254
FXUS02 KWBC 091949
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
349 PM 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 TO NORTHEAST MAY ALSO BECOME UNSETTLED/WET WITH
NORTHERN STREAM ENERGY POSSIBLY DIGGING TO THE LEE OF THE RIDGE.
HEAVY RAIN POTENTIAL MAY PERSIST THROUGH LATE WEEK FROM FLORIDA
TO/OFFSHORE THE COASTAL SOUTHEAST/CAROLINAS AS DEEPENED MOISTURE
INTERACTS WITH A WAVY AND WINDY WESTERN ATLANTIC COOL FRONT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES ARE AGREEABLE AT THE START OF THE MEDIUM
RANGE PERIOD IN SHOWING AN ELONGATED CLOSED UPPER LOW THROUGH THE
INTERMOUNTAIN WEST, RIDGING ACROSS THE CENTRAL U.S., AND LINGERING
TROUGHING ALONG THE EASTERN SEABOARD. MODELS AGREE THAT THE FIRST
TROUGH IN THE WEST PIVOTS EAST/NORTHEAST WHILE PUSHING THE RIDGE
AXIS GRADUALLY FROM THE PLAINS INTO THE MISSISSIPPI VALLEY, AND
ANOTHER TROUGH MOVES INTO THE WEST COAST EARLY NEXT WEEK. THE MOST
UNCERTAIN ASPECT OF THE FORECAST IS THE POTENTIAL FOR ENERGY TO
DIVE TOWARD THE GREAT LAKES TO NORTHEAST REGION IN SOME FORM AND
ENHANCE UPPER TROUGHING THERE. YESTERDAY'S GUIDANCE WAS FAVORING A
COMPACT CLOSED LOW TO MOVE AND MEANDER NEAR THE GREAT LAKES, BUT
THE 00/06Z AND NOW THE INCOMING 12Z MODEL RUNS DO NOT FAVOR A
FEATURE LIKE THIS. CMC AND ECMWF RUNS DO DIVE ENERGY SOUTHEAST
EVENTUALLY BUT INTO THE NORTHEAST U.S., CLOSING OFF A LARGER UPPER
LOW THERE. GFS RUNS JUST SKIRT TROUGHING THROUGH SOUTHEASTERN
CANADA AND PERHAPS MAINE. WHILE THE NON-NCEP CONSENSUS CAN VERIFY
WELL, MOST OF THE 00Z AI/ML MODELS THAT ARE BOTH GFS AND EC BASED
DO NOT SHOW AN UPPER LOW OVER THE NORTHEAST LIKE THIS, SO DID NOT
WANT TO DISCOUNT THE GFS TYPE SOLUTIONS. THUS THE WPC FORECAST USED
A MULTI-MODEL DETERMINISTIC BLEND INITIALLY, BUT QUICKLY RAMPED UP
THE PROPORTION OF GEFS AND EC ENSEMBLE MEANS TO JUST OVER HALF DAY
6 AND MORE DAY 7 GIVEN THE INCREASED SPREAD. THE AVERAGE OF THE
GEFS/EC MEANS SHOW SOME TROUGHING OVER THE NORTHEAST NEXT WEEK, BUT
WEAKER. THE EVENTUAL RIDGE OR TROUGH PATTERN IN THE OHIO
VALLEY/GREAT LAKES/NORTHEAST WILL GREATLY IMPACT SENSIBLE WEATHER,
LIKE POSSIBLE WELL ABOVE NORMAL (GFS SUITE) OR CLOSER TO NORMAL (EC
SUITE) TEMPERATURES THERE. SOME CHANGES TO THE PREVIOUS FORECAST
NEEDED TO BE MADE IN THE EAST BECAUSE OF THE RECENT MODEL TRENDS,
AND FUTURE CHANGES ARE CERTAINLY POSSIBLE AS THE PATTERN EVOLVES.
