745
FXUS02 KWBC 200727
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
327 AM EDT TUE MAY 20 2025
VALID 12Z FRI MAY 23 2025 - 12Z TUE MAY 27 2025
...MULTI-DAY HEAVY RAIN THREAT IN THE OZARKS PEAKING THIS
WEEKEND...
..OVERVIEW
AN OMEGA-TYPE PATTERN IS FORECAST ATOP NORTH AMERICA AS THE MEDIUM
RANGE PERIOD BEGINS FRIDAY, AS RIDGING AMPLIFIES IN THE CENTRAL
U.S. WHILE ROUNDS OF TROUGHING MOVE THROUGH THE NORTHWEST AND AN
UPPER LOW SPINS OVER THE GREAT LAKES/NORTHEAST. COOLER THAN AVERAGE
TEMPERATURES SHOULD PREVAIL UNDER THE EASTERN TROUGH ALONG WITH
SOME SHOWERS IN THE NORTHEAST CONTINUING FRIDAY, WHILE WARMER THAN
AVERAGE TEMPERATURES ARE LIKELY UNDERNEATH THE RIDGE IN THE FOUR
CORNERS STATES TO SOUTHERN PLAINS AND THEN OVER THE GREAT BASIN
EARLY NEXT WEEK AS THE RIDGE REBUILDS FARTHER WEST. FRONTAL SYSTEMS
EMERGING FROM THE WEST TOWARD THE PLAINS AND MOIST INFLOW AHEAD OF
THEM WILL ALLOW FOR INCREASING RAIN AND THUNDERSTORM CHANCES IN
THE CENTRAL U.S. FROM LATE WEEK INTO THE WEEKEND. MULTIPLE DAYS OF
HEAVY RAIN MAY OCCUR FOCUSED IN THE OZARKS AND VICINITY AND CAUSE
FLASH FLOODING CONCERNS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN REASONABLY GOOD AGREEMENT WITH THE OVERALL
PATTERN FRIDAY, WITH SOME DIVERGENCE IN SOLUTIONS AFTER THAT. A
SMALL EASTERN UPPER LOW (EMBEDDED WITHIN A TROUGH ALSO SUPPORTING A
GREAT LAKES UPPER LOW) WILL SUPPORT A NEW ENGLAND COASTAL LOW THAT
IS SHOWING BETTER CONSENSUS IN DEPTH AND POSITION. THE MAIN MODEL
THAT WENT AWRY WITH THIS EASTERN TROUGH WAS THE 12Z UKMET, DIGGING
ENERGY FARTHER SOUTH INTO SATURDAY. BEHIND THIS TROUGH, GUIDANCE IS
AGREEABLE WITH THE UPPER RIDGE.
THE MOST UNCERTAIN PART OF THE FORECAST HAS BEEN WITH THE FLOW
PATTERN IN THE EASTERN PACIFIC AND TROUGHING COMING INTO THE WEST.
CMC RUNS, INCLUDING THE NEWER 00Z RUN, HAVE SHOWN MORE ENERGY
FORMING A CLOSED LOW MAKING ITS WAY INTO THE NORTHWEST BY SATURDAY,
STRONGER AND SLOWER THAN CONSENSUS. THE 12/18Z GFS AND 12Z ECMWF
WERE RELATIVELY AGREEABLE THOUGH IN INDICATING A SHORTWAVE TROUGH
REACHING THE WEST COAST BY FRIDAY AND THE INTERMOUNTAIN WEST
SATURDAY SUPPORTING A FRONTAL SYSTEM OR TWO. THIS TROUGH LOOKS TO
BECOME POSITIVELY TILTED EARLY NEXT WEEK ACROSS THE NORTH-CENTRAL
CONUS. LEANED TOWARD THIS GFS/ECMWF CONSENSUS FOR THE FORECAST, BUT
BY MONDAY-TUESDAY FELT THAT THE 18Z GFS HELD TOO MUCH ENERGY BACK
IN THE NORTHERN PLAINS. THE 00Z ECMWF AND ESPECIALLY THE GFS ARE
SOMEWHAT WEAKER WITH THIS SHORTWAVE ENERGY AND IT LOOKS TO GET
ABSORBED MORE QUICKLY INTO THE REMAINING EASTERN TROUGH AND HELPING
IT TO DIG SOUTH A LITTLE MORE. THIS IMPACTS THE FRONTAL POSITION
AND THE QPF PLACEMENT EARLY NEXT WEEK. THERE WAS ALREADY SOME
SPREAD WITH WHEN THE FRONT/QPF GET SUPPRESSED SOUTH IN THE 12/18Z
GUIDANCE THAT COULD BE USED DURING FORECAST PRODUCTION. THE WPC
FORECAST LOWERED QPF SOMEWHAT ON THE NORTHERN SIDE (OVER THE MID-MS
VALLEY AND VICINITY) BY MONDAY COMPARED TO THE 01Z NBM, AND THE
NEWER 00Z GUIDANCE MAY SUGGEST THAT THE BULK OF THE QPF COULD GO
EVEN FARTHER SOUTH. REGARDLESS, THERE IS MODEL CONSENSUS FOR
ANOTHER UPPER RIDGE TO FORM BEHIND THIS TROUGHING AND AS A BROAD
UPPER LOW SPINS OVER THE NORTHEAST PACIFIC, ALLOWING FOR ANOTHER
OMEGA BLOCK TYPE PATTERN EARLY NEXT WEEK.
