136
FXUS02 KWBC 201858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT MON MAY 20 2024
VALID 12Z THU MAY 23 2024 - 12Z MON MAY 27 2024
...HEAVY RAINFALL/FLOODING THREATS FROM THE SOUTHERN PLAINS
THROUGH THE MID-SOUTH AND VICINITY MIDWEEK THROUGH THE WEEKEND...
..SOUTH TEXAS TO CENTRAL GULF COAST AND SOUTH FLORIDA HEAT RISK
..OVERVIEW
MULTIPLE AND GENERALLY PROGRESSIVE UPPER SHORTWAVES/POSSIBLE
CLOSED LOWS AND SURFACE LOW PRESSURE/FRONTAL SYSTEMS WILL TRAVERSE
THE WEST TO THE PLAINS AND MIDWEST/SOUTH DURING THE MEDIUM RANGE
PERIOD. BY THURSDAY, A POTENT SHORTWAVE AND DEEP SURFACE LOW WILL
BE EXITING THE UPPER GREAT LAKES WHILE ITS ATTENDANT COLD FRONT
WILL PUSH ACROSS THE EAST AND PARTWAY INTO THE SOUTH BEYOND
MIDWEEK, WITH RAIN AND STORMS ALONG AND AHEAD OF IT AND COOLER
TEMPERATURES BEHIND. THERE IS SOME RECURRING THREAT FOR HEAVY
RAINFALL ALONG THE WESTERN SIDE OF THIS FRONT FROM PARTS OF TEXAS
INTO THE MID- SOUTH/TENNESSEE VALLEY TO PARTS OF THE MID- ATLANTIC
AS THE WAVY BOUNDARY STALLS AND LIFTS BACK NORTH AS A WARM FRONT.
ADDITIONAL ENERGY/CLOSED LOWS LOOK TO TRAVERSE THE NORTHERN AND
SOUTHERN TIERS OF THE NATION LATE WEEK AND NEXT WEEKEND, BUT WITH
MORE UNCERTAINTY AS STRONG UPPER RIDGING BUILDS INTO SOUTH TEXAS
AND THE CENTRAL GULF COAST TO SPREAD A CONTINUED THREAT FOR
HAZARDOUS HEAT AS INDICATED IN THE WPC AND CPC HAZARDS OUTLOOKS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MULTI-MODEL AND ENSEMBLE FORECAST SPREAD AND CYCLE TO CYCLE RUN
CONTINUITY REMAINS DECENT THURSDAY TO SATURDAY IN A PATTERN WITH
NEAR AVERAGE OVERALL UNCERTAINTY AT MID-LARGER SCALES. SMALLER
SCALE SYSTEM AND WEATHER FOCUS IS NOT IDEAL, BUT A COMPOSITE OF
THE LATEST GFS/ECMWF/UKMET/CANADIAN MODELS ALONG WITH THE NATIONAL
BLEND OF MODELS (NBM) AND WPC CONTINUITY SEEMS TO PROVIDE A
REASONABLE FORECAST BASIS AS CONSISTENT WITH INDIVIDUAL SYSTEM
PREDICTABILITY. FORECAST SPREAD GROWTH AND RUN TO RUN CONTINUITY
SUFFERS AT LONGER TIME FRAMES, SO PREFER A COMPOSITE OF BEST
CLUSTERED GUIDANCE OF THE GFS/ECMWF AND GEFS/ECMWF ENSEMBLE MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
MAIN FOCUS FOR LATE WEEK CONVECTION WILL BE FROM PARTS OF THE
SOUTHERN PLAINS INTO THE LOWER OHIO VALLEY AS THE WESTERN PART OF A
FRONTAL BOUNDARY STALLS/LIFTS NORTH AHEAD OF THE NEXT UPPER LOW
INTO THE REGION. THE DAY 4/THURSDAY EXCESSIVE RAINFALL OUTLOOK
CONTINUES TO DEPICT A FAIRLY LARGE SLIGHT RISK AREA FROM NORTHEAST
TEXAS THROUGH ARKANSAS AND INTO WESTERN TENNESSEE WHERE AMPLE
MOISTURE/INSTABILITY SHOULD BE PRESENT WITHIN A VERY RECENTLY WET
REGION. HEAVY RAINFALL POTENTIAL ACROSS THIS REGION IS ALSO
POSSIBLE AT THE END OF THE SHORT RANGE PERIOD/WEDNESDAY. BY FRIDAY,
SOME HEAVY RAIN/FLOOD POTENTIAL WILL BE POSSIBLE FARTHER NORTH AND
EAST ACROSS THE TENNESSEE VALLEY TO THE SOUTHERN APPALACHIANS
WHERE A MARGINAL RISK IS IN PLACE FOR THE DAY 5 ERO.
THE UPPER LOW OVER THE NORTHWEST/NORTHERN ROCKIES ON THURSDAY MAY
ALSO BRING SOME HEAVIER RAIN TO PARTS OF THE NORTHERN HIGH PLAINS,
BUT WITH AN OVERALL LACK OF INSTABILITY AND ANOMALOUS MOISTURE,
COMBINED WITH DRYER ANTECEDENT CONDITIONS, NOT ANTICIPATING A FLASH
FLOOD RISK AT THIS TIME, DESPITE SOME 1-2 INCH QPF TOTALS FOR
CENTRAL-EASTERN MONTANA. SHOWERS AND STORMS SHOULD PROGRESS WITH
THE ACCOMPANYING COLD FRONT LATE WEEK INTO THE WEEKEND THROUGH THE
MIDWEST. AN ADDITIONAL HEAVY RAINFALL THREAT MAY DEVELOP FARTHER
SOUTH ACROSS THE MIDDLE MISSISSIPPI VALLEY/MID-SOUTH REGION LATE
THIS WEEKEND OR EARLY NEXT WEEK DEPENDING ON STILL VERY UNCERTAIN
UPPER LEVEL DYNAMICS AND STREAM ENERGIES.
EXPECT A HAZARDOUS HEAT THREAT TO EXPAND FROM SOUTH TEXAS THROUGH
THE CENTRAL GULF COAST AND ALSO SOUTH FLORIDA SEE MULTIPLE DAYS OF
HAZARDOUS HEAT DURING THE PERIOD WITH HIGHS PERSISTENTLY RUNNING
10-15F ABOVE NORMAL WITH MAX HEAT INDEX VALUES POSSIBLY REACHING AT
LEAST 110F. HIGHS NEAR 100 DEGREES COULD STRETCH FARTHER NORTH
ACROSS THE SOUTHERN HIGH PLAINS LATER IN THE PERIOD AS AN UPPER
HIGH BEGINS TO BUILD MORE INTO THE REGION. SOME DAILY RECORDS FOR
HIGHS/WARM LOWS WILL BE POSSIBLE. ABOVE NORMAL HIGHS WILL ALSO
TRACK EAST INTO THE NORTHEAST/MID-ATLANTIC ON THURSDAY, BUT SHOULD
MODERATE THEREAFTER AS THE COLD FRONT PUSHES THROUGH THE REGION.
THE FORECAST PATTERN WILL FAVOR BELOW AVERAGE HIGHS OVER THE
NORTHWEST TO NORTHERN PLAINS FOR MOST OF NEXT WEEK BUT RELATIVELY
NORMAL TEMPERATURES EVERYWHERE ELSE.
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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