786
FXUS02 KWBC 232000
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
400 PM EDT TUE SEP 23 2025
VALID 12Z FRI SEP 26 2025 - 12Z TUE SEP 30 2025
...HEAVY RAIN THREAT FOR PORTIONS OF THE MID-ATLANTIC TO THE
SOUTHEAST BEGINNING ON FRIDAY, WITH HEAVY RAINS LIKELY ACROSS THE
SOUTHWEST THROUGH THE WEEKEND...
..OVERVIEW
AN UPPER-LEVEL PATTERN THAT FEATURES EASTWARD PROGRESSIVE WAVES
ACROSS CANADA WILL BE CONTRASTED WITH A SLOW-TO-EVOLVE OMEGA BLOCK
ACROSS MAINLAND U.S. THROUGH THE MEDIUM-RANGE PERIOD. AS A LARGE
BERMUDA HIGH REMAINS ANCHORED OVER THE ATLANTIC, THE PROGRESSION OF
TROUGHING NEAR BOTH THE WEST AND EAST COASTS WILL BE FURTHER
OBSTRUCTED. MEANWHILE, OCCASIONAL INJECTIONS OF ENERGY COMING FROM
THE PROGRESSIVE HIGHER LATITUDE TROUGHS IN CONJUNCTION WITH TWO
TROPICAL DISTURBANCES/LOWS APPROACHING FROM THE BAHAMAS AND WESTERN
ATLANTIC COULD DETACH THE UPPER LOW OVER THE SOUTHEAST WITH HIGHLY
UNCERTAIN POTENTIAL INTERACTIONS OF THE TWO TROPICAL LOWS OFF THE
COAST OF THE SOUTHEAST U.S. LATE IN THE PERIOD.
THE CLOSED LOW OVER THE SOUTHWEST IS FORECAST TO EVENTUALLY OPEN UP
AND LIFT TOWARD THE NORTHERN/CENTRAL PLAINS EARLY NEXT WEEK AS A
LONGWAVE TROUGH IS FORECAST TO EDGE TOWARD THE WEST COAST FROM THE
PACIFIC LATE IN THE PERIOD.
THE ASSOCIATED COLD FRONT WILL FOCUS WIDESPREAD RAINS
FROM THE GULF COAST/SOUTHEAST IN PARTS OF THE MID- ATLANTIC THROUGH
AT LEAST FRIDAY. MEANWHILE, PACIFIC MOISTURE AHEAD OF ANOTHER
CUTOFF LOW NEAR THE CALIFORNIA COAST COULD LEAD TO DAILY RAIN
CHANCES OVER PARTS OF CALIFORNIA INTO MUCH OF THE SOUTHWEST AS IT
DRIFTS SOUTHEASTWARD. AN UPPER LEVEL RIDGE IN BETWEEN THESE TWO
SYSTEMS WILL ALLOW FOR ABOVE NORMAL TEMPERATURES MUCH OF THE PERIOD
FROM THE INTERIOR WEST TO THE NORTHERN PLAINS AND THE NORTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT ON THE
AFOREMENTIONED SYNOPTIC SET UP THROUGH MUCH OF THE PERIOD, WITH
MUCH OF THE UNCERTAINTY CENTERED OVER THE SOUTHEAST U.S. INTO THE
WESTERN ATLANTIC. PERSISTENT UPPER TROUGHING NEAR THE EAST COAST
AND INTO THE SOUTHEAST WILL TEND TO MAINTAIN A FRONTAL BOUNDARY
NEAR OR JUST OFF THE COAST THROUGH THE PERIOD. A PAIR OF POTENTIAL
TROPICAL LOWS ROUNDING THE WEST SIDE OF THE BEMUDA HIGH WILL ADD
CONSIDERABLE UNCERTAINTY TO THE FORECASTS FOR THE SOUTHEAST FOR
EARLY NEXT WEEK. THE UPPER TROUGH MAY TEND TO STEER THE TROPICAL
SYSTEM JUST OFFSHORE ALTHOUGH COMPLEX INTERACTION BETWEEN THE UPPER
TROUGH AND THE TROPICAL SYSTEMS CANNOT BE RULED OUT.
