058
FXUS02 KWBC 290742
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 AM EDT MON SEP 29 2025
VALID 12Z THU OCT 02 2025 - 12Z MON OCT 06 2025
..OVERVIEW
CONSENSUS STEERS IMELDA EAST AWAY FROM THE U.S. BY MIDWEEK WHICH
GREATLY REDUCES/NEGATES ASSOCIATED IMPACTS FOR THE MEDIUM RANGE
PERIOD. MUCH OF THE CONUS WILL BE IN A RELATIVELY SLOW-MOVING AND
BLOCKY PATTERN. THIS WILL LEAD TO MEAN TROUGHING IN THE WEST WITH
MULTIPLE FRONTAL PASSAGES WITH COOLER TEMPERATURES AND ROUNDS OF
PRECIPITATION. MEANWHILE, AN UPPER RIDGE WILL STRETCH FROM THE
DESERT SOUTHWEST 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 EXTENDED PERIOD BEGINS WITH A REASONABLY WELL CLUSTERED
PATTERN. RIDGING WILL BE IN PLACE FROM MUCH OF THE EASTERN
THIRD/HALF OF THE CONUS ONCE THE UPPER TROUGHING COMPLETELY LIFT
OUT OF THE NORTHEAST; HOWEVER THERE MAY BE LINGERING ENERGY FOR THE
GULF REGION TO THE SOUTH OF THE RIDGE AXIS. FURTHER WEST, A
PRIMARY UPPER LOW NEAR BRITISH COLUMBIA IS EXPECTED TO USHER IN
TROUGHING TO THE NORTHWEST/INTERMOUNTAIN WEST. INDIVIDUAL MODEL
VARIANCES IN REGARDS TO THIS FEATURE HAS SOMEWHAT LOWERED FORECAST
CONFIDENCES FOR TIMING OF QPF AND AMOUNTS AS MULTIPLE IMPULSES
EJECT FROM THE LOW.
THE GFS HAS JOINED THE REST OF THE GUIDANCE BY TRACKING AN OPEN
TROUGH THROUGH THE WEST BY THE END OF THE WEEK AN ALSO NOTING THAT
THE ECMWF REMAINS PERSISTENT IN BEING THE MORE PROGRESSIVE/FURTHER
EAST SOLUTION WITHIN THE CLUSTER. THE EVOLUTION WILL ALSO DEPEND
ON ADDITIONAL UPSTREAM ENERGY DROPPING THROUGH WESTERN CANADA.
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. THIS APPROACH
PROVIDED CONSISTENCY AND SMOOTHING OUT THE 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.
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. RAIN ACCUMULATIONS AND HOURLY RATES SEEM TO BE
BELOW THE THRESHOLD FOR EXCESSIVE RAINFALL, 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.
WARMER THAN SEASONAL AVERAGE TEMPERATURES ARE EXPECTED FOR A VAST
MAJORITY OF THE CENTRAL U.S., MOST ANOMALOUS FOR THE NORTHERN
PLAINS TO UPPER MIDWEST. WITH THE BUILDING RIDGE, DAILY MAXIMUMS
WILL AVERAGE 10 TO 20 DEGREES ABOVE NORMAL THROUGH LATE WEEK. 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.
CAMPBELL/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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