840
FXUS02 KWBC 311956
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
356 PM EDT MON AUG 31 2026
VALID 12Z THU SEP 3 2026 - 12Z MON SEP 7 2026
...DANGEROUS HEAT CONTINUES FROM THE CENTRAL TO THE SOUTHEAST U.S.
THROUGH LATE WEEK...
20Z UPDATE: THE 12Z MODEL GUIDANCE SUITE IS INITIALLY IN VERY GOOD
SYNOPTIC SCALE AGREEMENT ACROSS THE CONTINENTAL U.S. TO CLOSE OUT
THE WORK WEEK, WITH A GENERAL DETERMINISTIC MODEL BLEND USED FOR
FRONTS AND PRESSURES. MEANINGFUL DIFFERENCES START EMERGING BY
SATURDAY WITH THE ECMWF BRINGING A STRONGER TROUGH ACROSS SOUTH-
CENTRAL CANADA, AND THE GFS/GEFS BECOMING MORE AMPLIFIED WITH THE
TROUGH NEAR THE WEST COAST. THIS DEEPER TROUGH SOLUTION HAS
IMPLICATIONS ON WHAT THE FUTURE TROPICAL DISTURBANCE OVER THE
PACIFIC WILL DO, AND ITS EVENTUAL TRACK. RECENT RUNS OF THE GFS
HAVE DEPICTED A TRACK WELL TO THE NORTH OF THE NON-NCEP CONSENSUS,
AND BRING IT MUCH CLOSER TO SOUTHERN CALIFORNIA. THE OTHER GUIDANCE
SHOWS A SOLUTION WELL TO THE SOUTHWEST AND FAR OFFSHORE GIVEN LESS
INTERACTION WITH THE UPPER TROUGH.
IN TERMS OF THE NBM, THE QPF WAS REDUCED OVER LARGE PORTIONS OF
CALIFORNIA, ARIZONA, NEVADA, AND UTAH GIVEN THE FORECAST PREFERENCE
FOR THE STORM AND ITS MOISTURE PLUME TO STAY WELL OFFSHORE,
ALTHOUGH MONSOONAL MOISTURE WILL STILL BE IN PLACE ACROSS THE
REGION REGARDLESS OF THE OUTCOME WITH THE TROPICAL SYSTEM. IN TERMS
OF TEMPERATURES, HIGHS WERE REDUCED A DEGREE OR TWO FROM THE
DAKOTAS TO IOWA WHERE THE NBM APPEARED A LITTLE HIGH ON THE
NORTHERN PERIPHERY OF THE UPPER RIDGE, AND ALSO SLIGHTLY REDUCED
ACROSS PORTIONS OF THE CAROLINAS. THE PREVIOUS FORECAST DISCUSSION
IS APPENDED BELOW FOR REFERENCE. /HAMRICK
-------------
..PATTERN OVERVIEW
EXTREME LATE SUMMER HEAT WILL CONTINUE ACROSS THE CENTRAL AND
SOUTHEASTERN U.S. THROUGH FRIDAY BEFORE A COLD FRONT BRINGS SOME
RELIEF THIS WEEKEND. IN CONTRAST, PERSISTENT TROUGHING WILL KEEP
MUCH OF THE PACIFIC NORTHWEST COOL, SHOWERY, AND UNSETTLED INTO
EARLY NEXT WEEK. DOWNSTREAM, LOCALLY HEAVY RAINFALL AND SEVERE
WEATHER WILL BE POSSIBLE FROM THE NORTHERN PLAINS AND THE UPPER
MIDWEST TO THE GREAT LAKES AND MID-ATLANTIC THURSDAY AND FRIDAY.
ACROSS THE SOUTHERN U.S., MONSOONAL MOISTURE RETURNS LATE WEEK INTO
THE WEEKEND WITH A POSSIBLE TROPICAL CONNECTION POTENTIALLY
LEADING TO ENHANCED RAINFALL FOR PARTS OF THE SOUTHWEST. MEANWHILE,
LINGERING RAIN FROM DECAYING TROPICAL MOISTURE WILL GRADUALLY
DIMINISH ACROSS SOUTHEAST TEXAS THROUGH THE END OF THE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LARGE SCALE PATTERN ACROSS THE CONUS CONTINUES TO BE DOMINATED
BY DEEP AND PERSISTENT TROUGHING ALONG THE WEST COAST, EXPANSIVE
RIDGING WHICH RETROGRADES AND AMPLIFIES INTO THE CENTRAL U.S., AND
INCREASING TROUGHING ALONG THE EAST COAST. IN GENERAL, THE LATEST
MODELS ARE IN GOOD OVERALL AGREEMENT ACROSS THE CONUS, WITH
GENERALLY MINOR DIFFERENCES IN SMALLER SCALE FEATURES. A GENERAL
MODEL BLEND OF DETERMINISTIC AND MACHINE LEARNING GUIDANCE WITH
INCREASING WEIGHTING TOWARDS ENSEMBLE MEANS DID WELL TO PRESERVE
THE LARGE SCALE FEATURES WHILE MINIMIZING THE SPREAD OF SMALLER
SCALE ONES.
