492
FXUS02 KWBC 060733
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
333 AM 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 WILL ESPECIALLY PERSIST ACROSS
FLORIDA AND WITHIN A DEEPLY MOIST AXIS CHANNEL UP ALONG/JUST OFF
THE COASTAL SOUTHEAST/CAROLINAS. THIS ACTIVITY WILL REMAIN ON THE
LEADING EDGE OF COOLED CANADIAN AIRMASS INSURGENCE WITH MULTIPLE
FRONTAL SURGES DOWN 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 LINGER TIME FRAMES
INSTEAD FAVORS LESS PROGRESSIVE/MORE AMPLIFIED GEFS/ECMWF/CANADIAN
ENSEMBLE MEANS GIVEN PATTERN NATURE. THE MEANS ALSO ACT TO
MITIGATE RUN TO RUN MODEL VARIANCES AS CONSISTENT WITH INDIVIDUAL
SYSTEM PREDICTABILITY. THIS APPROACH MAINTAINS EXCELLENT CONTINUITY
WITH THE PREVIOUS WPC FORECAST AND IS MORE IN LINE WITH THE LATEST
00 UTC MODEL SUITE THAT TRENDED SIGNIFICANTLY IN THIS DIRECTION.
..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 MOISTURE TO
POOL, LEADING TO DAILY ENHANCED RAINFALL POTENTIAL. SATURATED
GROUNDS FROM PRE-CURSOR RAINFALL WARRANT WPC EXCESSIVE RAINFALL
OUTLOOK MARGINAL RISK AREA INTRODUCTION FOR TUESDAY INTO WEDNESDAY
FROM FLORIDA TO THE COASTAL CAROLINAS. HOWEVER, 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.
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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