219
FXUS02 KWBC 032004
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 PM EDT THU AUG 03 2023
VALID 12Z SUN AUG 06 2023 - 12Z THU AUG 10 2023
...HEATWAVE TO PERSIST OVER THE SOUTH AND WORK BACK INTO THE
SOUTHWEST...
...EXCESSIVE RAIN/FLASH FLOOD THREAT FOR THE UPPER MIDWEST/GREAT
LAKES SUNDAY AND INTO THE NORTHEAST EARLY NEXT WEEK...
..OVERVIEW
A MONSOONAL MOISTURE CONNECTION OUT FROM THE WEST AND A
SUBSTANTIAL GULF MOISTURE AND INSTABILITY FEED WITH DEEPENED
LOW/FRONTAL APPROACH WILL FUEL AN EXCESSIVE RAINFALL THREAT WHOSE
FOCUS IS SLATED TO REACH THE UPPER MIDWEST/GREAT LAKES SUNDAY
BEFORE EJECTING ACROSS THE NORTHEAST EARLY NEXT WEEK. AN INITIALLY
CLOSED UPPER SYSTEM ENERGY WILL SLIDE EASTWARD OVER TOP A MAIN
UPPER RIDGE AS KICKED BY ADDITIONAL NORTHERN STREAM UPPER
TROUGHING FROM THE CANADIAN PRAIRIES. THIS SCENARIO ALSO ACTS TO
SUPPRESS A CENTRAL U.S. UPPER RIDGE AXIS TO THE U.S. SOUTHERN TIER
AS THEIR HEATWAVE PERSISTS AND ALSO SPREADS BACK INTO THE
SOUTHWEST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00/06Z GUIDANCE FROM THIS MORNING WAS IN REASONABLE AGREEMENT
REGARDING THE EVOLUTION OF THE SYNOPTIC PATTERN DURING THE MEDIUM
RANGE PERIOD. A GENERAL MODEL BLEND CONSISTING OF THE 00Z
EC/CMC/UKMET AND 06Z GFS WERE EXCLUSIVELY USED THROUGH DAY 4. THIS
GMB IS VERY WELL CLUSTERED AROUND THE AMPLIFYING SHORTWAVE TROUGH
OVER THE UPPER MIDWEST LATE THIS WEEKEND INTO EARLY NEXT WEEK. THE
06Z GFS AND 00Z CMC IS MORE PROGRESSIVE THAN THE REST OF THE
GUIDANCE WITH THE RESULTING QPF FOOTPRINT OVER THE MIDWEST ON
SUNDAY. THE 00Z ECE AND 06Z GEFS WERE INTRODUCED ON DAY 5 TO
MITIGATE SOME OUTLIER AMPLIFICATION BY THE DETERMINISTIC GUIDANCE
OVER NORTHERN PLAINS. THE 00Z CMCE IS INTRODUCED ON DAY 6 AND THE
ENSEMBLES MAKE UP A MAJORITY OF THE BLEND THROUGH THE END OF THE
PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE VERY WET PATTERN FOR THE NORTH-CENTRAL U.S. AND MAIN HEAVY
CONVECTIVE RAIN FOCUS SHOULD SLOWLY SHIFT TO THE UPPER MIDWEST AND
GREAT LAKES BY SUNDAY AS THE UPPER RIDGE AXIS CENTERED OVER THE
HIGH PLAINS WEAKENS/SUPPRESSES SOUTH AND NORTHERN TIER FLOW
FLATTENS. A LINGERING MONSOONAL MOISTURE CONNECTION AND SLOW
MOVING AND DEEPENED SURFACE LOW/FRONTAL SYSTEM AND UPPER SYSTEM
ENERGIES COMBINE WITH A CONTINUED AND PRONOUNCED GULF MOISTURE AND
INSTABILITY FEED TO FUEL AN EXCESSIVE RAIN THREAT. AN UPGRADE TO A
SLIGHT RISK FOR EXCESSIVE RAINFALL HAS BEEN OUTLINED OVER PORTIONS
OF AN INCREASINGLY WET UPPER MIDWEST FOR SUNDAY, CENTERED ON
WISCONSIN, ALONG WITH A SURROUNDING MARGINAL RISK AREA ALSO SPREAD
DOWNSTREAM ACROSS THE GREAT LAKES SUNDAY AND WITH TRANSLATION FOR
PARTS OF THE NORTHEAST MONDAY WHERE STILL FAVORABLE INGREDIENTS
COMBINE WITH LOCALLY INCREASED TERRAIN LIFT.
