113
FXUS02 KWBC 281958
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
358 PM EDT SUN SEP 28 2025
VALID 12Z WED OCT 01 2025 - 12Z SUN OCT 05 2025
..OVERVIEW
AS THERE IS BETTER CONSENSUS FOR IMELDA TO CURVE EAST AWAY FROM THE
U.S. BEFORE MIDWEEK, ATTENTION TURNS TO OTHER FORECAST ASPECTS
DURING THE MEDIUM RANGE PERIOD. A RELATIVELY SLOW-MOVING AND BLOCKY
PATTERN WILL SET UP ACROSS THE U.S., WITH MEAN TROUGHING IN THE
WEST PROMOTING FRONTAL PASSAGES WITH COOLER TEMPERATURES AND ROUNDS
OF PRECIPITATION, WHILE AN UPPER RIDGE SETS UP FROM THE SOUTHWEST
NORTHEASTWARD INTO THE MIDWEST PROMOTING WARM TEMPERATURES AND
MAINLY DRY CONDITIONS. SOUTHERN STREAM ENERGY AND A POSSIBLE
FRONTAL BOUNDARY ATOP THE GULF COAST/FLORIDA COULD ALLOW FOR ROUNDS
OF RAIN AND STORMS THERE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE EARLY PART OF THE MEDIUM RANGE PERIOD (STARTING WEDNESDAY)
SHOWS REASONABLY GOOD AGREEMENT ON THE LARGE SCALE WITH THE PATTERN
DESCRIBED ABOVE. INITIAL TROUGHING WILL BE QUICKLY LIFTING OUT OF
THE NORTH-CENTRAL U.S. WHILE A PRIMARY UPPER LOW IS FORECAST JUST
OFFSHORE BRITISH COLUMBIA AND SUPPORTS TROUGHING ATOP THE EASTERN
PACIFIC AND NORTHWEST. IN THE EAST, MOST UPPER TROUGHING WILL BE
EXITING MIDWEEK BUT COULD LEAVE SOME ENERGY BEHIND AROUND THE GULF
COAST OR SO THAT WOULD MEANDER THROUGH MUCH OF THE WEEK SOUTH OF
THE AGREEABLE RIDGE AXIS. THE MOST UNCERTAIN PART OF THE FORECAST
IS HOW TROUGHING IN THE WEST EVOLVES. GFS RUNS FROM 00Z/06Z
MAINTAINED A CLOSED LOW FOR LONGER AS IT SLOWLY PUSHES INTO THE
NORTHWEST COMPARED TO THE FASTER/OPEN TROUGHING OF THE ECMWF, CMC,
AND MOST EC-BASED AI MODELS BY THURSDAY-FRIDAY. THE NEWER 12Z GFS
HAS JUMPED TO AN OPEN TROUGH, MORE LIKE CONSENSUS, WITH A POSSIBLE
SHORTWAVE FARTHER IN THE CENTRAL ROCKIES OR SO ON SATURDAY. THE
EVOLUTION ALSO DEPENDS ON ADDITIONAL UPSTREAM ENERGY DROPPING
THROUGH WESTERN CANADA. FOR THE MOST PART THE NEWER 12Z MODEL SUITE
SHOWS THIS ENERGY BEING STRONGER AS IT MOVES INTO THE NORTHWEST
NEXT WEEKEND, AND PUSHING THE FIRST SHORTWAVE EAST MORE QUICKLY.
WILL SEE IF THESE TRENDS CONTINUE.
