243
FXUS02 KWBC 301900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT WED APR 30 2025
VALID 12Z SAT MAY 03 2025 - 12Z WED MAY 07 2025
..BLOCKY CLOSED LOWS FOR THE WEST AND THE EAST
..OVERVIEW
RECENT GUIDANCE CONTINUES TO SHOW THE GENERAL THEME OF AN
INCREASINGLY BLOCKY PATTERN ACROSS THE LOWER 48, AND WITH BETTER
RELATIVE AGREEMENT FOR THE UPPER LOW CLOSING OFF OVER CALIFORNIA
DURING THE WEEKEND AND DRIFTING GRADUALLY INLAND VERSUS THE PATTERN
OVER THE EAST. THE WESTERN UPPER LOW WILL SUPPORT A BROAD AREA OF
RAIN AND HIGH ELEVATION SNOW ACROSS THE REGION, AS WELL AS AN
INCREASING THREAT FOR AREAS OF HEAVY RAIN ACROSS PARTS OF THE
CENTRAL/SOUTHERN PLAINS NEXT WEEK. MEANWHILE, SOLUTIONS DIVERGE
OVER TIME IN THE EAST, ALBEIT WITH RECENT GUIDANCE RUNS ADDING TO
RECENT TRENDS TOWARD CLOSING OF AN UPPER LOW WELL INLAND, LEAVING
THE MORE PROGRESSIVE GFS/GEFS THAT ALTERNATELY BUILDS A RIDGE INTO
THE EAST-CENTRAL U.S. AS AN OUTLIER IN THE VAST MINORITY OF
SOLUTIONS. THE MAJORITY SCENARIO INCREASES THE PROBABILITY OF A
MUCH WETTER PATTERN FOR PARTS OF THE EAST THIS WEEKEND/NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE REMAINS CLUSTERED BETTER THAN NORMAL THROUGH MED-RANGE
TIME SCALES WITH THE DEVELOPMENT AND SLOW PROGRESSION OF A
SIGNIFICANT UPPER TROUGH/CLOSED LOW AND MID-LARGER SCALE FEATURES
WORKING INTO/ACROSS THE WEST, EVENTUALLY AFFECTING THE CENTRAL
U.S.. A MODEL COMPOSITE SEEMS TO PROVIDE A REASONABLE FORECAST
BASIS WITH GOOD CONTINUITY AND ENSEMBLE SUPPORT.
OVER THE EAST, RECENT INDIVIDUAL MODELS AND ENSEMBLE MEMBERS, BUT
ESPECIALLY THE GFS/GEFS, HAVE OFFERED LESS THAN STELLAR AGREEMENT
FROM THE WEEKEND INTO EARLY NEXT WEEK WITH DEPICTION AND DIGGY
NATURE OF A POTENTIAL CLOSED UPPER TROUGH/LOW. HOWEVER, GIVEN WELL
CLUSTERED GUIDANCE SHOWING AMPLE FLOW AMPLITUDE UPSTREAM, THE
PATTERN CONTINUES TO STRONGLY FAVOR A SOLUTION ON THE MORE
AMPLIFIED/CLOSED SIDE OF THE FULL ENVELOPE OF MODEL AND ENSEMBLE
SOLUTIONS. ACCORDINGLY, THE WPC PRODUCT SUITE WAS PRIMARILY DERIVED
FROM BEST CLUSTERED GUIDANCE IN THIS VEIN WITH USAGE OF THE 00 UTC
ECMWF/CANADIAN/UKMET AND ECMWF/CANADIAN ENSEMBLE MEANS ALONG WITH
MOST MACHINE LEARNING MODELS. THIS SOLUTION MAINTAINS REASONABLY
GOOD WPC PRODUCT CONTINUITY. RECENT GFS AND GEFS RUNS SEEMED WAY
TOO PROGRESSIVE, BUT THE LATEST 12 UTC GEFS AND GFS BASED GRAPHCAST
MACHINE LEARNING MODEL TRENDED TOWARD THE AFOREMENTIONED FAVORED
CLUSTER OF MOST OTHER GUIDANCE, BOLSTERING FORECAST GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
LATEST MACHINE LEARNING (ML) MODELS AND NON-GFS DYNAMICAL MODELS
ARE STEADILY SHOWING MORE PRONOUNCED CLUSTERING TOWARD CLOSURE OF
AN UPPER LOW THAT MAY PERSIST FOR A COUPLE DAYS OR SO TO THE WEST
OF THE APPALACHIANS. THIS SUPPORTS SOME AREAS OF MODERATE TO
LOCALLY HEAVY RAINFALL DEPENDING ON THE ORIENTATION AND
PERSISTENCE OF ANY PARTICULAR BANDS AND FAVORED TERRAIN LIFT.