SOUTH OF THE MAIN LOW, A TRAILING FRONT WILL SPREAD DRIER
AIR/MODERATED TEMPERATURES ACROSS PARTS OF THE CENTRAL TO EASTERN
U.S. THIS WEEKEND. SHOWERS AND THUNDERSTORMS WILL ALSO TAP POOLED
MOISTURE NEAR THE ELONGATED FRONT FROM THE WEEKEND INTO NEXT WEEK
AND AS WITH ADDITIONAL LOW PRESSURE/FRONTAL SYSTEM AND SECONDARY
SURGES DOWN ACROSS THE EASTERN/SOUTHEASTERN TO THE CENTRAL U.S.,
WITH SHOWERS/STORMS ALSO TRAILING BACK ACROSS THE ROCKIES TO
MONITOR GIVEN POTENTIAL MOISTURE FEED AND LOCAL TERRAIN
ENHANCEMENT.
MEANWHILE, AN ONGOING HEATWAVE SHOULD SETTLE A BIT SOUTH OVER THIS
WEEKEND TO THE SOUTH OF THE TRAILING FRONT OVER THE SOUTH AS
UPPER-TROUGHING SHIFTS SOUTHWARD AND THE UPPER-HIGH FLATTENS OUT.
HIGH TEMPERATURES WILL BE 5 TO 10 DEGREES ABOVE NORMAL WITH HIGH
HUMIDITY LEADING TO HEAT INDICES IN THE 110-115F RANGE IN SOME
AREAS, PARTICULARLY THE LOWER MISSISSIPPI RIVER VALLEY. RECORD
HIGH MAXIMUM AND ESPECIALLY MINIMUM TEMPERATURES ARE WIDELY
FORECAST IN THESE REGIONS. ADDITIONALLY, AFTER A BRIEF DROP IN
TEMPERATURES OVER THE DESERT SOUTHWEST, HIGHS WILL ONCE AGAIN WARM
INTO THE 110S. SOME ABOVE AVERAGE TEMPERATURES WILL ALSO SPREAD UP
THE WEST COAST FOLLOWING A BIT OF UPPER-RIDGE AMPLIFICATION, WITH
HIGHS IN THE CENTRAL CALIFORNIA VALLEYS CLIMBING INTO THE MID-100S
INTO THE WEEKEND AND EARLY NEXT WEEK.
KEBEDE/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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE UPPER GREAT LAKES, SUN, AUG 6.
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHEAST AND THE GREAT LAKES,
MON, AUG 7.
- SEVERE WEATHER ACROSS PORTIONS OF THE MIDWEST, SUN, AUG 6.
- SEVERE WEATHER ACROSS PORTIONS OF THE OHIO VALLEY, THE
MID-ATLANTIC, AND THE NORTHEAST, MON, AUG 7.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI
VALLEY, AND THE NORTHERN PLAINS.
- FLOODING LIKELY ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHWEST, THE SOUTHERN
PLAINS, THE GULF COAST, AND FLORIDA, SUN-THU, AUG 6-AUG 10.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHEAST AND CALIFORNIA,
SUN-MON, AUG 6-AUG 7.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHERN PLAINS, THE LOWER
TO MIDDLE MISSISSIPPI VALLEY, AND TENNESSEE VALLEY, SUN, AUG 6.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHEAST, MON-TUE, AUG
7-AUG 8.
- HEAVY RAIN ACROSS PORTIONS OF SOUTHERN ALASKA, SUN, AUG 6.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE NORTH SLOPE OF ALASKA,
SUN, AUG 6.
- HAZARDOUS HEAT ACROSS PORTIONS OF INTERIOR ALASKA, SUN-MON, AUG
6-AUG 7.
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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