004
FXUS02 KWBC 070725
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
325 AM EDT SUN SEP 7 2025
VALID 12Z WED SEP 10 2025 - 12Z SUN SEP 14 2025
..OVERVIEW
IT REMAINS THE CASE THAT AN OVERALL MULTI-STREAMED AND AMPLIFIED
MEAN UPPER PATTERN OVER THE LOWER 48 AND VICINITY FOR THIS WEEK
SHOULD PROVE SLOW TO DISLODGE AS BROADLY HIGHLIGHTED BY A WARMING
CENTRAL U.S. RIDGE SANDWICHED BETWEEN WEST COAST AND EAST COAST
TROUGHS. IN THIS PATTERN, WAVY FRONTAL SYSTEMS WILL FURTHER FOCUS
RAIN CHANCES FROM THE NORTHWEST/WEST TO THE ROCKIES/PLAINS WITH
GRADUAL FLOW TRANSLATION. HEAVY RAIN POTENTIAL REMAINS PRESENT
FROM FLORIDA THROUGH THE COASTAL CAROLINAS AND POSSIBLY SOUTHEAST
NEW ENGLAND AS DEEPENED MOISTURE INTERACTS/OVERRUNS A WAVY WESTERN
ATLANTIC FRONT. THIS ACTIVITY WILL FOCUS ON THE LEADING EDGE OF A
COOL CANADIAN AIRMASS INSURGENCE FOR THE CENTRAL AND EASTERN U.S..
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST GFS/ECMWF/UKMET MODEL SOLUTIONS SEEM WELL CLUSTERED FOR
MID- LATE THIS WEEK AND A FAVORED COMPOSITE IS WELL SUPPORTED BY
ENSEMBLES IN A FLOW PATTERN WITH ABOVE NORMAL PREDICTABILITY.
HEADING INTO/THROUGH NEXT WEEKEND, MODEL UNCERTAINTY FOCUS IS WITH
ENERGY AND SHORTWAVES FEEDING THROUGH THE WESTERN U.S. MEAN TROUGH
AND HOW ENERGY EJECTS DOWNSTREAM WITH TIME TO THE ROCKIES/PLAINS.
THE WPC FORECAST BLEND AT THESE LONGER TIME FRAMES FAVOR CONSISTENT
SOLUTIONS ON THE SLIGHTLY LESS PROGRESSIVE AND MORE AMPLIFIED SIDE
OF THE FULL ENVELOPE OF SOLUTIONS GIVEN THE BLOCKY PATTERN NATURE.
ACCORDINGLY, A BEST MATCHING GFS AND GEFS/ECMWF ENSEMBLE MEAN
BLEND FITS THE BILL. WPC PRODUCT CONTINUITY IS GOOD WITH THIS PLAN.
..WEATHER/HAZARDS HIGHLIGHTS
A PERSISTENT AND WAVY FRONTAL SYSTEM OVER THE GULF AND FLORIDA
ALSO EXTENDS JUST OFF/UP THE EASTERN SEABOARD. THIS PROVIDES A
MAIN FOCUS FOR TROPICAL MOISTURE TO POOL, LEADING TO DAILY ENHANCED
RAINFALL POTENTIAL ASSOCIATED WITH SCATTERED THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO BE MORE NUMEROUS DAILY FROM LATE
AFTERNOON INTO EARLY EVENING. A NEARLY STATIONARY VORTEX OVER THE
EASTERN GULF COULD HELP TRIGGER AND PUSH SOME ORGANIZED BANDS OF
THUNDERSTORMS ALSO ONSHORE INTO WESTERN FLORIDA PENINSULA INTO
MID-LATE THIS WEEK. MODEL CONSENSUS APPEARS TO INDICATE THAT THE
FRONT WILL ADVANCE FARTHER SOUTH TOWARD THE VORTEX, THEREBY
INCREASING THE CHANCE FOR THE VORTEX TO BE FRONTAL IN NATURE LATER
NEXT WEEK. SATURATED GROUNDS FROM PRE-CURSOR RAINFALL WARRANT A
MARGINAL RISK OF EXCESSIVE RAINFALL OUTLOOK AREA TO BE KEPT ACROSS
THE FLORIDA PENINSULA AND COASTAL NORTH CAROLINA FOR WEDNESDAY,
WITH THE MARGINAL RISK EXTENDED FOR THURSDAY OVER THE FLORIDA
PENINSULA. NOTE THAT DAILY RAINFALL AMOUNTS FROM THE COASTAL
SOUTHEAST/CAROLINAS AND UP THE COAST OFFERS UNCERTAINTY FOR HOW
MUCH CONVECTION OCCURS ONSHORE/OFFSHORE ON ANY GIVEN DAY. SMALL
SHIFTS IN THE WAVY FRONTAL BOUNDARY COULD PRODUCE SIGNIFICANT
DIFFERENCES IN ONSHORE RAINFALL AMOUNTS. THE AMPLIFIED AND SLOWED
PATTERN NATURE MAY LEND FAVOR TO ONSHORE FLOW TRENDS AND BEHAVIOR.
AN UPPER TROUGH/CLOSED LOW WORKING OVER THE NORTHWEST/WEST WILL
SUPPORT MULTIPLE DAYS WITH POTENTIAL RAINFALLS INTO MID-LATE WEEK,
SHIFTING SLOWLY WITH TIME FROM THE PACIFIC NORTHWEST/NORTHERN
CALIFORNIA TO THE NORTH-CENTRAL GREAT BASIN/INTERMOUNTAIN WEST.
THIS COOL SEASON TYPE OF RAINFALL SHOULD BE MARKED BY MODERATE
RATES THAT ARE GENERALLY NOT ENOUGH TO CAUSE FLOODING CONCERNS. THE
UNSETTLING LOWERED HEIGHTS ALOFT WILL YIELD COOLER TEMPERATURES
SUPPORTIVE OF SOME SNOW FOR THE HIGHEST ELEVATIONS. MONSOONAL FLOW
GENERALLY WANES INTO THIS WEEK FOR THE WEST/SOUTHWEST, BUT
LINGERING MOISTURE AND INSTABILITY FUELING SHOWERS REMAIN POSSIBLE.
ACTIVITY FOCUS MAY INCREASE THROUGH LATER WEEK AS SOME RENEWED
LOWER LATITUDE MOISTURE CHANNELS BETWEEN THE TRANSITIONING WESTERN
U.S. TROUGH AND THE CENTRAL U.S. RIDGE. SHOWERS AND STORMS WILL
INCREASINGLY SPREAD FROM THE ROCKIES TO THE NORTH-CENTRAL PLAINS
TO MONITOR FOR POSSIBLE RUNOFF ISSUES LATE WEEK INTO NEXT WEEKEND
GIVEN LOCALLY GROWING INSTABILITY AND BOUNDARY FOCUS/HEIGHT FALLS.
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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