS THE GREAT
BASIN/SOUTHWEST INTO THE PLAINS. MUCH WARMER THAN AVERAGE
TEMPERATURES ARE LIKELY TO CONTINUE INTO EARLY NEXT WEEK AS THE
CENTRAL U.S. UPPER RIDGE BUILDS. THE EASTERN U.S. CAN EXPECT MORE
TRANSIENT ABOVE AND BELOW AVERAGE TEMPERATURES AS FRONTS PASS
THROUGH. MEANWHILE THE NORTHERN TIER IS FORECAST TO SEE SHOTS OF
COLD AIR WITH SHORTWAVES AND COLD SURFACE HIGHS BEHIND COLD FRONTS.
CURRENTLY THE COLDEST AIR IS EXPECTED FRIDAY MORNING, WITH LOWS
WELL BELOW ZERO IN PORTIONS OF NORTH DAKOTA AND MINNESOTA.
SANTORELLI/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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