273
FXUS02 KWBC 281900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST TUE JAN 28 2025
VALID 12Z FRI JAN 31 2025 - 12Z TUE FEB 04 2025
..GENERAL OVERVIEW
THE FORECAST PERIOD BEGINS FRIDAY WITH A CLOSED UPPER LOW TRACKING
EASTWARD FROM THE CENTRAL PLAINS AND EVOLVING INTO AN OPEN WAVE AS
IT REACHES THE EAST COAST SATURDAY MORNING. THIS FEATURE SHOULD
PRODUCE WIDESPREAD RAIN AND SOME THUNDERSTORMS FROM THE CENTRAL
GULF COAST TO THE MID-ATLANTIC AND SOUTHERN NEW ENGLAND. A COUPLE
ROUNDS OF SNOW ARE POSSIBLE ACROSS THE NORTHERN TIER THROUGH THE
PERIOD. BACK ACROSS THE PACIFIC NORTHWEST, A COLD FRONT AND
ASSOCIATED MOISTURE FEED AHEAD OF IT WILL LEAD TO THE RETURN OF
RAIN AND MOUNTAIN SNOW BY FRIDAY AND CONTINUING INTO THE WEEKEND.
MOST GUIDANCE DEVELOPS AN EASTERN PACIFIC UPPER TROUGH BY NEXT
TUESDAY, HELPING TO MAINTAIN THE FLOW OF MOISTURE INTO THE WEST,
WHILE GUIDANCE DIFFERS ON HOW MUCH TROUGHING MAY EXIST OVER THE
EAST. MOST OF THE COUNTRY WILL HAVE NEAR OR ABOVE NORMAL
TEMPERATURES THROUGH THE PERIOD, ASIDE FROM PARTS OF THE NORTHEAST
ON SATURDAY AND THEN SUNDAY-TUESDAY WHEN AN ARCTIC AIRMASS SETTLES
ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST (POSSIBLY EXTENDING
EASTWARD SOMEWHAT) BEHIND A STRONG COLD FRONT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE UPDATED FORECAST STARTED WITH A 00Z/06Z MODEL BLEND ON FRIDAY,
WITH SUBSEQUENT REMOVAL OF THE UKMET DUE TO ITS SLOW PROGRESSION OF
THE NORTHERN TIER SYSTEM/TRAILING COLD FRONT SATURDAY ONWARD (AN
ISSUE ALSO EVIDENT IN THE NEW 12Z RUN) WHILE KEEPING CMC WEIGHT
FAIRLY LOW DUE TO BEING ON THE SLOW EDGE OF THE SPREAD FOR THE
UPPER SHORTWAVE REACHING THE EAST COAST BY EARLY SATURDAY. GFS
INPUT WAS SPLIT BETWEEN THE 06Z/00Z RUNS AS ONE OR THE OTHER
COMPARED BETTER TO CONSENSUS THAN THE OTHER DEPENDING ON THE
FEATURE. THE FORECAST INCLUDED AT LEAST MODEST ENSEMBLE MEAN INPUT
(06Z GEFS/00Z ECENS) FROM SATURDAY ONWARD. THE RESULTING BLEND
YIELDED FAIRLY GOOD CONTINUITY.
MODELS/ENSEMBLE MEANS HAVE TRENDED NOTABLY FASTER OVER THE PAST
COUPLE DAYS WITH THE OPENING PLAINS/MISSISSIPPI VALLEY UPPER LOW
ON FRIDAY AND REACHING THE EAST COAST BY EARLY SATURDAY. 00Z
MACHINE LEARNING (ML) MODELS STILL SHOWED A FAIR AMOUNT OF SPREAD
BUT THE TRENDS OVER RECENT DAYS ARGUE AGAINST THE SLOW CMC/CMCENS
SIDE. THE NEW 12Z RUN HAS IMPROVED SOMEWHAT.
BY MID-LATE PERIOD, THERE ARE COMBINED UNCERTAINTIES WITH THE
EASTERN PACIFIC/WEST COAST EVOLUTION AND LEADING ENERGY THAT
SHOULD PROMOTE A NORTHERN TIER SURFACE SYSTEM/TRAILING COLD FRONT.
RECENT TRENDS AND A MODEST MAJORITY OF ML GUIDANCE SUPPORT THE IDEA
OF AN UPPER LOW DRIFTING JUST OFF VANCOUVER ISLAND BY EARLY NEXT
WEEK WHILE SOME RIDGING DEVELOPS OVER THE INTERIOR WEST WITH
TROUGHING FARTHER EAST. HOWEVER SOME 12Z SOLUTIONS INCLUDING THE
CMC IN PARTICULAR AND EVEN TO SOME DEGREE ECMWF/GFS HAVE BACKED
AWAY FROM MEANINGFUL EASTERN TROUGHING AND THUS DO NOT PUSH THE
COLD FRONT AS FAR SOUTH OVER THE CENTRAL/EASTERN U.S. ML MODELS
SHOWED SOME SPREAD AT THE SURFACE AND ALOFT LATE IN THE PERIOD BUT
GENERALLY DID NOT SEEM TO FAVOR THE FLATTER SIDE OF THE DYNAMICAL
SPREAD ALOFT OR THE NORTHERNMOST SIDE FOR THE SURFACE FRONT.
