830
FXUS02 KWBC 310659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT MON JUL 31 2023
VALID 12Z THU AUG 03 2023 - 12Z MON AUG 07 2023
..HEATWAVE ACROSS THE SOUTH THIS WEEK
...HEAVY RAIN/FLASH FLOOD THREAT TO FOCUS INTO THE NORTH-CENTRAL
ROCKIES/PLAINS INTO LATER THIS WEEK...
..OVERVIEW
AN ELONGATING UPPER RIDGE WILL SUPPORT ABOVE NORMAL TEMPERATURES
FROM THE SOUTHERN PLAINS THROUGH THE SOUTHEAST THIS WEEK ALONG
WITH HIGH HEAT INDICES. 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 ROCKIES/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
APPALACHIANS/SOUTHEAST/MID-ATLANTIC. ACTIVITY SHOULD ALSO INCREASE
UP TO THE NORTHEAST LATER WEEK AS NEW NORTHERN STREAM TROUGH
ENERGY COMBINES WITH AN ATLANTIC MOISTURE PLUME AND TERRAIN. THIS
SCENARIO IS ALSO IN ADVANCE OF AN ORGANIZED CANADIAN SURFACE LOW
AND TRAILING FRONT THAT SHOULD 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 GFS/ECMWF AND
GEFS/ECMWF ENSEMBLE MEANS ALONG WITH WPC CONTINUITY TO EASE RUN TO
RUN CHANGES OF CONVECTIVE FOCUS. APPLIED GREATER WEIGHTING IN THE
BLEND TO THE ECMWF/ECMWF ENSEMBLE MEAN THAT HAVE RECENTLY SHOWED
BETTER RUN TO RUN CONTINUITY. THE 18 UTC GFS/GEFS OFFERED OUTLIER
SOLUTIONS OVER TIME, WITH SIGNIFICANTLY DIFFERENT QPF AND RELATED
FIELD RUN TO RUN DIFFERENCES. THE CANADIAN/UKMET ALSO SHOW MORE
RUN-RUN CONTINUITY FEATURE ISSUES THAN THE ECMWF, INCLUDING THE
LATEST 00 UTC RUN CYCLE.
..WEATHER/HAZARDS HIGHLIGHTS
AN ONGOING HEATWAVE SHOULD SETTLE THIS PERIOD ACROSS THE SOUTHERN
PLAINS AND THE LOWER MISSISSIPPI VALLEY, WHERE ABOVE NORMAL
TEMPERATURES BY 5 TO 10+ DEGREES ARE LIKELY WITH ACTUAL
TEMPERATURES NEAR OR EXCEEDING 100F. HEAT INDICES MAY RISE TO
110-115F IN SOME AREAS. RECORD HOT HIGHS AND WARM MINIMUM
TEMPERATURES ARE WIDELY POSSIBLE IN THESE REGIONS.
THE NORTH-CENTRAL ROCKIES/PLAINS WILL SEE A FOCUS FOR DIURNALLY
DRIVEN CONVECTION AS FUELED BY DEEPENED MONSOONAL MOISTURE AND
SLOW MOVING/ORGANIZED EMBEDDED ENERGIES AROUND THE PERIPHERY OF
THE MAIN UPPER RIDGE INTO LATER THIS WEEK. IN PARTICULAR, QPF,
MOISTURE, TERRAIN AND INSTABILITY SEEM TO SUPPORT A "SLIGHT RISK"
OF EXCESSIVE RAINFALL INTO DAY 4/THURSDAY.
MEANWHILE, EXPECT AREAS OF THUNDERSTORMS WILL ALSO WORK OUT OF THE
MIDWEST TO THE EAST/SOUTHEAST AS SHORTWAVES WORK INTO THE REGION.
A HEAVY RAIN/FLASH FLOODING THREAT WILL LIKELY BE TIED TO THE
POTENTIAL FOR ORGANIZED CONVECTIVE SYSTEMS IN THE NORTHWESTERLY
FLOW. MARGINAL RISKS HAVE BEEN INCLUDED ON BOTH DAYS 4 AND 5 TO
COVER THIS POTENTIAL INTO THE APPALACHIANS/MID-ATLANTIC/SOUTHEAST,
SOUTHWARD SHIFTED FROM CONTINUITY. AMPLE ACTIVITY IS ALSO EXPECTED
TO DEVELOP AND WORK ACROSS THE NORTHEAST LATER THIS WEEK WHERE A
DAY 5 "MARGINAL RISK" AREA IS PLANNED AS NORTHERN STREAM UPPER
TROUGH AMPLITUDE TAPS A DEEPENED ATLANTIC MOISTURE PLUME. ACTIVITY
WILL ALSO BE AIDED AS AN ORGANIZED LOW PRESSURE SYSTEM
SUBSEQUENTLY TRACKS EASTWARD ACROSS CANADA, AND A COLD FRONT
TRAILS BACK ACROSS THE LOWER 48 AND STALLS BACK INTO THE CENTRAL
PLAINS FOR FOCUS.
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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