684
FXUS02 KWBC 191953
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
353 PM EDT FRI SEP 19 2025
VALID 12Z MON SEP 22 2025 - 12Z FRI SEP 26 2025
...HEAVY RAIN THREAT FOR PORTIONS OF THE CENTRAL U.S. TO SOUTHERN
APPALACHIANS NEXT WEEK...
..OVERVIEW
THE MAIN PATTERN DRIVER DURING THE MEDIUM RANGE PERIOD WILL BE A
DEEPENING SHORTWAVE OVER THE NORTHWEST/ROCKIES ON MONDAY. THERE IS
STILL SOME UNCERTAINTY IN HOW THIS EVOLVES AFTER MONDAY, BUT RECENT
MODELS SHOW INCREASING CONSENSUS FOR AN UPPER LOW TO FORM OVER THE
CENTRAL PLAINS ON TUESDAY, THEN CUT OFF AND LINGER OVER THE MID-
MISSISSIPPI TO OHIO VALLEYS WEDNESDAY-FRIDAY. THIS WOULD FOCUS RAIN
THAT COULD BE HEAVY NEAR A RESULTANT SURFACE LOW PRESSURE/FRONTAL
SYSTEM IN THE SOUTH-CENTRAL PLAINS, LOWER/MID-MISSISSIPPI VALLEY,
OHIO VALLEY/MID-SOUTH, AND SOUTHERN APPALACHIANS. MEANWHILE,
ANOTHER CUTOFF LOW OFF THE CALIFORNIA COAST COULD LEAD TO A ROUND
OF RAIN OVER SOUTHERN CALIFORNIA INTO THE DESERT SOUTHWEST AS IT
LIFTS NORTH, AND A POSSIBLE UPPER RIDGE OVER THE SOUTHWEST COULD
LEAD TO A PERIOD OF TRIPLE DIGIT HEAT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
AN OMEGA BLOCK PATTERN MAY SET UP OVER THE CONUS NEXT WEEK,
CONSISTING OF AN UPPER LOW OVER CALIFORNIA, A LARGE CUTOFF LOW OVER
THE CENTRAL U.S., AND AN AMPLIFIED RIDGE IN BETWEEN. THE
DEVELOPMENT AND EVOLUTION OF THE CENTRAL U.S. UPPER LOW IS MOST
UNCERTAIN. AFTER MODELS HAVE A GOOD HANDLE ON THE SHORTWAVE MOVING
THROUGH THE NORTHERN ROCKIES/HIGH PLAINS ON MONDAY, HOW FAR SOUTH
AND EAST THE ENERGY DIVES WILL AFFECT THE DEVELOPING UPPER LOW
TRACK. THE ECMWF HAS BEEN THE MOST CONSISTENT WITH THE UPPER LOW
CLOSING OFF AND IN A MORE SOUTHERN POSITION THAN SOME GUIDANCE, BUT
MATCHING WELL WITH THE AIFS AND GFS GRAPHCAST AS WELL AS THE
ENSEMBLE MEANS. RECENT GFS RUNS HAVE BEEN TRENDING TOWARD A
SOLUTION LIKE THIS AS WELL, THOUGH A BIT NORTH WITH ITS LOW/TROUGH.
THE 00Z CMC WAS AN OUTLIER IN SHOWING AN UPPER LOW CLOSING OFF
WELL WEST OF CONSENSUS. HOWEVER, AFTER SEVERAL RUNS IN A ROW WITH A
SIMILAR UPPER LOW TRACK, THE NEW 12Z ECMWF IS NOW FARTHER NORTH
THAN ITS PREVIOUS RUNS WITH THE TRACK OF ITS UPPER LOW CENTER. NOW
IT AND THE GFS AGREE FAIRLY WELL BUT THIS JUMP NORTH MAKES
CONFIDENCE REMAIN LOW WITH THE EXACT POSITION.
THE EASTERN PACIFIC TO CALIFORNIA UPPER LOW SHOWS REASONABLE
AGREEMENT IN MOVING NORTHEASTWARD THROUGH MIDWEEK, WITH SOME TIMING
SPREAD AFTER THAT, INCLUDING THE 12Z ECMWF AND CMC STALLING THE
UPPER LOW OVER SOUTHERN CALIFORNIA/DESERT SOUTHWEST. MEANWHILE
THERE IS ALSO MODEL UNCERTAINTY WITH A TROUGH PUSHING THROUGH THE
NORTHEASTERN U.S. AROUND MIDWEEK. NEW 12Z MODEL RUNS OF THE GFS AND
ECMWF (BUT NOT THE CMC) NOW SHOW THIS TROUGH MORE PROGRESSIVE
PULLING OUT OF THE NORTHEAST BY THURSDAY, WHICH WOULD AFFECT
SENSIBLE WEATHER LIKE FRONTAL PLACEMENT/QPF THERE.
THE WPC FORECAST STAYED STEADY IN LEANING TOWARD A ECMWF-HEAVY
SOLUTION ALONG WITH ENSEMBLE MEANS, MAINTAINING GOOD CONTINUITY
WITH PREVIOUS FORECASTS.
