107
FXUS02 KWBC 211831
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
231 PM EDT WED MAY 21 2025
VALID 12Z SAT MAY 24 2025 - 12Z WED MAY 28 2025
...MULTI-DAY HEAVY RAIN THREAT IN THE OZARKS AND VICINITY THIS
WEEKEND...
..OVERVIEW
AS THE MEDIUM RANGE PERIOD BEGINS SATURDAY, A SHORTWAVE ATOP THE
ROCKIES WILL UNDERCUT A BROADER OMEGA-TYPE PATTERN CONSISTING OF A
NORTHEAST PACIFIC UPPER LOW, A CENTRAL CANADA AND U.S. RIDGE, AND
TROUGHING OVER THE EAST. THIS SHORTWAVE AND A FRONTAL SYSTEM WILL
PROVIDE SUPPORT FOR HEAVY RAIN AND THUNDERSTORMS IN A MOIST AND
UNSTABLE ENVIRONMENT IN PARTS OF THE CENTRAL U.S. THIS WEEKEND.
FLASH FLOODING IS POSSIBLE IN THE OZARKS AND VICINITY. THE
SHORTWAVE IS FORECAST TO MERGE WITH THE WESTERN SIDE OF THE TROUGH
IN THE EAST AND CAUSE IT TO DIG INTO THE EAST-CENTRAL U.S. EARLY
NEXT WEEK, WHICH SHOULD PRESS THE FRONT SOUTH AND EAST, SHIFTING
PRECIPITATION ACROSS THE SOUTHERN TIER INTO THE APPALACHIANS AND
EVENTUALLY THE EASTERN SEABOARD. THE ROUNDS OF TROUGHING ALOFT WILL
CAUSE COOLER THAN NORMAL TEMPERATURES IN PARTS OF THE CENTRAL AND
EASTERN U.S., WHILE UPPER RIDGING BUILDING IN THE INTERMOUNTAIN
WEST SHOULD ALLOW FOR WARMER THAN AVERAGE TEMPERATURES THERE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
OVERALL, MODEL GUIDANCE AGREES THROUGH THE PERIOD ON THE PATTERN
EVOLUTION, BUT DOES SHOW SOME KEY DIFFERENCES IN THE DETAILS WHICH
HAS SIGNIFICANT IMPLICATIONS ON SENSIBLE WEATHER IMPACTS -
PARTICULARLY ACROSS THE SOUTH-CENTRAL U.S.. MODELS REMAIN IN GOOD
AGREEMENT WITH A WAVY UPPER PATTERN THIS WEEKEND, BUT ISSUES BEGIN
TO ARISE AS A SHORTWAVE OVER THE WEST MOVES OVER THE UPPER RIDGE
AND EVENTUALLY MERGES WITH TROUGHING OVER THE GREAT LAKES TO UPPER
MIDWEST. THE GFS IS THE OUTLIER THIS CYCLE WITH ENERGY HANGING BACK
OVER THE NORTHERN PLAINS WHILE THE REST OF THE GUIDANCE SUGGEST
FULL MERGING WITH THE TROUGH AND THIS NEW TROUGH DIGGING FARTHER
SOUTH AND EAST NEXT WEEK. THIS CAUSES THE TROUGH OVER THE EAST-
CENTRAL U.S. NEXT WEEK TO BE MORE ELONGATED THAN IS INDICATED IN
THE GFS. BETTER CONSENSUS OF MODELS ALSO DIGS THE TROUGH A BIT
FARTHER SOUTH THAN THE GFS (BUT THE CMC MAY BE TOO FAR SOUTH).
ELSEWHERE, THE NEXT TROUGH SWINGS INTO THE WEST AROUND MONDAY, AND
MODELS SHOW SOME DIFFERENCES IN THE TIMING OF THAT. THE GFS IS THE
QUICKEST AND ALSO FORMS A STRONGER CLOSED LOW OVER THE GREAT BASIN
COMPARED TO THE REST OF THE GUIDANCE/THE ENSEMBLES.
