796
FXUS02 KWBC 160753
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 AM 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 ROUNDS OF ATMOSPHERIC RIVERS (ARS)
CAUSING 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 FOR THE 12/18Z CYCLE AND THE NEWER 00Z CYCLE IS IN
REASONABLY GOOD AGREEMENT WITH THE PATTERN DESCRIBED ABOVE. A
MULTI-MODEL BLEND FAVORING THE ECMWF AND GFS WORKED WELL FOR THE
FIRST TROUGH MOVING THROUGH THE EAST ON FRIDAY. THEN THE FLAT FLOW
WITH SHALLOW TROUGHS/RIDGES MAKES IT HARD TO DETERMINE MODEL
OUTLIERS. 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 HAD LESS TROUGHING WITH THIS FEATURE COMPARED TO THE EC/GFS/AI
RUNS. THEN THERE IS GENERAL 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 EXACT
AXIS/ORIENTATION/PLACEMENT FOR THESE ARS WILL BE IMPACTFUL, SO EVEN
SMALL DIFFERENCES COULD CAUSE ISSUES DESPITE THE LOW SPREAD FOR A
LATE MEDIUM RANGE FORECAST. OVERALL, USED SOME ENSEMBLE MEANS
TOWARD THE LATTER PART OF THE PERIOD TO TEMPER INDIVIDUAL MODEL
DIFFERENCES, BUT WAS ABLE TO MAINTAIN A MAJORITY OF DETERMINISTIC
MODELS FOR THE MASS FIELDS THROUGH THE PERIOD GIVEN THE BROAD SCALE
CONSENSUS.
..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.
DURING 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 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 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 GENERALLY 15-25 DEGREES ABOVE NORMAL, LOCALLY EVEN
HIGHER. 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.
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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