018
FXUS02 KWBC 101946
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
346 PM EDT WED SEP 10 2025
VALID 12Z SAT SEP 13 2025 - 12Z WED SEP 17 2025
..OVERVIEW
OVER THE WEEKEND, UPPER TROUGHING ATOP THE INTERMOUNTAIN WEST WILL
CAUSE MOIST SOUTHERLY FLOW TO STREAM INTO THE HIGH PLAINS AND
CAUSE SOME MODERATE TO HEAVY RAIN. THIS TROUGH IS FORECAST TO
GRADUALLY LIFT OUT EARLY NEXT WEEK WHILE ANOTHER TROUGH WILL RELOAD
IN THE WEST AND SPREAD ENHANCED RAIN CHANCES FROM THE
NORTHWEST/WEST TO OUT ACROSS THE ROCKIES/PLAINS. TROUGHING IN THE
EAST MAY ALSO GET RENEWED EARLY NEXT WEEK AND BRING SOME NORTHEAST
RAIN, BUT THIS PATTERN AND RAIN AMOUNTS ARE MORE UNCERTAIN. A WAVY
AND WINDY LINGERING FRONT FARTHER SOUTH ACROSS THE WESTERN ATLANTIC
COULD CAUSE SOME LINGERING HEAVY RAIN IN SOUTH FLORIDA AND
ALONG/OFFSHORE THE COASTAL CAROLINAS. IN BETWEEN THE RENEWING UPPER
TROUGHS, THE CENTRAL U.S. SHOULD SEE ABOVE NORMAL TEMPERATURES
WITH SOME AREAS WELL INTO THE 90S UNDERNEATH RIDGING ALOFT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES AGREE ON THE GENERAL TROUGH-RIDGE-TROUGH
PATTERN OVER THE LOWER 48 THROUGH MUCH OF THE MEDIUM RANGE PERIOD,
WITH MORE SPREAD ON ENERGIES SERVING TO RENEW THE TROUGHS. NAMELY,
IN THE EAST MODELS SHOW AN UPPER LOW DIVING SOUTH OVER QUEBEC THIS
WEEKEND AND MAKING IT TO THE NORTHEAST U.S. BY MONDAY. NON-NCEP
MODELS CONTINUE TO BE FARTHER WEST AND DEEPER WITH THIS UPPER LOW
COMPARED TO THE GFS/GEFS RUNS, FOR THE 00/06Z CYCLE AND CONTINUED
INTO THE NEWER 12Z CYCLE. WPC CONTINUES TO FAVOR AN INTERMEDIATE
SOLUTION MORE LIKE THE EC/CMC ENSEMBLE MEANS, THUS DEEPER THAN THE
GFS/GEFS BUT NOT COMPLETELY TOWARD THE DETERMINISTIC EC/CMC
POSITION, FOR THE MASS FIELDS AND FOR RESULTANT SENSIBLE WEATHER
LIKE QPF (HEAVIER THAN THE GFS AND NBM) INTO NEXT WEEK.
IN THE WEST, THE FIRST TROUGH WILL PIVOT NORTHEAST THROUGH THE
NORTHERN PLAINS BY MONDAY WHILE THERE IS RELATIVELY MORE SPREAD IN
THE TROUGH INCOMING BEHIND IT. WITH THIS SECOND TROUGH, NEW 12Z
MODELS INDICATE LESS DIGGING OF ENERGY IN THE EASTERN PACIFIC
SUNDAY THAN MOST 00/06Z GUIDANCE, LEADING TO SHALLOWER TROUGHING IN
THE WEST EARLY NEXT WEEK. WILL CONTINUE TO MONITOR THE TIMING OF
THIS FEATURE'S EJECTION EAST BY MIDWEEK AS MODELS SHOW A FAIR
AMOUNT OF VARIABILITY.
THE WPC FORECAST USED A MULTI-MODEL DETERMINISTIC BLEND EARLY IN
THE MEDIUM RANGE PERIOD, BUT QUICKLY RAMPED UP THE PROPORTION OF
THE EC/CMC ENSEMBLE MEANS TO MORE THAN HALF BY THE LATE PERIOD
GIVEN THE INCREASING SPREAD BY THEN.
