113
FXUS02 KWBC 290658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST WED JAN 29 2025
VALID 12Z SAT FEB 01 2025 - 12Z WED FEB 05 2025
***PROLONGED ATMOSPHERIC RIVER EVENT EXPECTED FOR THE PACIFIC
NORTHWEST THIS WEEKEND***
..GENERAL OVERVIEW
THE OVERALL UPPER LEVEL FLOW PATTERN ACROSS THE CONTINENTAL U.S. IS
EXPECTED TO BECOME MORE QUASI-ZONAL GOING INTO THE WEEKEND, WHILE
AT THE SURFACE AN ARCTIC AIRMASS EDGES SOUTHWARD ACROSS THE
NORTHERN PLAINS AND NORTHERN ROCKIES. A SLOW MOVING UPPER LEVEL LOW
SITUATED NORTHWEST OF THE WASHINGTON COAST, COMBINED WITH A FAST
MID-UPPER LEVEL FLOW AND SHORTWAVE PASSAGES, WILL LIKELY SUSTAIN A
PROLONGED ATMOSPHERIC RIVER EVENT ACROSS NORTHERN CALIFORNIA AND
WESTERN OREGON. MEANWHILE, BROAD CYCLONIC FLOW ALOFT OVER THE GREAT
LAKES INTO THE NORTHEAST SHOULD BE IN PLACE FOR THE FIRST HALF OF
NEXT WEEK, AND A BROAD UPPER RIDGE TRYING TO DEVELOP OVER THE GULF
COAST REGION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THERE IS GOOD OVERALL SYNOPTIC SCALE AGREEMENT IN THE 00Z GUIDANCE
AMONG THE DETERMINISTIC SOLUTIONS TO BEGIN THE FORECAST PERIOD
SATURDAY. THERE ARE STILL SOME TIMING AND AMPLITUDE DIFFERENCES
SEEN IN THE GUIDANCE WITH NORTHERN STREAM SHORTWAVE AND THE ARRIVAL
OF THE ARCTIC FRONT OVER THE NORTHERN PLAINS, AND MORE SO IN THE
CMC AND UKMET GUIDANCE. THEREFORE, THE MODEL PREFERENCE THROUGH
THE UPCOMING WEEKEND WAS HEDGED MORE IN THE DIRECTION OF THE
ECMWF/GFS AND SOME OF THEIR RESPECTIVE ENSEMBLE MEANS.
LOOKING AHEAD TO EARLY NEXT WEEK, THE UPPER LEVEL FLOW PATTERN
BECOMES MORE ZONAL ACROSS THE CONTINENTAL U.S. OVERALL. THE
GUIDANCE HAS COME INTO BETTER AGREEMENT WITH THE CLOSED LOW NEAR
THE PACIFIC NORTHWEST. THE USE OF THE ENSEMBLE MEANS INCREASED TO
ABOUT HALF BY WEDNESDAY, WHILE STILL KEEPING ABOUT 25% EACH OF THE
GFS AND ECMWF.
..WEATHER/HAZARDS HIGHLIGHTS
THE MOST IMPACTFUL WEATHER EVENT DURING THIS FORECAST PERIOD WILL
BE THE PROLONGED ATMOSPHERIC RIVER THAT IS LIKELY TO BRING EXTENDED
PERIODS OF MODERATE TO HEAVY RAINFALL FROM SOUTHWESTERN OREGON INTO
THE NORTHERN THIRD OF CALIFORNIA. AN ANOMALOUS MOISTURE FLUX
ORIENTED NEARLY ORTHOGONAL TO THE TERRAIN AHEAD OF A STATIONARY
FRONT IS LIKELY TO PRODUCE WIDESPREAD 2-4 INCH RAINFALL TOTALS
BETWEEN SANTA ROSA AND THE OREGON STATE LINE DURING THE DAY 4
PERIOD SATURDAY, AND THEREFORE A SLIGHT RISK OF EXCESSIVE RAINFALL
IS PLANNED. THERE SHOULD BE SOME REDUCTION IN RAINFALL INTENSITY
GOING INTO SUNDAY ACROSS NORTHERN CALIFORNIA, BUT THERE SHOULD
STILL BE ENOUGH MOISTURE AND FORCING TO PRODUCE ADDITIONAL 1 TO
LOCALLY 3 INCH TOTALS FOR THE DAY 5 SUNDAY, AND THEREFORE A
MARGINAL RISK IS PLANNED FOR NORTHERN CALIFORNIA AND INCLUDING THE
FOOTHILLS OF THE CENTRAL AND NORTHERN SIERRA. ADDITIONAL HEAVY
RAINFALL IS LIKELY ACROSS THE STATE GOING INTO EARLY NEXT WEEK AS
THE MOISTURE MOVES VERY SLOWLY SOUTHWARD.
ELSEWHERE ACROSS THE COUNTRY, HEAVY SNOW IS EXPECTED FOR THE HIGHER
TERRAIN OF THE INTERMOUNTAIN WEST AND THE NORTHERN ROCKIES AS THE
PACIFIC MOISTURE ADVECTS FARTHER INLAND, WITH SEVERAL FEET OF
ACCUMULATION LIKELY FOR THE HIGHEST ELEVATIONS OVER THE 5 DAY
PERIOD. LIGHTER SNOW IS LIKELY FROM THE NORTHERN GREAT LAKES TO
NORTHERN NEW ENGLAND AS A SURFACE LOW PASSES THROUGH THE REGION
MONDAY WITH SOME LAKE EFFECT SNOW BEHIND IT.
TEMPERATURES ARE EXPECTED TO BE MILD FOR EARLY FEBRUARY ACROSS MUCH
OF THE CONTINENTAL U.S., AND HIGHS REACHING 15 TO 25 DEGREES ABOVE
NORMAL ARE POSSIBLE FROM THE SOUTHERN PLAINS TO THE MIDWEST STATES
FOR THIS WEEKEND. IT SHOULD BE CLOSE TO SEASONAL AVERAGES FOR THE
MID- ATLANTIC AND SLIGHTLY BELOW AVERAGE FOR NEW ENGLAND, AND THE
ARCTIC FRONT STARTS TO BRING MUCH COLDER WEATHER STARTING IN
MONTANA ON SUNDAY. THE ARCTIC AIRMASS OOZES SOUTHEASTWARD ACROSS
THE DAKOTAS AND INTO MINNESOTA GOING INTO EARLY NEXT WEEK, BUT IS
PROBABLY GOING TO BE HALTED IN ITS SOUTHWARD PROGRESS BY THE TIME
IT REACHES THE CENTRAL PLAINS DUE TO A DEVELOPING RIDGE ACROSS THE
SOUTHERN PLAINS BY MIDWEEK. ABOVE AVERAGE READINGS ARE FORECAST
FOR THE SOUTHERN U.S. THROUGH THE ENTIRE PERIOD.
HAMRICK
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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