024
FXUS02 KWBC 181909
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SUN JUN 18 2023
VALID 12Z WED JUN 21 2023 - 12Z SUN JUN 25 2023
...PROLONGED HEAT WAVE CONTINUES ACROSS THE SOUTHERN PLAINS
THROUGHOUT THIS WEEK INTO THE WEEKEND...
...MULTIPLE DAYS OF POTENTIAL FLOODING RAINS ACROSS THE SOUTHEAST
INTO THE SOUTHERN APPALACHIANS...
..OVERVIEW
AN AMPLIFIED AND BLOCKY PATTERN WILL REMAIN IN PLACE THROUGH THIS
WEEK ACROSS THE MAINLAND U.S. THIS PATTERN WILL FEATURE (1) A
DEEP POSITIVELY-TILTED TROUGH ACROSS THE NORTHWESTERN U.S. THAT IS
FORECAST TO BE LESS AMPLIFIED WITH TIME, (2) A WARM RIDGE TO
REMAIN ANCHORED OVER TEXAS/NORTHERN MEXICO, WITH SOME EXTENSION OF
THE RIDGE TRAVERSING THE GREAT LAKES REGION, (3) A BROAD TROUGH
LIFTING OUT OF NEW ENGLAND WITH A COOL SURFACE HIGH FEEDING
ATLANTIC MOISTURE TOWARD THE EAST COAST, AND (4) AN UPPER LOW THAT
WILL LIKELY BRING HEAVY RAIN AND POTENTIAL FOR FLOODING INTO THE
SOUTHEAST/SOUTHERN APPALACHIANS. MEANWHILE, THE POTENTIAL FOR
HEAVY RAIN EXISTS FROM THE CENTRAL HIGH PLAINS TO THE NORTHERN
PLAINS AS A FRONT IS FORECAST TO BECOME QUASI-STATIONARY IN THE
VICINITY MIDWEEK. IN ADDITION, TROPICAL MOISTURE COULD STREAM
NORTHWARD INTO FLORIDA BY THE END OF THE WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
DESPITE THE PREVAILING BLOCKY SYNOPTIC PATTERN AS NOTED ABOVE,
MODEL GUIDANCE CONTINUES TO SHOW RELATIVELY GOOD AGREEMENT WITH
EACH OTHER THROUGH NEXT WEEKEND. THE TROUGH OVER THE NORTHWEST AND
THE RIDGE OVER TEXAS REMAIN PARTICULARLY AGREEABLE. MEANWHILE,
MODELS CONTINUE TO INDICATE SUBTLE AMPLIFICATIONS OF THE UPPER LOW
THAT IS FORECAST TO MOVE INTO AND THEN MEANDER OVER THE SOUTHEAST
BY THE MIDDLE OF THIS WEEK. THIS FEATURE, WHICH ALREADY CONTAINS
A WELL-DEFINED CIRCULATION ALOFT OVER MISSOURI TODAY, WILL PLAY A
CRITICAL ROLE IN PRODUCING MULTIPLE DAYS OF HEAVY RAIN AND
POTENTIALLY FLOODING IMPACTS ACROSS PARTS OF THE SOUTHEAST THIS
WEEK. SINCE YESTERDAY, THE ECMWF AND THE EC MEAN HAVE BECOME THE
MOST BULLISH GUIDANCE IN TERMS OF THE QPF AMOUNTS ALONG THE
EASTERN SLOPES OF THE APPALACHIANS AS A STRONGER AND DEEPER INFLUX
OF ATLANTIC MOISTURE IS FORECAST AHEAD OF A STRONGER AND BROADER
UPPER LOW OVER THE SOUTHEAST. THE GEFS IS NOT TOO DISSIMILAR TO
THE EC QPF PATTERN WHILE THE CMC/CMC MEAN FAVOR A FASTER NORTHWARD
PROGRESSION OF THE RAIN BY THE END OF THE WEEK WITH HIGHER AMOUNTS
STAYING CLOSER TO THE COAST. THE ECMWF APPEARS TO HAVE
INITIALIZED BETTER FOR THE UPPER LOW THIS MORNING. THIS MAY LEND
US A HIGHER CONFIDENCE TO ITS FORECAST PERFORMANCE FOR THIS HEAVY
RAIN EVENT.
THE WPC MEDIUM-RANGE FORECASTS BEGIN WITH A COMPOSITE BLEND OF 40%
FROM THE 06Z GFS/GEFS, 40% FROM THE 00Z EC/EC MEAN, AND 20% FROM
THE 00Z CMC/CMC MEAN, AND THEN LEAN TOWARD THE EC MEAN SOLUTION
FOR DAYS 6 AND 7.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER LOW MEANDERING OVER THE SOUTHEAST/TENNESSEE VALLEY OR SO
WILL PROVIDE SUPPORT FOR MULTIPLE ROUNDS OF RAIN AND THUNDERSTORMS
FOR THE SOUTHEASTERN QUADRANT OF THE COUNTRY THROUGH MUCH OF THIS
WEEK. INTO THE MEDIUM RANGE PERIOD STARTING WEDNESDAY, A BROAD
SLIGHT RISK IS IN PLACE FROM THE FLORIDA BIG BEND INTO GEORGIA AND
THE CAROLINAS AS TROPICAL MOISTURE FROM THE CARIBBEAN AND FROM THE
GULF FOCUSES NEAR AND OVERRUNS THE FRONTAL SYSTEM IN THE REGION.
