722
FXUS02 KWBC 181907
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
307 PM EDT SAT OCT 18 2025
VALID 12Z TUE OCT 21 2025 - 12Z SAT OCT 25 2025
..GENERAL OVERVIEW
A WELL DEVELOPED CLOSED LOW OVER THE GREAT LAKES ON TUESDAY WILL
SUSTAIN AN OCCLUDED SURFACE LOW WITH A COLD FRONT THAT WILL CROSS
THE EASTERN U.S. AND EXIT THE COAST BY LATE WEDNESDAY, WITH A
RETURN TO COOLER CONDITIONS TO CLOSE OUT THE WEEK AS CANADIAN HIGH
PRESSURE SETTLES INTO THE REGION. MEANWHILE, A CLOSED UPPER LOW
INITIALLY OFF THE COAST OF CALIFORNIA MOVES INLAND ACROSS THE
SOUTHERN ROCKIES AND EVOLVES INTO AN UPPER TROUGH IN THE SOUTHERN
STREAM TO SUPPORT A SURFACE LOW OVER THE PLAINS WITH RAINFALL,
POSSIBLY HEAVY, SPREADING ACROSS THE SOUTH-CENTRAL U.S. A STRONGER
STORM SYSTEM IS LIKELY TO APPROACH THE PACIFIC NORTHWEST THURSDAY
INTO FRIDAY WITH A POTENTIAL ATMOSPHERIC RIVER AHEAD OF A STRONG
COLD FRONT, BRINGING WIDESPREAD RAIN AND MOUNTAIN SNOW.
..GUIDANCE/PREDICTABILITY ASSESSMENT
UPDATED GUIDANCE CONTINUES TO SHOW A QUASI-ZONAL AND PROGRESSIVE
PATTERN HEADING INTO EARLY NEXT WEEK. THE 00Z ECMWF/CMC/UKMET AND
00/06Z GFS ARE GENERALLY AGREEABLE ON THE BROADER DETAILS, WITH AN
INITIAL UPPER-TROUGH LIFTING NORTH OVER THE NORTHEAST FOLLOWED
QUICKLY BY A SECOND UPPER-TROUGH AND DEVELOPING CLOSED LOW SETTLING
IN OVER THE GREAT LAKES REGION. GUIDANCE IS ALSO AGREEABLE THAT
THE PATTERN WILL BEGIN TO AMPLIFY MID- TO LATE NEXT WEEK AS THIS
DEVELOPING CLOSED LOW EXPANDS OVER THE EASTERN U.S. AND AN UPPER-
RIDGE BUILDS NORTH OVER THE WESTERN TO CENTRAL NORTHERN TIER OF THE
COUNTRY. GUIDANCE HAS ALSO COME INTO BETTER AGREEMENT ON THE
PRESENCE AND TIMING OF A SOUTHERN STREAM UPPER-LOW JUST OFF THE
PACIFIC COAST MOVING EAST OVER THE SOUTHWEST TO SOUTH-CENTRAL U.S.
