155
FXUS02 KWBC 090742
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 AM EDT TUE SEP 9 2025
VALID 12Z FRI SEP 12 2025 - 12Z TUE SEP 16 2025
..OVERVIEW
THE MEAN UPPER FLOW PATTERN FOR THIS UPCOMING MEDIUM RANGE PERIOD
WILL BE HIGHLIGHTED BY RENEWING TROUGH POSITIONS OVER BOTH THE
EASTERN AND THE WESTERN LOWER 48 THAT WILL SANDWICH A WARMING
CENTRAL U.S. RIDGE. SLOWLY PROGRESSIVE SYSTEMS WILL REPEATEDLY WORK
THROUGH THE MEAN WESTERN MEAN TROUGH TO SHIFT FOCUS FOR ENHANCED
RAIN CHANCES FROM THE NORTHWEST/WEST OUT TO THE ROCKIES/PLAINS.
THE GREAT LAKES REGION MAY ALSO BECOME UNSETTLED/WET WITH NORTHERN
STREAM ENERGY SET TO DIG TO THE LEE OF THE RIDGE. HEAVY RAIN
POTENTIAL MAY PERSIST FROM FLORIDA TO/OFFSHORE THE COASTAL
SOUTHEAST/CAROLINAS AS DEEPENED MOISTURE INTERACTS WITH A WAVY AND
WINDY WESTERN ATLANTIC FRONT. THIS ACTIVITY WILL FOCUS ON THE
LEADING EDGE OF A COOL CANADIAN AIRMASS SETTLING OVER THE EAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES OFFER A REAONABLY SIMILAR LARGER SCALE PATTERN
EVOLUTION THROUGH MEDIUM RANGE TIME SCALES, BUT FORECAST SPREAD
INCREASES OVER THE WEEKEND DUE TO MORE VARIED EMBEDDED SYSTEMS. IN
THIS FLOW, UPPER TROUGHING PIVOTS THROUGH THE WEST THROUGH THE END
OF THE WEEK AND ANOTHER TROUGH MOVES INTO THE WEST COAST EARLY
NEXT WEEK. UPPER RIDGING IS FORECAST DOWNSTREAM OVER THE CENTRAL
U.S. WHILE LINGERING AND RENEWING TROUGH ENRGIES DIG/MOVE SLOWLY
INTO/OVER THE EAST. A RECENT MODEL TREND IN SOME GUIDANCE IS FOR A
COMPACT CLOSED LOW TO DIVE SOUTH FROM THE HUDSON BAY TO BE LOCATED
SOMEWHERE OVER THE GREAT LAKES BY SUNDAY/MONDAY. TREND SUPPORT IS
VARIABLE IN GUIDANCE, BUT ANY ENHANCED HEIGHT FALLS WOULD FAVOR AN
INCREASE QPF/POPS COMPARED TO THE 01 UTC NATIONAL BLEND OF MODELS.
THE WPC PRODUCT SUITE WAS DERIVED FROM A GFS/ECMWF/CANADIAN/UKMET
BLEND VALID FOR FRIDAY/SATURDAY. SWITCHED PREFERENCE TO THE ECMWF
ENSEMBLE MEAN FOR LONGER TIME FRAMES GIVEN BETTER COMPATABILITY
WITH LATEST AMPLITUDE TRENDS AND WPC PRODUCT CONTINNUITY.
..WEATHER/HAZARDS HIGHLIGHTS
IT OVERALL REMAINS THE CASE THAT A PERSISTENT AND WAVY FRONTAL
SYSTEM OVER THE GULF AND FLORIDA ALSO EXTENDS JUST OFF/UP THE
EASTERN SEABOARD. THIS WILL PROVIDE A MAIN FOCUS FOR TROPICAL
MOISTURE TO POOL, LEADING TO DAILY ENHANCED AND DIURNALLY DRIVEN
RAINFALL POTENTIAL ASSOCIATED WITH SCATTERED THUNDERSTORMS.
SATURATED GROUNDS FROM PRECURSOR RAINFALL WARRANTS A MARGINAL RISK
OF EXCESSIVE RAINFALL OUTLOOK (ERO) LINGERING THREAT AREA SHIFTED
DOWN TO THE SOUTHERN FLORIDA PENINSULA FOR FRIDAY. FARTHER NORTH,
RAINS FOR THE COASTAL SOUTHEAST/CAROLINAS STILL OFFER UNCERTAINTY
FOR HOW MUCH CONVECTION OCCURS ONSHORE/OFFSHORE ON ANY GIVEN DAY.
FOR THE MOST PART, RAIN LOOKS TO REMAIN OFFSHORE, BUT SMALL SHIFTS
IN THE WAVY FRONTAL BOUNDARY MAY PRODUCE SIGNIFICANT DIFFERENCES IN
ONSHORE RAINFALL AMOUNTS, BUT EXPECT WINDY COASTAL/MARITIME FLOW.
FOR THE WEST, A SERIES OF UPPER TROUGHS/CLOSED LOWS SET TO WORK
OVER THE NORTHWEST/WEST WILL SUPPORT LOCALLY ENHANCED RAINFALL INTO
LATER THIS WEEK AND AGAIN INTO EARLY NEXT WEEK. RAINFALL AREAS
WITH EACH SYSTEM MAY TRANSLATE SLOWLY FROM THE PACIFIC
NORTHWEST/NORTHERN CALIFORNIA TO THE GREAT BASIN/INTERMOUNTAIN WEST
AND THEN TOWARD THE PLAINS. TERRAIN AND FRONTAL LIFT MAY FOCUS
SOME RUNOFF THREAT OVER THE NORTHERN ROCKIES/HIGH PLAINS AND ALSO
SOUTHWEST COLORADO AND VICINITY WHERE DEEPER MOISTURE MAY CHANNEL
BETWEEN EJECTING WESTERN U.S. TROUGHING AND THE CENTRAL U.S. RIDGE.
MARGINAL RISK ERO THREAT AREAS ARE IN PLACE FOR FRIDAY/SATURDAY
WHERE MODEST INSTABILITY WILL COMBINE WITH SHORTWAVE ENERGIES
PROVIDING LIFT AND PW ANOMALIES OF +3 STANDARD DEVIATIONS,
ESPECIALLY IN THE NORTHERN TIER. ALSO, THIS PATTERN MAY YIELD
COOLER TEMPERATURES SUPPORTIVE OF SOME SNOW FOR THE HIGHEST
ELEVATIONS OF THE ROCKIES. GRADUAL FLOW AND FRONTAL TRANSLATION
DOWNSTREAM SHOULD ALSO SUPPORT AFOREMENTIONED RAINFALL THROUGH THE
GREAT LAKES REGION AND VICINITY WITH FRONTAL PASSAGE AS NORTHERN
STREAM ENERGY DIGS TO THE LEE OF THE MAIN RIDGE.
COOLER THAN NORMAL TEMPERATURES ESPECIALLY FOR HIGHS ARE LIKELY
ACROSS THE WESTERN U.S. UNDERNEATH PERIODS OF UPPER TROUGHING. NEAR
TO BELOW AVERAGE TEMPERATURES ARE ALSO FORECAST FOR THE EAST. BUT
UNDERNEATH THE UPPER RIDGE IN BETWEEN THESE FEATURES, EXPECT ABOVE
AVERAGE TEMPERATURES FOR THE PLAINS TO MISSISSIPPI VALLEY.
TEMPERATURE ANOMALIES OF +10 TO +20 DEGREES WILL LEAD TO HIGHS IN
THE 90S AS FAR NORTH SOME DAYS AS SOUTH DAKOTA AND IOWA.
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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