059
FXUS02 KWBC 151958
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
358 PM EDT WED OCT 15 2025
VALID 12Z SAT OCT 18 2025 - 12Z WED OCT 22 2025
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE DEPICTION OF THE LARGE SCALE PATTERN BY THE LATEST MODEL
GUIDANCE REMAINS REASONABLY GOOD TO START OFF THE MEDIUM RANGE
PERIOD, BUT UNCERTAINTY INCREASES QUITE A BIT FOR DAY 5 AND BEYOND.
GIVEN ONLY MINOR DIFFERENCES OF THE STRENGTH AND TIMING OF AN
EASTERN U.S. RIDGE, CENTRAL U.S. TROUGH AND WESTERN U.S. RIDGE, A
COMPOSITE BLEND OF THE 00Z EC, 00Z UKMET, 00Z CMC AND 06Z GFS WERE
UTILIZED FOR THE DAY 3 AND DAY 4 FORECAST. BY DAY 5, THE TROUGH
PROGGED TO PUSH FROM THE PACIFIC ACROSS THE PACIFIC NORTHWEST IS
TRENDING TO BE MUCH MORE PROGRESSIVE COMPARED TO YESTERDAY'S
PACKAGE. IN FACT, MOST OF YESTERDAY'S GUIDANCE ASIDE FROM THE CMC
WAS ON BOARD WITH A MUCH SLOWER AND MORE AMPLIFIED SOLUTION, WITH A
DEEPENING TROUGH DIGGING SOUTHWARD ALONG THE WEST COAST. INSTEAD,
THE MORE PROGRESSIVE SOLUTION IS NOW LOOKING MORE LIKELY, WITH ALL
GUIDANCE INCLUDING THE LATEST MACHINE LEARNING GUIDANCE ALL
DEPICTING THIS EVOLUTION FAIRLY SIMILARLY. THE LATEST 00Z AND 06Z
RUNS OF THE GFS WERE SLOW TO CATCH ON (AND THUS WERE NOT USED IN
THE COMPOSITE BLEND FOR DAYS 5-7) BUT THE MOST RECENT 12Z RUN HAS
JOINED CONSENSUS AS WELL. GIVEN THE STRENGTH AND AMPLITUDE OF THE
EASTERN U.S. RIDGE AT THE BEGINNING OF THE PERIOD, THE FASTER AND
MORE PROGRESSIVE FLOW UPSTREAM IS LEADING TO A SHARPER AND MORE
NEGATIVELY TILTED TROUGH PUSHING FROM THE CENTRAL U.S. INTO THE
EASTERN U.S. THIS WEEKEND INTO EARLY NEXT WEEK. AS A RESULT, A
STRONGER AND MORE CONSOLIDATED SURFACE LOW IS LOOKING MORE LIKELY
TO TRACK ACROSS THE GREAT LAKES, WITH IMPLICATIONS TO QPF AND
HAZARDS. MORE ON THAT BELOW. GIVEN THE ABOVE, THE DAYS 5-7 FORECAST
CONSISTED OF A BLEND THAT INCREASINGLY RELIED ON THE ENSEMBLE MEANS
OF THE EPS, CMCE, AND GEFS, WHICH PROVIDED MORE STABILITY AND LESS
NOISE FROM INDIVIDUAL DETERMINISTIC GUIDANCE SOURCES.
..WEATHER/HAZARDS HIGHLIGHTS
A SHARPENING UPPER TROUGH/SHORTWAVE AND STRENGTHENING SURFACE LOW
PRESSURE PUSHING ACROSS THE GREAT LAKES REGION THIS WEEKEND WILL
DRAW ANOMALOUS MOISTURE AND INSTABILITY NORTHWARD IN ADVANCE OF A
COLD FRONT. PW ANOMALIES OF >200% OF NORMAL COMBINED WITH
INSTABILITY OF 500-1500 J/KG WILL SUPPORT AN AXIS OF HEAVIER
RAINFALL ACROSS PARTS OF THE UPPER MIDWEST, OHIO VALLEY AND MID-
SOUTH ON SATURDAY. AS A RESULT, THE DAY 4/SATURDAY EXCESSIVE
RAINFALL OUTLOOK (ERO) EXPANDED THE MARGINAL RISK NORTHWARD TO
INCLUDE SOUTHEAST WISCONSIN AND SOUTHWEST MICHIGAN. THE RECENTLY
INTRODUCED SLIGHT RISK AREA CENTERED OVER THE MID-SOUTH WAS
MAINTAINED GIVEN THE OVERLAP WITH THE GREATEST INSTABILITY AND
RELATIVELY LOWER FFG. SPC ALSO SHOWS A THREAT FOR SEVERE WEATHER IN
THIS PATTERN. THE SLOWLY PROGRESSIVE NATURE OF THE UPPER-LEVEL AND
SURFACE FEATURES WILL THEN SPREAD ORGANIZED RAINFALL EASTWARD INTO
THE EAST/NORTHEAST SUNDAY INTO EARLY NEXT WEEK. THIS WILL
ESPECIALLY BE THE CASE NEAR AND ALONG THE TRACK OF A
DEEPENING/CONSOLIDATING COASTAL LOW PRESSURE SYSTEM (AND MORE
MODESTLY INTO THE SOUTHEAST AHEAD OF THE COLD FRONT). A DAY
5/SUNDAY ERO MARGINAL RISK AREA WAS MAINTAINED AND BROADENED TO
CAPTURE LOCAL RUNOFF POTENTIAL INTO THE APPALACHIANS AND PARTS OF
THE OHIO VALLEY.
OUT WEST, THE NOW MORE PROGRESSIVE TROUGH AND SURFACE LOW WILL
QUICKLY APPROACH AND PUSH ACROSS THE PACIFIC NORTHWEST AND NORTHERN
ROCKIES OVER THE WEEKEND TO PRODUCE A PERIOD OF MODERATELY HEAVY
COASTAL AND VALLEY RAINS ALONG WITH HIGHER MOUNTAIN SNOW. THE DAY
4/SATURDAY ERO MAINTAINS A COASTAL WASHINGTON MARGINAL RISK AREA
GIVEN A FAVORABLE QPF SIGNAL WHILE OUR DAY 4-7 WINTER WEATHER
OUTLOOK SHOWS MOUNTAIN SNOW POTENTIAL INLAND FROM THE NORTHWEST TO
THE NORTHERN ROCKIES SUNDAY INTO MONDAY.
MILLER/SCHICHTEL
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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