THE WPC FORECAST USED A MULTI-MODEL BLEND OF DETERMINISTIC
GUIDANCE EARLY IN THE FORECAST PERIOD. AS THE PERIOD PROGRESSED,
INCREASED THE PROPORTION OF GEFS AND EC ENSEMBLE MEANS, REACHING
HALF MEANS FOR DAYS 6-7 AMID INCREASING SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
A WEAK ATMOSPHERIC RIVER IS FORECAST TO PUSH ACROSS THE PACIFIC
NORTHWEST INTO CALIFORNIA WEDNESDAY WITH A COLD FRONT AHEAD OF THE
UPPER TROUGH. RAIN TOTALS GENERALLY UNDER AN INCH OR TWO DO NOT
APPEAR TO CAUSE HAZARDOUS CONDITIONS IN THE COASTAL MOUNTAIN AREAS
THAT ARE ACCUSTOMED TO SEEING MULTIPLE INCHES OF RAIN. RAIN COULD
CONTINUE IN THE WEST COAST STATES THROUGH THURSDAY WITH ANOTHER
FRONT. ROUNDS OF PRECIPITATION WILL BE LIKELY ACROSS PARTS OF THE
INTERMOUNTAIN WEST/ROCKIES THROUGH MULTIPLE DAYS THIS WEEK, AND THE
HIGHER ELEVATIONS CAN EXPECT SNOW. MOISTURE LEVELS WILL BE ABOVE
NORMAL, BUT THE RAIN SEEMS UNLIKELY TO CAUSE FLOODING CONCERNS WITH
NOT MUCH INSTABILITY IN PLACE, LIMITING RAIN RATES. PRECIPITATION
CHANCES SHOULD INCREASE LATER WEEK INTO NEXT WEEKEND ACROSS THE
NORTH-CENTRAL U.S. ONCE THE FRONTAL SYSTEM EMERGES IN THE PLAINS.
AFTER IMELDA TRACKS EAST AWAY FROM THE SOUTHEAST U.S., SOME WEAK
ENERGY ALOFT IN THE SOUTHERN STREAM COULD STALL SOUTH OF THE
NORTHEASTWARD ORIENTED TROUGH, WHICH ALONG WITH A FRONTAL BOUNDARY
AND SUFFICIENT MOISTURE COULD LEAD TO SCATTERED SHOWERS AND STORMS
ACROSS FLORIDA AND FOR THE SOUTHEAST, ESPECIALLY ALONG THE GULF
COAST. THROUGH WEDNESDAY AND THURSDAY RAIN AMOUNTS AND RATES LOOK
TO STAY BELOW MARGINAL RISK ERO THRESHOLDS, BUT MOISTURE AND
INSTABILITY LOOK TO INCREASE BY NEXT WEEKEND. MEANWHILE MOST AREAS
UNDER THE UPPER TROUGH STAY DRY THROUGH THE LATTER HALF OF THE WEEK
INTO THE WEEKEND, INCLUDING THE SOUTHWEST/SOUTHERN PLAINS
EXTENDING INTO THE OHIO VALLEY AND THE NORTHEAST/MID-ATLANTIC.
WITH UPPER RIDGING BUILDING OVERHEAD, WARMER THAN SEASONAL AVERAGE
TEMPERATURES ARE EXPECTED ACROSS THE CENTRAL U.S., MOST ANOMALOUS
FOR THE NORTHERN PLAINS TO UPPER MIDWEST. HIGHS OF 10 TO 20 DEGREES
ABOVE NORMAL WILL BE COMMON IN THOSE AREAS THROUGH LATE WEEK, WITH
HIGHS OF 80F REACHING TO THE CANADIAN BORDER BY WEDNESDAY. 90S ARE
LIKELY TO CONTINUE FOR EARLY OCTOBER INTO THE DESERT SOUTHWEST AND
TEXAS. BY NEXT WEEKEND, WARMER THAN AVERAGE TEMPERATURES COULD
SHIFT A BIT EAST AND COVER THE GREAT LAKES REGION AND NORTHEAST.
MEANWHILE, BELOW NORMAL TEMPERATURES ESPECIALLY FOR HIGHS ARE
LIKELY ACROSS THE WEST DUE TO UPPER TROUGHING AND RAINY/CLOUDY
CONDITIONS.
TATE
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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