UNDER THE UPPER-RIDGE MID- TO LATE NEXT WEEK. GUIDANCE BEGINS TO
DIVERGE A BIT WITH AN ENERGETIC UPPER-TROUGH UPSTREAM OF THE
AMPLIFYING RIDGE OVER THE NORTHEASTERN PACIFIC AND THE TIMING OF
INIVIDIAL ASSOCIATED SHORTWAVES/SURFACE SYSTEMS. HOWEVER, ALL
GUIDANCE AT LEAST AGREES IN ONE PARTICULARLY DEEP SURFACE LOW AND
ASSOCIATED ATMOSPHERIC RIVER IMPACTING THE PACIFIC NORTHWEST/CALIFORNIA
LATE NEXT WEEK AND INTO THE WEEKEND. DIFFERENCES ARE LIMITED TO
TIMING/ORIENTATION ON THE GREATEST MOISTURE AND ASSOCIATED
PRECIPITATION. THE CMC IS NOTABLY MORE AGGRESSIVE IN BRINGING
ADDITIONAL UPSTREAM UPPER-ENERGY AND AN ASSOCIATED VERY STRONG
SURFACE LOW OVER THE PACIFIC TOWARDS THE PACIFIC NORTHWEST NEXT
WEEKEND, WHILE THIS FEATURE IS COMPARITIVELY MUCH WEAKER IN THE
OTHER GUIDANCE. THE UPDATED WPC FORECAST USED A COMPOSITE BLEND OF
THE ECMWF/CMC/UKMET/GFS FOR THE FIRST PART OF THE PERIOD GIVEN GOOD
OVERALL AGREEMENT. THE CMC WAS REMOVED MID-PERIOD AND REPLACED
WITH THE ECENS AND GEFS, INCREASING TO 40% OF THE BLEND BY THE END
OF THE PERIOD, AS THE CMC DIVERGED FROM THE OTHER SOLUTIONS AND
TYPICAL LONGER-RANGE DIFFERENCES BEGAN TO GROW WITIN THE
DETERMINSTIC GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
THE CLOSED LOW OVER THE GREAT LAKES ON TUESDAY IS LIKELY TO RESULT
IN MODEST AMOUNTS OF RAINFALL, BUT NOTHING HEAVY ENOUGH TO WARRANT
ANY RISK AREAS IN THE EXCESSIVE RAINFALL OUTLOOK. THE PROGRESSIVE
PATTERN WITH CONSISTENT POST-FRONTAL NORTHWESTERLY FLOW OVER THE
WARMER GREAT LAKES WILL ALSO BRING THE LIKELIHOOD OF LAKE EFFECT
SHOWERS THROUGH MUCH OF NEXT WEEK.
THE WEATHER PATTERN GETS MORE ACTIVE ACROSS THE WEST COAST REGION
GOING INTO THE THURSDAY-FRIDAY TIME PERIOD, AS AN AMPLIFYING
TROUGH AND STRONG COLD FRONT ADVECTS COPIOUS PACIFIC MOISTURE
TOWARDS THE COAST. THIS WILL INITIALLY AFFECT THE WESTERN PORTIONS
OF WASHINGTON AND OREGON THURSDAY NIGHT, AND THEN NORTHERN
CALIFORNIA GOING INTO FRIDAY, WITH A FEW INCHES OF RAINFALL
POSSIBLE FOR THE COASTAL MOUNTAIN RANGES WITH A POTENTIAL
ATMOSPHERIC RIVER AFFECTING THE REGION. SHOWERS AND STORMS ALSO
INCREASE IN COVERAGE ACROSS THE SOUTH-CENTRAL U.S. BY LATE WEEK AS
WELL IN ASSOCIATION WITH THE SURFACE LOW THAT DEVELOPS. GUIDANCE
HAS CONTINUED TO SHOW A SIGNAL THAT SOME LOCALLY HEAVY RAINFALL MAY
BE POSSIBLE FROM THE SOUTHERN PLAINS TO THE LOWER MISSISSIPPI
VALLEY.
HIGH TEMPERATURES ACROSS THE SOUTH-CENTRAL U.S. ARE FORECAST TO
REMAIN ABOVE AVERAGE FOR NEXT WEEK, ESPECIALLY FOR TEXAS WHERE
HIGHS INTO THE 90S MAY TIE/BREAK A FEW DAILY HIGH TEMPERATURE
RECORDS. THERE MAY BE SOME PERIODS OF BELOW AVERAGE TEMPERATURES
FOR THE MIDWEST/NORTHEAST FOLLOWING COLD FRONTAL PASSAGES, THOUGH
HIGHS IN GENERAL LOOK TO REMAIN NEAR FALL AVERAGES THROUGH MUCH OF
NEXT WEEK. THE NORTHERN-TIER FROM THE ROCKIES EAST TO THE
PLAINS/UPPER MIDWEST WILL SEE INCREASINGLY ABOVE AVERAGE HIGHS LATE
NEXT WEEK AND INTO THE WEEKEND AS AN UPPER-RIDGE BUILDS OVERHEAD.
THE PACIFIC SYSTEM WILL BRING COOLER, WELL BELOW AVERAGE
TEMPERATURES TO PORTIONS OF THE WEST COAST BY EARLY NEXT WEEKEND.
PUTNAM/HAMRICK
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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