662
FXUS02 KWNH 210758
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EST SUN DEC 21 2025
VALID 12Z WED DEC 24 2025 - 12Z SUN DEC 28 2025
...MAJOR SERIES OF ATMOSPHERIC RIVERS WITH HIGHLY ANOMALOUS
MOISTURE TO FUEL ROUNDS OF HEAVY RAINFALL TO IMPACT THE WEST
COAST, BUT ESPECIALLY CALIFORNIA THROUGH THE HOLIDAYS...
..OVERVIEW
IT REMAINS FORECAST THAT AN AMPLIFIED UPPER RIDGE WILL SHIFT FROM
THE INTERIOR WEST/ROCKIES THROUGH THE EAST-CENTRAL U.S. THIS WEEK
AND DEVELOP A SOUTH-CENTRAL U.S. UPPER HIGH. THIS WILL OCCUR IN
RESPONSE TO A SLOW BUT STEADY EASTWARD TRANSLATION OF A DEEPENED
UPPER TROUGH POSITION FROM THE EASTERN PACIFIC INTO THE WEST COAST.
IN THIS IMPACTFUL PATTERN, ONSHORE FLOW WILL CONTINUE TO DIRECT
LEADING ATMOSPHERIC RIVERS (ARS) TO FUEL ROUNDS OF HEAVY
PRECIPITATION AFFECTING CALIFORNIA IN PARTICULAR, BUT WITH
WIDESPREAD ACTIVITY FROM THE WEST COAST TO THE INTERMOUNTAIN
WEST/ROCKIES. TEMPERATURE- WISE, UNSEASONABLY TO POTENTIALLY
RECORD-BREAKING WARM TEMPERATURES ARE FORECAST TO SPREAD THIS WEEK
FROM THE WEST/SOUTHWEST THROUGH THE SOUTH-CENTRAL ROCKIES/PLAINS TO
THE EAST-CENTRAL U.S.. THE NORTHERN TIER CAN SEE COLDER PERIODS
WITH SNOW CHANCES AS MORE NORTHERN STREAM SHORTWAVES AND ASSOCIATED
FRONTS PASS THROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT MODEL AND ENSEMBLE RUNS OVERALL OFFERED SIMILAR PATTERN
EVOLUTIONS AND THREAT POTENTIALS ACROSS MEDIUM-RANGE TIME SCALES,
THAT SAID, GUIDANCE CONTINUES TO SUFFER FROM TOO NUMEROUS FLOW
EMBEDDED SYSTEM TIMINGS AND INTERACTION VARIANCES THAT WORSEN OVER
TIME. ACCORDINGLY, FAVOR A BLEND OF THE BEST CLUSTERED GUIDANCE OF
THE GEFS/ECNWF ENSEMBLE MEANS. THIS STRATEGY SHOULD HELP MITIGATE
SMALLER SCALE SYSTEMS AS CONSISTENT WITH INDIVIDUAL PREDICTABILITY.
..WEATHER/HAZARDS HIGHLIGHTS
A PREMIER STORY DURING THE PERIOD WILL FOCUS OUT WEST WITH
AMPLIFYING UPPER TROUGHING AND SYSTEM GENESIS WORKING TOWARD THE
WEST COAST AND LEAD DEEP ONSHORE FLOW DIRECTING PACIFIC MOISTURE
INTO THE WEST COAST THROUGH THE WEEK. HIGH MOISTURE ANOMALIES WITH
ATMOSPHERIC RIVERS IMPACTING NORTHERN/CENTRAL CALIFORNIA EARLY WEEK
WILL SHIFT TO CENTRAL TO SOUTHERN CALIFORNIA CHRISTMAS
EVE/CHRISTMAS BEFORE AFFECTING PARTS OF THE SOUTHWEST.
ATMOSPHERIC RIVERS WILL FUEL A PROLONGED WET PERIOD FOR ESPECIALLY
CALIFORNIA DURING THIS BUSY HOLIDAY WEEK. BY MIDWEEK INTO LATER
WEEK AND LINGERING INTO NEXT WEEKEND, SOME CONNECTION TO TROPICAL
PACIFIC MOISTURE IS LIKELY TO STREAM IN AND INCREASINGLY IMPACT
SOUTHERN CALIFORNIA AS SURFACE LOW/FRONTAL SYSTEM APPROACHES THE
COAST. MARGINAL AND EMBEDDED SLIGHT RISK ERO THREAT AREAS ARE
DEPICTED FOR WEDNESDAY/THURSDAY, STRETCHING FROM NORTH-CENTRAL
CALIFORNIA TO SOUTHERN CALIFORNIA AND THE SOUTHERN GREAT BASIN.
SIGNIFICANT RAINFALL IS EXPECTED, PARTICULARLY FOR THE TRANSVERSE
RANGES OF SOUTHERN CALIFORNIA. HIGHER ELEVATIONS OF THE SIERRA
SHOULD SEE AN EXTENDED HEAVY SNOW EVENT. TO THE NORTH, THE PACIFIC
NORTHWEST CAN ALSO EXPECT ORGANIZED PRECIPITATION EARLY WEEK, BUT
WITH LESSER AMOUNTS. ADDITIONALLY, MOISTURE IS FORECAST TO SPILL
OVER THE CASCADES TO THE INTERMOUNTAIN WEST AND NORTHERN/CENTRAL
ROCKIES NEXT WEEK TO PRODUCE HEAVY SNOW AT HIGHER ELEVATIONS.
SHALLOW SHORTWAVES MOVING THROUGH THE NORTHERN TIER AND ASSOCIATED
SURFACE SYSTEM REFLECTION FOCUS WILL BRING LIGHT PRECIPITATION
FROM THE NORTH-CENTRAL TO NORTHEASTERN U.S. THIS WEEK. FARTHER
SOUTH, WEAK TO MODERATE GULF MOISTURE MAY STREAM INTO TRAILING TO
RENEWED FRONTAL SYSTEMS ACROSS THE SOUTH AND EAST-CENTRAL U.S. AND
LEAD TO LIGHT PRECIPITATION CHANCES TO THE LOWER MISSISSIPPI,
TENNESSEE, AND OHIO VALLEYS THIS WEEK.
WARMER THAN AVERAGE TEMPERATURES ARE FORECAST ACROSS THE INTERIOR
WEST AND CENTRAL U.S. THIS WEEK. THE HIGHEST ANOMALIES WILL LIKELY
BE ACROSS THE INTERIOR WEST INTO THE PLAINS, WITH WIDESPREAD
TEMPERATURE ANOMALIES UPWARDS TO 20-30 DEGREES ABOVE NORMAL. HIGHS
INTO THE 80S ACROSS PARTS OF THE SOUTHWEST TO TEXAS COULD SET DAILY
RECORDS. UNSEASONABLE WARMTH IS LIKELY TO SPREAD EAST ACROSS THE
MID-LATITUDES TO THE MISSISSIPPI, OHIO, AND TENNESSEE VALLEYS AND
THE EAST OVER THE CHRISTMAS HOLIDAY PERIOD.
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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