404
FXUS02 KWBC 010701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT TUE AUG 01 2023
VALID 12Z FRI AUG 04 2023 - 12Z TUE AUG 08 2023
..HEATWAVE TO PERSIST OVER THE SOUTH
...EXCESSIVE RAIN/FLASH FLOOD THREAT TO FOCUS OVER THE
NORTH-CENTRAL GREAT PLAINS FRIDAY INTO SATURDAY...
..OVERVIEW
DEEPENED MONSOONAL MOISTURE AND UPPER SYSTEM ENERGY WORKING
THROUGH THE ROCKIES ON THE WESTERN TO NORTHERN PERIPHERY OF AN
AMPLIFIED UPPER RIDGE WILL FAVOR A SLOW SHIFT OF A MAIN CONVECTIVE
RAINFALL FOCUS INTO THE NORTH-CENTRAL PLAINS. MEANWHILE, AMPLE
NORTHERN STREAM UPPER TROUGHING FROM THE CANADIAN PRAIRIES WILL
DIG SOUTHEAST TO THE GREAT LAKES FRIDAY THROUGH THIS WEEKEND WHICH
ALONG WITH UPPER ENERGIES WORKING FROM THE ROCKIES INTO THE PLAINS
WILL ACT TO SUPPRESS 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. DOWNSTREAM, SHORTWAVES
ROUNDING THE TOP OF THE RIDGE IN THE NORTHWEST FLOW WILL SPARK
STRONG TO SEVERE THUNDERSTORMS, AND LOCALLY HEAVY RAIN, INTO LATER
THIS WEEK FROM THE MID-SOUTH TO THE SOUTHERN
APPALACHIANS/SOUTHEAST. ACTIVITY SHOULD ALSO INCREASE UP TO THE
NORTHEAST AROUND FRIDAY AS THE NEW NORTHERN STREAM TROUGH ENERGY
COMBINES WITH AN ATLANTIC MOISTURE PLUME AND TERRAIN AHEAD OF AN
ORGANIZED EASTERN CANADIAN SURFACE LOW AND TRAILING FRONT TO BRING
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 12 UTC ECMWF/UKMET AND
THE 12 UTC ECENS/18 UTC GEFS ENSEMBLE MEANS ALONG WITH THE 01 UTC
NATIONAL BLEND OF MODELS THROUGH THIS FORECAST PERIOD. THE LATEST
00 UTC GFS/CANADIAN HAVE TRENDED A TAD MORE IN LINE WITH THIS
BLEND COMPARED TO THEIR PRIOR RUN. LOCAL CONVECTIVE FOCUS RUN TO
RUN CONTINUITY HAS BEEN LESS THAN STELLAR DESPITE A REASONABLY
ESTABLISHED MID-LARGER SCALE SUMMERTIME PATTERN, BUT MORE
ORGANIZED THREAT AREAS HAVE TENDED TO SHOW SIGNALS IN GUIDANCE
INTO MEDIUM RANGE TIME SCALES.
..WEATHER/HAZARDS HIGHLIGHTS
THE NORTH-CENTRAL PLAINS WILL SEE A FOCUS FOR DIURNALLY DRIVEN
CONVECTION FRIDAY INTO SATURDAY 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. RECENT GUIDANCE AGREES ON AN EASTWARD SHIFT TO
THE HEAVY RAIN FOCUS ONTO THE PLAINS WITH A PLAN TO UPGRADE TO A
NEW DAY 4 ERO SLIGHT RISK FOR EXCESSIVE RAINFALL FROM EASTERN MT
INTO THE CENTRAL DAKOTAS. THE MORE ZONAL FLOW FOR SATURDAY/DAY 5
ALLOWS THE HEAVY RAIN FOCUS TO EXPAND EAST/SOUTHEAST ACROSS THE
DAKOTAS INTO MN/IA WITH GENERAL LOCATION UNCERTAINTY LENDING AN
ERO MARGINAL RISK AREA.
FARTHER DOWNSTREAM AND AROUND THE UPPER RIDGE, EXPECT AREAS OF
THUNDERSTORMS TO SHIFT OUT FROM THE MID-SOUTH/TN VALLEY TO THE
SOUTHERN APPALACHIANS/SOUTHEAST ON FRIDAY. A HEAVY RAIN/FLASH
FLOODING THREAT FROM ORGANIZED CONVECTIVE SYSTEMS IN THE
NORTHWESTERLY FLOW OVER LINGERING FRONTS WARRANTS A MARGINAL RISK
FOR EXCESSIVE RAINFALL.
MEANWHILE, APPROACH OF AN AMPLIFIED NORTHERN STREAM UPPER TROUGH
AND LEADING LOW/FRONTAL SYSTEM SHOULD TAP A DEEPENED ATLANTIC
MOISTURE PLUME OVER THE NORTHEAST. PLAN TO MAINTAIN AN ASSOCIATED
FRIDAY/DAY 5 MARGINAL RISK FOR EXCESSIVE RAINFALL OVER NEW
ENGLAND, ESPECIALLY TERRAIN AND EASTERN LONG ISLAND TO ADDRESS THE
THREAT.
THE ONGOING HEATWAVE SHOULD SETTLE A BIT 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 POST-FRONTAL COOLER AND DRIER AIR SPREAD DOWN
OVER THE CENTRAL AND EASTERN CONUS THIS WEEKEND.
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, 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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