683
FXUS02 KWBC 170736
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
236 AM 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 TO
EASTERN U.S. OVER THE WEEKEND WITHIN RELATIVELY FLAT FLOW.
UPSTREAM, LOW AMPLITUDE RIDGING IS FORECAST TO MOVE THROUGH THE
INTERIOR WEST AND THE 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. THE
MEAN WESTERLY AND LATER SOUTHWESTERLY FLOW INTO THE WEST COAST WILL
CONTINUE TO BRING ROUNDS OF ATMOSPHERIC RIVERS (ARS) CAUSING HEAVY
PRECIPITATION TO NORTHERN CALIFORNIA IN PARTICULAR, WITH SOME
PRECIPITATION PUSHING INTO THE INTERMOUNTAIN WEST/ROCKIES AS WELL.
TEMPERATURE-WISE, UNSEASONABLY TO RECORD-BREAKING WARM TEMPERATURES
ARE FORECAST ACROSS THE SOUTHWEST TO PLAINS, THOUGH THE NORTHERN
TIER CAN EXPECT COLDER PERIODS WITH SHORTWAVES MOVING THROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON THE LARGE SCALE WITH
THE PATTERN DESCRIBED ABOVE. CMC RUNS HAVE SHOWN A SHALLOWER
SOLUTION COMPARED TO CONSENSUS WITH THE INITIAL TROUGH MOVING
THROUGH THE NORTHERN TIER, BUT THE NEWEST 00Z RUN ALIGNS BETTER
WITH OTHER GUIDANCE. 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, A MULTI-MODEL BLEND
WORKED WELL FOR THE EARLY PART OF THE PERIOD, AND ADDED SOME
ENSEMBLE MEAN GUIDANCE TO THE BLEND FOR THE LATTER PART OF THE
PERIOD TO TEMPER INDIVIDUAL MODEL DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
MOIST INFLOW IS FORECAST TO AFFECT NORTHERN CALIFORNIA AS THE
MEDIUM RANGE PERIOD BEGINS SATURDAY, ESPECIALLY BY LATE IN THE
PERIOD AS ANOTHER AR APPROACHES. CONTINUE TO SHOW A MARGINAL RISK
FOR ISOLATED FLOODING IN THE DAY 4 ERO. BY SUNDAY THE NEXT AR IS
FORECAST TO ARRIVE IN EARNEST ACROSS NORTHERN CALIFORNIA WITH IVT
INCREASING. RAIN RATES ARE FORECAST TO INCREASE WITH THE MOISTURE
SURGE, WITH GLOBAL MODELS SHOWING POCKETS OF 3 HOUR RAIN AMOUNTS OF
OVER AN INCH. THIS POTENTIAL COMBINED WITH THIS BEING THE THIRD
DAY OF MODERATE TO HEAVY PRECIPITATION IN A ROW ALLOWS FOR A SLIGHT
RISK ISSUANCE FOR NORTHERN CALIFORNIA IN THE NEW DAY 5/SUNDAY ERO.
SOME PRECIPITATION IS ALSO POSSIBLE FARTHER NORTH INTO THE PACIFIC
NORTHWEST, BUT WITH LESSER AMOUNTS. ADDITIONAL ROUNDS OF MODERATE
TO HEAVY PRECIPITATION ARE LIKELY INTO MONDAY-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 IN HIGHER ELEVATION AREAS 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
WESTERN 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.
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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