880
FXUS02 KWBC 061856
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 PM EDT WED AUG 6 2025
VALID 12Z SAT AUG 9 2025 - 12Z WED AUG 13 2025
...MAJOR HEAT THREAT FOCUS SHIFTS FROM THE SOUTHWEST AND SOUTH-
CENTRAL PLAINS TO THE MIDWEST/GREAT LAKES/NORTHEAST THIS PERIOD...
19Z UPDATE: THE MODEL GUIDANCE CONTINUES TO INDICATE VERY GOOD
AGREEMENT ACROSS THE COUNTRY GOING INTO THIS WEEK, WITH A MULTI-
DETERMINISTIC MODEL BLEND USED FOR FRONTS/PRESSURES, AND THE
ECMWF/GFS/NBM AS A STARTING POINT FOR QPF. GOING INTO MONDAY, THE
GFS BECOMES MORE AMPLIFIED WITH THE TROUGH OVER THE CENTRAL PLAINS,
AND STRONGER WITH THE LOW PRESSURE SYSTEM OFF THE NORTHEAST COAST.
MORE NOTEWORTHY MODEL DIFFERENCES BECOME APPARENT OVER WESTERN
CANADA INTO THE NORTHWESTERN U.S. BY TUESDAY AS SHORTWAVE ENERGY
FROM THE NORTHEASTERN PACIFIC MAKES ITS WAY INTO THE DOMAIN, AND
THIS ESPECIALLY HOLDS TRUE BY WEDNESDAY WITH BELOW AVERAGE
CONFIDENCE BY THIS TIME. IN GENERAL, THE ECMWF HOLDS ONTO THE UPPER
RIDGE/HIGH ACROSS THE DESERT SOUTHWEST AND OVER FLORIDA MORE SO
THAN THE OTHER GUIDANCE. TAKING THESE FACTORS INTO ACCOUNT, THE
ENSEMBLE MEANS WERE GRADUALLY INCREASED TO ABOUT HALF BY WEDNESDAY,
AND THE PREVIOUS FORECAST DISCUSSION FOLLOWS BELOW FOR REFERENCE.
/HAMRICK
-----------------------------
..OVERVIEW
DYNAMIC MEAN UPPER TROUGHING WILL GRADUALLY WORK EAST ACROSS THE
NORTHERN U.S., DRIVING STRONG TO SEVERE THUNDERSTORM CHANCES FROM
THE NORTH-CENTRAL PLAINS TO THE MIDWEST/GREAT LAKES. A WAVY
FRONTAL BOUNDARY WILL LINGER ALONG THE GULF AND SOUTHEAST COASTS,
RESULTING IN UNSETTLED WET WEATHER FOR PORTIONS OF THE
SOUTHEAST/FLORIDA AND SOUTHERN MID-ATLANTIC AS NHC MONITORS A
COASTAL LOW FOR POTENTIAL TROPICAL DEVELOPMENT. MEANWHILE, AN
EXPANDING UPPER RIDGE WILL SPREAD A HEATWAVE FROM THE SOUTHWEST
AND SOUTH-CENTRAL PLAINS TO THE MIDWEST/GREAT LAKES/NORTHEAST THIS
WEEKEND INTO NEXT WEEK. THERE MAY ALSO BE AN UPTICK IN MONSOONAL
MOISTURE FLOW INTO THE SOUTHWEST/SOUTHERN ROCKIES BY THE WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT GUIDANCE CONTINUES TO SHOW REALLY GOOD AGREEMENT ON THE
UPPER LEVEL PATTERN THROUGH THE PERIOD, RESULTING IN ABOVE AVERAGE
FORECAST CONFIDENCE. ALL AVAILABLE GUIDANCE IS CAPTURING THE
SYNOPTIC PATTERN WELL, WITH STRONG UPPER RIDGING THAT HAS ANCHORED
OVER THE SOUTHWEST EXPANDING HEAT RISKS THROUGH THE SOUTH-CENTRAL
PLAINS TO THE MIDWEST/GREAT LAKES/NORTHEAST IN ADVANCE OF A DEEP
TROUGH AND LEAD SURFACE FRONTAL SYSTEM SLATED TO MOVE SLOWLY
EASTWARD OVER THE NORTHERN U.S. WITH SEVERAL EMBEDDED SHORTWAVES.
