199
FXUS02 KWBC 141953
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
353 PM EDT SUN SEP 14 2025
VALID 12Z WED SEP 17 2025 - 12Z SUN SEP 21 2025
..OVERVIEW
A GENERALLY BLOCKY/SLOW MOVING UPPER AIR PATTERN DEVELOPS OVER
NORTH AMERICA BY MIDWEEK WITH RIDGING OVER THE MOUNTAIN WEST AND
MIDWEST AND TROUGHING OVER THE WEST COAST, NORTH-CENTRAL STATES,
AND NORTHEAST LINGERING INTO THIS WEEKEND. WETTER THAN NORMAL
CONDITIONS CAN BE EXPECTED MIDWEEK OVER THE MID-ATLANTIC, SOUTH
FLORIDA, MUCH OF THE GREAT PLAINS INTO THE MIDWEST, AND THE DESERT
SOUTHWEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST MODEL AND ENSEMBLE GUIDANCE AGREES ON A SOMEWHAT
BLOCKED PATTERN FROM A RIDGE SHIFTING OVER CENTRAL CANADA WEDNESDAY
TO FRIDAY WHICH MAINTAINS SLOW MOVING TROUGHS OVER THE WEST COAST,
NORTH- CENTRAL STATES (WITH A LIKELY CLOSED LOW) AND OVER THE
NORTHEAST. THE GUIDANCE SHOWS BETTER AGREEMENT WITH A CLOSED LOW
MOVING UP THE MID-ATLANTIC COAST EARLY IN THE PERIOD, BUT SOME
QUESTION ON TIMING OF THAT. SAME STORY WITH THE UPPER LOW OVER THE
DAKOTAS INTO THE MIDWEST, AGREEMENT ON THE EXISTENCE BUT TIMING
UNCERTAINTIES (GFS WAS NOTABLY SLOWER). ALSO, THERE'S BEEN A TREND
FOR THE LOW ALONG THE CALIFORNIA COAST THURSDAY/FRIDAY TO
RETROGRADE OFFSHORE FRIDAY NIGHT THEN POTENTIALLY SHIFTING BACK TO
SHORE (CMC/GFS) OR CONTINUING OUT TO SEA (EC). TIMING UNCERTAINTIES
ALSO EXIST ACROSS THE NORTHWEST WITH A COUPLE OF WEAK SHORTWAVES
IN THE FLOW.
OVERALL, WAS ABLE TO USE A GENERAL MODEL COMPROMISE FOR ABOUT THE
FIRST HALF OF THE PERIOD WITH REASONABLE AGREEMENT. TRENDED TOWARDS
GREATER WEIGHTING OF THE ENSEMBLE MEANS LATER IN THE PERIOD (ALONG
WITH THE ECMWF AND THE GFS). DID NOT USE THE CMC FOR DAYS 6 OR 7
DUE TO IT BEING MORE AGGRESSIVE WITH BRINGING THE UPPER LOW OFF THE
CALIFORNIA COAST INLAND THIS WEEKEND.
..WEATHER/HAZARDS HIGHLIGHTS
SOUTHWARD SHIFTING OF THE UPPER TROUGH/LOW DOWN THE DAKOTAS
WEDNESDAY WILL CONTINUE TO BRING ENHANCED GULF MOISTURE UP THE
PLAINS WITH CONVERGENCE AHEAD OF A SLOW MOVING FRONTAL SYSTEM.
AREAS OF AT LEAST LOCALLY HEAVY RAIN ARE LIKELY TO CONTINUE
DRIFTING EAST FROM THE CENTRAL PLAINS TO THE MIDWEST
WEDNESDAY/THURSDAY AND WARRANT MARGINAL EROS FOR BOTH DAYS 4 AND 5.
INCREASING MONSOONAL MOISTURE OVER NEW MEXICO THROUGH THE TEXAS
PANHANDLE ON WEDNESDAY WARRANTS MAINTENANCE OF THE MARGINAL ERO
THERE.
A NOTABLE PACIFIC MOISTURE SURGE UP INTO CALIFORNIA AND THE LOWER
COLORADO RIVER REGION INTO THE GREAT BASIN IS ON TAP FOR THURSDAY
AS THE UPPER RIDGE AXIS OVER CA EARLY THIS WEEK SHIFTS EAST TO THE
INTERMOUNTAIN WEST. GUIDANCE IS QUITE VARIED IN QPF THERE, BUT
DIURNALLY DRIVEN CONVECTION INITIATING ON TERRAIN CONTINUES A DAY 5
MARGINAL ERO FOR SOUTHERN CA.
A STALLED FRONT OVER THE SOUTHERN FLORIDA PENINSULA PROVIDES FOCUS
FOR MUCH ABOVE NORMAL MOISTURE AND COMBINED WITH WET ANTECEDENT
CONDITIONS SUPPORTS BOTH A DAY 4 AND DAY 5 ERO.
ELSEWHERE, THE SOUTHWEST RIDGE AXIS SHIFTING EAST TO THE
INTERMOUNTAIN WEST ON WEDNESDAY FOCUSES MORE INTERIOR SOUTHWEST
HEAT LATER THIS WEEK. AN UPPER RIDGE WILL PROMOTE HEAT OVER THE
SOUTHEAST THROUGH LATE IN THE WEEK TEMPERATURES CENTERED ON THE
MIDWEST AND MISSISSIPPI VALLEY THROUGH AT LEAST MID-NEXT WEEK, WITH
ANOMALIES OF 10-15 DEGREES ABOVE AVERAGE. WARMER THAN AVERAGE
TEMPERATURES MOVE FROM THE MIDWEST TO THE NORTHEAST IN THE LATER
HALF OF THE WEEK AS WELL.
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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