475
FXUS02 KWBC 081919
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
319 PM EDT SAT AUG 8 2026
VALID 12Z TUE AUG 11 2026 - 12Z SAT AUG 15 2026
...MULTI-DAY HEAVY RAINFALL THREAT EXTENDING FROM PARTS OF THE
MID- MISSISSIPPI VALLEY TO OHIO VALLEY NEXT WEEK...
...HAZARDOUS HEAT BUILDS ACROSS MUCH OF THE SOUTH-CENTRAL AND
SOUTHEAST U.S. THROUGH THE END OF NEXT WEEK...
..OVERVIEW
UPPER RIDGE OVER THE FOUR CORNERS SHIFTS EAST MIDWEEK AND REMAINS
STRETCHED OUT ACROSS MUCH OF THE SOUTHEAST AND SOUTH-CENTRAL U.S.
THROUGH FRIDAY. MEANWHILE, SHORTWAVE DISTURBANCES AND TROUGHING
ACROSS THE NORTHERN TIER (PARTICULARLY NORTHEAST AND PACIFIC
NORTHWEST) BRINGS SHOWER AND THUNDERSTORM CHANCES. MULTIPLE DAYS
OF HEAVY RAINFALL MAY LEAD TO FLOODING CONCERNS ACROSS PARTS OF THE
MID-MISSISSIPPI AND OHIO VALLEYS. TROUGHING EXTENDING ALONG THE
WEST COAST AND GREAT BASIN BY MIDWEEK WILL ALSO INCREASE SOUTHERLY
FLOW AND MONSOONAL MOISTURE INTO THE REGION, INCREASING THE
COVERAGE OF SHOWER AND THUNDERSTORM CHANCES THROUGHOUT SOUTHWEST,
INTERMOUNTAIN WEST, AND INTERIOR/SOUTHERN CALIFORNIA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST DETERMINISTIC AND ENSEMBLE GUIDANCE GENERALLY AGREES ON THE
LARGE-SCALE EVOLUTION, ALTHOUGH UNCERTAINTY REMAINS REGARDING THE
AMPLITUDE AND TIMING OF INDIVIDUAL SHORTWAVE IMPULSES EMBEDDED
WITHIN THE NORTHERN-STREAM FLOW. MODEL SPREAD INCREASES TOWARDS THE
LATTER PORTION OF THE PERIOD, ESPECIALLY WITH THE LATITUDINAL
PLACEMENT OF THE CENTRAL PLAINS FRONTAL BOUNDARY. THIS WILL IMPACT
THE CONFIDENCE IN THE LOCATION FOR THE GREATEST HEAVY RAINFALL
THREAT BETWEEN THE HIGH PLAINS AND MIDWEST/OHIO VALLEY. THE 06Z GFS
WAS A SOUTHERN OUTLIER WITH RESPECT TO THIS FEATURE, BUT TRENDED
FAVORABLY TOWARDS CONSENSUS WITH THE 12Z RUN. THE BROADER SIGNAL
FOR PRECIPITATION POTENTIAL ACROSS PARTS OF THE UPPER MIDWEST INTO
THE GREAT LAKES AND NORTHEAST IS REASONABLY WELL SUPPORTED. GENERAL
MODEL WEIGHTS WERE USED IN THE FORECAST THROUGH DAY 6 BEFORE
TRENDING AWAY FROM THE 06Z GFS AND TOWARDS ENSEMBLE MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
THE INCREASING TROUGHING OVER NORTHERN/EASTERN U.S. WILL BRING
THUNDERSTORM AND SHOWERS DEVELOPMENT, ESPECIALLY OVER AREAS WHERE
DEEP MOISTURE, INSTABILITY, AND SLOW- MOVING BOUNDARIES OVERLAP.
ADDITIONALLY, THE SHORTWAVE CROSSING THE NORTHERN ROCKIES/HIGH
PLAINS WILL MOVE TOWARDS THE GREAT LAKES/UPPER MIDWEST ON TUESDAY.
