325
FXUS02 KWBC 240719
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
319 AM EDT WED SEP 24 2025
VALID 12Z SAT SEP 27 2025 - 12Z WED OCT 01 2025
...HEAVY RAIN THREAT CONTINUES ACROSS THE SOUTHWEST THROUGH THE
WEEKEND...
..OVERVIEW
AN UPPER TROUGH/LOW OVER THE SOUTHEAST WILL BE SLOW TO DISLODGE
THROUGH THE PERIOD DUE TO A LARGE BERMUDA HIGH ANCHORED OVER THE
ATLANTIC. NORTHERN STREAM SHORTWAVES FROM THE NORTHERN PLAINS TO
THE GREAT LAKES AND NORTHEAST WILL BE MUCH MORE PROGRESSIVE. AN
UPPER LOW OVER SOUTHERN CALIFORNIA WILL SHIFT SLOWLY THROUGH THE
SOUTHWEST U.S. THIS WEEKEND AND WEAKEN AS IT LIFTS TOWARDS THE HIGH
PLAINS. A RIDGE IN BETWEEN THESE TWO UPPER LOWS WILL STRENGTHEN
EARLY NEXT WEEK WITH AMPLIFIED TROUGHING DEVELOPING OVER THE WEST
COAST. HEAVY RAINFALL THREATS THIS WEEKEND WILL FOCUS MOSTLY OVER
THE SOUTHWEST AS WELL AS THE CAROLINAS/APPALACHIANS ALONG A
STATIONARY COASTAL FRONT. INCREASING AND MORE WIDESPREAD
PRECIPITATION WILL SPREAD INTO MUCH OF THE WEST NEXT WEEK WITH SNOW
POSSIBLE IN THE HIGHEST ELEVATIONS. A PAIR OF POSSIBLE TROPICAL
SYSTEMS MAY PASS BETWEEN THE EAST COAST AND BERMUDA WITH HIGH
UNCERTAINTY ON HOW THESE INTERACT OR HOW MUCH IMPACT MAY BE SEEN
FOR PARTS OF THE SOUTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT ON THE LARGE
SCALE SYNOPTIC SET UP THROUGH AT LEAST THE FIRST HALF OF THE
PERIOD, BUT STILL WITH SOME UNCERTAINTY IN THE DETAILS. THE BIGGEST
AND POTENTIALLY MOST IMPACTFUL AREA OF UNCERTAINTY REMAINS THE
SOUTHEAST AND WESTERN ATLANTIC AS A PAIR OF POTENTIAL TROPICAL LOW
ROUND THE WEST SIDE OF THE BERMUDA HIGH AND PASS SOMEWHERE BETWEEN
THE EAST COAST AND BERMUDA. THE SOUTHEAST UPPER TROUGH MAY TEND TO
STEER THE TROPICAL SYSTEM AWAY FROM THE COAST, BUT COMPLEX
INTERACTIONS BETWEEN THE SOUTHEAST TROUGH AND THE TROPICAL
SYSTEM(S) CANNOT BE RULED OUT LEADING TO A POSSIBLE MORE DIRECT
IMPACT TO AREAS ALONG THE COAST. REFER TO THE TROPICAL WEATHER
OUTLOOK FROM THE NATIONAL HURRICANE CENTER FOR THE LATEST ON THESE
SYSTEMS OF CONCERN.
OUT WEST, THE GUIDANCE SHOWS JUST SOME MINOR TIMING UNCERTAINTIES
WITH THE EXITING SOUTHWEST LOW. AMPLIFIED TROUGHING LOOKS TO
OVERTAKE THE WESTERN U.S. BY THE END OF THE PERIOD, BUT THERE ARE
QUESTIONS WITH INDIVIDUAL SHORTWAVES/ENERGY EMBEDDED WITHIN.
THE WPC FORECAST TONIGHT USED A BLEND OF THE DETERMINISTIC
GUIDANCE FOR THE FIRST HALF OF THE PERIOD, INCREASING TO 60 PERCENT
OF THE ENSEMBLE MEANS WITH 40 PERCENT COMBINED OF THE
ECMWF/GFS/CMC FOR THE LATTER HALF. THIS OVERALL MAINTAINS GOOD
CONTINUITY WITH THE PREVIOUS SHIFT.
..WEATHER/HAZARDS HIGHLIGHTS
A FRONTAL BOUNDARY LINGERING ALONG THE EAST COAST WILL SUPPORT
DAILY SHOWERS AND STORMS INTO NEXT WEEK. ANOMALOUS MOISTURE WITH A
POSSIBLE TROPICAL CONNECTION WILL MAINTAIN AT LEAST A LOCALIZED
HEAVY RAINFALL THREAT FOR PARTICULARLY THE CAROLINAS AND
SOUTHERN/CENTRAL APPALACHIANS. MARGINAL RISK AREAS ARE HIGHLIGHTED
ON THE DAYS 4 AND 5 (SATURDAY AND SUNDAY) EXCESSIVE RAINFALL
OUTLOOKS FOR THIS REGION. THE THREAT MAY CONTINUE INTO NEXT WEEK
WITH POTENTIAL FOR ADDITIONAL MOISTURE ASSOCIATED WITH POSSIBLE
TROPICAL SYSTEMS TO MONITOR.
MEANWHILE, PACIFIC MOISTURE AHEAD OF AN UPPER LOW OVER SOUTHERN
CALIFORNIA WILL RESULT IN INCREASING RAINFALL CHANCES CONTINUING
THIS WEEKEND 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 REGION REMAINS
HIGHLIGHTED WITH A MARGINAL RISK FOR BOTH FRIDAY AND SATURDAY EROS
WITH A MORE TARGETED SLIGHT RISK ON DAY 4 ACROSS SOUTHEAST ARIZONA
TO SOUTHWEST NEW MEXICO AND ON DAY 5 ACROSS CENTRAL NEW MEXICO
WHERE QPF AMOUNTS LOOK GREATEST. THE ACTIVITY WILL SHIFT SLOWLY
EASTWARD WITH TIME AND SHOULD BEGIN TO TAPER OFF BY MONDAY.
PRECIPITATION WILL INCREASE BY NEXT WEEK ACROSS THE NORTHWEST U.S.
ASSOCIATED WITH AMPLIFIED TROUGHING OVER THE REGION. WIDESPREAD
RAIN IS EXPECTED ACROSS THE PACIFIC NORTHWEST AND INTO THE NORTHERN
GREAT BASIN/ROCKIES. THE HEAVIEST PRECIPITATION IS EXPECTED FROM
WESTERN WASHINGTON TO NORTHERN CALIFORNIA AND THE SIERRA NEVADA.
SOME SNOW MAY FALL IN THE HIGHEST ELEVATIONS OF THE WEST.
WARMER THAN AVERAGE TEMPERATURES WILL SLOWLY SHIFT FROM THE
NORTHWEST THIS WEEKEND INTO THE NORTHERN PLAINS WITH A GRADUAL
SOUTHERN SHIFT INTO THE CENTRAL PLAINS AS UPPER RIDGING BUILDS OVER
THE REGION NEXT WEEK. DAYTIME HIGHS COULD BE 10-15 DEGREES ABOVE
NORMAL FOR SOME LOCATIONS. BELOW NORMAL TEMPERATURES OVER THE
SOUTHWEST WILL EXPAND ALONG MUCH OF THE WEST COAST BY NEXT WEEK.
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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