093
FXUS02 KWBC 201739
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
139 PM EDT SUN APR 20 2025
VALID 12Z WED APR 23 2025 - 12Z SUN APR 27 2025
..MULTI-DAY HEAVY RAIN THREAT FOR THE SOUTH-CENTRAL U.S.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES CONTINUE TO OFFER DECENT AGREEMENT ON THE
OVERALL UPPER FLOW EVOLUTION INTO NEXT WEEKEND, BUT CONSIDERABLE
UNCERTAINTY IN THE DETAILS OF INDIVIDUAL SYSTEMS. ENERGY
PROGRESSION FROM THE SOUTHERN PLAINS TO MISSISSIPPI VALLEY MID TO
LATE WEEK WILL TAKE UNTIL THE SHORT RANGE TO RESOLVE DETAILS, BUT
WILL HAVE IMPLICATIONS ON HEAVY RAINFALL DISTRIBUTION AND AMOUNTS
ACROSS THIS AREA. BIG DIFFERENCES ARISE BY FRIDAY AS AN UPPER LOW
FROM THE GULF OF ALASKA DROPS SOUTHWARD ALONG THE COAST WITH SOME
ENERGY LIKELY TO SPLIT FROM THE MAIN LOW. THE GFS IS QUICKER TO
SPLIT THIS THAN OTHER GUIDANCE, AND THE ECMWF HAS AN OPEN SHORTWAVE
EXTENDING MORE SOUTH. PLACEMENT WISE, THE CMC WAS IN THE MIDDLE OF
THE TWO, BUT ALSO SHOWS A STRONGER THAN CONSENSUS UPPER LOW
CENTERED OVER THE CALIFORNIA/NEVADA ON DAY 7. THUS, IT SEEMED
NECESSARY TO TRANSITION THE EARLY PERIOD DETERMINISTIC MODEL BLEND
TO A MAJORITY ENSEMBLE MEAN BLEND MID TO LATE PERIOD TO SMOOTH OUT
THESE DIFFERENCES WHILE STILL MAINTAINING GOOD CONTINUITY WITH THE
PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A SCATTERED SERIES OF GENERALLY PROGRESSIVE UPPER FEATURES AND
ASSOCIATED SURFACE BASED SYSTEMS ARE SET TO WORK OVER THE LOWER 48
NEXT WEEK IN MULTIPLE STREAM FLOWS TO LOCALLY FOCUS LATE APRIL
WEATHER, BUT THERE IS SOME SIGNAL TO AMPLIFY THE FLOW FROM THE
NORTHEAST/EASTERN PACIFIC INTO THE WEST HEADING INTO NEXT WEEKEND.
WPC EXCESSIVE RAINFALL BROAD MARGINAL RISK AREAS FOR PORTIONS OF
THE SOUTH-CENTRAL PLAINS INTO THE MISSISSIPPI VALLEY FOR DAY
4/WEDNESDAY AND DAY 5/THURSDAY ARE IN PLACE, BUT THERE IS STILL
CONSIDERABLE UNCERTAINTY ON EXACTLY WHERE HEAVIEST AMOUNTS WILL BE.
REGARDLESS, THE PATTERN SUPPORTS A MOIST AND UNSTABLE FLOW FOR A
FAVORABLE, AT LEAST LOCAL, FLASH FLOOD SETUP. SOME OF THIS REGION,
PARTICULARLY OKLAHOMA INTO NORTH TEXAS, HAVE SEEN HEAVY RAINFALL
THIS WEEKEND AND THUS REMAINS PARTICULARLY SUSCEPTIBLE TO
ADDITIONAL RAINS, AND A SLIGHT RISK UPGRADE MAY BE NEEDED IN FUTURE
UPDATES. BUT WITH THE MODEL UNCERTAINTY, OPTED TO HOLD OFF ON ANY
UPGRADES AT THIS TIME. HEAVY RAIN AND RUNOFF THREATS ALONG WITH
STRONG CONVECTIVE POTENTIAL IN THIS REGION AND INTO THE MISSISSIPPI
VALLEY/SOUTHEAST ALONG A LINGERING BOUNDARY WILL ALSO BE MONITORED
FOR LATER WEEK AND NEXT WEEKEND GIVEN LINGERING SUPPORT AND MULTI-
DAY POTENTIAL.
THE EXTENT OF UPPER TROUGH AMPLIFICATION AND DIGGING IS NOT A DONE
DEAL IN GUIDANCE, BUT THE PROSPECT OF SURFACE SYSTEM GENESIS AND
SLOW BUT STEADY TRANSLATION FROM THE NORTHEAST/EASTERN PACIFIC TO
THE WEST COAST FRIDAY AND INLAND OVER THE WEST NEXT WEEKEND STILL
OFFERS INCREASED LIGHT TO MODERATE WIDESPREAD RAIN CHANCES AND
MOUNTAIN SNOWS.
SANTORELLI/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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