814
FXUS02 KWBC 300659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT WED APR 30 2025
VALID 12Z SAT MAY 03 2025 - 12Z WED MAY 07 2025
..OVERVIEW
LATEST 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 RAPIDLY
DIVERGE OVER THE EAST, WITH NEW 00Z RUNS ADDING TO RECENT TRENDS
TOWARD CLOSING OF AN UPPER LOW WELL INLAND--LEAVING THE MORE
PROGRESSIVE GFS/GEFS THAT BUILD A RIDGE INTO THE EAST-CENTRAL U.S.
IN THE VAST MINORITY. THE MAJORITY SCENARIO INCREASES THE
PROBABILITY OF A WETTER PATTERN OVER PORTIONS OF THE EAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
FOR THE DEVELOPING WESTERN UPPER LOW, THE NEW 00Z UKMET STRAYS A
LITTLE SOUTHWEST OF CONSENSUS WHILE GFS/GEFS RUNS HAVE SOMETIMES
BEEN LEANING A BIT FAST AND NORTH LATER IN THE PERIOD. RECENT
MACHINE LEARNING (ML) RUNS HAVE BEEN FAVORING THE SOUTHERN HALF OF
THE ENVELOPE, WHILE DIVERGING A LITTLE FOR TIMING LATER IN THE
FORECAST. MULTI-DAY TRENDS HAVE GENERALLY BEEN SLOWER BUT THE 00Z
CMC MAY BE TOO SLOW AS IT HOLDS THE UPSTREAM PACIFIC UPPER TROUGH
(WHICH SHOULD BRING A COLD FRONT INTO THE NORTHWEST TUESDAY-
WEDNESDAY) WEST OF CONSENSUS. RECENT ECMWF/ECENS RUNS HAVE BEEN
MOST CONSISTENT WITH THE UPPER LOW'S PATH AND TIMING WITH RELATIVE
SUPPORT FROM ML MODELS.
GUIDANCE THROUGH THE 12Z/18Z GUIDANCE CYCLES MAINTAINED THE
TREMENDOUS SPREAD FOR EASTERN U.S. EVOLUTION FROM SATURDAY ONWARD.
ML MODELS STARTING WITH THE 12Z/28 CYCLE HAVE BEEN SHOWING
POTENTIAL FOR INITIAL MISSISSIPPI VALLEY ENERGY TO CLOSE OFF AN
UPPER LOW AS FAR WEST AS THE TENNESSEE/OHIO VALLEYS, WITH THE ECMWF
TRENDING THAT WAY OVER THE PAST DAY. THE 12Z UKMET BROUGHT ITS
CLOSED LOW INTO THE CAROLINAS WHILE THE 12Z CMC WAS PROGRESSIVE
UNTIL USING CANADIAN ENERGY TO CLOSE OFF A LOW OVER THE NORTHEAST
(BUT THE CMCENS MEAN WAS A COMPROMISE WITH THE ECMWF). ON THE MOST
PROGRESSIVE EXTREME WERE THE GFS/GEFS (ALBEIT WITH A HEAVY RAIN
PRODUCING TROUGH/UPPER LOW PASSING OVER FLORIDA). ML MODEL
CONSISTENCY ALONG WITH SOME TRENDS IN NON- GFS/GEFS GUIDANCE
FAVORED SOME TRENDING TOWARD A MORE INLAND UPPER LOW, BUT NOT YET
TO THE POINT OF MATCHING THE ECMWF GIVEN THE WIDE GUIDANCE SPREAD.
BY MIDWEEK THE ML MODELS SUGGEST THE UPPER LOW WOULD EITHER DRIFT
INTO THE NORTHERN MID-ATLANTIC OR LIFT INTO THE GREAT LAKES AND
PHASE WITH A CANADIAN TROUGH. THESE SOLUTIONS DO NOT SUPPORT THE
NEW 00Z CMC THAT DROPS ITS UPPER LOW TO THE SOUTHEAST COAST. THE
NEW 00Z UKMET HAS JOINED THE LATEST ECMWF RUNS. THE FULL ARRAY OF
00Z RUNS SO FAR COULD ALLOW FOR SOME ADDED WESTWARD TRENDING OF THE
UPPER LOW AND GRADUAL ENHANCEMENT OF EXPECTED RAINFALL.
COMBINING GUIDANCE PREFERENCES FOR THE WESTERN UPPER LOW AND THE
EASTERN U.S. EVOLUTION, THE FIRST HALF OF THE FORECAST STARTED WITH
A BLEND OF 12Z AND 00Z/29 ECMWF RUNS, ALONG WITH INPUT FROM THE
12Z UKMET, ECENS, AND CMCENS. ECENS/CMCENS WEIGHT INCREASED A
LITTLE AFTER EARLY MONDAY TO MAKE UP FOR THE UKMET. LOCAL
UNAVAILABILITY OF THE 12Z ECENS VALID 12Z TUESDAY REQUIRED GREATER
WEIGHT OF THE CMCENS AT THAT EXACT TIME.
..WEATHER/HAZARDS HIGHLIGHTS
LATEST 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 WOULD SUPPORT SOME AREAS OF MODERATE TO PERHAPS LOCALLY HEAVY
RAINFALL DEPENDING ON THE ORIENTATION AND PERSISTENCE OF ANY
PARTICULAR BANDS. THERE IS STILL A LOT OF SPREAD FOR RAINFALL
SPECIFICS ACROSS AREAS WITH VARYING SOIL MOISTURE, SO FOR NOW HAVE
OPTED NOT TO DEPICT ANY MARGINAL RISK AREAS IN THE DAYS 4-5
EXCESSIVE RAINFALL OUTLOOKS. IT APPEARS LIKELY THAT ONE OR MORE
RISK AREAS WOULD BECOME WARRANTED AS SOON AS A LITTLE BETTER DETAIL
CLUSTERING EMERGES. THE DRIER SCENARIO, ASIDE FROM SOME HEAVY RAIN
POTENTIAL OVER FLORIDA/SOUTHEAST COAST, REPRESENTED BY THE GFS
SEEMS TO BE TRENDING LOWER IN PROBABILITY.
EASTERLY FLOW AND ADEQUATE MOISTURE/INSTABILITY OVER THE FAR
SOUTHERN PLAINS SHOULD MAINTAIN THE THREAT FOR SOME LOCALLY HEAVY
RAINFALL OVER THE SOUTHWESTERN HALF OF TEXAS ON SATURDAY, THOUGH
WITH A DIMINISHED SIGNAL COMPARED TO THE PRIOR DAY. THE CURRENT
MARGINAL RISK OVER THAT AREA IN THE DAY 4 ERO APPEARS REASONABLE.
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/MONDAY 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 ERO INTRODUCES 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 ACROSS THE REGION, FROM THE SIERRA NEVADA AND INLAND
NORTHWEST INTO 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
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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