871
FXUS02 KWBC 260711
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
211 AM EST FRI DEC 26 2025
VALID 12Z MON DEC 29 2025 - 12Z FRI JAN 02 2026
..OVERVIEW
A BROAD UPPER RIDGE/TROUGH PATTERN ACROSS THE LOWER 48 TO START
THE WEEK NEXT WEEK WILL TRANSITION TO A MORE TYPICAL WAVELENGTH
TROUGH/RIDGE/TROUGH PATTERN. WITH THE PACIFIC LARGELY BLOCKED FROM
INCOMING MOISTURE, MOST OF THE CONUS WILL BE DRY EXCEPT FOR
DOWNWIND OF THE GREAT LAKES DUE TO LAKE-EFFECT SNOW. BY THE END OF
THE PERIOD, THE STRONG UPPER RIDGING INITIALLY OVER THE WEST COAST
WILL BREAK DOWN AND ALLOW BOTH NORTHERN STREAM AND SUBTROPICAL
TROUGHING TO PUSH INLAND, BRINGING ANOTHER ROUND OF RAIN AND
MOUNTAIN SNOW TO MUCH OF THE WEST BY THE END OF NEXT WEEK (BUT WITH
MUCH LESS INTENSITY THAN THE CURRENT EVENT).
..GUIDANCE/PREDICTABILITY ASSESSMENT
OVERALL, THE ENSEMBLE SYSTEMS AGREED ON THE SYNOPTIC EVOLUTION BUT
DID DIFFER ON THE EXTENT OF LOWER HEIGHTS AROUND THE GREAT LAKES
BY LATER NEXT WEEK. THE GEFS WAS HIGHER WITH HEIGHTS THAN THE ECMWF
EPS, CANADIAN GEPS, AND AI-GEFS, AND WAS DISCOUNTED. DESPITE THE
GOOD AGREEMENT AT 500MB, THERE WAS A LARGE DISAGREEMENT ON
TEMPERATURES JUST EAST OF THE DIVIDE BY LATER NEXT WEEK AS HIGH
PRESSURE SLIPS SOUTH-SOUTHEASTWARD THROUGH WESTERN CANADA,
REINFORCING A STATIONARY BOUNDARY JUST EAST OF THE ROCKIES. FOR THE
DETERMINISTIC MODELS, EACH WAS WITHIN THE ACCEPTABLE NOISE OF THE
ENSEMBLE SPREAD AND A BLEND OF THE 18Z GFS AND 12Z ECMWF/CANADIAN
OFFERED A REASONABLE STARTING POINT FOR THE DAY 3-5 PERIOD.
THEREAFTER, USED AN INCREASED AMOUNT OF THE ECMWF ENSEMBLE MEAN TO
DISCOUNT THE MORE ROBUST SOLUTIONS (E.G., GFS IN THE GREAT
LAKES/NORTHEAST) NOTING THAT ANY EMBEDDED SYSTEM AROUND THE LARGE
MULTI-PRONGED UPPER LOW OVER HUDSON BAY HAS THE POTENTIAL TO
BRIEFLY AMPLIFY AS IT ROUNDS THE BASE OF THE TROUGH THROUGH THE
GREAT LAKES.
..WEATHER/HAZARDS HIGHLIGHTS
A VIGOROUS SYSTEM WILL LEAD OFF THE PERIOD ON MONDAY THROUGH THE
GREAT LAKES AS IT RAPIDLY DEEPENS INTO SOUTHEASTERN ONTARIO/WESTERN
QUEBEC. THIS WILL BRING A WINTRY MIX OF SNOW/SLEET/FREEZING RAIN
TO THE NORTHEAST AS WARM AIR OVERRIDES THE COLD SURFACE AND LAKE
ENHANCED/EFFECT SNOW OVER THE GREAT LAKES AS THE LOW PROMOTES
NORTHERLY TO NORTHWESTERLY FLOW. THE PATTERN WILL TURN QUIET
MIDWEEK WITH HIGH PRESSURE IN CONTROL BUT CONTINUED CHANCE OF LAKE
EFFECT SNOW THAT WILL BE ENHANCED BY QUICK CLIPPER SYSTEMS AND/OR
MID-LEVEL TROUGHS. BY THU/FRI, THE WEST WILL SEE AN INCREASE IN
PRECIPITATION AS A FRONT FROM THE PACIFIC COMES INTO THE PACNW AND
A WEAKENING OCCLUDED SYSTEM OUT OF THE SUBTROPICAL PACIFIC MOVES
INTO CALIFORNIA AND THE SOUTHWEST. THE MOISTURE ANOMALIES WILL
INCREASE, ACTUAL RAINFALL AMOUNTS APPEAR TO BE MODEST AT THIS TIME.
HOWEVER, GIVEN THE RECENT VERY HEAVY RAINFALL OVER MUCH OF
CALIFORNIA, THIS SYSTEM BEARS WATCHING.
TEMPERATURES WILL BE SOMEWHAT VARIABLE OVER THE LOWER 48, BUT
GENERALLY COLDER THAN NORMAL AROUND THE GREAT LAKES INTO THE
NORTHEAST DUE TO THE PERSISTENT TROUGHING AND MILDER THAN NORMAL
OVER THE INTERIOR WEST/ROCKIES. WIDESPREAD RECORD COLD OR WARM
TEMPERATURES ARE NOT EXPECTED.
FRACASSO
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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