229
FXUS02 KWNH 010800
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
359 AM EDT TUE SEP 1 2026
VALID 12Z FRI SEP 04 2026 - 12Z TUE SEP 08 2026
...DANGEROUS LATE-SUMMER HEAT WAVE CONTINUES FROM THE CENTRAL AND
SOUTHERN PLAINS TO THE SOUTHEAST U.S. THROUGH LATE WEEK...
..PATTERN OVERVIEW
DANGEROUSLY HOT WEATHER WILL CONTINUE ACROSS MUCH OF THE CENTRAL
U.S. THROUGH THE WEEKEND INTO EARLY NEXT WEEK WHILE A COLD FRONT
WILL BRING RELIEF TO THE MID-ATLANTIC AND PARTS OF THE SOUTHEAST
AFTER A COUPLE MORE VERY HOT DAYS ON FRIDAY AND SATURDAY. IN
CONTRAST, PERSISTENT TROUGHING WILL KEEP MUCH OF THE PACIFIC
NORTHWEST COOL, SHOWERY, AND UNSETTLED INTO EARLY NEXT WEEK.
LOCALLY HEAVY RAINFALL AND SEVERE WEATHER WILL BE POSSIBLE ALONG A
FRONTAL ZONE FROM THE MIDWEST TO THE OHIO VALLEY, CENTRAL
APPALACHIANS, AND MID-ATLANTIC ON FRIDAY, WITH ADDITIONAL CHANCES
FARTHER SOUTH INTO THE CAROLINAS ON SATURDAY. MONSOONAL MOISTURE
RETURNS LATE WEEK INTO THE WEEKEND WITH A TROPICAL CONNECTION
POTENTIALLY LEADING TO ENHANCED RAINFALL FOR PARTS OF THE SOUTHWEST
INTO NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
DEEP TROUGHING ALONG THE WEST COAST, HIGHLY AMPLIFIED RIDGING OVER
THE CENTRAL U.S., AND MORE TROUGHING ALONG THE EAST COAST WILL
CONTINUE TO BE THE DOMINANT FEATURES OF THE LARGE SCALE PATTERN
INTO EARLY NEXT WEEK. MODELS ARE GENERALLY IN GOOD AGREEMENT WITH
THE PATTERN THROUGH MOST OF THE WEEKEND, BUT UNCERTAINTY INCREASES
LEADING INTO NEXT WEEK. THE PRIMARY SOURCE OF UNCERTAINTY SEEMS TO
STEM FROM THE EVOLUTION OF SHORTWAVE ENERGIES EMBEDDED WITHIN THE
DEEP TROUGHING ACROSS THE WEST COAST, INCLUDING DETAILS ON HOW AND
WHEN THOSE ENERGIES EJECT NORTHEASTWARD AND POTENTIALLY INTERACT
WITH THE ANOMALOUSLY STRONG RIDGE DOWNSTREAM, AS WELL AS ENERGY
DIGGING INTO SOUTH-CENTRAL CANADA.
ADDITIONALLY, THE EVOLUTION OF THE WESTERN U.S. TROUGHING WILL
HAVE IMPLICATIONS ON THE FUTURE TRACK OF INVEST 95E. AS HAS BEEN
THE CASE FOR SEVERAL RUNS NOW, THE GFS CONTINUES TO BE AN OUTLIER
WITH DEEPER AND MORE SOUTHERLY WEST COAST TROUGHING, LEADING TO
MORE INTERACTION WITH 95E AND THUS BRINGING MORE DIRECT IMPACTS TO
SOUTHERN CALIFORNIA AND THE SOUTHWEST AS IT TRACKS NORTHWARD. NON-
NCEP GUIDANCE (INCLUDING A MAJORITY OF AI/ML GUIDANCE) HOWEVER
GENERALLY FAVORS LESS TROUGH INTERACTION AND TURNS 95E SHARPLY
WESTWARD UPON REACHING 20-25N LATITUDE.
