741
FXUS02 KWBC 120621
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 AM EDT TUE AUG 12 2025
VALID 12Z FRI AUG 15 2025 - 12Z TUE AUG 19 2025
..OVERVIEW
TROUGHING IN THE WEST AND RIDGING IN THE EAST WILL START THE
MEDIUM RANGE PERIOD (FRI), WITH A SLOW RETROGRESSION WESTWARD OF
THE ENTIRE PATTERN INTO EARLY NEXT WEEK. THIS WILL ALLOW THE
RIDGING TO BUILD INTO THE SOUTHERN PLAINS/ROCKIES WITH TROUGHING
DIPPING INTO THE NORTHEAST. TEMPERATURES WILL START COOL IN THE
WEST AND WARM/HOT IN THE EAST BUT MODERATE WITH TIME. THE HEAT WILL
SLIP WESTWARD AS WELL IN LOCK STEP WITH THE STRONGEST RIDGING.
RAINFALL WILL FOCUS OVER THE NORTHERN TIER (UPPER MIDWEST/GREAT
LAKES) IN ASSOCIATION WITH THE STORM TRACK, ACROSS THE SOUTHEAST,
AND OVER THE SOUTHWEST. IN ADDITION, A MODESTLY STRONG COLD FRONT
WILL BRING APPRECIABLE RAIN TO THE PACIFIC NORTHWEST ON
FRIDAY/SATURDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 12/18Z DETERMINISTIC GUIDANCE SHOWED REASONABLE CLUSTERING
THROUGH THE PERIOD WITH THE ENSEMBLE MEANS AND THAT BROAD CONSENSUS
FORMED THE STARTING POINT TO THE FRONTS/PRESSURES. EMBEDDED
SHORTWAVE TIMING WAS SMOOTHED OUT BUT THESE FEATURES HAVE HIGH
UNPREDICTABILITY AT THIS TIME RANGE ANYWAY. TRENDS SEEMS TO SUPPORT
THE CURRENT PACE OF RETROGRESSION AS THE PAST 48HRS OF ENSEMBLE
RUNS HAVE BEEN RATHER STABLE. NOTE THAT THE NATIONAL HURRICANE
CENTER IS TRACKING TROPICAL STORM ERIN, WHICH MAY START TO GET
CLOSE TO THE SOUTHEASTERN BOUNDARY OF THE DOMAIN BY NEXT TUESDAY
PER THE LATEST FORECAST. PLEASE SEE THE NHC WEBSITE FOR THE MOST
UP-TO-DATE INFORMATION.
..WEATHER/HAZARDS HIGHLIGHTS
FOR FRIDAY AND SATURDAY, THERE ARE THREE AREAS WITH MARGINAL RISKS
FOR EXCESSIVE RAINFALL/FLASH FLOODING -- THE UPPER MIDWEST,
SOUTHERN APPALACHIANS/SOUTHEAST, AND THE SOUTHWEST. THE FIRST IS
DUE TO AN APPROACHING COLD FRONT ON BOTH DAYS WHICH MAY TRIGGER
SHOWERS/STORMS ALONG AND AHEAD OF THE FRONT. THE SECOND AREA IS DUE
TO STUBBORNLY HIGH MOISTURE LEVELS IN THE SOUTHEAST. WHEN COMBINED
WITH AFTERNOON HEATING, SHOWERS AND STORMS WILL FIRE IN THE
AFTERNOON. THE LAST AREA (SOUTHWEST) WILL SEE AN INCREASE IN
MOISTURE INTO THE REGION OUT OF MEXICO THURSDAY AND CONTINUING INTO
THE MEDIUM RANGE (FRI/SAT). THOUGH AMOUNTS MAY BE LIGHT OVERALL,
SOME STORMS WILL STILL BE CAPABLE OF PRODUCING HEAVIER RAINFALL
THAT MAY FALL OVER MORE SENSITIVE AREAS (STEEP TERRAIN, IN/AROUND
BURN SCARS, ETC.). FOR THE REST OF THE PERIOD, RAINFALL MAY EASE A
BIT IN THE SOUTHWEST REMAIN WIDESPREAD ACROSS THE UPPER
MIDWEST/GREAT LAKES AS THE FRONTAL BOUNDARY STALLS ACROSS THE
REGION.
TEMPERATURES WILL BE VERY WARM OVER MUCH OF THE CENTRAL TO EASTERN
STATES FRIDAY INTO THE WEEKEND. MANY AREAS WILL SEE TEMPERATURES
INTO THE 90S AND HEAT INDICES AROUND 100F. THIS WILL DRIVE HEATRISK
VALUES INTO THE THE MODERATE (LEVEL 2) TO MAJOR (LEVEL 3 OUT OF 4)
CATEGORY FROM THE CORN BELT THROUGH THE MIDWEST INTO THE MID-
ATLANTIC. HIGH TEMPERATURES AND HUMIDITY WILL COMBINE TO MAKE FOR
VERY UNCOMFORTABLE CONDITIONS AS WELL OVER FLORIDA LATE THIS WEEK
AND ALONG THE GULF COAST INTO THE WEEKEND. SOME RELIEF IS EXPECTED
OVER THE GREAT LAKES AND NORTHEAST BY NEXT WEEK AS THE COLD FRONT
PUSHES THROUGH. OVER THE PACIFIC NORTHWEST INTO CALIFORNIA,
TEMPERATURES WILL BE MUCH COOLER THAN NORMAL FRI/SAT THEN START TO
SLOWLY REBOUND AS THE TROUGHING EASES BACK WESTWARD. COASTAL AREAS
MAY ONLY SEE HIGHS INTO THE 60S AND LOW 70S WITH INLAND AREAS ONLY
IN THE 80S TO LOW 90S. EVEN THE SOUTHWEST WILL LIKELY SEE
TEMPERATURES A BIT COOLER THAN NORMAL -- 90S TO LOW 100S FOR THE
DESERT CITIES INSTEAD OF 100-110F+. HOWEVER, THE HEAT MAY START TO
RETURN OVER THE FOUR CORNERS REGION BY TUESDAY AS THE UPPER RIDGE
MOVES INTO THE AREA FROM THE EAST.
FRACASSO
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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