..WEATHER/HAZARDS HIGHLIGHTS
RAIN AND THUNDERSTORMS ARE LIKELY TO FOCUS OVER THE NORTHERN
PLAINS THIS WEEKEND AHEAD OF THE WESTERN TROUGH AND NEAR A FRONTAL
SYSTEM, YIELDING MARGINAL RISKS IN THE ERO SATURDAY/SUNDAY FOR
POSSIBLE FLOODING CONCERNS. AMPLE LIFT AND SOME INSTABILITY
(1000-1500 J/KG OF MUCAPE PER THE ECMWF) COULD ALSO ALLOW FOR HEAVY
RAIN IN CONVECTION FOR THE SOUTHERN HIGH PLAINS SATURDAY INTO
SATURDAY NIGHT, AND HAVE DELINEATED A MARGINAL RISK FOR THOSE AREAS
FOR SOME POSSIBLE ISOLATED FLOODING. LIGHTER RAIN MAY MAKE IT INTO
THE UPPER MIDWEST EARLY NEXT WEEK. MEANWHILE 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.
A PERSISTENT AND WAVY FRONTAL SYSTEM OVER THE GULF AND FLORIDA
WILL LINGER JUST OFF/UP THE EASTERN SEABOARD INTO NEXT WEEK. THIS
WILL PROVIDE A MAIN FOCUS FOR TROPICAL MOISTURE TO POOL TO FUEL A
ELONGATED PLUME OF ENHANCED WRAPPING RAINS. A DAY 4/SATURDAY
EXCESSIVE RAINFALL OUTLOOK (ERO) MARGINAL RISK AREA REMAINS OVER
SOUTH FLORIDA FOR RAINFALL BEFORE A LATER DAY FRONTAL PASSAGE.
SCATTERED SHOWERS COULD CONTINUE INTO NEXT WEEK BEHIND THE MAIN
FRONT, BUT WITH MOISTURE LEVELS CLOSER TO NORMAL. FARTHER NORTH,
MODELS NOW SHOW MOST MOISTURE ALONG/JUST OFFSHORE THE COASTAL
CAROLINAS/MID-ATLANTIC; EXPECT WINDY COASTAL/MARITIME FLOW AND
HAZARDS TO MONITOR REGARDLESS. THE COASTAL BOUNDARY MAY ALSO PLAY A
ROLE IN ENHANCED RAINFALL COMING INTO THE NORTHEAST UNDER THE
LIKELY TROUGH WITH ANOTHER FRONT. MODERATE QPF IS NOW SHOWN FOR THE
INTERIOR NORTHEAST FOR SUNDAY, WITH SOME MODEST INSTABILITY
POTENTIALLY ENHANCING RAIN RATES, BUT WILL HOLD OFF ON AN EXCESSIVE
RAINFALL AREA GIVEN UNCERTAINTIES IN THE RAIN AMOUNTS AND THE
OVERALL PATTERN.
SLIGHTLY COOLER THAN NORMAL TEMPERATURES ESPECIALLY FOR HIGHS ARE
LIKELY ACROSS THE WESTERN U.S. UNDERNEATH PERIODS OF UPPER
TROUGHING. BUT THE UPPER RIDGE TO THE EAST WILL PROMOTE WARM
TEMPERATURES ACROSS THE CENTRAL U.S., WITH GREATEST ANOMALIES OF
10-20 DEGREES ABOVE AVERAGE IN THE MISSISSIPPI VALLEY WITH LESSER
ANOMALIES INTO THE PLAINS AND EAST INTO THE GREAT LAKES, OHIO
VALLEY, AND SOUTHEAST. TEMPERATURES WELL IN THE 90S WILL BE COMMON
EVEN UP THROUGH PARTS OF IOWA AND ILLINOIS INTO THE WEEKEND, BUT
BECOMING MORE SUPPRESSED TO THE SOUTH NEXT WEEK (THOUGH POTENTIALLY
STILL REMAINING WARMER THAN AVERAGE INTO THE MIDWEST, JUST WITH
LESSER ANOMALIES). A HANDFUL OF RECORD HIGHS ARE POSSIBLE ACROSS
THE MID-SOUTH. MEANWHILE THE EAST SHOULD GENERALLY SEE NEAR NORMAL
TEMPERATURES FOR MID-SEPTEMBER.
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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