478
FXUS02 KWBC 270620
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 AM EDT THU AUG 27 2026
VALID 12Z SUN AUG 30 2026 - 12Z THU SEP 03 2026
...HAZARDOUS HEAT TO BROADLY EXPAND ACROSS THE SOUTH-CENTRAL U.S.
THEN MIDWEST TO SOUTH NEXT WEEK...
..OVERVIEW
DANGEROUS LATE-SUMMER HEAT WILL BROADLY SPREAD ACROSS THE
CENTRAL/SOUTHERN PLAINS THEN MIDWEST/SOUTH THIS WEEKEND INTO NEXT
WEEK. SURGES OF MONSOONAL MOISTURE WILL MEANWHILE CONTINUE TO
SUPPORT DAILY SHOWERS AND THUNDERSTORMS FROM PORTIONS OF THE
SOUTHWEST TO THE INTERMOUNTAIN WEST/ROCKIES WITH LOCALIZED FLASH
FLOODING POSSIBLE. MEANWHILE, LOW PRESSURE SYSTEMS TRAVERSING
SOUTHERN AND WESTERN CANADA WILL PUSH A WAVY FRONT ACROSS THE
NORTHERN TIER OF THE CONUS AND LATER DIP INTO THE EAST-CENTRAL
U.S. WHERE ROUNDS OF SHOWERS AND POSSIBLY STRONG TO SEVERE
THUNDERSTORMS WITH LOCALLY HEAVY DOWNPOURS ARE POSSIBLE. SLOWLY
DISSIPATING LEADING FRONTAL BOUNDARIES ACROSS THE SOUTHERN MID-
ATLANTIC AND SOUTHEAST WILL ALSO OFFER LINGERING RISKS FOR STORMS
WITH HEAVY RAIN AND LOCAL RUNOFF ISSUES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE FORECAST SPREAD HAS IMPROVED THROUGH MEDIUM-
RANGE TIME SCALES, BOLSTERING FORECAST CONFIDENCE IN THE PATTERN
EVOLUTION AND MAIN SYSTEMS ALONG WITH THREAT MESSAGING. FAVOR A
MODEL, ENSEMBLE MEAN AND MACHINE LEARNING GUIDANCE BLEND THAT
PROVIDES A GOOD FORECAST BASIS IN LINE WITH CONTINUITY. THE BLEND
PROCESS TENDS TO MITIGATE LINGERING FLOW EMBEDDED SYSTEM
DIFFERENCES CONSISTENT WITH INDIVIDUAL PREDICTABILITY.
..WEATHER/HAZARDS HIGHLIGHTS
UNDER THE INFLUENCE OF A MAIN UPPER HIGH/RIDGE, DAILY MAXIMUM
TEMPERATURES ACROSS THE SOUTHERN PLAINS WILL CONTINUE TO RISE INTO
THE 90S AND 100S WITH OPPRESSIVE HEAT INDICES. RECORD-BREAKING
WARM OVERNIGHT TEMPERATURES ACROSS THE SOUTHERN TIER WILL FURTHER
LIMIT RECOVERY FROM THE HEAT, RESULTING IN WIDESPREAD MAJOR TO
EXTREME HEATRISK THAT MAY CAUSE HEAT RELATED ILLNESSES. AS THE
UPPER RIDGE/HIGH SHIFTS EASTWARD THIS WEEKEND/NEXT WEEK, HAZARDOUS
HEAT OVER THE SOUTHERN PLAINS WILL STEADILY EXPAND NORTHEASTWARD
OVER THE SOUTH-CENTRAL U.S AND LOWER/MID MISSISSIPPI VALLEY/MID-
SOUTH. HEAT THREAT WILL OVERSPREAD THE OHIO VALLEY/SOUTH/SOUTHEAST
MID- LATER NEXT WEEK. IN THIS UPPER PATTERN TRANSITION, THE
EXCESSIVE HEAT THREAT MODERATES OVER THE DESERT SOUTHWEST. PLEASE
SEE WPC'S KEY MESSAGES FOR MORE EXTREME HEAT DETAILS.
MONSOONAL MOISTURE STREAMING NORTHWARD ON THE WESTERN TO NORTHERN
PERIPHERY OF THE UPPER RIDGE AND AHEAD OF LOCALLY SHOWERY NORTHWEST
U.S. UPPER TROUGHING WILL CONTINUE TO FUEL SCATTERED, DIURNALLY
DRIVEN CONVECTION FROM THE SOUTHWEST AND INTERMOUNTAIN WEST TO THE
ROCKIES. INDIVIDUAL CELLS MAY LEAD TO ISOLATED INSTANCES OF FLASH
FLOODING FOR SENSITIVE LOCATIONS SUCH AS BURN SCARS, FAVORED
TERRAIN LIKE SLOT CANYONS, AND URBAN AREAS. MARGINAL RISK AREAS
COVER PORTIONS OF THESE AREAS ON THE WPC DAY 4/SUNDAY AND DAY
5/MONDAY EXCESSIVE RAINFALL OUTLOOKS (EROS).
MULTIPLE SHORTWAVES ROUNDING THE TOP OF THE RIDGE AND PIVOTING
INTO THE DOWNSTREAM AND SLOWLY DEAMPLIFYING MEAN UPPER TROUGH,
WILL INTERACT WITH WAVY FRONTAL SYSTEMS WILL BRING MUCH OF
EXPECTED HEAVY RAIN AND THUNDERSTORMS INCREASINGLY OFF THE EAST
COAST THIS WEEKEND. MARGINAL RISK ERO AREAS SPOTLIGHT AN UPSTREAM
FOCUS OVER THE UPPER MIDWEST/GREAT LAKES SUNDAY INTO MONDAY AHEAD
OF THE TRIPLE-POINT ASSOCIATED WITH THE EASTWARD MOVING LOW
PRESSURE SYSTEM ACROSS SOUTHERN CANADA. MARGINAL RISK ERO AREAS
ALSO HIGHLIGHT A LINGERING THREAT FOR LOCALLY HEAVY RAINFALL OVER
THE COASTAL SOUTHEAST/EASTERN GULF COAST/FLORIDA SUNDAY AND MONDAY
AS WAVY FRONT GRADUALLY DISSIPATES INTO EARLY NEXT WEEK.
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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