ONE FEATURE OF NOTE THAT COULD HAVE IMPLICATIONS TO THE QPF
FORECAST ACROSS THE SOUTHWEST U.S. THIS WEEKEND INTO NEXT WEEK IS
THE POTENTIAL TROPICAL CONNECTION FROM A POSSIBLE TROPICAL SYSTEM
THAT MAY SPIN UP WELL OFFSHORE SOUTHWEST OF MEXICO IN THE EASTERN
PACIFIC (CURRENTLY IDENTIFIED AS INVEST 95E). RIGHT NOW, MOST
GUIDANCE (BOTH DYNAMICAL AND MACHINE LEARNING, INCLUDING THE EC-
AIFS AND AI- GFS) TRACK THIS ENTITY NORTHWESTWARD TO ABOUT 25N
LATITUDE BEFORE TURNING MORE WESTWARD OUT TO SEA. HOWEVER, A
SMALLER CONTINGENT OF GUIDANCE, INCLUDING THE LATEST 18Z AND 00Z
RUNS OF THE GFS, TAKE THIS SYSTEM NORTHWARD TO THE POINT OF
DIRECTLY IMPACTING SOUTHERN CALIFORNIA AND VICINITY. WHILE THIS
SCENARIO IS WITHIN A WIDE RANGE OF POSSIBLE OUTCOMES AT THIS TIME
RANGE AND CAN'T BE COMPLETELY RULED OUT JUST YET, WE CURRENTLY DO
NOT FAVOR THIS SUBSET OF GUIDANCE AND THUS TAILORED THE QPF
FORECAST TO REFLECT THIS THINKING.
..WEATHER/HAZARDS HIGHLIGHTS
DANGEROUS HEAT WITH HIGH TEMPERATURES WELL INTO THE 90S TO LOW
100S WILL PERSIST ACROSS THE CENTRAL AND SOUTHERN PLAINS, MIDWEST,
MID- ATLANTIC, AND SOUTHEAST THROUGH THE END OF THE WEEK AS A LARGE
AND SPRAWLING MID/UPPER RIDGE DOMINATES THE REGION. SOME RELIEF IS
EXPECTED FRIDAY INTO THE WEEKEND FOR PARTS OF THE OHIO VALLEY AND
MID- ATLANTIC AS A COLD FRONT DROPS IN FROM THE NORTH, BUT THE
CORE OF THE HEAT WILL LIKELY CONTINUE FROM THE CENTRAL/SOUTHERN
PLAINS TO THE MID/LOWER MISSISSIPPI VALLEY INTO NEXT WEEK AS THE
RIDGE RETROGRADES AND AMPLIFIES BACK OVER THE CENTRAL U.S. WELL
ABOVE NORMAL TEMPERATURES COMBINED WITH HIGH HUMIDITY AND VERY WARM
OVERNIGHT LOWS IN THE 70S TO NEAR 80 DEGREES WILL RESULT IN
WIDESPREAD AREAS OF MAJOR TO EXTREME HEATRISK AND A CONCERN FOR
HEAT-RELATED ILLNESSES. PLEASE SEE WPC'S KEY MESSAGES FOR MORE
DETAILS.
IN STARK CONTRAST FROM THE CENTRAL AND EASTERN U.S. HEAT, COOLER
THAN NORMAL TEMPERATURES WILL REMAIN IN PLACE ACROSS THE PACIFIC
NORTHWEST THROUGH THE END OF THE WEEK AS 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.
DOWNSTREAM, A SLOW-MOVING FRONTAL SYSTEM AND A SERIES OF MID-LEVEL
IMPULSES TRACKING EASTWARD ALONG THE NORTHERN PERIPHERY OF THE
MID/UPPER RIDGE WILL INTERACT WITH ANOMALOUS MOISTURE AND
INSTABILITY TO PRODUCE EPISODES OF HEAVY RAINFALL AND POSSIBLE
SEVERE WEATHER FROM THE NORTHERN PLAINS, UPPER MIDWEST, GREAT
LAKES, AND MID-ATLANTIC THROUGH THURSDAY AND FRIDAY. THE STRONGEST
STORMS WILL BE CAPABLE OF PRODUCING DAMAGING WINDS AND HAIL, AND
PERHAPS A FEW TORNADOES. STORMS WILL ALSO CONTAIN HEAVY RAINFALL
RATES WHICH COULD LEAD TO SCATTERED INSTANCES OF FLASH FLOODING.
AFTER A BRIEF REPRIEVE, ANOTHER SURGE OF MONSOONAL MOISTURE IS
LIKELY TO BRING A RETURN TO MORE NUMEROUS SHOWERS AND THUNDERSTORMS
ACROSS PARTS OF THE SOUTHWEST AND INTERMOUNTAIN WEST BY THURSDAY
OR FRIDAY. ADDITIONAL SURGES OF MOISTURE ARE LIKELY THIS WEEKEND
INTO EARLY NEXT WEEK, AND A TROPICAL CONNECTION WITH A POTENTIAL
TROPICAL SYSTEM COULD BRING ENHANCED RAINFALL AND A HEIGHTENED RISK
OF FLASH FLOODING TO THE REGION. FARTHER EAST, ADDITIONAL SMALLER
SCALE DISTURBANCES INTERACTING WITH GULF MOISTURE WILL SPARK DAILY
THUNDERSTORM ACTIVITY ACROSS PARTS OF THE SOUTHEAST, FLORIDA, AND
THE GULF COAST THROUGH THE WEEKEND, WITH THE POTENTIAL FOR HEAVY
RAINFALL AND LOCALIZED FLASH FLOODING.
MILLER/HAMRICK
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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