..WEATHER/HAZARDS HIGHLIGHTS
A PERSISTENT AND WAVY FRONTAL SYSTEM OVER THE GULF AND FLORIDA
EXTENDS JUST OFF/UP THE EASTERN SEABOARD THROUGH LATE WEEK. THIS
WILL PROVIDE A MAIN FOCUS FOR TROPICAL MOISTURE TO POOL, LEADING TO
ENHANCED AND DIURNALLY DRIVEN RAINFALL POTENTIAL ASSOCIATED WITH
SCATTERED THUNDERSTORMS. PER COORDINATION WITH THE SHORT RANGE, THE
MAIN URBANIZED CORRIDOR OF SOUTH FLORIDA HAS BEEN UPGRADED TO A
SLIGHT RISK OF EXCESSIVE RAINFALL THROUGH DAY 4/FRIDAY AS
FLOODING/FLASH FLOODING IMPACTS ARE POSSIBLE OVER THE NEXT FEW
DAYS, BUT DIFFICULT TO TELL WHICH DAY(S) MAY SEE THE MAXIMUM
IMPACTS. DURING DAY 5/SATURDAY, THE FRONT IS FORECAST TO CLEAR
SOUTH FLORIDA AND REDUCE AVAILABLE MOISTURE. HAVE A MARGINAL RISK
IN PLACE FOR SOUTHERN AREAS OF FLORIDA BEFORE THE FRONT EXITS.
SCATTERED SHOWERS AND THUNDERSTORMS COULD CONTINUE INTO EARLY NEXT
WEEK BEHIND THE MAIN FRONT, BUT WITH MOISTURE LEVELS CLOSER TO
NORMAL. FARTHER NORTH, MODELS CONTINUE TO SHOW MOST MOISTURE
REMAINING OFFSHORE OF THE CAROLINA COAST, BUT COASTAL SHOWERS ARE
POSSIBLE AND SMALL SHIFTS IN THE WAVY FRONTAL BOUNDARY MAY PRODUCE
SIGNIFICANT DIFFERENCES IN ONSHORE RAINFALL AMOUNTS. EXPECT WINDY
COASTAL/MARITIME FLOW THERE REGARDLESS.
FOR THE WEST, AN INITIAL UPPER TROUGH AND FRONTAL SYSTEM ARE
FORECAST TO IMPACT THE ROCKIES ON FRIDAY AND SUPPORT LOCALLY
ENHANCED RAINFALL. 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 AREAS ARE DELINEATED FOR THESE AREAS FOR FRIDAY,
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. RAIN AND THUNDERSTORMS SHOULD AGAIN
FOCUS IN THE NORTHERN HIGH PLAINS ON DAY 5/SATURDAY, YIELDING
ANOTHER MARGINAL RISK FOR POSSIBLE FLOODING CONCERNS. GRADUAL FLOW
AND FRONTAL TRANSLATION DOWNSTREAM COULD SUPPORT RAIN INTO THE
MIDWEST SUNDAY WHILE UNCERTAIN FLOW MAY YIELD SOME RAIN IN THE
NORTHEAST EARLY NEXT WEEK, WITH LOW CONFIDENCE. THE NEXT ROUND OF
TROUGHING WILL PUSH INTO THE WEST THIS WEEKEND AND SPREAD ANOTHER
ROUND OF PRECIPITATION FIRST TO THE PACIFIC NORTHWEST AND INTO THE
NORTHERN GREAT BASIN AND ROCKIES EARLY NEXT WEEK.
COOLER THAN NORMAL TEMPERATURES ESPECIALLY FOR HIGHS ARE LIKELY
ACROSS THE WESTERN U.S. UNDERNEATH PERIODS OF UPPER TROUGHING. NEAR
TO SLIGHTLY 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 AS NEBRASKA AND IOWA INTO LATE THIS
WEEK, THOUGH POTENTIALLY BECOMING MORE SUPPRESSED TO THE SOUTH BY
EARLY NEXT WEEK DEPENDING ON UPPER-LEVEL FLOW.
TATE/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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