SINCE YESTERDAY, THE PREFERENCE FOR THE FRONTS/PRESSURES FORECAST
HAS BEEN TO LEAN ON A MULTI-MODEL NON-GFS CONSENSUS WITH THE MOST
WEIGHT GIVEN TO THE AI/ML GUIDANCE AS WELL AS THE EC/GEFS ENSEMBLE
MEANS (PARTICULARLY FOR DAYS 5-7 FOR THE LATTER). THAT STRATEGY
CONTINUES WITH THIS FORECAST PACKAGE, WHICH DOES WELL TO MITIGATE
SMALLER SCALE DIFFERENCES AND PRESERVE THE PRIMARY LARGE SCALE
FEATURES WHILE ENSURING LESS WEST COAST TROUGH INTERACTION WITH
95E.
..WEATHER/HAZARDS HIGHLIGHTS
INTENSE LATE-SUMMER HEAT WILL CONTINUE ACROSS THE CENTRAL U.S.
THROUGH THE WEEKEND INTO NEXT WEEK AS A LARGE MID/UPPER RIDGE
DOMINATES THE REGION. BEFORE THEN, RELIEF FROM THE HEAT IS EXPECTED
THIS WEEKEND FOR PARTS OF THE OHIO VALLEY, MID-ATLANTIC, AND
SOUTHEAST AS A COLD FRONT DROPS IN FROM THE NORTH. THE WELL ABOVE
NORMAL TEMPERATURES COMBINED WITH HIGH HUMIDITY AND VERY WARM
OVERNIGHT LOWS IN THE MID 70S WILL RESULT IN WIDESPREAD AREAS OF
MAJOR TO EXTREME HEATRISK AND A CONCERN FOR HEAT-RELATED ILLNESSES.
PLEASE CONTINUE TO SEE WPC'S KEY MESSAGES FOR MORE DETAILS ON THIS
LONG LASTING HEAT WAVE.
IN STARK CONTRAST FROM THE HEAT ACROSS THE CENTRAL AND EASTERN
U.S., COOLER THAN NORMAL TEMPERATURES WILL REMAIN IN PLACE ACROSS
THE PACIFIC NORTHWEST THROUGH EARLY NEXT WEEK AS PERSISTENT CLOUDS
AND SHOWERS ASSOCIATED WITH DEEP TROUGHING OVER THE WEST COAST
LINGER OVER THE REGION. HIGH TEMPERATURES WILL MOSTLY TOP OUT IN
THE 50S, 60S, AND 70S, WHICH IS ROUGHLY 10-15 DEGREES BELOW
SEASONAL NORMS.
THE FRONTAL SYSTEM WHICH WILL BRING RELIEF FROM THE HEAT ACROSS
PARTS OF THE EASTERN U.S. THIS WEEKEND WILL FIRST INTERACT WITH
SUFFICIENT MOISTURE AND INSTABILITY TO PRODUCE LOCALLY HEAVY
RAINFALL AND SEVERE WEATHER FROM THE MIDWEST TO THE OHIO VALLEY,
CENTRAL APPALACHIANS, AND MID-ATLANTIC ON FRIDAY, WITH ADDITIONAL
CHANCES FARTHER SOUTH INTO THE CAROLINAS ON SATURDAY. THE STRONGEST
STORMS WILL BE CAPABLE OF PRODUCING DAMAGING WINDS AND HAIL, AND
PERHAPS A FEW ISOLATED TORNADOES. STORMS WILL ALSO CONTAIN HEAVY
RAINFALL RATES WHICH COULD LEAD TO SCATTERED INSTANCES OF FLASH
FLOODING.
SURGING MONSOONAL MOISTURE WILL FOSTER MORE NUMEROUS SHOWERS AND
THUNDERSTORMS ACROSS PARTS OF THE SOUTHWEST AND INTERMOUNTAIN WEST
ON FRIDAY, WITH A GROWING POTENTIAL FOR ISOLATED TO SCATTERED
FLASH FLOODING. MORE SURGES OF MOISTURE ARE LIKELY THIS WEEKEND
INTO EARLY NEXT WEEK, REGARDLESS OF WHAT HAPPENS WITH WHAT BECOMES
OF INVEST 95E. WHILE THE CURRENT THINKING FAVORS A TRACK THAT STAYS
FAR AWAY FROM SOUTHERN CALIFORNIA, THERE IS STILL A THREAT OF
TROPICAL MOISTURE ENHANCING MONSOONAL RAINFALL AND THUS LEADING TO
ADDITIONAL CONCERNS FOR FLASH FLOODING.
MILLER
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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