..WEATHER/HAZARDS HIGHLIGHTS
WIDESPREAD RAIN LOOKS TO FOCUS ALONG SURFACE FRONTAL BOUNDARIES ON
MONDAY FROM THE NORTH-CENTRAL ROCKIES INTO THE CENTRAL PLAINS AND
MIDWEST ASSOCIATED WITH NORTHERN STREAM ENERGY ACROSS THE GREAT
LAKES AND THE SHORTWAVE DIVING THROUGH THE NORTHERN HIGH PLAINS AND
DEVELOPING INTO A CLOSED LOW. SHOWERS AND THUNDERSTORMS WILL BE
SUPPORTED BY INCREASINGLY ANOMALOUS MOISTURE, WITH PWS OF 1.5-1.75"
MONDAY INTO TUESDAY. THIS MOISTURE WHEN COMBINED WITH ADEQUATE
INSTABILITY AND FORCING IS SUFFICIENT FOR EXCESSIVE RAINFALL
CONCERNS WITH SLOW MOVING ACTIVITY/FLOW PARALLEL TO ANY BOUNDARIES.
A MARGINAL RISK IS HIGHLIGHTED FROM THE CENTRAL PLAINS INTO THE
MIDWEST ON MONDAY ON THE ERO. AS THE UPPER LOW BECOMES MORE DEFINED
ON TUESDAY, RAINFALL MAY INCREASE IN INTENSITY AND FOCUS MORE INTO
THE SOUTH-CENTRAL PLAINS AND MID-MISSISSIPPI VALLEY. WILL CONTINUE
TO HOLD OFF ON ANY EMBEDDED SLIGHT RISK GIVEN UNCERTAINTY IN
HEAVIEST RAINFALL PLACEMENT DUE TO MODEL SPREAD AND DRY ANTECEDENT
CONDITIONS. FARTHER EAST, RAIN IS BECOMING MORE LIKELY IN THE
NORTHEAST ESPECIALLY TUESDAY AHEAD OF THE EASTERN PART OF THE
FRONTAL SYSTEM, BUT RAIN AMOUNTS AND PLACEMENT ARE UNCERTAIN THERE
AS WELL. THE RAIN ACTIVITY WITH THE PRIMARY LOW WILL MOVE SLOWLY
EASTWARD WITH TIME NEXT WEEK INTO THE MID-SOUTH AND OHIO VALLEY AND
EVENTUALLY PARTS OF THE EAST LATE WEEK, WITH A LIKELY HEAVY
RAINFALL FOCUS IN THE SOUTHERN APPALACHIANS.
ELSEWHERE, AN UPPER LOW NEAR CALIFORNIA EARLY IN THE WEEK SHOULD
RESULT IN SOME RAINFALL OVER THE STATE AND POSSIBLY INTO THE
SOUTHWEST. CURRENTLY THE RAINFALL DOES NOT APPEAR TO BE AS HEAVY AS
THE RECENT EVENT, BUT WILL CONTINUE TO MONITOR IF THE ABOVE
AVERAGE MOISTURE AND INSTABILITY IN SOUTHERN CALIFORNIA WOULD
REQUIRE A MARGINAL RISK IN THE ERO PARTICULARLY TUESDAY. LIGHTER
PRECIPITATION IS FORECAST TO SPREAD INTO PARTS OF THE INTERMOUNTAIN
WEST AS THE ENERGY MOVES NORTH AND EAST. THE NORTHWEST SHOULD
GENERALLY BE DRY UNTIL POSSIBLY LATE WEEK AHEAD OF A POSSIBLE UPPER
TROUGH. MEANWHILE, THE FLORIDA PENINSULA CAN EXPECT MAINLY
DIURNALLY DRIVEN SHOWERS AND STORMS.
A STRONG SURFACE HIGH LINGERING ALONG THE NORTHEASTERN SEABOARD
INTO MONDAY SHOULD MAINTAIN COOL AIR DAMMING EAST OF THE
APPALACHIANS AND SOUTH THROUGH THE CAROLINA PIEDMONT. THIS RESULTS
IN NEAR TO BELOW NORMAL TEMPERATURES EAST OF THE APPALACHIANS.
TEMPERATURES SHOULD TREND A BIT WARMER FOR THE EAST LATER INTO THE
WEEK AS WEAK RIDGING BUILDS AHEAD OF THE CENTRAL U.S. UPPER LOW.
UNDERNEATH THAT LOW, HIGHS WILL GENERALLY BE COOLER THAN AVERAGE
WHILE LOWS SHOULD BE CLOSE TO NORMAL. MEANWHILE, A RIDGE AXIS WILL
BUILD FROM THE FOUR CORNERS STATES TOWARD THE NORTHERN TIER AND
BRING SOME WARM TEMPERATURES. THE NORTHWEST TO UPPER MIDWEST SHOULD
SEE INCREASING TEMPERATURES INTO TUESDAY THROUGH THURSDAY.
MEANWHILE THE DESERT SOUTHWEST CAN EXPECT TEMPERATURES IN THE 100S,
A FEW DEGREES ABOVE AVERAGE, BUT THE POTENTIAL FOR RECORD
TEMPERATURES HAS TRENDED DOWN.
TATE/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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