391
FXUS02 KWBC 291855
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 PM EDT TUE APR 29 2025
VALID 12Z FRI MAY 02 2025 - 12Z TUE MAY 06 2025
..OVERVIEW
BEHIND A SYSTEM TRACKING ACROSS SOUTHEASTERN CANADA ON FRIDAY WITH
SOME RAIN AND THUNDERSTORMS ACROSS THE EAST/SOUTH, GUIDANCE
CONTINUES TO SHOW A MORE BLOCKY PATTERN SETTLING OVER THE LOWER 48.
WITH ONLY MODERATE DETAIL DIFFERENCES/ADJUSTMENTS, MOST SOLUTIONS
HAVE BEEN FAIRLY WELL BEHAVED AS AN UPPER TROUGH APPROACHES THE
WEST COAST BY SATURDAY AND CLOSES OFF AN UPPER LOW THAT SHOULD
DRIFT INTO THE SOUTHWESTERN U.S. EARLY NEXT WEEK, SPREADING RAIN
AND HIGH ELEVATION SNOW ACROSS THE WEST. THIS SYSTEM MAY START TO
GENERATE HEAVIER SOUTHERN HIGH PLAINS RAINFALL TOWARD THE END OF
THE PERIOD. A LEADING RIDGE SHOULD SETTLE OVER THE PLAINS INTO THE
MISSISSIPPI VALLEY. IN CONTRAST TO THE WESTERN CONSENSUS,
INDIVIDUAL MODELS AND ENSEMBLES CONTINUE TO SHOW REMARKABLY
DIFFERENT IDEAS FOR THE ULTIMATE EVOLUTION OF ENERGY WITHIN AN
UPPER TROUGH REACHING THE EAST DURING THE WEEKEND INTO EARLY NEXT
WEEK. THIS SPREAD KEEPS CONFIDENCE MUCH LOWER THAN AVERAGE FOR
DETAILS OF EASTERN U.S. SENSIBLE WEATHER.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE IS 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 PORTION OF
THE NATION. A MODEL COMPOSITE SEEMS TO PROVIDE A REASONABLE
FORECAST BASIS WITH GOOD CONTINUITY AND ENSEMBLE SUPPORT.
HOWEVER OVER THE EAST, INDIVIDUAL MODELS AND ENSEMBLE MEMBERS AND
RECENT MACHINE LEARNING MODELS CONTINUE TO DIVERGE CONSIDERABLY
FROM THE WEEKEND INTO EARLY NEXT WEEK WITH DEPICTION AND DIGGY
NATURE OF A POTENTIAL CLOSED UPPER TROUGH/LOW. GIVEN WELL CLUSTERED
GUIDANCE SHOWING AMPLE FLOW AMPLITUDE UPSTREAM, FAVOR A SOLUTION
OVER THE EAST SOMEWHERE ON THE MORE AMPLIFIED/CLOSED SIDE OF THE
FULL ENVELOPE OF MODEL AND ENSEMBLE SOLUTIONS. ACCORDINGLY, THE
WPC PRODUCT SUITE INCORPORATED BEST CLUSTERED GUIDANCE IN THIS VEIN
FROM THE 00 UTC ECMWF/CANADIAN ENSEMBLE MEANS THAT OFFER BETTER
CYCLE TO CYCLE CONTINUITY THAN INDIVIDUAL MODELS. RECENT GFS AND
GEFS RUNS SEEM TOO PROGRESSIVE GIVEN UPSTREAM AMPLITUDE. LATEST 12
UTC MODEL GUIDANCE REMAINS MIXED AND UNCERTAIN.
..WEATHER/HAZARDS HIGHLIGHTS
EXPECT SOME SHOWERS AND THUNDERSTORMS AHEAD OF A COLD FRONT
PUSHING THROUGH THE EAST ON FRIDAY. LATEST GUIDANCE SIGNALS HAVE
BECOME A LITTLE MORE DIFFUSE REGARDING HOW MUCH FLASH FLOOD
POTENTIAL THERE MAY BE OVER THE CENTRAL AND NORTHERN APPALACHIANS
WHERE GROUND CONDITIONS ARE ON THE WETTER SIDE, BUT ENOUGH
INSTABILITY MAY EXIST TO PROMOTE RAIN RATES THAT COULD CAUSE
LOCALIZED RUNOFF ISSUES. MODELS ARE STARTING TO DEVELOP SOME
CLUSTERING FOR THE IDEA OF FRONTAL WAVINESS PRODUCING A BAND OF
ENHANCED RAINFALL OVER PARTS OF THE NORTHEAST ON SATURDAY. THIS IS
AN EMERGING TREND AND THERE IS A QUESTION OF HOW MUCH INSTABILITY
MAY EXIST IN THIS RAIN BAND, SO INITIALLY OPTED FOR NO RISK AREA IN
THE DAY 5 ERO FOR THIS ACTIVITY. WILL CONTINUE TO MONITOR THIS
ASPECT OF THE FORECAST IN FUTURE RUNS. PRECIPITATION COVERAGE AND
AMOUNTS OVER THE EAST BECOME INCREASINGLY UNCERTAIN AFTER SATURDAY,
DEPENDING ON EVOLUTION OF UPPER TROUGHING AND POSSIBLE CLOSED LOW.
