869
FXUS02 KWBC 061900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SAT SEP 6 2025
VALID 12Z TUE SEP 09 2025 - 12Z SAT SEP 13 2025
..OVERVIEW
AN OVERALL MULTI-STREAMED AND AMPLIFIED MEAN UPPER PATTERN OVER
THE LOWER 48 AND VICINITY FOR NEXT 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 ACROSS FLORIDA
AND COASTAL NORTH CAROLINA WHERE TROPICAL MOISTURE IS FORECAST TO
INTERACT WITH THE WAVY FRONTAL BOUNDARY. THIS ACTIVITY WILL REMAIN
ON THE LEADING EDGE OF A COOL CANADIAN AIRMASS INSURGENCE THROUGH
THE CENTRAL AND EASTERN U.S. NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT GFS/ECMWF/UKMET AND CANADIAN MODEL SOLUTIONS CONTINUE TO BE
GENERALLY WELL CLUSTERED FOR EARLY/MID NEXT WEEK AND A FAVORED
COMPOSITE BLEND IS WELL SUPPORTED BY ENSEMBLES AND MACHINE LEARNING
GUIDANCE IN A PATTERN WITH OVERALL ABOVE NORMAL PREDICTABILITY.
FOR LATER NEXT WEEK, THERE IS GROWING RECENT MODEL UNCERTAINTY
WITH ENERGY AND SHORTWAVES FEEDING THROUGH THE WESTERN U.S. MEAN
TROUGH AND HOW THAT ENERGY EJECTS DOWNSTREAM WITH TIME TO THE
ROCKIES/PLAINS. THE WPC FORECAST BLEND AT THESE LONGER TIME FRAMES
INSTEAD FAVORS LESS PROGRESSIVE/MORE AMPLIFIED GEFS/ECMWF/CANADIAN
ENSEMBLE MEANS GIVEN PATTERN NATURE. THE ENSEMBLE MEANS ARE ALSO
INCLUDED TO MITIGATE RUN TO RUN MODEL VARIANCES AS CONSISTENT WITH
INDIVIDUAL SYSTEM PREDICTABILITY. THIS APPROACH MAINTAINS
EXCELLENT CONTINUITY WITH THE PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A WAVY FRONTAL SYSTEM SET TO LINGER OVER FLORIDA AND UP JUST OFF
THE EASTERN SEABOARD WILL PROVIDE A MAIN FOCUS FOR TROPICAL MOISTURE
TO POOL, LEADING TO DAILY ENHANCED RAINFALL POTENTIAL ASSOCIATE
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 ONSHORE INTO
WESTERN FLORIDA PENINSULA THROUGH MIDWEEK. 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 TUESDAY INTO WEDNESDAY, WITH THE MARGINAL RISK
EXTENDED INTO THURSDAY FOR 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 THE RAINFALL
AMOUNTS. THE AMPLIFIED/SLOWED PATTERN SHIFT MAY ALLOW MORE ONSHORE
NUDGING.
AN UPPER TROUGH/LOW WORKING THROUGH THE EASTERN PACIFIC TO THE
NORTHWEST/WEST WILL PRODUCE MULTIPLE DAYS OF RAINFALL NEXT WEEK,
EXPANDING EASTWARD WITH TIME FROM THE PACIFIC NORTHWEST/NORTHERN
CALIFORNIA INTO THE NORTHERN GREAT BASIN AND INTERMOUNTAIN WEST.
THIS COOL SEASON TYPE OF RAINFALL SHOULD BE MARKED BY MODERATE
RATES THAT ARE GENERALLY NOT ENOUGH TO CAUSE FLOODING CONCERNS. THE
LOWERING HEIGHTS ALOFT YIELDING COOLER TEMPERATURES COULD PRODUCE
SNOW FOR THE HIGHEST ELEVATIONS. LEAD MONSOONAL FLOW SHOULD
GENERALLY RELAX BY NEXT WEEK FOR THE WEST/SOUTHWEST, BUT LINGERING
MOISTURE/INSTABILITY FUELING SHOWERS ARE STILL POSSIBLE. ACTIVITY
MAY INCREASE LATER NEXT WEEK AS LOWER LATITUDE MOISTURE CHANNELS
BETWEEN THE WESTERN TROUGH AND CENTRAL U.S. RIDGE. SHOWERS AND
STORMS COULD REACH OUT FROM THE ROCKIES TO THE PLAINS AS CONSISTENT
WITH A REGION WITH LOCALLY GROWING INSTABILITY AND BOUNDARY FOCUS.
KONG/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page