212
FXUS02 KWBC 231858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT FRI MAY 23 2025
VALID 12Z MON MAY 26 2025 - 12Z FRI MAY 30 2025
...HEAVY RAIN AND FLASH FLOODING THREATS FOCUS ACROSS THE SOUTH
EARLY NEXT WEEK...
..OVERVIEW
THE MEDIUM RANGE PERIOD WILL FEATURE AN AMPLIFIED AND SLOW UPPER
LEVEL PATTERN WITH A COUPLE CUTOFF LOWS THAT WILL DRIVE SURFACE
FRONTAL SYSTEMS ACROSS THE LOWER 48. ONE LOW WILL WANDER ACROSS THE
NORTH-CENTRAL U.S. AND MIDWEST WHILE THE SECOND GRADUALLY
APPROACHES THE SOUTHWEST. THE EASTERN LOW SHOULD GAIN MOMENTUM LATE
IN THE PERIOD AS IT SYNCS UP WITH A BROAD UPPER LEVEL TROUGH, BUT
THE WESTERN LOW WILL LIKELY SLOW DOWN AS RIDGING BUILDS INTO THE
WEST. THIS PATTERN WILL RESULT IN WET UNSETTLED WEATHER FOR
PORTIONS OF THE SOUTH AND SOUTHEAST, INCLUDING A THREAT OF HEAVY
RAIN AND FLASH FLOODING FOR THE SOUTH ON MEMORIAL DAY. SCATTERED
PRECIPITATION CHANCES WILL ALSO SPREAD FROM THE PLAINS TO THE MID-
ATLANTIC MID-TO-LATE NEXT WEEK, AND ISOLATED PRECIPITATION CHANCES
WILL ALSO RETURN TO THE NORTHWEST AS A COUPLE OF FRONTAL SYSTEMS
PUSH ONSHORE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AGREEMENT IS FAIRLY GOOD AT THE BEGINNING OF THE MEDIUM RANGE
PERIOD, AND ALL AVAILABLE GUIDANCE INDICATED TROUGHING ALONG THE
EAST AND WEST COASTS WITH RIDGING IN THE CENTRAL U.S. AND SOUTHERN
CANADA AND A SHORTWAVE CUTTING THROUGH THE WEST. AGREEMENT
DETERIORATES THROUGH THE PERIOD AS MODELS STRUGGLE TO RESOLVE HOW
THE RELATIVELY WEAK SHORTWAVE WILL EVOLVE AS IT CUTS THROUGH UPPER
LEVEL RIDGING TO THE EAST. OVERALL, THE GFS AND ECMWF ARE THE BEST
CLUSTERED WHILE THE UKMET AND CMC TEND TO DEVIATE MORE FROM THE
MEAN SOLUTION. FOR THIS REASON, THE UKMET AND CMC WERE GIVEN THE
LEAST WEIGHT IN WPCS AFTERNOON FORECAST BLEND. BY DAY 5
(WEDNESDAY), THE CMC AND UKMET WERE PHASED OUT OF THE BLEND AND
ENSEMBLE MEANS FROM THE GEFS AND ECENS WERE ADDED IN INCREASING
AMOUNTS. THIS PROVIDED A GOOD STARTING POINT FOR THE FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A WET AND WAVY WEST-EAST ORIENTED FRONT WILL BE IN PLACE OVER THE
SOUTH ON MEMORIAL DAY. PLENTIFUL MOISTURE AND HIGH INSTABILITY WILL
FUEL NUMEROUS SHOWERS AND THUNDERSTORMS THAT MAY RESULT IN HEAVY
RAIN. RAINFALL IN THE SHORT TERM PERIOD WILL LIKELY PRIME SOILS IN
THE SOUTH AHEAD OF MEMORIAL DAY AND COULD INCREASE THE THREAT OF
FLASH FLOODING. THE DAY 4 (MONDAY/MEMORIAL DAY) EXCESSIVE RAINFALL
OUTLOOK (ERO) DEPICTS A BROAD MARGINAL RISK (LEVEL 1/4) AREA ACROSS
PORTIONS OF THE SOUTHERN PLAINS, MID/LOWER MISSISSIPPI VALLEY, AND
TENNESSEE VALLEY WITH AN EMBEDDED SLIGHT RISK (LEVEL 2/4) AREA
FROM STRETCHING FROM NASHVILLE, TENNESSEE TO DALLAS, TEXAS. BY
TUESDAY AND WEDNESDAY, THE MAIN LOW ALONG THE FRONTAL SYSTEM SHOULD
PROGRESS EAST, BRINGING LOCALIZED HEAVY RAIN TO THE MID-ATLANTIC,
WHILE THE TRAILING FRONT LINGERS ACROSS THE SOUTH. THE DAY 5 ERO
DEPICTS A MARGINAL RISK (LEVEL 1/4) FOR THIS ELONGATED THREAT AREA
GIVEN STILL DEEP MOISTURE AND UPPER LEVEL SUPPORT.
ELSEWHERE, MODERATE PRECIPITATION CHANCES WILL EXTEND FROM THE
CENTRAL ROCKIES TO THE NORTHERN AND CENTRAL PLAINS AS THE INITIAL
UPPER LEVEL SHORTWAVE CUTS TROUGH THE WEST EARLY NEXT WEEK, AND
SOME LATE SEASON SNOW MAY BE POSSIBLE IN THE HIGHEST PEAKS OF THE
CENTRAL ROCKIES AS WELL. A STATIONARY FRONT CURLING BACK INTO THE
SOUTHERN/CENTRAL ROCKIES AND HIGH PLAINS COULD HELP PRODUCE
SCATTERED CONVECTION THERE NEXT WEEK AS WELL. MEANWHILE, TWO SWIFT-
MOVING FRONTS MOVING THROUGH THE PACIFIC NORTHWEST COULD ALLOW FOR
LIGHT TO MODERATE PRECIPITATION, AND SUMMERTIME SCATTERED STORMS
ARE ALSO LIKELY ACROSS THE FLORIDA PENINSULA.
HOT WEATHER WILL LINGER ON MONDAY IN SOUTH TEXAS WHERE HIGH
TEMPERATURES WILL REACH THE 90S AND LOW 100S. MEANWHILE, COOLER
THAN NORMAL TEMPERATURES BY 10 TO 20 DEGREES WILL TAKE HOLD OVER
THE NORTH-CENTRAL AND EASTERN U.S. MONDAY INTO TUESDAY UNDERNEATH
UPPER TROUGHING. TEMPERATURES SHOULD GRADUALLY MODERATE CLOSER TO
NORMAL AS NEXT WEEK PROGRESSES. IN THE WEST, A BUILDING UPPER RIDGE
WILL LEAD TO WARMER THAN AVERAGE TEMPERATURES BY 10 TO 20 DEGREES
DURING THE SECOND HALF OF NEXT WEEK, AND HAZARDOUS HEAT MAY DEVELOP
OVER THE CALIFORNIA CENTRAL VALLEY BY NEXT WEEKEND.
DOLAN/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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