938
FXUS02 KWBC 151900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT FRI AUG 15 2025
VALID 12Z MON AUG 18 2025 - 12Z FRI AUG 22 2025
..OVERVIEW
AN EXPANSIVE RIDGE ACROSS THE SOUTHERN TIER STATES WILL RETROGRADE
AND FOCUS ACROSS THE FOUR CORNERS REGION BY MID-WEEK. THE JET
STREAM WILL MAINTAIN A FAIRLY ACTIVE WEATHER PATTERN ACROSS THE
NORTH-CENTRAL STATES THROUGH THE START OF THE WEEK BEFORE IT SHIFTS
FARTHER SOUTHEAST AS TROUGHING BUILDS OVER THE EAST. THIS
TROUGHING SHOULD HELP STEER ERIN AWAY FROM THE EAST COAST.
SIGNIFICANT HEAT ACROSS THE MIDWEST EARLY ON IN THE PERIOD WILL
EASE WHILE TEMPERATURES ACROSS PARTS OF THE INTERMOUNTAIN WEST AND
SOUTHWEST GRADUALLY RAMP UP TOWARDS MIDWEEK AND BEYOND. RAINFALL
LOOKS TO FOCUS OVER THE UPPER MIDWEST/GREAT LAKES INTO THE MIDWEST
AND NORTHEAST/MID-ATLANTIC, AND BACK TOWARDS THE SOUTHWEST/SOUTHERN
ROCKIES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LARGE SCALE PATTERN CONTINUES TO SHOW ABOVE AVERAGE AGREEMENT
THROUGH THE MEDIUM RANGE PERIOD, WITH A BLEND OF THE 00Z/06Z
DETERMINISTIC MODELS OFFERING A SOLID STARTING POINT TO THE
FORECAST. A 30 TO 40 PERCENT PROPORTION OF THE BLEND WAS
CONSTRUCTED USING THE EC AND GEFS ENSEMBLE MEANS BY DAYS 6 AND 7
FOR GREATER STABILITY AND SMOOTHING OF SMALLER SCALE DIFFERENCES.
SHORTWAVE ENERGY ROUNDING OVER TOP OF A RETROGRADING RIDGE ACROSS
THE CENTRAL U.S. WILL HELP FLATTEN THE FLOW OVER THE NORTHERN TIER
AND ALLOW FOR THE DEVELOPMENT OF DEEPER TROUGHING ACROSS THE
EASTERN HALF OF NORTH AMERICA. THIS WEAKNESS IN THE 500MB FLOW
PATTERN SHOULD HELP PULL ERIN POLEWARD WITH TIME BEFORE AN UPSTREAM
KICKER SHORTWAVE WITHIN THE EASTERN U.S. TROUGH HELPS TO QUICKLY
SWEEP ERIN TO THE NORTHEAST AWAY FROM THE EAST COAST. DESPITE ABOVE
AVERAGE CONFIDENCE, SHORTWAVE TIMING AND THE DEPTH OF THE TROUGH
WILL ULTIMATELY DETERMINE HOW FAR WEST ERIN REACHES BEFORE TURNING
NORTHWARD AND SWEPT AWAY FROM THE U.S. COASTLINE. AS A RESULT,
PLEASE CONSULT THE NHC WEBSITE FOR THE LATEST INFORMATION AS ERRORS
IN POSITION 5+ DAYS OUT CAN BE SIGNIFICANT.
..WEATHER/HAZARDS HIGHLIGHTS
A GENERALLY EAST-WEST ORIENTED AND SLOW MOVING FRONTAL BOUNDARY
WILL BE THE FOCUS FOR HEAVY RAINFALL THE FIRST PART OF THE PERIOD
FROM THE GREAT LAKES INTO THE MIDWEST AND OHIO VALLEY. ABOVE NORMAL
PW VALUES AND AMPLE INSTABILITY WILL SUPPORT AT LEAST ISOLATED
INSTANCES OF EXCESSIVE RAINFALL. ON MONDAY/DAY 4, MAINTAINED A
MARGINAL RISK ERO ACROSS THE UPPER MIDWEST/GREAT LAKES, BUT AN
UPGRADE TO A SLIGHT RISK MAY EVENTUALLY BE NEEDED IF MODELS
CONVERGE ON WHERE THE HEAVIEST QPF WILL FOCUS. RAINFALL COVERAGE
WILL EXPAND AND SHIFT SOUTH WITH A BROAD MARGINAL RISK DEPICTED ON
THE TUESDAY/DAY 5 ERO FROM THE MID-MISSISSIPPI VALLEY INTO THE OHIO
VALLEY AND INTERIOR NORTHEAST/LOWER GREAT LAKES. THE FRONT WILL
SAG INTO THE SOUTHEAST AS WEAKEN BY LATER IN THE WEEK WITH
INCREASED CONVECTION FROM THE SOUTHERN PLAINS TO THE SOUTHEAST
LATER IN THE WEEK.
ELSEWHERE, SURGES OF MOISTURE INTO THE SOUTHWEST COMBINED WITH
DIURNAL HEATING MAY TRIGGER STORMS CAPABLE OF PRODUCING HEAVIER
RAINFALL OVER MORE SENSITIVE AREAS (STEEP TERRAIN, IN/AROUND BURN
SCARS, ETC.). A MARGINAL RISK ERO CONTINUES TO BE DEPICTED FOR BOTH
DAYS 4-5. RAINFALL SHOULD DECREASE IN COVERAGE BY THE SECOND HALF
OF THE WEEK AS THE RIDGE SHIFTS MORE INTO THE REGION. SOME
LINGERING MOISTURE WILL BE PRESENT ACROSS THE FLORIDA PENINSULA
EARLY WEEK. THE HEAVIEST RAINFALL ASSOCIATED WITH ERIN SHOULD
REMAIN WELL OFFSHORE, BUT SOME NEARBY MOISTURE MAY GET DRAWN INTO
THE SOUTHEAST FRONTAL BOUNDARY, LEADING TO THE POTENTIAL FOR
MODERATE TO HEAVIER RAINFALL ALONG THE EAST COAST MID TO LATE NEXT
WEEK.
IN THE WAKE OF A COLD FRONT, COOLER AND LESS HUMID CONDITIONS WILL
MAKE FOR MUCH MORE PLEASANT WEATHER FROM THE NORTHEAST INTO THE
MID-ATLANTIC NEXT WEEK. FARTHER WEST, ABOVE NORMAL TEMPERATURES
AND MAJOR TO EXTREME HEATRISK WILL CONTINUE THROUGH TUESDAY FOR
MUCH OF THE MIDWEST. HEAT WILL MODERATE ACROSS THIS REGION BY MID
WEEK WITH LOWER HEIGHTS ALOFT, BUT WILL INCREASE ACROSS PARTS OF
THE INTERMOUNTAIN WEST, FOUR CORNERS, AND DESERT SOUTHWEST.
TEMPERATURES FOR THE LOWER DESERTS OF THE SOUTHWEST MAY EXCEED 110F
BY LATER IN THE WEEK WITH WIDESPREAD MODERATE TO MAJOR HEATRISK
ACROSS THE SOUTHWEST, SOUTHERN/CENTRAL ROCKIES AND EVEN INTO PARTS
OF THE CENTRAL HIGH PLAINS.
MILLER/SANTORELLI
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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