LATEST GUIDANCE PREFERENCES SUGGEST MORE LIKELY CLOSED LOW
DEVELOPMENT AND SETTLING OVER THE EAST INTO EARLY NEXT WEEK THAT
WOULD SUPPORT PROTRACTED UNSETTLED CONDITIONS INCLUDING WRAPBACK
WESTERN ATLANTIC LOW MOISTURE TO FUEL LIGHT TO MODERATE RAIN
POTENTIAL, POSSIBLY WITH FOCUS INTO THE NORTHERN MID-ATLANTIC.
MULTIPLE DAYS OF LOW LEVEL FLOW COMING IN FROM THE GULF, ALONG
WITH SOME WEAK SHORTWAVE ENERGY APPROACHING FROM THE SOUTHWEST AND
EVENTUALLY HEIGHT FALLS AHEAD OF THE DEEPER WESTERN UPPER LOW, WILL
SUPPORT MULTIPLE EPISODES OF RAINFALL OVER PORTIONS OF THE
SOUTHERN AND EVENTUALLY ALSO CENTRAL PLAINS. WITH A FAIR AMOUNT OF
VARIANCE IN THE DETAILS, GUIDANCE CONTINUES TO MAINTAIN SUPPORT IN
PRINCIPLE FOR THE EXISTING MARGINAL RISK AREA FROM SOUTHEASTERN NEW
MEXICO INTO TEXAS ON DAY 4/FRIDAY. LATEST SOLUTIONS ARE INCREASING
POTENTIAL FOR IMPACTFUL RAIN TO EXTEND FARTHER EAST ALONG A
SURFACE FRONT, NOW FAVORING EXTENSION OF THE MARGINAL RISK AREA
INTO PARTS OF LOUISIANA. MOISTURE/INSTABILITY AND PATTERN
PERSISTENCE SHOULD LEAD TO ADDITIONAL POCKETS OF ENHANCED RAINFALL
OVER THE SOUTHWESTERN HALF OF TEXAS INTO SATURDAY, MERITING A
MARGINAL RISK OVER THAT REGION ON DAY 5. THE SOUTHWEST UPPER LOW
STILL LOOKS TO DRIFT FAR ENOUGH EASTWARD TO START GENERATING
HEAVIER RAINFALL OVER THE SOUTHERN HALF OF THE HIGH PLAINS DURING
THE FIRST HALF OF NEXT WEEK.
THE PACIFIC SYSTEM MOVING INTO THE WEST WILL BRING RAIN AND HIGH
ELEVATION SNOW INTO THE NORTHWEST AROUND FRIDAY, WITH PRECIPITATION
THEN CONTINUING ACROSS THE SIERRA NEVADA/GREAT BASIN/NORTHERN
PARTS OF THE SOUTHWEST AND INTO THE NORTHERN-CENTRAL ROCKIES.
HIGHEST TOTALS WILL BE DEPENDENT ON THE EXACT TRACT OF THE FORECAST
EVOLVING UPPER LOW, AND ARE CURRENTLY MOST LIKELY TO BE OVER THE
GREAT BASIN AND NORTH-CENTRAL ROCKIES. LATEST GUIDANCE IS KEYING ON
POTENTIAL FOR A BAND OF LOCALLY HEAVY RAINFALL OVER NEVADA ON DAY
5/SATURDAY AS THE UPPER LOW CLOSES OFF OVER CALIFORNIA, WITH
ANOMALOUS MOISTURE AND SOME INSTABILITY. THE DAY 5 ERO DEPICTS A
MARGINAL RISK AREA TO REFLECT THIS POSSIBLE THREAT. LEADING WEAK
SHORTWAVE/UPPER LOW ENERGY MAY PRODUCE LIGHTER PRECIPITATION FROM
THE SIERRA NEVADA EAST INTO THE ROCKIES ON FRIDAY.
WELL ABOVE NORMAL TEMPERATURES SHOULD MIGRATE FROM THE NORTHERN
HALF OR SO OF THE WEST ON FRIDAY INTO THE NORTHERN PLAINS BY THE
WEEKEND AND EARLY NEXT WEEK. PLUS 15-25F ANOMALIES SHOULD BE MOST
COMMON OVER FAR NORTHERN AREAS DURING FRIDAY-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. PERSISTENT CLOUDS AND PRECIPITATION SHOULD KEEP THE
SOUTHERN HIGH PLAINS HIGHS BELOW NORMAL AS WELL. LOCATIONS NEAR THE
EAST COAST WILL SEE A WARM DAY ON FRIDAY AHEAD OF A COLD FRONT,
FOLLOWED BY A TREND TO NEAR OR SLIGHTLY BELOW NORMAL READINGS.
HOWEVER CONFIDENCE IN SPECIFICS FROM SUNDAY ONWARD IS LOWER THAN
AVERAGE DUE TO VERY UNCERTAIN UPPER LEVEL FLOW DETAILS.
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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