OUT WEST, THERE HAS NOT BEEN TOO MUCH OF A CHANGE FROM THE
PREVIOUS FORECAST CYCLE APART FROM SOME EXPECTED FLUCTUATIONS IN
THE PLACEMENT OF THE QPF FOOTPRINT ACROSS THE SOUTHWEST, WITH
FOCUS SLIDING EAST INTO NEW MEXICO FROM SUNDAY INTO MONDAY.
THE WPC FORECAST PACKAGE TODAY WAS BASED THE CONSENSUS OF THE
DETERMINISTIC AND ENSEMBLE MEANS OF 40% FROM THE 06Z GFS/GEFS, 40%
FROM THE 00Z ECMWF/EC MEAN, AND 20% FROM THE 00Z CMC/CMC MEAN.
OVERALL, MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS SHIFT'S
FORECASTS.
..WEATHER/HAZARDS HIGHLIGHTS
WIDESPREAD RAIN AND CONVECTION WILL FOCUS ALONG AND AHEAD OF A
COLD FRONT AS IT SLOWLY MOVES INTO THE EAST LATER THIS WEEK.
ANOMALOUS MOISTURE AND AMPLE INSTABILITY WILL BE IN PLACE,
A BROAD MARGINAL RISK ON THE DAYS 4/FRIDAY ERO STRETCHING FROM THE
GULF COAST TO THE MID-ATLANTIC IS MAINTAINED. DRY ANTECEDENT
CONDITIONS MAY LIMIT THE OVERALL FLOOD THREAT, BUT FUTURE UPGRADES
REMAIN POSSIBLE WITHIN THE BROADER MARGINAL RISKS, AND WILL BE
REEVALUATED SHOULD THE GUIDANCE SHOW BETTER CONSENSUS. RAINFALL MAY
LINGER ACROSS PARTS OF THE EAST INTO THE WEEKEND, AND A MARGINAL
RISK WAS INCLUDED ON THE DAY 5/SATURDAY ERO FROM EASTERN GEORGIA TO
SOUTHEAST VIRGINIA. A HEAVY RAIN AREA IS EXPECTED ACROSS VIRGINIA
INTO NORTH CAROLINAS ON THE HAZARDS MAP.
MEANWHILE, PACIFIC MOISTURE AHEAD OF AN UPPER LOW NEAR CALIFORNIA
WILL RESULT IN INCREASING RAINFALL CHANCES ACROSS MUCH OF THE
SOUTHWEST INTO CALIFORNIA. MOISTURE ANOMALIES 2 TO 3 STANDARD
DEVIATIONS ABOVE NORMAL AND SUFFICIENT INSTABILITY WILL RESULT IN
AT LEAST A LOCALIZED FLASH FLOOD THREAT, PARTICULARLY FOR
VULNERABLE BURN SCAR AREAS. THIS ENTIRE REGION IS HIGHLIGHTED WITH
A MARGINAL RISK FOR BOTH FRIDAY AND SATURDAY EROS WITH A MORE
TARGETED SLIGHT RISK ON BOTH DAYS ACROSS SOUTHEAST ARIZONA TO
SOUTHWEST NEW MEXICO WHERE QPF AMOUNTS LOOK GREATEST. THIS ACTIVITY
WILL CONTINUE INTO AT LEAST SUNDAY AS THE UPPER LOW DROPS SLOWLY
SOUTH AND EASTWARD THROUGH THE REGION AND MAY BEGIN TO TAPER OFF BY
MONDAY.
A RIDGE AXIS WILL BUILD FROM THE FOUR CORNERS STATES INTO THE WEST
WITH THE MOST ANOMALOUSLY WARM TEMPERATURES EXPECTED FROM THE
NORTHWEST INTO THE NORTHERN ROCKIES AND PLAINS WHICH MAY HOLD MUCH
OF THE PERIOD WITH ONLY A GRADUAL EASTWARD SHIFT. TEMPERATURES
ACROSS THE SOUTHWEST WILL BE BELOW NORMAL UNDERNEATH THE LINGERING
UPPER LOW, WITH NEAR NORMAL TEMPERATURES ELSEWHERE ACROSS THE
CONUS.
KONG/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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