HOWEVER, THERE IS SOME UNCERTAINTY IN THE DETAILS OF THE SENSIBLE
WEATHER AT THE SURFACE, WITH SOME DIFFERENCES IN PRECIPITATION
AMOUNTS AND LOCATIONS. OVERALL, THE GENERAL CONSENSUS IS FOR THE
HEAVIEST RAIN TO FOCUS OVER THE NORTH-CENTRAL PLAINS/UPPER MIDWEST
AND FROM THE SOUTHEAST COAST/FLORIDA TO THE SOUTHERN MID-ATLANTIC.
IN THE SOUTHEAST AND EASTERN GULF/FLORIDA, PRECIPITATION INTENSITY
AND LOCATION IS ALSO PENDING ANY FRONTAL WAVE OR TROPICAL
DEVELOPMENT. GUIDANCE HAS VARIED WITH THE SYSTEM AND QPF FOCUS.
THE WPC MEDIUM-RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM A
COMPOSITE OF COMPATIBLE GFS/ECMWF/UKMET/CANADIAN FEATURES FOR THE
WEEKEND ALONG WITH WPC CONTINUITY AND THE NATIONAL BLEND OF MODELS
(NBM). OPTED TO INCREASINGLY SWITCH TO BETTER CLUSTERED GUIDANCE OF
THE GEFS/ECMWF/CANADIAN ENSEMBLE MEANS THROUGH EARLY-MID NEXT WEEK
AMID SLOWLY GROWING FORECAST SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
A SLOW TO DISLODGE COOLED HIGH PRESSURE AIRMASS WILL LINGER OVER
PORTIONS OF THE EASTERN U.S. WEEKEND, FURTHER MODERATING NEXT
WEEK. HIGH MOISTURE CONTENT AND INSTABILITY NEAR A FRONT ON THE
LEADING EDGE OF THIS AIRMASS WILL LIKELY FOCUS SOME LOCALIZED
HEAVY RAIN OVER THE COASTAL SOUTHEAST AND ACROSS CENTRAL AND
NORTHERN FLORIDA, BUT IT NOW APPEARS MOST OF THE EXPECTED RAINFALL
SHOULD BE GENERALLY AN INCH OR LESS FOR BOTH DAYS, AND THEREFORE
THE MARGINAL RISK AREA FOR THIS REGION HAS BEEN DROPPED.
LOCALLY STRONG CONVECTION AND HEAVY RAINS MAY ALSO BE POSSIBLE IN
THE NORTH-CENTRAL U.S. AS SHORTWAVES ROUND TO THE EASTERN EDGE OF
THE UPPER RIDGE FROM THE ROCKIES/PLAINS AND INTERACT WITH A
DOWNSTREAM FRONTAL ZONE. LATE WEEK, EXPECT THE NORTHERN TO CENTRAL
PLAINS/UPPER MIDWEST/GREAT LAKES TO SEE PERIODIC RAIN AND
THUNDERSTORMS. WPC'S DAY 4/5 EROS DEPICT MARGINAL RISK AREAS FOR
THESE REGIONS THIS WEEKEND GIVEN MOISTURE/INSTABILITY POOLING WITH
SHORTWAVE PASSAGES. ACTIVITY WILL SPREAD INTO THE GREAT LAKES AND
THE CENTRAL PLAINS/MIDWEST THIS WEEKEND INTO NEXT WEEK. MEANWHILE,
THE SOUTHWEST/SOUTHERN ROCKIES STATES COULD SEE SOME INCREASING
MONSOON SHOWERS BY THIS WEEKEND, WITH MARGINAL RISK AREAS
INTRODUCED FOR PORTIONS OF ARIZONA AND NEW MEXICO FOR DAY 4/5.
COOLER THAN AVERAGE TEMPERATURES WILL CONTINUE ON THE COOL SIDE OF
THE MAIN FRONTAL SYSTEM FOR THE EAST/SOUTHEAST U.S., WHILE HEAT
LINGERS ACROSS THE SOUTHWEST AND SOUTHERN/CENTRAL PLAINS.
HEAT WILL ALSO SPREAD ACROSS PORTIONS OF THE MIDWEST AND GREAT
LAKES LATE THIS WEEKEND THEN EVENTUALLY THE NORTHEAST, WHICH MAY
CREATE A MAJOR HEATRISK. FLORIDA IS FORECAST TO SEE SEASONABLE
TEMPERATURES IN THE 90S, BUT WITH AMPLE HUMIDITY ALLOWING FOR SOME
AREAS OF MAJOR HEATRISK THERE AS WELL.
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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