856
FXUS02 KWBC 161917
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
317 PM EDT TUE SEP 16 2025
VALID 12Z FRI SEP 19 2025 - 12Z TUE SEP 23 2025
..OVERVIEW
THE UPPER AIR PATTERN FRIDAY INTO THIS WEEKEND FEATURES A DEEP LOW
CENTERED OVER THE LABRADOR SEA WITH A TROUGH THAT DESCENDS OVER
THE NORTHEAST, FILLING/WEAKENING LOW PRESSURE TRACKING FROM THE
NORTHERN PLAINS TO THE UPPER MIDWEST, A TROUGH ALONG THE CALIFORNIA
COAST THAT WEAKENS/SHEDS A LOW OFFSHORE, WITH RIDGING IN BETWEEN
OVER THE MOUNTAIN WEST AND MIDWEST. POTENT TROUGHING IS THEN
FORECAST TO ENTER THE PACIFIC NORTHWEST SATURDAY NIGHT AND REACH
THE MIDWEST OR GREAT LAKES BY TUESDAY. WETTER THAN NORMAL
CONDITIONS CAN BE EXPECTED FRIDAY OVER THE GREAT PLAINS STATES,
SOUTH FLORIDA, AND CALIFORNIA INTO THE DESERT SOUTHWEST, AND THE
UPPER MIDWEST THIS WEEKEND. COOL AIR DAMMING IS LIKELY TO SPREAD
DOWN THE EASTERN SEABOARD INTO THE CAROLINA PIEDMONT SATURDAY AND
LINGER INTO EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LARGE SCALE PATTERN THROUGH THE MEDIUM RANGE PERIOD WILL
CONTINUE TO BE HIGHLIGHTED BY A DEEP TROUGH SPINNING OVER EASTERN
CANADA, A CUT-OFF LOW OFF THE COAST OF CALIFORNIA, WEAKENING
TROUGHING OVER THE NORTHERN PLAINS/UPPER MIDWEST, AND AN ENERGETIC
NORTHERN JET STRETCHING FROM THE PACIFIC ACROSS THE PACIFIC
NORTHWEST. WHILE GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH THE
EVOLUTION OF THE LARGE SCALE FEATURES, THE SMALLER SCALE SPATIAL
AND TEMPORAL DETAILS OF INDIVIDUAL SHORTWAVES, PARTICULARLY WITH
THE STRONG JET STREAM NOSING INTO THE PACIFIC NORTHWEST LATER IN
THE PERIOD, REMAINS IN SIGNIFICANT FLUX. GIVEN THE ABOVE, DECIDED
TO UTILIZE INCREASED WEIGHTING OF THE EC AND GEFS ENSEMBLE MEANS
FOR THE SECOND HALF OF THE PERIOD, INCREASING TO 30 PERCENT BY DAY
5 AND 60 PERCENT FOR DAYS 6 AND 7. THE DAY 3 AND 4 WPC FORECAST
COMPRISED OF A BLEND OF 80% DETERMINISTIC GUIDANCE AND 20% ENSEMBLE
MEANS, ANCHORED BY THE 00Z AND 06Z RUNS OF THE EC AND GFS.
..WEATHER/HAZARDS HIGHLIGHTS
ENHANCED GULF MOISTURE CONTINUES TO SURGE UP THE PLAINS TO MEET
FRONTAL PATTERNS AHEAD OF THE OCCLUDING LOW PRESSURE SYSTEM OVER
THE UPPER MISSISSIPPI VALLEY FRIDAY INTO SATURDAY. THE DAY 4
MARGINAL RISK WAS EXPANDED NORTHWARD TO INCLUDE NORTHWEST MINNESOTA
AND NORTHEAST NORTH DAKOTA BASED ON THE LATEST QPF CONSENSUS AND
PW GRADIENT THAT FEATURES ANOMALIES AROUND +2 SIGMA. A DAY 5
MARGINAL RISK ALSO REMAINS IN PLACE FOR CENTRAL AND SOUTHERN
WISCONSIN BUT WAS BROADENED SLIGHTLY TO INCLUDE NORTHEAST IOWA AND
MUCH OF EASTERN MINNESOTA WHERE THE QPF SIGNAL IS MOST ROBUST.
REMNANT TROPICAL MOISTURE CONTINUES A SURGE INTO CALIFORNIA AND
EXPANDS EAST OVER THE DESERT SOUTHWEST FRIDAY AS THE UPPER RIDGE
AXIS OVER CA SHIFTS EAST TO THE INTERMOUNTAIN WEST AND TROUGHING
AMPLIFIES ALONG/OFF THE COAST. GIVEN HIGH MOISTURE ANOMALIES OF 2
TO 3 SIGMA OVER SOUTHWEST AZ AND 1.5 INTO NM, THE INHERITED DAY 4
MARGINAL RISK REMAINS IN PLACE WITH LITTLE ADJUSTMENTS NEEDED.
A STALLED FRONT OVER THE SOUTHERN FLORIDA PENINSULA CONTINUES TO
PROVIDE FOCUS FOR MUCH ABOVE NORMAL MOISTURE AND THE DEVELOPMENT OF
ADDITIONAL ROUNDS OF SHOWERS AND THUNDERSTORMS ON FRIDAY. COMBINED
WITH WET ANTECEDENT CONDITIONS, THE HIGHLIGHTED DAY 4 MARGINAL ERO
STILL LOOKS ON TRACK FOR SOUTHERN FLORIDA.
AN UPPER RIDGE WILL PROMOTE HEAT OVER THE MIDWEST AND SOUTHEAST
FRIDAY INTO THE WEEKEND WITH MAX TEMP ANOMALIES OF 5-15 DEGREES
ABOVE NORMAL. A STRONG SURFACE HIGH CROSSING THE NORTHEAST SATURDAY
SHOULD SEND A DECENT COLD FRONT DOWN MUCH OF THE EASTERN SEABOARD
WITH COOL AIR DAMMING LINGERING EAST OF THE APPALACHIANS AND LIKELY
THROUGH THE CAROLINA PIEDMONT AT LEAST INTO MONDAY. BELOW NORMAL
TEMPERATURES FROM ONSHORE FLOW, SCATTERED CLOUDS, AND POSSIBLE
SHOWERS CAN BE EXPECTED.
MILLER/JACKSON
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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