118
FXUS02 KWBC 180710
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 AM EDT FRI SEP 18 2026
VALID 12Z MON SEP 21 2026 - 12Z FRI SEP 25 2026
...WET PATTERN WITH POSSIBLE FLOODING THREAT IN THE SOUTHERN HIGH
PLAINS/ROCKIES NEXT WEEK...
..OVERVIEW
AN UPPER LOW HOVERING OVER THE GREAT LAKES NEXT WEEK WILL INTERACT
WITH SOUTHERN STREAM ENERGY MOVING NORTHWARD FROM THE GULF ACROSS
THE EASTERN SEABOARD. AT THE SURFACE, A FRONTAL SYSTEM IS FORECAST
TO PUSH THROUGH THE EAST WITH A COLD AIR DAMMING WEDGE OF HIGH
PRESSURE BEHIND IT. THIS SETUP WILL ALLOW FOR MULTIPLE ROUNDS OF
RAIN IN THE EAST, AS WELL AS COOLER TEMPERATURES AND NOTABLE
ONSHORE FLOW ACROSS THE NORTHEAST AND MID-ATLANTIC. MEANWHILE, AN
EASTERN PACIFIC/SOUTHWESTERN U.S. UPPER TROUGH AND WARM UPPER
RIDGING STICKING AROUND THE SOUTH-CENTRAL U.S. WILL DIRECT MOIST
SOUTHERLY MONSOONAL FLOW INTO PARTS OF THE WESTERN U.S. TO THE
PLAINS. MULTIPLE DAYS OF HEAVY RAIN ARE POSSIBLE IN THE SOUTHERN
ROCKIES/HIGH PLAINS IN PARTICULAR, WHICH COULD CAUSE FLOODING
CONCERNS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE BEGINS THE MEDIUM RANGE PERIOD MONDAY IN REASONABLY
GOOD AGREEMENT WITH THE PATTERN DESCRIBED ABOVE. UPPER TROUGHING
IN THE NORTH-CENTRAL U.S. COULD CLOSE OFF INTO AN UPPER LOW AS IT
MOVES INTO THE GREAT LAKES BY MIDWEEK. WEAK ENERGY IN THE GULF
EARLY NEXT WEEK SHOULD SHEAR NORTH AND TRACK ACROSS THE EAST. ONE
ISSUE WITH THE NORTHERN/EASTERN PATTERN IS THAT THE 00Z GFS AND CMC
HAVE A STRONGER SHORTWAVE IN THE DAKOTAS BY TUESDAY COMPARED TO
OTHER MODELS. BUT IN GENERAL, THE UPPER LOW IN THE GREAT LAKES
SHOULD SLOWLY PUSH INTO THE EAST LATE WEEK AS IT OPENS UP INTO A
TROUGH.
SOUTHERN STREAM TROUGHING IS FORECAST TO HOVER OVER THE EASTERN
PACIFIC AND SLOWLY TRACK INTO CALIFORNIA MONDAY-TUESDAY. AFTER THAT
ITS EVOLUTION BECOMES QUESTIONABLE AS SOME ENERGY MAY LINGER WHILE
SOME TRACKS NORTHEASTWARD ACROSS THE INTERMOUNTAIN WEST. THE 00Z
ECMWF IS ON THE STRONG SIDE AS IT TRACKS MOST OF THE ENERGY
NORTHEAST AND REACHES THE NORTH-CENTRAL PLAINS AS A STRONG
SHORTWAVE BY THURSDAY. OTHER MODELS TEND TO FAVOR RIDGING REACHING
FARTHER NORTH INTO THE PLAINS FROM THE MORE AGREEABLE SOUTH-CENTRAL
U.S. UPPER RIDGE, SO SOME OUT OF PHASE DIFFERENCES DEVELOP.
FARTHER NORTH, NORTHEAST PACIFIC TROUGHING COULD REACH THE
NORTHWEST AT TIMES, POTENTIALLY STRONGER BY LATE NEXT WEEK. BY
FRIDAY, THE 00Z GFS AND THE EC-AIFS ARE ON THE FASTER SIDE IN
REACHING THE PACIFIC NORTHWEST COMPARED TO THE SLIGHTLY SLOWER EC
AND AI-GFS, AND THE CMC IS THE SLOWEST.
OVERALL, THE WPC FORECAST FAVORED A MULTI-MODEL BLEND OF THE
DYNAMICAL AND AI GUIDANCE EARLY IN THE PERIOD, BUT TRANSITIONED TO
FAVOR INCREASING PROPORTIONS OF ENSEMBLE MEANS TO HALF DAY 6 AND
MORE DAY 7 GIVEN THE INCREASING MODEL SPREAD, ESPECIALLY WITH THE
SMALLER SCALE FEATURES.
..WEATHER/HAZARDS HIGHLIGHTS
UPPER-LEVEL SUPPORT AND A SURFACE FRONTAL SYSTEM WILL LEAD TO
MULTIPLE ROUNDS OF MODERATE TO HEAVY RAIN IN THE EAST NEXT WEEK.
THE PLACEMENT OF THE HEAVIEST AMOUNTS WILL VARY FROM DAY TO DAY,
BUT GENERALLY THE MID-ATLANTIC LOOKS LIKE A FOCUS. A RELATIVELY
STRONG SURFACE HIGH FOR SEPTEMBER SHOULD SET UP OVER QUEBEC AND
SPILL A COLD AIR DAMMING WEDGE SOUTH BEHIND THE FRONT, YIELDING
COLDER THAN AVERAGE TEMPERATURES ACROSS THE NORTHEAST/MID-ATLANTIC,
WITH HIGHS GENERALLY IN THE 60S AND UPPER 50S TUESDAY-WEDNESDAY.
THIS PATTERN WILL ALSO ALLOW FOR ONSHORE WINDS AND POTENTIALLY SOME
CONCERN FOR COASTAL FLOODING FOR PORTIONS OF THE NORTHEAST AND
MID-ATLANTIC.
PACIFIC AND GULF MOISTURE ARE FORECAST TO COMBINE AS THEY STREAM
INTO THE INTERIOR WEST, INCREASING BY TUESDAY AND PERSISTING
THROUGH AT LEAST THURSDAY. RAIN AMOUNTS MAY BECOME HEAVY IN NEW
MEXICO IN PARTICULAR, AND FLOODING WILL BE POSSIBLE--SEE THE
EXCESSIVE RAINFALL OUTLOOKS FOR MORE INFORMATION. SOME CHANCE OF
RAIN WILL EXTEND NORTH ACROSS THE ROCKIES TO HIGH PLAINS TUESDAY
AND INTO THE PLAINS WEDNESDAY-THURSDAY.
MEANWHILE, A WET PATTERN WILL BE IN PLACE ACROSS FLORIDA THROUGH
THE PERIOD, PARTICULARLY FOR THE KEYS AND SOUTHERN PORTIONS OF THE
PENINSULA. WARMER THAN AVERAGE TEMPERATURES SHOULD STAY FARTHER
NORTH ACROSS TEXAS TO THE SOUTHEAST UNDER AN UPPER RIDGE, BUT
GRADUALLY REDUCING IN SCOPE AND MAGNITUDE AS NEXT WEEK PROGRESSES.
TATE
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY MESSAGES
ARE AT:
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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