654
FXUS02 KWBC 312111
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
510 PM EDT MON JUL 31 2023
VALID 12Z THU AUG 03 2023 - 12Z MON AUG 07 2023
..SOUTHERN HEATWAVE PERSISTS/SHIFTS FARTHER SOUTH THIS WEEKEND
...HEAVY RAIN/FLASH FLOOD THREAT FOCUSES OVER THE NORTH-CENTRAL
GREAT PLAINS THURSDAY INTO FRIDAY...
..OVERVIEW
TROUGHING FROM THE CANADIAN PRAIRIES DIGS SOUTHEAST TO THE GREAT
LAKES FRIDAY THROUGH THIS WEEKEND WHICH SUPPRESSES THE CENTRAL
CONUS UPPER RIDGE AXIS SOUTH TO THE SOUTHERN TIER OF STATES WHERE
ABOVE NORMAL TEMPERATURES/HEATWAVES PERSIST. ANOMALOUSLY HOT
WEATHER WILL ALSO SPREAD BACK INTO THE DESERT SOUTHWEST. PRIOR TO
THAT, DEEPENED MONSOONAL MOISTURE WORKING ON THE WESTERN PERIPHERY
OF THE RIDGE WILL FAVOR A SLOW SHIFT OF A MAIN CONVECTIVE RAINFALL
FOCUS INTO THE NORTH-CENTRAL PLAINS. MEANWHILE, SHORTWAVES
ROUNDING THE TOP OF THE RIDGE IN THE NORTHWEST FLOW WILL SPARK
STRONG TO SEVERE THUNDERSTORMS, AND LOCALLY HEAVY RAIN, PAST
MIDWEEK ACROSS THE MID-SOUTH/SOUTHEAST/SOUTHERN APPALACHIANS.
ACTIVITY SHOULD ALSO INCREASE UP TO THE NORTHEAST AROUND FRIDAY AS
NEW NORTHERN STREAM TROUGH ENERGY COMBINES WITH AN ATLANTIC
MOISTURE PLUME AND TERRAIN IN ADVANCE OF AN ORGANIZED EASTERN
CANADIAN SURFACE LOW AND TRAILING FRONT THAT SHOULD WILL DRIER
AIR/MODERATED TEMPERATURES TO PARTS OF THE CENTRAL TO EASTERN U.S.
IN THE WAKE OF PASSAGE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A
BLEND OF BEST CLUSTERED GUIDANCE FROM THE 00 UTC ECMWF/CMC/UKMET
AND 06Z GFS WITH INCLUSION OF THE 00Z ECENS/06Z GEFS ENSEMBLE
MEANS FOR DAYS 5/6. APPLIED GREATER WEIGHTING IN THE BLEND TO THE
ECMWF/ECMWF ENSEMBLE MEAN THAT HAVE RECENTLY SHOWED BETTER RUN TO
RUN CONTINUITY. SINCE THEN, THE 12Z CONSENSUS IS STRONGER ON THE
SOUTHERN SUPPRESSION OF THE MID-LEVEL RIDGE OVER THE CENTRAL CONUS
WITH TYPICAL SUMMER TIME DIFFERENCES BETWEEN GUIDANCE ON IMPULSES
THAT DRIVE MESOSCALE CONVECTION.
..WEATHER/HAZARDS HIGHLIGHTS
THE NORTH-CENTRAL PLAINS WILL SEE A FOCUS FOR DIURNALLY DRIVEN
CONVECTION THURSDAY INTO FRIDAY AS THE UPPER RIDGE AXIS CENTERED
OVER THE HIGH PLAINS WEAKENS/SUPPRESSES SOUTH AND NORTHERN TIER
FLOW BECOMES MORE ZONAL. DEEP MONSOONAL MOISTURE AND SLOW
MOVING/ORGANIZED EMBEDDED ENERGIES ROUNDING THIS RIDGE WILL
PRODUCE HEAVY RAIN. 12Z GUIDANCE IS IN AGREEMENT ON AN EASTWARD
SHIFT TO THE HEAVY RAIN FOCUS ONTO THE PLAINS WITH THE DAY 4
SLIGHT RISK FOR EXCESSIVE RAINFALL NOW OVER THE EASTERN WY/MT
BORDER INTO THE CENTRAL DAKOTAS. THE MORE ZONAL FLOW FOR
FRIDAY/DAY 5 ALLOWS THE HEAVY RAIN FOCUS TO EXPAND EAST/SOUTHEAST
INTO CENTRAL MN/IA WITH GENERAL LOCATION UNCERTAINTY AND MOST OF
THIS AREA BEING DRY CONTINUING TO WARRANT A MARGINAL RISK FOR DAY
5.
FARTHER DOWNSTREAM AND AROUND THE UPPER RIDGE, EXPECT AREAS OF
THUNDERSTORMS TO SHIFT FROM THE MID-MISSISSIPPI VALLEY THROUGH THE
TN VALLEY TO THE SOUTHERN APPALACHIANS BOTH THURSDAY AND FRIDAY. A
HEAVY RAIN/FLASH FLOODING THREAT FROM ORGANIZED CONVECTIVE SYSTEMS
IN THE NORTHWESTERLY FLOW WARRANTS EXPANDED MARGINAL RISKS FOR
EXCESSIVE RAINFALL ACROSS THESE AREAS.
12Z GUIDANCE IS ALSO FARTHER EAST WITH A NORTHERN STREAM UPPER
TROUGH TAPS A DEEPENED ATLANTIC MOISTURE PLUME OVER THE NORTHEAST.
THE DAY 5 MARGINAL RISK FOR EXCESSIVE RAINFALL IS SHUNTED FARTHER
EAST OVER NEW ENGLAND AND LONG ISLAND AS A RESULT.
THE ONGOING HEATWAVE SHOULD SETTLE SOUTH OVER THIS WEEKEND, CLOSER
TO THE SOUTHERN BORDER AND ALONG THE GULF COAST, WHERE HIGH
TEMPERATURES WILL BE 5 TO 10 DEGREES ABOVE NORMAL. HEAT INDICES
WILL RISE TO 110-115F IN SOME AREAS, PARTICULARLY THE LOWER
MISSISSIPPI RIVER VALLEY. RECORD HIGH MAXIMUM AND ESPECIALLY
MINIMUM TEMPERATURES ARE WIDELY FORECAST IN THESE REGIONS.
OTHERWISE, WELCOME COOLER AIR SPREAD OVER THE NORTHERN AND CENTRAL
CONUS THIS WEEKEND BEHIND A COLD FRONT.
JACKSON
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHERN PLAINS, THU-FRI, AUG
3-AUG 4.
- HEAVY RAIN ACROSS THE CENTRAL HIGH PLAINS INTO PORTIONS OF THE
SOUTHERN PLAINS, SAT-SUN, AUG 5-AUG 6.
- HAZARDOUS HEAT ACROSS THE SOUTH-CENTRAL PLAINS INCLUDING THE
OZARKS, THU-SAT, AUG 3-AUG 5.
- HAZARDOUS HEAT ACROSS THE SOUTHERN TIER OF THE MAINLAND U.S.
INCLUDING THE INTERIOR DESERT SOUTHWEST, AND INTO THE
MID-MISSISSIPPI VALLEY, AS WELL AS THE WESTERN HALF OF FLORIDA,
THU-MON, AUG 3-AUG 7.
- HAZARDOUS HEAT ACROSS MUCH OF THE SOUTHEAST INCLUDING THE
EASTERN PORTION OF FLORIDA, SAT-MON, AUG 5-AUG 7.
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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