..WEATHER/HAZARDS HIGHLIGHTS
AN OCCLUDED LOW PRESSURE SYSTEM SHOULD TRACK ACROSS MISSOURI AND
THEN OVER THE OHIO VALLEY BY FRIDAY MORNING. IN THE WARM SECTOR OF
THE SURFACE LOW, WARM AIR ADVECTION IN COMBINATION WITH FORCING
ALOFT MAY PRODUCE SOME POCKETS OF HEAVY RAINFALL FROM THE
PANHANDLE OF FLORIDA TO THE SOUTHERN APPALACHIANS, BUT WITH
COVERAGE/INTENSITY LIKELY TO BE LESS THAN ON THURSDAY. CONTINUED
GUIDANCE TRENDS TOWARD FASTER PROGRESSION OF THIS SYSTEM HAVE
LOWERED QPF IN MOST GUIDANCE, WITH CURRENT CLUSTERING FOR
HEAVY RAIN RATES NOW APPEARING TOO DIFFUSE TO SUPPORT A MARGINAL
RISK AREA IN THE DAY 4 EXCESSIVE RAINFALL OUTLOOK. THEREFORE THIS
AREA HAS BEEN REMOVED IN THE AFTERNOON UPDATE. MEANWHILE THIS
SYSTEM WILL LIKELY PRODUCE SNOW OR A WINTRY MIX OVER PARTS OF THE
NORTHEAST. CURRENT FORECASTS SHOW THE POTENTIAL FOR WINTER WEATHER
TO LINGER ACROSS UPSTATE NEW YORK TO INTERIOR NEW ENGLAND THROUGH
SATURDAY MORNING. ANOTHER ROUND OF WINTER WEATHER COULD TRACK
ACROSS THE GREAT LAKES TO THE NORTHEAST ON SUNDAY INTO MONDAY WITH
A CLIPPER TYPE SYSTEM.
EXPECT MOIST INFLOW TO RETURN TO THE WEST COAST LATE THIS WEEK,
EXPANDING INTO THE NORTHERN GREAT BASIN/ROCKIES, WITH ROUNDS OF LOW
PRESSURE/FRONTAL SYSTEMS TRACKING THROUGH THE REGION. AN
ATMOSPHERIC RIVER EVENT IS BECOMING MORE LIKELY FOR THE FRIDAY-
SATURDAY TIME PERIOD FROM NORTHERN CALIFORNIA TO THE OLYMPIC
PENINSULA. A DAY 4 MARGINAL RISK REMAINS VALID FOR THE COASTAL
RANGES AND THE FOOTHILLS OF THE OREGON CASCADES, AND A DAY 5
MARGINAL RISK COVERS AREAS A LITTLE FARTHER SOUTH TO INCLUDE MORE
OF NORTHERN CALIFORNIA AND EXTENDING INTO SOUTHWESTERN OREGON, WITH
THE HEAVIEST RAINFALL LIKELY TO FALL ON SATURDAY. NEW 12Z GUIDANCE
IS CONTINUING TO SHOW SOME SIGNAL FOR GREATER ENHANCEMENT OF
RAINFALL AROUND NORTHERN CALIFORNIA AROUND SATURDAY. THERE IS STILL
ENOUGH SPREAD FOR LOCATION/MAGNITUDE TO HOLD OFF INTRODUCING AN
EMBEDDED SLIGHT RISK AREA FOR NOW, BUT IT WOULD NOT TAKE MUCH
IMPROVEMENT IN CLUSTERING TO MERIT THAT ACTION. THE EVOLVING UPPER
TROUGH FORECAST TO EVOLVE JUST OFF THE WEST COAST EARLY NEXT WEEK
MAY CONTINUE THE FLOW OF MOISTURE INTO THE WEST, WITH HIGHEST
TOTALS LIKELY OVER NORTHERN CALIFORNIA AND VICINITY WITH SNOW
CONTINUING OVER THE NORTHERN ROCKIES.
ABOVE AVERAGE TEMPERATURES WILL PREVAIL LATE THIS WEEK ACROSS MUCH
OF THE CENTRAL AND EASTERN U.S., WITH DECENT COVERAGE OF PLUS
10-20 DEGREE ANOMALIES FOR HIGHS AND MORNING LOWS. THIS ALSO HOLDS
TRUE GOING INTO THE WEEKEND, ALTHOUGH NEW ENGLAND AND NEW YORK
STATE MAY BE QUITE CHILLY ON SATURDAY INTO EARLY SUNDAY WITH THE
MID-ATLANTIC REGION CLOSER TO SEASONAL AVERAGES. THE NEXT ROUND OF
ARCTIC COLD ARRIVES ACROSS MONTANA ON SUNDAY AND EXTENDS INTO THE
DAKOTAS BY MONDAY, WITH HIGHS POTENTIALLY 15-25 DEGREES BELOW
AVERAGE IN MANY CASES. COLDER WEATHER THEN ENCOMPASSES MORE OF THE
CENTRAL AND NORTHERN U.S. GOING INTO TUESDAY. HOWEVER, AT THAT TIME
TEMPERATURES OVER THE EASTERN HALF OF THE COUNTRY BECOME MORE
UNCERTAIN AS REFLECTED IN GUIDANCE SPREAD FOR HOW MUCH UPPER
TROUGHING EXISTS OVER THE EAST AND POSITION OF THE PRIMARY SURFACE
FRONT. UPPER RIDGING THAT DEVELOPS OVER THE WEST/ROCKIES SHOULD
PROMOTE A WARMING TREND OVER THE SOUTHERN HALF OR SO OF THOSE
AREAS.
RAUSCH/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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