434
FXUS02 KWBC 091849
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM 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 PACIFIC NORTHWEST
AND ABOVE NORMAL HEIGHTS FOR MUCH OF THE REST OF THE LOWER 48 FOR A
TIME. SLOW-MOVING FRONTAL BOUNDARIES IN THE EAST WILL SPARK
CONVECTION AND LOCALLY HEAVY RAINFALL IN AMID SEASONABLY WARM TO
HOT TEMPERATURES, WITH SOME SIGNAL FOR MONSOON CONVECTION IN THE
SOUTHWEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z/06Z GUIDANCE OFFERED REASONABLE CLUSTERING THROUGH THE
PERIOD WITH THE ENSEMBLE MEANS. THE PRESSURES, FRONTS, 500 HPA
HEIGHTS, AND WINDS STARTED OUT WITH AN EVEN SPLIT OF THE 00Z ECMWF,
00Z UKMET, 00Z CANADIAN, AND 06Z GFS, WITH SOME 00Z ECMWF ENSEMBLE
MEAN AND 00Z NAEFS MEAN INPUT LATE IN THE PERIOD TO ACCOUNT FOR
UNCERTAINTY. THE REMAINDER OF THE GRIDS HAVE A STRONG RESEMBLANCE
TO THE 13Z NBM, WITH SOME 06Z EC AIFS INCLUSION.
..WEATHER/HAZARDS HIGHLIGHTS
NEAR AND AHEAD OF A COLD FRONT MOVING THROUGH THE GREAT LAKES,
MIDWEST, AND PORTIONS OF THE APPALACHIANS, LOCALLY HEAVY RAIN IS
EXPECTED WITHIN A MOIST AND UNSTABLE AIR MASS. LOCALLY HEAVY
RAINFALL IS ALSO POSSIBLE NEAR A RETURNING WARM FRONT IN AND NEAR
NORTH DAKOTA. TO THE SOUTH, AMPLE MOISTURE AND INSTABILITY NEAR A
DYING FRONT/SURFACE CONVERGENCE ZONE WILL ALSO ACT AS AN IMPETUS
FOR SOME HEAVIER RAIN TUESDAY INTO WEDNESDAY NEAR THE CENTRAL GULF
COAST AND LOWER MS VALLEY. THESE THREE AREAS ARE DENOTED WITH A
MARGINAL RISK OF FLASH FLOODING (EXCESSIVE RAINFALL). MUCH OF NEW
MEXICO AND INTO SOUTHEASTERN ARIZONA MAY SEE SOME LOCALIZED MODEST
RAINFALL AMID SENSITIVE TERRAIN AND BURN SCARS 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 LATE THIS WEEK. 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.
FOR PUERTO RICO AND THE U.S. VIRGIN ISLANDS, A BROAD TROPICAL WAVE
WITH SOME ROTATION LEAVING THE AFRICAN COAST IS EXPECTED TO TRACK
WEST TO WEST-NORTHWEST, ENDING UP NORTHEAST OF THE LEEWARD ISLANDS
FRIDAY INTO NEXT WEEKEND. THIS COULD LEAD TO A TRAILING TROUGH FROM
ITS SOUTHWEST SIDE MOVING ACROSS THE REGION WHICH WOULD FOCUS
SHOWER AND THUNDERSTORM ACTIVITY AND WEAKEN THE TRADE WINDS. THE
SYSTEM'S TRACK THEREAFTER REMAINS UNCERTAIN DUE TO UNCERTAINTY
REGARDING THE UPPER LEVEL PATTERN FROM THE APPALACHIANS EAST INTO
THE WESTERN SUBTROPICAL ATLANTIC AT THAT LONG TIME RANGE. SEE
NATIONAL HURRICANE CENTER TROPICAL WEATHER OUTLOOKS FOR MORE
CONCERNING ITS POTENTIAL FOR TROPICAL CYCLONE DEVELOPMENT.
ROTH/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page