966
FXUS02 KWBC 090654
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EDT SAT AUG 9 2025
VALID 12Z TUE AUG 12 2025 - 12Z SAT AUG 16 2025
..OVERVIEW
STRONG UPPER RIDGING OVER THE NORTHEASTERN PACIFIC WILL RETREAT
WESTWARD, FAVORING INCREASED TROUGHING INTO THE PACNW AND ABOVE
NORMAL HEIGHTS FOR MUCH OF THE REST OF THE LOWER 48. SLOWLY-MOVING
FRONTAL BOUNDARIES IN THE EAST WILL SPARK CONVECTION AND LOCALLY
HEAVY RAINFALL IN TYPICAL SUMMERTIME FASHION AMID WARM TO HOT
TEMPERATURES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MOST OF THE RECENT 12Z/18Z GUIDANCE OFFERED REASONABLE CLUSTERING
THROUGH THE PERIOD WITH THE ENSEMBLE MEANS. THE 12Z CANADIAN AND
UKMET WERE NOTICEABLY DIFFERENT IN TIMING OVER SOUTHWESTERN
CANADA/NORTHERN WA/MT THAN THE GFS/ECMWF (SLOWER AND FASTER,
RESPECTIVELY), BUT MOSTLY WITHIN TOLERANCE. TRENDED TOWARD A SPLIT
BETWEEN THE GFS/ECMWF/CANADIAN AND THE GEFS/EPS BY THE END OF THE
WEEK OWING TO GREATER UNCERTAINTY IN TIMING OF EMBEDDED SHORTWAVES.
THE ECMWF AIFS-ENS WAS A BIT SLOWER THAN ITS DYNAMICAL COUNTERPART
AND FIT A LITTLE BETTER WITH THE DETERMINISTIC GUIDANCE. HOWEVER,
RUN-TO-RUN CHANGES WERE NOTED SO CONFIDENCE IN ANY ONE RUN IS
LIMITED.
..WEATHER/HAZARDS HIGHLIGHTS
A COLD FRONT OVER THE GREAT LAKES BACK TO THE PLAINS TUESDAY WILL
BE A FOCUS FOR SOME LOCALLY HEAVY RAIN OVER THE MIDWEST IN THE
WARMER AND MOISTURE-LADEN ENVIRONMENT. THIS HEAVY RAIN THREAT MAY
SINK INTO THE CENTRAL/SOUTHERN APPALACHIANS WEDNESDAY EVEN AS THE
FRONT STALLS JUST TO THE NORTH. TO THE SOUTH, A WEAKENING
STATIONARY BOUNDARY DRAPED ALONG THE I-10 CORRIDOR AMID HIGHER THAN
NORMAL MOISTURE LEVELS WILL ALSO ACT AS AN IMPETUS FOR SOME
HEAVIER RAIN TUES-WEDS. BOTH OF THESE AREAS ARE DENOTED WITH A
MARGINAL RISK OF FLASH FLOODING (EXCESSIVE RAINFALL). IN ADDITION,
MUCH OF NEW MEXICO AND INTO SOUTHEASTERN ARIZONA MAY SEE SOME
LOCALIZED MODEST RAINFALL AMID SENSITIVE TERRAIN TUESDAY, AND A
MARGINAL RISK EXISTS THERE. FOR THE REST OF THE WEEK INTO THE START
OF THE WEEKEND, RAINFALL CHANCES WILL BE MODESTLY HIGH OVER THE
EASTERN 1/3 OF THE COUNTRY AS THE NORTHERN FRONTAL BOUNDARY WAVERS
OVER THE REGION (GREAT LAKES TO NORTHEAST).
TEMPERATURES WILL START THE PERIOD QUITE WARM INTO THE NORTHEAST
TO NEAR RECORD LEVELS TUESDAY WITH HIGHS INTO THE 90S. THIS WILL
PUSH HEATRISK LEVELS INTO THE MODERATE (LEVEL 2) TO PERHAPS MAJOR
(LEVEL 3 OUT OF 4) CATEGORY. LINGERING HEAT OVER THE SOUTHWEST WITH
RECORD HIGHS TUESDAY WILL SLOWLY SUBSIDE THROUGH THE PERIOD,
THOUGH TEMPERATURES WILL REMAIN SLIGHTLY ABOVE NORMAL UNTIL LATER
IN THE WEEK.
OVER THE PACIFIC NORTHWEST, TEMPERATURES WILL TREND COOLER THAN
NORMAL AS TROUGHING INCREASES. TEMPERATURES IN THE 70S/80S/90S
TUESDAY WILL DROP BY 10-20 DEGREES BY THU/FRI. THROUGH COASTAL CA,
TEMPERATURES WILL HOVER NEAR TO BELOW NORMAL AS THE COOLER THAN
NORMAL SUMMER CARRIES ON. EVEN INLAND LOCATIONS WILL COOL BY THE
END OF THE WEEK AS UPPER TROUGHING TAKES A HOLD.
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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