THE WPC FORECAST FOR TODAY WAS ABLE TO UTILIZE A GENERAL MODEL
COMPROMISE FOR THE FIRST FEW DAYS OF THE PERIOD AMIDST BETTER
AGREEMENT IN THE GUIDANCE. AFTER THIS, REPLACED THE UKMET AND GFS
WITH THE ENSEMBLE MEANS AND GRADUALLY INCREASED CONTRIBUTIONS OF
THE MEANS IN THE BLEND THROUGH DAY 7. OVERALL, THIS MAINTAINED GOOD
CONSISTENCY WITH THE PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A HEAVY RAINFALL PATTERN WILL BE IN PLACE BY SATURDAY AS AMPLE
GULF MOISTURE AND INSTABILITY STREAM NORTH DUE TO RETURN FLOW FROM
SURFACE HIGH PRESSURE OVER THE SOUTHEAST AND IN RESPONSE TO A
SHORTWAVE/RIGHT ENTRANCE REGION OF THE UPPER JET COMING INTO THE
NORTH- CENTRAL ROCKIES AND HIGH PLAINS. RAIN AND STORMS ARE LIKELY
TO OVERLAP WITH FRIDAY'S (DAY 3 ERO PERIOD) CONVECTION WHERE THERE
WILL BE WETTER ANTECEDENT CONDITIONS. A SLIGHT RISK REMAINS
CENTERED OVER THE OZARKS (WHICH CAN BE SENSITIVE TO FLASH FLOODING
ANYWAY) IN THE DAY 4/SATURDAY ERO. CONVECTION ONGOING FROM SATURDAY
NIGHT COULD CONTINUE EAST INTO SUNDAY ACROSS THE MID-MISSISSIPPI
VALLEY, WITH UNCERTAINTY IN IF/WHERE IT COULD PERSIST INTO THE
TENNESSEE OR OHIO VALLEYS. THEN ADDITIONAL CONVECTION IS FORECAST
TO FORM FARTHER SOUTHWEST IN THE SOUTHERN PLAINS/LOWER MISSISSIPPI
VALLEY AS WELL ON SUNDAY. A FAIRLY LARGE SLIGHT RISK FROM
NORTHEASTERN TEXAS ACROSS PARTS OF THE LOWER AND MIDDLE MISSISSIPPI
VALLEY CONTINUES FOR THE DAY 5/SUNDAY ERO TO COVER BOTH AREAS.
INTO THE WORKWEEK, THE FRONT WILL PRESS SOUTH FARTHER INTO THE
SOUTHERN TIER AND EAST INTO THE APPALACHIANS AND EVENTUALLY THE
EASTERN SEABOARD. AREAS OF HEAVY RAINFALL ARE POSSIBLE WITH DETAILS
TO BE REFINED WITH TIME.
PRECIPITATION, MOSTLY RAIN EXCEPT FOR SNOW IN THE HIGHEST PEAKS,
IS POSSIBLE ACROSS THE NORTH-CENTRAL ROCKIES AND PLAINS INTO
SATURDAY UNDERNEATH UPPER TROUGHING AND AS FRONTAL SYSTEMS MOVE
THROUGH. THE DETAILS ARE UNCERTAIN BASED ON THE MODEL SPREAD WITH
THE SUPPORTING ENERGIES. BUT THE SHORTWAVE PROVIDING DYNAMICAL
SUPPORT, ABOVE NORMAL PWS, AND THE CUSP OF THE INSTABILITY GRADIENT
COULD PROVIDE SOME HEAVY RAIN AND A LOW END FLASH FLOOD RISK IN
THE NORTH-CENTRAL HIGH PLAINS. A MARGINAL RISK REMAINS IN PLACE
THERE FOR THE DAY 4/SATURDAY ERO.
ELSEWHERE, LIGHT SHOWERS COULD CONTINUE ACROSS THE NORTHEAST BUT
GRADUALLY LESSEN IN MAGNITUDE THROUGH THE WEEKEND AS THE UPPER AND
SURFACE LOWS ARE SLOW TO PULL AWAY THERE. SUMMERTIME SCATTERED
STORMS ARE LIKELY ACROSS THE FLORIDA PENINSULA THROUGH THE PERIOD.
THE NORTHWEST MAY SEE RENEWED PRECIPITATION CHANCES EARLY NEXT
WEEK.
WARMER THAN NORMAL TEMPERATURES WILL BE IN PLACE ACROSS THE
SOUTHERN PLAINS ON SATURDAY UNDERNEATH A CENTRAL U.S. RIDGE.
TEMPERATURES WELL INTO THE 90S TO AROUND 100 WILL SUPPORT AREAS OF
MAJOR HEATRISK IN PARTS OF TEXAS AND LOUISIANA THIS WEEKEND. THEN
AS THE MEAN UPPER RIDGE REBUILDS FARTHER WEST, THE GREAT BASIN AND
NORTHERN/CENTRAL ROCKIES CAN EXPECT TEMPERATURES GENERALLY AROUND
10 TO 15 DEGREES ABOVE AVERAGE. MEANWHILE, COOLER THAN NORMAL
TEMPERATURES BY 5 TO 15 DEGREES WILL TAKE HOLD OVER THE NORTH-
CENTRAL TO EASTERN U.S. INTO THE WEEKEND UNDERNEATH UPPER
TROUGHING. THE TROUGH WILL ALLOW FOR TEMPERATURES TO COOL IN THE
SOUTHERN TIER DURING THE WORKWEEK COMPARED TO THE HOT WEEKEND, BUT
OVERALL TEMPERATURES SHOULD GRADUALLY TREND CLOSER TO NORMAL AS
NEXT WEEK PROGRESSES.
SANTORELLI/TATE
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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