THERE IS STILL SPREAD FOR RAINFALL SPECIFICS ACROSS AREAS WITH
VARYING SOIL MOISTURE, BUT GIVEN THE GROWING SIGNAL AND FAVORABLE
PATTERN RECOGNITION, OPTED TO INTRODUCE WPC DAY 4/DAY 5 EXCESSIVE
RAINFALL OUTLOOK MARGINAL RISK AREAS FOR THE SOUTHERN AND CENTRAL
APPALACHIANS REGION THROUGH THE NORTHERN MID- ATLANTIC FOR AT LEAST
THIS SATURDAY AND SUNDAY. A DRIER SCENARIO OF THE GFS IS TRENDING
LOWER IN PROBABILITY.
EASTERLY FLOW AND ADEQUATE MOISTURE/INSTABILITY OVER THE FAR
SOUTHERN PLAINS STILL OFFERS SOME THREAT FOR SPOTTY LOCALLY HEAVY
RAINFALL OVER THE SOUTHWESTERN HALF OF TEXAS INTO THE WEEKEND,
THOUGH WITH A DIMINISHED SIGNAL COMPARED PRIOR DAYS, SO NO WPC ERO
MARGINAL RISK AREAS REMAIN IN PLACE. MEANWHILE GUIDANCE HAS BEEN
CONSISTENT IN SHOWING A BAND OF POTENTIALLY HEAVY RAINFALL ALIGNED
OVER WEST-CENTRAL NEVADA ON SATURDAY AS THE UPPER LOW CLOSES OFF
OVER CALIFORNIA, SO THAT MARGINAL RISK REMAINS NEARLY UNCHANGED AS
WELL. BY DAY 5/SUNDAY THE RAINFALL SIGNAL OVER THE WEST LOOKS A
LITTLE MORE DIFFUSE BUT WITH SOME GUIDANCE CLUSTERING TOWARD
ENHANCED RAINFALL OVER THE SENSITIVE TERRAIN IN THE EASTERN HALF OF
NEW MEXICO AS GRADUAL PROGRESS OF THE SOUTHWEST UPPER LOW PUSHES A
COLD FRONT TOWARD THE REGION. THUS THE DAY 5 WPC ERO STILL HAS A
MARGINAL RISK AREA FOR THIS THREAT. ADDITIONAL GRADUAL DRIFT OF THE
SOUTHWEST UPPER LOW SHOULD RAISE THE POTENTIAL FOR AREAS OF HEAVY
RAINFALL OVER PARTS OF THE CENTRAL/SOUTHERN PLAINS FROM MONDAY
ONWARD, WITH DETAILS DEPENDING ON EXACT PATH AND TIMING OF THE
UPPER LOW. OTHERWISE, THE SYSTEM MOVING INTO THE WEST WILL BRING A
BROAD AREA OF RAIN AND HIGH ELEVATION SNOW TO THE REGION, FROM THE
SIERRA NEVADA AND INLAND NORTHWEST TO THE NORTHERN-CENTRAL ROCKIES.
WELL ABOVE NORMAL TEMPERATURES SHOULD EXTEND FROM THE NORTHERN
ROCKIES AND EASTERN GREAT BASIN INTO THE NORTHERN PLAINS ON
SATURDAY, WITH ANOMALIES GRADUALLY MODERATING AS THE WARMTH MOVES
EASTWARD TOWARD THE UPPER MIDWEST. PLUS 15-25F ANOMALIES SHOULD BE
MOST COMMON OVER FAR NORTHERN AREAS DURING SATURDAY-SUNDAY. IN
CONTRAST, THE UPPER LOW TRACKING INTO THE SOUTHWEST WILL BRING MUCH
COOLER TEMPERATURES TO THE REGION. HIGHS SHOULD BE 10-20F BELOW
NORMAL ON SUNDAY-MONDAY, WITH SOME RECORD COLD HIGHS POSSIBLE NEAR
THE UPPER LOW'S PATH ESPECIALLY ON SUNDAY. PERSISTENT CLOUDS AND
PRECIPITATION SHOULD KEEP THE SOUTHERN HIGH PLAINS HIGHS BELOW
NORMAL AS WELL. THE POTENTIALLY UNSETTLED PATTERN OVER THE EAST MAY
FAVOR TEMPERATURES WITHIN A FEW DEGREES OF NORMAL AFTER SOME
MODEST WARMTH ALONG THE EAST COAST ON SATURDAY.
RAUSCH/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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