A SURFACE LOW AND TRAILING FRONTAL BOUNDARY WILL ACCOMPANY THIS
FEATURE AS IT INTERACTS WITH MOIST AND UNSTABLE AIRMASS, LEADING TO
THUNDERSTORM DEVELOPMENT ALONG THE FRONT WITHIN WEST-NORTHWEST FLOW
ALOFT. WITH THE SLOW- MOVING, ORGANIZED CONVECTION, LOCALLY HEAVY
RAINFALL WILL BE POSSIBLE ACROSS THE GREAT LAKES/MIDWEST INTO THE
OHIO VALLEY AND PORTIONS OF THE MID- ATLANTIC. THE 00Z RUN OF THE
ECMWF EFI HIGHLIGHTS PARTS OF THE UPPER OHIO VALLEY FOR POTENTIALLY
EXTREME RAINFALL THROUGH WEDNESDAY. BY THE MIDDLE TO LATER PART OF
NEXT WEEK ACROSS PORTIONS OF THE HIGH PLAINS AND CENTRAL U.S., A
DECENT MOISTURE CONNECTION FROM THE EASTERN SUBTROPICAL PACIFIC IN
CONNECTION TO TROUGHING OVER THE WEST WILL ALLOW FOR MOISTURE TO
OVERRUN A FRONTAL BOUNDARY DRAPED ACROSS THE CENTRAL U.S., THIS
WILL LEAD TO A STRIPE OF ADDITIONAL HEAVY RAIN AND FLASH FLOODING
POTENTIAL EXTENDING FROM THE CENTRAL HIGH PLAINS TO THE OHIO
VALLEY, WITH DAILY THUNDERSTORM CHANCES OCCURRING ALONG THIS AXIS
THROUGH SATURDAY. THE DAY 4 AND 5 EXCESSIVE RAINFALL OUTLOOKS
MAINTAIN BROAD MARGINAL RISKS WITH EMBEDDED SLIGHT RISKS CENTERED
AROUND THE UPPER OHIO VALLEY.
OVER INTO SOUTHWESTERN U.S., THE PERSISTENT RIDGING WILL START TO
MOVE EASTWARD, BUT MONSOONAL MOISTURE WILL CONTINUE TO GENERATE
THUNDERSTORMS OVER THE SOUTHWEST AND INCREASE IN COVERAGE
THROUGHOUT THE WEEK. MULTIPLE DAYS OF SHOWERS AND THUNDERSTORMS
MAY LEAD TO LOCALLY HEAVY RAINFALL AND FLASH FLOODING ACROSS THE
SOUTHWEST, CENTRAL GREAT BASIN, ROCKIES, AND PARTS OF
INTERIOR/SOUTHERN CA, PARTICULARLY OVER BURN SCARS AND STEEP
TERRAIN.
THE RIDGE WILL SUPPORT HAZARDOUS HEAT OVER THE SOUTHERN PLAINS,
SOUTHEAST AND GULF COAST THROUGHOUT MUCH OF THE WEEK. WIDESPREAD
MAJOR HEATRISK IS FORECAST TO EXTEND INTO PARTS OF THE CENTRAL
PLAINS AND LOWER OHIO VALLEY ON TUESDAY BEFORE THE AREA SHRINKS
SOUTHWARD WITH THE APPROACHING FRONTAL BOUNDARY AND
SHOWER/THUNDERSTORM CHANCES. LONGEST DURATION OF ABOVE AVERAGE AND
POTENTIALLY DANGEROUS LEVELS OF HEAT ARE EXPECTED THROUGH SATURDAY
ACROSS PARTS OF THE SOUTHERN PLAINS TO SOUTHEAST. THIS IS DEPICTED
ON THE WPC DAY 3-7 HAZARDS CHART. HIGHS ARE FORECAST IN THE MID-
UPPER 90S (TRIPLE DIGITS ACROSS PARTS OF OK AND TX), WITH LOWS ONLY
DROPPING INTO UPPER 70S. HEAT- RELATED IMPACTS COULD BECOME
SIGNIFICANT WHERE THE COMBINATION OF HIGH TEMPERATURES AND HUMIDITY
PERSIST FOR SEVERAL CONSECUTIVE DAYS.
OUDIT/SNELL
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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