047
FXUS02 KWBC 220810
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 AM EST MON DEC 22 2025
VALID 12Z THU DEC 25 2025 - 12Z MON DEC 29 2025
...ATMOSPHERIC RIVER WITH ANOMALOUS MOISTURE TO FUEL HEAVY
RAIN WITH CALIFORNIA FOCUS OVER THE HOLIDAYS TO ABATE LATE WEEK...
..OVERVIEW
A QUITE AMPLIFIED AND WARMING UPPER RIDGE WILL SHIFT FROM THE
INTERIOR WEST/ROCKIES THROUGH THE EAST-CENTRAL U.S. THIS WEEK AND
DEVELOP A GULF UPPER HIGH. THIS WILL OCCUR IN RESPONSE TO A SLOW
EASTWARD TRANSLATION OF A DEEPENED/SPLIT UPPER TROUGH POSITIONS
FROM THE EASTERN AND NORTHEASTERN PACIFIC INTO WESTERN NORTH
AMERICA. IN THIS PATTERN, ONSHORE FLOW LINGERING INTO LATE WEEK
WILL DIRECT A LEADING ATMOSPHERIC RIVER (AR) AND BRING ADDITIONAL
HEAVY PRECIPITATION TO CALIFORNIA, AND WIDESPREAD MODERATED
ACTIVITY FROM THE WEST COAST STATES TO THE INTERMOUNTAIN
WEST/ROCKIES. TEMPERATURE-WISE, UNSEASONABLE WARMTH IS FORECAST TO
SPREAD THIS WEEK FROM THE WEST DOWNSTREAM THROUGH THE SOUTH-
CENTRAL ROCKIES/PLAINS TO THE CENTRAL TO EASTERN U.S.. THE COLDER
NORTHERN TIER MAY SEE PLOWABLE SNOW CHANCES FROM THE UPPER GREAT
LAKES TO THE NORTHEAST AS SHORTWAVES AND FRONTS PASS THROUGH IN A
PERIOD WITHIN SPLIT AND UNCERTAIN/AMPLIFYING LARGER SCALE FLOW.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE SOLUTION CLUSTERING DECREASES BY LATER THIS WEEK. IN
PARTICULAR, UNCERTAINTY INCREASES REGARDING TIMING OF A MAIN
SOUTHERN STREAM UPPER TROUGH/CLOSED LOW AS IT SHIFTS INTO THE
SOUTHWEST, FINALLY BRINGING AN END TO THE RELENTLESS ATMOSPHERIC
RIVERS FOR CALIFORNIA. RECENT GFS RUNS HAVE BEEN THE SLOWEST TO
PROGRESS FEATURES IN THIS STREAM INLAND, WITH THE ECMWF AND CMC
GENERALLY FASTER. THIS HAS RAMIFICATIONS TO THE EXTENT OF NORTHERN
STREAM TROUGH DIGGING DOWNSTREAM INTO THE LOWER 48. MACHINE
LEARNING MODEL SOLUTIONS ARE MIXED. GIVEN UNCERTAINTIES, THE WPC
MEDIUM RANGE FORECAST SUITE WAS MAINLY DERIVED FROM A COMPOSITE OF
THE GEFS MEAN AND ECMWF ENSEMBLE MEAN MASS FIELDS AND WPC
CONTINUITY TO FORGE A SOLUTION NEAR THE MIDDLE OF THE OVERALL
FORECAST ENVELOPE WITH RESPECT TO AMPLITUDE AND PROGRESSION. THIS
SOLUTION SEEMS REASONABLY IN LINE WITH THE 01 UTC NBM.
..WEATHER/HAZARDS HIGHLIGHTS
EASTERN PACIFIC AMPLIFIED UPPER TROUGHING AND SYSTEM GENESIS
WILL WORK TOWARD THE WEST COAST WITH LEAD DEEP ONSHORE FLOW
DIRECTING PACIFIC MOISTURE INTO THE WEST COAST THIS WEEK IN HIGHLY
WET ATMOSPHERIC RIVER FLOW TO FUEL SIGNIFICANT RUNOFF ISSUES. THIS
IMPACTFUL EVENT WILL STEADILY LOSE INFLUENCE LATE WEEK AS SURFACE
LOW/FRONTAL SYSTEM WORKS ILAND WITH UPPER TROUGH PROGRESSION. MARGINAL
AND EMBEDDED SLIGHT RISK ERO THREATS CONTINUE TO BE DEPICTED FOR
THURSDAY/FRIDAY, FROM CENTRAL TO SOUTHERN CALIFORNIA AND THE
SOUTHERN GREAT BASIN. HIGHER ELEVATIONS OF THE SIERRA SHOULD SEE
AN EXTENDED HEAVY SNOW EVENT. TO THE NORTH, THE PACIFIC NORTHWEST
CAN ALSO EXPECT ORGANIZED PRECIPITATION THIS WEEK, BUT WITH LESSER
AMOUNTS. ADDITIONALLY, MOISTURE IS FORECAST TO SPILL OVER THE
CASCADES TO THE INTERMOUNTAIN WEST AND NORTHERN/CENTRAL ROCKIES TO
PRODUCE HEAVY SNOW AT HIGHER ELEVATIONS.
ELSEWHERE, LEADING SHALLOW SHORTWAVES MOVING THROUGH THE NORTHERN
TIER AND ASSOCIATED SURFACE SYSTEM REFLECTION AND POSSIBLE FLOW
AMPLIFICATION WITH THE DIGGING OF NORTHERN STREAM UPPER TROUGHING
INTO THE LOWER 48 MAY BRING GENERALLY LIGHT PRECIPITATION FROM THE
NORTH-CENTRAL U.S. TO THE GREAT LAKES AND OHIO VALLEY AND
NORTHEAST. THIS MAY INCLUDE CHANCES FOR SOME ENHANCED SNOWS WITH
MAIN FOCUS FROM THE UPPER GREAT LAKES TO INCREASINGLY SOUTHWARD
ACROSS THE NORTHEAST TO MONITOR.
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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