PARTS OF THIS REGION COULD BE RATHER SENSITIVE TO ADDITIONAL
RAINFALL BY WEDNESDAY AFTER A WET PATTERN IN THE SHORT RANGE
PERIOD. IT STILL APPEARS THAT THE BIGGEST THREAT OF THE HEAVY RAIN
IN THE SOUTHEAST WILL BE THROUGH MIDWEEK, BUT WITH SOME
CONTINUATION OF RAIN CHANCES THROUGH THE LATTER PART OF THE WEEK
AS WELL. BY DAY 5/THURSDAY, A BROAD MARGINAL RISK IS IN PLACE
EXCEPT FOR AN EMBEDDED SLIGHT FOR THE SOUTHERN APPALACHIANS, WHERE
UPSLOPE FLOW COULD CAUSE RAIN TOTALS POTENTIALLY NEARING 10 INCHES
OVER THE NEXT 5 DAYS OR SO. FUTURE MODERATE RISKS ARE CERTAINLY
POSSIBLE FOR THE SOUTHERN APPALACHIANS IN FUTURE FORECAST CYCLES,
BUT MAY TAKE UNTIL THE SHORT RANGE ONCE IT BECOMES CLEARER
IF/HOW/WHERE THE EARLY WEEK RAINFALL CAUSES FLOODING. BY LATE WEEK
INTO NEXT WEEKEND, RAIN AND THUNDERSTORMS COULD SPREAD FARTHER
NORTH ACROSS THE EAST COAST, BUT WITH UNCERTAINTY IN PLACEMENT AND
AMOUNTS DEPENDENT ON THE UPPER LOW TRACK.
UPPER TROUGHING WITH EMBEDDED UPPER LOWS IN THE NORTHWEST WILL
CAUSE AN INITIALLY EASTWARD-MOVING COLD FRONT TO THEN STALL AROUND
MID-LATE WEEK, PROVIDING ANOTHER FOCUS FOR THUNDERSTORMS IN THE
NORTHERN/CENTRAL PLAINS. THERE SHOULD BE AMPLE INSTABILITY IN THIS
AREA AND THUS HIGH RAIN RATES ESPECIALLY WITH EVENING/OVERNIGHT
CONVECTION ON WEDNESDAY NIGHT WHEN THE LOW-LEVEL JET IS ENHANCED.
A SLIGHT RISK HAS BEEN MAINTAINED IN THE WEDNESDAY-WEDNESDAY NIGHT
ERO WITH THIS ACTIVITY NEAR THE FRONT, WITHIN THE BROADER MARGINAL
COVERING THE NORTHERN/CENTRAL PLAINS WEDNESDAY AND THURSDAY.
CONSIDERED A SLIGHT RISK FOR THURSDAY AS WELL, BUT AT THIS POINT
IT APPEARS SUPPORT FOR HEAVY RAIN MAY WANE SLIGHTLY AS THE UPPER
PATTERN PIVOTS TOWARD MORE RIDGING BY THEN, BUT A SLIGHT MAY
EVENTUALLY BE NEEDED, ESPECIALLY IF THE QPF LOOKS TO FOCUS OVER
COLORADO GIVEN THE WET ANTECEDENT CONDITIONS THERE. COOLER THAN
NORMAL TEMPERATURES ARE FORECAST FOR THE WEST WITH THE UPPER
TROUGH OVERHEAD, BUT WITH A SLOW MODERATING TREND INTO NEXT
WEEKEND.
MEANWHILE, THE EXCESSIVE HEAT WILL CONTINUE THROUGH THIS WEEK
ACROSS MUCH OF TEXAS AND INTO PORTIONS OF LOUISIANA AND NEW
MEXICO, WITH WIDESPREAD 100S AND EVEN SOME 110S ACROSS CENTRAL AND
SOUTHERN PORTIONS OF TEXAS, AND 90S WITH HEAT INDICES WELL OVER
100F ELSEWHERE. MANY DAILY RECORD HIGH TEMPERATURES ARE POSSIBLE,
AND SOME MONTHLY RECORDS MAY EVEN BE CHALLENGED. HEAT INDICES AS
HIGH AS 115-120 DEGREES ARE POSSIBLE FOR PARTS OF SOUTHERN AND
SOUTHEASTERN TEXAS WHERE THE GREATEST COMBINATION OF HIGH
DEWPOINTS AND TEMPERATURES WILL LIKELY EXIST. AS MEAN UPPER
RIDGING EXPANDS FARTHER NORTH, HIGHS IN THE 90S ARE LIKELY ACROSS
MUCH OF THE PLAINS AND MISSISSIPPI VALLEY, WHILE 80S AND LOW 90S
IN THE UPPER MIDWEST/GREAT LAKES REGION WILL BE 10-15F ABOVE
NORMAL.
KONG/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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
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
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