358
FXUS02 KWBC 251853
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 PM EDT SUN MAY 25 2025
VALID 12Z WED MAY 28 2025 - 12Z SUN JUN 01 2025
..OVERVIEW
THIS MEDIUM RANGE PERIOD BEGINS MIDWEEK WITH A SLOW TO PROGRESS
UPPER LEVEL PATTERN LINGERING OVER THE LOWER 48, WITH SPLIT FLOW TO
INCLUDE A COUPLE OF EMBEDDED CUTOFF LOWS. A NORTHERN STREAM LOW
WILL MEANDER OVER THE NORTH-CENTRAL U.S. AND MIDWEST THIS WEEK
WHILE AN OFFSHORE SOUTHERN STREAM LOW WILL ONLY GRADUALLY APPROACH
THE SOUTHWEST U.S. AS UPPER RIDGING BUILDS HEAT OVER THE WEST. THE
NORTHERN STREAM LOW SHOULD GAIN MOMENTUM HEADING INTO NEXT WEEKEND
AS IT TENDS TO SYNC INTO AMPLIFIED UPPER LEVEL TROUGHING. THIS
PATTERN WILL RESULT IN A PERIOD WITH AREAS OF WET UNSETTLED WEATHER
TO FOCUS FROM THE SOUTH-CENTRAL U.S. TO THE EAST/SOUTHEAST U.S.
THIS WEEK. MEANWHILE, A SERIES OF PACIFIC FRONTAL APPROACHES
SLUGGISHLY TOWARD THE PACIFIC NORTHWEST MAY OFFER SOME MODEST
COASTAL RAINS CHANCES INTO LATER WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE FOR TODAY CONTINUES TO OFFER REASONABLE
AGREEMENT ON THE LARGE SCALE PATTERN THROUGH MUCH OF THE PERIOD.
THERE IS SOME QUESTION ON ENERGY DISTRIBUTION AROUND AN INITIAL
GREAT LAKES LOW THAT CREATES SOME VARIABILITY IN THE GUIDANCE AS IT
MERGES AND AMPLIFIES TROUGHING OVER THE EAST NEXT WEEKEND. THE
MAIN OUTLIER SEEMS TO BE THE GFS WHICH IS SLIGHTLY MORE AMPLIFIED
WITH THE TROUGH. ELSEWHERE, A LINGERING UPPER LOW JUST OFF THE
SOUTHERN CALIFORNIA COAST SHOWS UNCERTAINTY IN ITS EXACT POSITION
AND WHEN IT STARTS TO DRIFT INLAND, WHILE THERE IS SOME TIMING
QUESTIONS WITH A SHORTWAVE INTO THE WEST LATE PERIOD. THE WPC
FORECAST TODAY USED A BLEND OF THE DETERMINISTIC GUIDANCE (ANCHORED
BY THE ECMWF) THE FIRST HALF OF THE PERIOD, TRANSITIONING TO
MAJORITY ENSEMBLE MEANS BY THE END OF THE PERIOD TO ACCOUNT FOR
GROWING UNCERTAINTY. THIS MAINTAINED GOOD CONTINUITY WITH THE
PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
A SURFACE LOW OUT OF THE MIDWEST AND A SERIES OF ASSOCIATED
FRONTAL BOUNDARY DRAPED INTO THE SOUTH WILL CONTINUE TO SUPPORT
WIDESPREAD MOISTURE AND LOCALLY HEAVY RAINS FROM THE MID-
ATLANTIC/SOUTHEAST INTO THE SOUTHERN PLAINS. THERE IS A LOT OF
UNCERTAINTY STILL IN THE DETAILS AND LOCATIONS OF POTENTIALLY
IMPACTFUL/HAZARDOUS RAINFALL, BUT THE BEST GUESS AT THIS POINT IS
PARTS OF THE LOWER MISSISSIPPI VALLEY/GULF COAST, SOUTHERN PLAINS,
AND COASTAL MID- ATLANTIC REGIONS WHICH WILL ALSO SEE RAINFALL IN
THE SHORT-RANGE PERIOD. THIS IS REFLECTED AS BROAD MARGINAL RISKS
IN THE THE DAY 4 (WEDNESDAY) AND DAY 5 (THURSDAY) EXCESSIVE
RAINFALL OUTLOOKS. THIS ACTIVITY SHOULD CONTINUE THROUGH AT LEAST
THE WORK WEEK AS THE BOUNDARIES LINGER AND WEAKEN AND UPPER
TROUGHING BECOMES MORE ESTABLISHED OVER THE EAST INTO NEXT WEEKEND.
RAINS MAY LINGER LONGER OVER PARTS OF THE SOUTHERN HIGH PLAINS
ASSOCIATED WITH RETURN FLOW AHEAD OF A BUILDING UPPER RIDGE OVER
THE SOUTHWEST. TO THE NORTH, A SECONDARY COLD FRONT WILL SPREAD
RAIN OVER THE NORTHEAST LATE WEEK.
IN THE WEST, A BUILDING UPPER RIDGE WILL LEAD TO AN EXPANDING AREA
OF HEAT FROM THE INTERMOUNTAIN WEST INTO THE WEST COAST STATES
THIS WEEK, WITH TEMPERATURES RISING UPWARDS TO 10 TO 15+ DEGREES
ABOVE NORMAL. THIS IN PARTICULAR MAY LEAD TO A HAZARDOUS HEAT FOCUS
FOR THE CALIFORNIA CENTRAL VALLEY LATE WEEK/NEXT WEEKEND.
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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