435
FXUS02 KWBC 161839
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
239 PM EDT SAT AUG 16 2025
VALID 12Z TUE AUG 19 2025 - 12Z SAT AUG 23 2025
..OVERVIEW
A FOUR CORNERS SUBTROPICAL RIDGE WILL BE STEADFAST THROUGH MUCH OF THE
MEDIUM RANGE PERIOD, WITH SOME DEGREE OF UPPER TROUGHING FAVORED
DOWNSTREAM OVER THE EAST, WHICH KEEPS ERIN ON AN OUT TO SEA TRACK AND
LEAD TO ITS EXTRATROPICAL TRANSITION OFFSHORE NEW ENGLAND AND
ATLANTIC CANADA. SIGNIFICANT HEAT ACROSS THE MIDWEST EARLY ON WILL
EASE WHILE TEMPERATURES ACROSS PARTS OF THE INTERMOUNTAIN WEST AND
SOUTHWEST GRADUALLY RAMP UP. RAINFALL FOR THE PERIOD WILL FOCUS
OVER THE MIDWEST-NORTHEAST/MID-ATLANTIC STATES AND EVENTUALLY INTO
THE SOUTHEAST AND BACK INTO THE SOUTHERN PLAINS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LARGE SCALE PATTERN CONTINUES TO SHOW ABOVE AVERAGE AGREEMENT
THROUGH THE MEDIUM RANGE PERIOD. A BLEND OF THE DETERMINISTIC
MODELS OFFERING A GOOD STARTING POINT EARLY ON, WITH SOME ENSEMBLE
MEAN CONTRIBUTION USED LATE FOR THE PRESSURES, FRONTS, WINDS, AND
500 HPA HEIGHTS. THE 19Z NBM WAS PRIMARILY USED FOR MOST OTHER
FIELDS, WITH SOME ASSIST FROM THE 06Z ECMWF AIFS. PLEASE CONSULT
NHC PRODUCTS FOR THE LATEST INFORMATION ON THE INTENSITY AND TRACK
FORECAST FOR HURRICANE ERIN.
..WEATHER/HAZARDS HIGHLIGHTS
A GENERALLY EAST-WEST ORIENTED SECONDARY FRONT WILL BE THE FOCUS
FOR HEAVY RAINFALL MUCH OF NEXT WEEK. ABOVE NORMAL PW VALUES AND
AMPLE INSTABILITY WILL SUPPORT AT LEAST ISOLATED INSTANCES OF
EXCESSIVE RAINFALL. AT THE MOMENT, THE GUIDANCE IS AGREEABLE ON
MOISTURE IN AND AROUND ERIN REMAINING OUT AT SEA; THE THREAT OF
A PREDECESSOR HEAVY RAIN EVENT FOR THE NORTHEAST APPEARS TO BE A
LOW PROBABILITY ALTERNATIVE SCENARIO. ON TUESDAY/DAY 4, A BROAD
MARGINAL RISK IS IN PLACE FOR PORTIONS OF THE MIDWEST, OHIO
VALLEY, LOWER GREAT LAKES, AND PARTS OF THE NORTHEAST. BY DAY
5/WEDNESDAY, THE MARGINAL RISK SHIFTS SOMEWHAT, EXTENDING FROM THE
NORTHWEST GULF COAST EAST- NORTHEAST INTO THE OHIO VALLEY AND MUCH
OF THE APPALACHIANS. IT IS POSSIBLE FOR BOTH DAYS, EMBEDDED SLIGHT
RISKS MAY BE NEEDED IN THE FUTURE WHERE THE HEAVY RAIN THREAT
ULTIMATELY BECOMES MORE AGREEABLE AMONGST THE GUIDANCE. THE FRONT
WILL CONTINUE TO SAG INTO THE SOUTHEAST AND WEAKEN WITH TIME WITH
INCREASED CONVECTION CONTINUING FROM THE SOUTHERN PLAINS TO THE
SOUTHEAST LATER IN THE WEEK.
ELSEWHERE, SURGES OF MOISTURE INTO THE SOUTHWEST UNDER THE BASE OF
THE FOUR CORNERS RIDGE COMBINED WITH DIURNAL HEATING MAY TRIGGER
STORMS CAPABLE OF PRODUCING HEAVIER RAINFALL OVER MORE SENSITIVE
AREAS (STEEP TERRAIN, IN/AROUND BURN SCARS, DRY WASHES/ARROYOS,
URBAN AREAS). A MARGINAL RISK ERO CONTINUES TO BE DEPICTED FOR
BOTH DAYS 4-5/WEDNESDAY INTO THURSDAY. DESPITE MISSING THE EAST
COAST BY A HEALTHY MARGIN, ERIN WILL LIKELY BRING HIGH WAVES AND
AND INCREASED THREAT FOR RIP CURRENTS ALONG MUCH OF THE EAST COAST
DURING PORTIONS OF NEXT WEEK.
ABOVE NORMAL TEMPERATURES AND MAJOR TO EXTREME HEATRISK WILL
CONTINUE THROUGH TUESDAY FOR MUCH OF THE MIDWEST, WITH
HEAT/HUMIDITY EXPECTED TO MODERATE BY MID WEEK AS THE UPPER RIDGE
REGROUPS FARTHER WEST. HEAT THREATS WILL INCREASE ACROSS MUCH OF
THE INTERIOR WEST, WITH MAJOR TO LOCALIZED EXTREME HEATRISK BY LATE
WEEK ACROSS MUCH OF THE SOUTHWEST WITH DAYTIME TEMPERATURES
EXCEEDING 110F IN SOME LOCATIONS.
ROTH
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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