794
FXUS02 KWBC 300658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST THU JAN 30 2025
VALID 12Z SUN FEB 02 2025 - 12Z THU FEB 6 2025
***PROLONGED ATMOSPHERIC RIVER EVENT EXPECTED FOR THE PACIFIC
NORTHWEST THIS WEEKEND INTO NEXT WEEK***
..GENERAL OVERVIEW
THE OVERALL UPPER LEVEL FLOW PATTERN ACROSS THE CONTINENTAL U.S. IS
EXPECTED TO BE QUASI-ZONAL FOR THE UPCOMING WEEKEND, WHILE AT THE
SURFACE AN ARCTIC AIRMASS OOZES SOUTHWARD ACROSS THE NORTHERN
PLAINS AND NORTHERN ROCKIES, BUT ITS SOUTHWARD PROGRESS SHOULD BE
LIMITED BY A BUILDING UPPER RIDGE OVER THE SOUTH-CENTRAL STATES. A
SLOW MOVING UPPER LEVEL LOW SITUATED NORTHWEST OF THE WASHINGTON
COAST, COMBINED WITH A FAST MID-UPPER LEVEL FLOW AND SHORTWAVE
PASSAGES, WILL SUSTAIN A PROLONGED ATMOSPHERIC RIVER EVENT ACROSS
NORTHERN CALIFORNIA AND WESTERN OREGON WITH SEVERAL INCHES OF
RAINFALL EXPECTED. MEANWHILE, BROAD CYCLONIC FLOW ALOFT OVER THE
GREAT LAKES INTO THE NORTHEAST SHOULD BE IN PLACE FOR THE FIRST
HALF OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THERE IS GOOD OVERALL SYNOPTIC SCALE AGREEMENT IN THE 00Z GUIDANCE
AMONG THE DETERMINISTIC SOLUTIONS TO BEGIN THE FORECAST PERIOD
SUNDAY. THERE ARE STILL SOME TIMING AND AMPLITUDE DIFFERENCES SEEN
IN THE GUIDANCE WITH NORTHERN STREAM SHORTWAVES AND THE ARRIVAL OF
THE ARCTIC FRONT OVER THE NORTHERN PLAINS, BUT THE OVERALL TREND
HAS BEEN FOR THE ARCTIC FRONT TO MAKE LESS SOUTHWARD PROGRESS
COMPARED TO PREVIOUS DAYS. AT THE TIME OF FRONTS/PRESSURES
PREPARATION, THE 18Z GFS WAS FARTHER SOUTH WITH THE COLD FRONT
ACROSS THE PLAINS AND OHIO VALLEY, WHEREAS THE CMC/ECMWF/UKMET WERE
FARTHER NORTH AND HAD MORE SUPPORT FROM THE AI GUIDANCE, SO THE
FORECAST WAS HEDGED MORE IN THE ECMWF/CMC/UKMET DIRECTION THROUGH
TUESDAY.
LOOKING AHEAD TO THE MIDDLE OF NEXT WEEK, THE 00Z CMC IS QUICKER TO
DROP THE UPPER TROUGH SOUTHWARD ACROSS THE WEST COAST/INTERMOUNTAIN
WEST COMPARED TO THE OTHER GUIDANCE. THE USE OF THE ENSEMBLE MEANS
INCREASED TO ABOUT HALF BY THURSDAY TO ACCOUNT FOR INCREASING MODEL
DIFFERENCES BY THIS TIME.
..WEATHER/HAZARDS HIGHLIGHTS
THE MOST IMPACTFUL WEATHER EVENT DURING THIS FORECAST PERIOD WILL
BE THE PROLONGED ATMOSPHERIC RIVER THAT WILL BRING EXTENDED
PERIODS OF MODERATE TO HEAVY RAINFALL FOR CENTRAL AND ESPECIALLY
NORTHERN CALIFORNIA. AN ANOMALOUS MOISTURE FLUX ORIENTED NEARLY
ORTHOGONAL TO THE TERRAIN AHEAD OF A SLOW MOVING FRONT IS LIKELY
TO PRODUCE WIDESPREAD 2-4 INCH RAINFALL TOTALS DURING THE DAY 4
PERIOD SUNDAY, AND THEREFORE A SLIGHT RISK OF EXCESSIVE RAINFALL IS
PLANNED BETWEEN SANTA ROSA AND EUREKA. THIS CONTINUES GOING INTO
MONDAY (DAY 5) WITH HEAVY RAINFALL OVER THE COAST AND ADJACENT
TERRAIN, AND ALSO THE FOOTHILLS OF THE CENTRAL/NORTHERN SIERRA
WHERE A SLIGHT RISK IS PLANNED, WITH AN ADDITIONAL 2 TO 3 INCHES
OF RAIN DURING THIS TIME. ADDITIONAL HEAVY RAINFALL IS LIKELY
ACROSS THE STATE GOING INTO THE MIDDLE OF NEXT WEEK AS THE MOISTURE
MOVES VERY SLOWLY SOUTHWARD.
SNOW LEVELS WILL INITIALLY BE RATHER HIGH WITH THIS EVENT OVER
CALIFORNIA, BUT THEY SHOULD FALL A LITTLE TOWARDS MID-WEEK WITH
HEAVY SNOW BECOMING MORE LIKELY FOR THE HIGHER TERRAIN OF THE
SIERRA. 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 A
COUPLE FEET OF ACCUMULATION LIKELY FOR THE HIGHEST ELEVATIONS OVER
THE MEDIUM RANGE PERIOD. LIGHT TO MODERATE SNOW IS LIKELY FROM THE
NORTHERN GREAT LAKES TO NORTHERN NEW ENGLAND ON SUNDAY INTO SUNDAY
NIGHT AS A SURFACE LOW PASSES THROUGH THE REGION.
TEMPERATURES ARE EXPECTED TO BE PLEASANTLY 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 NEW ENGLAND ON SUNDAY, AND THE ARCTIC FRONT STARTS TO
BRING MUCH COLDER WEATHER STARTING IN MONTANA ON SUNDAY, AND THEN
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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