174
FXUS02 KWBC 180742
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 AM 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. 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
THE 00Z MODEL GUIDANCE SUITE FEATURES GOOD OVERALL SYNOPTIC SCALE
AGREEMENT ACROSS THE CONTINENTAL U.S. THROUGH THE MIDDLE OF THE
WEEK. HOWEVER, AT THE TIME OF FRONTS/PRESSURES PREPARATION, THE 12Z
CANADIAN MODEL WAS AN OUTLIER SOLUTION BEGINNING AS EARLY AS
TUESDAY NIGHT ACROSS THE ROCKIES AND NORTHERN PLAINS, WITH A BROAD
UPPER TROUGH THAT WAS OUT OF PHASE WITH THE MODEL CONSENSUS AND THE
AIFS GUIDANCE, SO THE 12Z CMC WAS NOT USED AS PART OF THE FORECAST
BLEND. THE LATEST 00Z CMC RUN DID TREND FAVORABLY WITH THE OTHER
GUIDANCE AND ENSEMBLE MEANS, AND IT WOULD BE MUCH PREFERRED OVER
THE PREVIOUS 12Z RUN. THE PAST TWO RUNS OF THE UKMET HAVE BEEN
FASTER WITH LIFTING OUT THE CLOSED UPPER LOW NEAR THE NORTHEAST
U.S., BUT STILL WITHIN THE REALM OF POSSIBILITY.
LOOKING AHEAD TO THE END OF THE FORECAST PERIOD NEXT SATURDAY, THE
GFS IS QUICKER TO BRING THE WEST COAST UPPER TROUGH INLAND COMPARED
TO THE GEFS MEAN AND ECMWF/CMC SOLUTIONS. THIS ALSO HOLDS TRUE FOR
THE TROUGH ACROSS THE MID-SOUTH. THEREFORE, THE GFS WAS WEIGHTED A
LITTLE LESS THAN THE ECMWF BY THIS TIME, WITH THE ENSEMBLE MEANS
ACCOUNTING FOR ABOUT HALF OF THE PREFERENCE.
..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 CENTRAL PLAINS BY LATE WEEK AS WELL
IN ASSOCIATION WITH THE SURFACE LOW THAT DEVELOPS.
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. HIGHS ACROSS THE NORTHERN-TIER FROM THE ROCKIES EAST TO
THE PLAINS WILL INITIALLY BE BELOW AVERAGE BEFORE AN AMPLIFYING
UPPER RIDGE BRINGS A RETURN TO ABOVE AVERAGE READINGS BY LATE NEXT
WEEK.
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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