THE WPC FORECAST WAS BASED ON A BLEND OF THE 12/18Z GFS AND 12Z
ECMWF EARLY IN THE PERIOD, GIVEN THE ISSUES WITH BOTH THE UKMET AND
CMC. AS THE PERIOD PROGRESSED, INCLUDED AND INCREASED THE
PROPORTION OF THE GEFS AND EC ENSEMBLE MEANS, WITH THE MEANS
REACHING OVER HALF BY DAY 7.
..WEATHER/HAZARDS HIGHLIGHTS
A PROLONGED HEAVY RAINFALL PATTERN OVER THE CENTRAL U.S. WILL SET
UP AHEAD OF FRONTAL SYSTEMS ON FRIDAY WITH AMPLE GULF MOISTURE
STREAMING NORTH FROM RETURN FLOW FROM HIGH PRESSURE OVER THE
SOUTHEAST. THIS CONVECTION IN THE MEAN NORTHWEST FLOW SHOULD BE
ORGANIZED AT TIMES STARTING FRIDAY AFTERNOON OVER THE SOUTH-CENTRAL
PLAINS TO THE OZARKS. A MARGINAL RISK REMAINS IN PLACE FOR DAY
4/FRIDAY IN THESE AREAS. THEN BY SATURDAY, MOISTURE AND INSTABILITY
ARE LIKELY TO FURTHER INCREASE IN THESE AREAS IN RESPONSE TO A
SHORTWAVE COMING INTO THE NORTH-CENTRAL ROCKIES AND HIGH PLAINS.
RAIN AND STORMS ARE LIKELY TO OVERLAP WITH FRIDAY'S CONVECTION
WHERE THERE WILL BE WETTER ANTECEDENT CONDITIONS. THUS PLAN TO SHOW
A SLIGHT RISK CENTERED OVER THE OZARKS (WHICH CAN BE SENSITIVE TO
FLASH FLOODING ANYWAY) FOR THE NEW DAY 5/SATURDAY ERO. YET ANOTHER
ROUND OF RAIN IS EXPECTED SUNDAY IN SIMILAR AREAS, BEFORE FINALLY
PRESSING SOUTH MONDAY, THOUGH THERE IS STILL UNCERTAINTY IN
POSITIONING OF HEAVY RAIN BY THEN.
PRECIPITATION, IN THE FORM OF RAIN EXCEPT FOR SNOW IN THE HIGHEST
PEAKS, IS POSSIBLE ACROSS THE NORTHWESTERN TO NORTH-CENTRAL U.S.
FRIDAY NIGHT/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
IS IN PLACE THERE FOR THE DAY 5/SATURDAY ERO.
ELSEWHERE, SHOWERS WITH MODEST QPF COULD CONTINUE ACROSS THE
NORTHEAST FRIDAY AND 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 FROM THE
SOUTHWEST AND FOUR CORNERS STATES INTO THE SOUTHERN PLAINS ON
FRIDAY UNDERNEATH THE UPPER RIDGE. TEMPERATURES ARE FORECAST TO
GRADUALLY MODERATE CLOSER TO NORMAL INTO THE WEEKEND, ASIDE FROM
TEXAS STAYING WARM. THEN AS THE MEAN UPPER RIDGE REBUILDS FARTHER
WEST, THE GREAT BASIN AND NORTHERN/CENTRAL ROCKIES CAN EXPECT
TEMPERATURES GENERALLY AROUND 10-15 DEGREES ABOVE AVERAGE.
MEANWHILE, COOLER THAN NORMAL TEMPERATURES WILL TAKE HOLD OVER THE
NORTH-CENTRAL TO EASTERN U.S. LATE THIS WEEK AND INTO THE WEEKEND
UNDERNEATH UPPER TROUGHING. HIGHS OF 10-20 DEGREES BELOW AVERAGE
WILL BE COMMON IN THE APPALACHIANS TO NORTHEAST ON FRIDAY IN
PARTICULAR BEFORE SLOWLY MODERATING AS THE UPPER LOW DRIFTS
NORTHEAST.
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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