070
FXUS02 KWBC 151746
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
146 PM EDT MON SEP 15 2025
VALID 12Z THU SEP 18 2025 - 12Z MON SEP 22 2025
..OVERVIEW
A BLOCKED UPPER AIR PATTERN DEVELOPS OVER NORTH AMERICA BY
THURSDAY WITH AN ANOMALOUS RIDGE THROUGH CENTRAL CANADA AND AN
UPPER LOW STALLED TO THE SOUTH OVER THE NORTHERN PLAINS INTO THIS
WEEKEND. MEANWHILE, TROUGHING LINGERS ALONG THE WEST COAST WHILE
RIDGING PERSISTS OVER THE MOUNTAIN WEST AND MIDWEST THROUGH
SOUTHEAST. THE PATTERN SHOULD BEGIN A SLOW SHIFT EASTWARD LATE WEEK
OR EARLY NEXT WEEK AS THE CANADIAN UPPER RIDGE WEAKENS. WETTER
THAN NORMAL CONDITIONS CAN BE EXPECTED LATER THIS WEEK INTO THE
WEEKEND OVER THE GREAT PLAINS STATES, SOUTH FLORIDA, AND CALIFORNIA
INTO THE DESERT SOUTHWEST. COOL AIR DAMMING IS LOOKING LIKELY BY
SATURDAY DOWN THE EASTERN SEABOARD INTO THE CAROLINA PIEDMONT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO SHOW PRETTY GOOD AGREEMENT ON THE
OVERALL PATTERN THROUGH MUCH OF THE MEDIUM RANGE PERIOD. THE UPPER
LOW CENTERED OVER THE DAKOTAS LATER THIS WEEK HAS SHOWN BETTER
AGREEMENT, BUT THE UKMET IS ON THE SLOW/WEST SIDE OF THE CONSENSUS
AND WAS NOT INCLUDED IN THE BLEND TODAY FOR WPC. MEANWHILE
TROUGHING DOWN THE WEST COAST LINGERS INTO SUNDAY, WITH SOME
QUESTION ON WHETHER AN UPPER LOW CUTSOFF/RETROGRADES WESTWARD OR
PUSHES INLAND TO CALIFORNIA. AS OF THIS MORNINGS MODELS, IT SEEMS
THERE MAY BE SLIGHTLY BETTER AGREEMENT FOR THE FORMER SCENARIO, A
CUTOFF LOW THAT RETROGRADES AWAY FROM THE COAST. THE ECMWF HAS BEEN
MOST CONSISTENT IN SHOWING THIS, BUT THE 06Z GFS THIS MORNING ALSO
TRENDED THIS DIRECTION. THE CMC CONTINUES TO BRING THE SYSTEM
INLAND AND WAS NOT INCLUDED IN THE LATER WPC BLEND PERIODS.
ELSEWHERE, LOOKS LIKE THE OVERALL PATTERN WILL SHIFT EAST WITH TIME
FINALLY BY THE WEEKEND, WITH THE DAKOTAS LOW WEAKENING AND ANOTHER
SHORTWAVE BEHIND IT INTO THE NORTHERN ROCKIES/HIGH PLAINS EARLY
NEXT WEEK.
THE WPC BLEND FOR TODAY WAS BASED ON A NON-UKMET CONSENSUS EARLY
ON, REMOVING THE CMC BY DAY 6 AND INCREASING WEIGHTING OF THE
ENSEMBLE MEANS TO HELP SMOOTH OUT SOME OF THE DETAIL DIFFERENCES
LATER IN THE PERIOD. THIS MAINTAINED GOOD AGREEMENT WITH THE
PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
ENHANCED GULF MOISTURE SURGES UP THE PLAINS TO MEET THE LOW
PRESSURE SYSTEM OVER THE NORTH-CENTRAL PLAINS THURSDAY/FRIDAY WITH
AN OVERALL SLOW PROGRESSION EASTWARD DUE TO A BLOCKY PATTERN.
MARGINAL RISKS CONTINUE TO BE HIGHLIGHTED ON THE DAYS 4 AND 5
EXCESSIVE RAINFALL OUTLOOKS GENERALLY FROM THE DAKOTAS TO THE UPPER
MIDWEST. ANOMALOUS MOISTURE WILL BE PRESENT AHEAD OF THE COLD
FRONT, BUT DRY ANTECEDENT CONDITIONS MAY TEMPER THE OVERALL FLASH
FLOOD RISK.
REMNANT TROPICAL MOISTURE SURGES INTO CALIFORNIA AND THE LOWER
COLORADO RIVER REGION INTO THE GREAT BASIN THURSDAY INTO FRIDAY AS
THE UPPER RIDGE AXIS DEVELOPING OVER CA TODAY SHIFTS EAST TO THE
INTERMOUNTAIN WEST AS TROUGHING AMPLIFIES ALONG/OFF THE COAST.
MOISTURE ANOMALIES ARE VERY HIGH FOR THIS TIME OF THE YEAR,
WARRANTING AT LEAST A MARGINAL RISK ACROSS MUCH OF SOUTHERN
CALIFORNIA AND FAR SOUTHWEST ARIZONA FOR THE DAY 4/THURSDAY ERO.
THERE ARE SOME LINGERING MOISTURE AND QPF UNCERTAINTIES FOR THE DAY
5 ERO PERIOD BUT FOR NOW CONTINUED A MARGINAL RISK FOR JUST THE
SIERRA NEVADA, BUT MAY NEED TO BE EXTENDED IN SUBSEQUENT UPDATES
GIVEN TRENDS.
A STALLED FRONT OVER THE SOUTHERN FLORIDA PENINSULA PROVIDES FOCUS
FOR MUCH ABOVE NORMAL MOISTURE AND COMBINED WITH WET ANTECEDENT
CONDITIONS THURSDAY WITH THE DAY 4 MARGINAL ERO MAINTAINED ALONG
THE SOUTHEAST COAST. THE MOISTURE FOCUS LOOKS TO SHIFT A BIT EAST
ON FRIDAY, SO NO ERO IS INTRODUCED THERE FOR NOW.
AN UPPER RIDGE WILL PROMOTE HEAT OVER THE MIDWEST AND SOUTHEAST
THURSDAY TO SATURDAY WITH MAX TEMP ANOMALIES OF 5-15 DEGREES ABOVE
NORMAL. A STRONG SURFACE HIGH LOOKS TO SEND A DECENT COLD FRONT
OVER MUCH OF THE EASTERN STATES BY SATURDAY WITH COOL AIR DAMMING
LINGERING EAST OF THE APPALACHIANS AND NORTH FROM THE CAROLINA
PIEDMONT AT LEAST INTO NEXT MONDAY. BELOW NORMAL TEMPERATURES FROM
ONSHORE FLOW, CLOUDS, AND POSSIBLE RAIN CAN BE EXPECTED.
SANTORELLI/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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