213
FXUS02 KWBC 091859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT SAT SEP 09 2023
VALID 12Z TUE SEP 12 2023 - 12Z SAT SEP 16 2023
..OVERVIEW
LATEST MODELS AND ENSEMBLES SHOW VARYING DEGREES OF UPPER
TROUGHING OVER EASTERN NORTH AMERICA DURING THE PERIOD. WITHIN
THIS MEAN TROUGH, THE MOST PROMINENT FEATURE WILL BE AN UPPER LOW
FORECAST TO CLOSE OFF OVER THE GREAT LAKES BY MIDWEEK AND THEN
LIFT NORTHEASTWARD AS DIFFUSE SHORTWAVE ENERGY ENTERING THE
WESTERN U.S./CANADA EVENTUALLY FEEDS INTO THE TROUGH. THE GREAT
LAKES LOW AND SURFACE SYSTEM SHOULD PRODUCE SOME MODERATE TO HEAVY
RAINFALL FROM THE GREAT LAKES/MID-ATLANTIC INTO THE NORTHEAST. BY
THE END OF NEXT WEEK INTO THE WEEKEND, THE TRACK AND TIMING OF
HURRICANE LEE WILL REQUIRE MONITORING FOR ANY POTENTIAL EFFECTS ON
NEW ENGLAND AND THE CANADIAN MARITIMES. OVER THE WEST, SHORTWAVE
ENERGY WILL PUSH THROUGH THE REGION EARLY IN THE PERIOD BEFORE
UPPER RIDGING ULTIMATELY SETTLES IN BY LATE NEXT WEEK INTO THE
WEEKEND. THE COMBINATION OF WESTERN SHORTWAVE ENERGY AND A
PERSISTENT SOUTHERN PLAINS FRONT WILL FAVOR MULTIPLE EPISODES OF
RAIN AND THUNDERSTORMS OVER THE SOUTHERN PLAINS THROUGH THE
PERIOD, AND EXTENDING AS FAR WEST AS ARIZONA TUESDAY-WEDNESDAY.
COOLER THAN AVERAGE HIGHS WILL PREVAIL OVER A MAJORITY OF THE
CENTRAL/EASTERN U.S. WHILE MODERATELY ABOVE NORMAL HIGHS SHOULD
BECOME ESTABLISHED OVER THE FAR NORTHERN PLAINS AND PACIFIC
NORTHWEST BY LATE NEXT WEEK/WEEKEND.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE FORECAST PERIOD BEGINS WITH TWO MAIN UPPER-LEVEL FEATURES OF
INTEREST INDICATED AMONGST THE GUIDANCE: AN UPPER
TROUGH/DEVELOPING CUTOFF LOW OVER THE UPPER MIDWEST/GREAT LAKES
SHIFTING EASTWARD AND MORE SUBTLE SHORTWAVE ENERGY APPROACHING THE
PACIFIC NORTHWEST FROM UPSTREAM OVER THE PACIFIC. THERE IS DECENT
CLUSTERING AROUND THE EVOLUTION OF THE DEVELOPING CUTOFF LOW
MOVING INTO THE NORTHEAST MID-PERIOD BY ALL GUIDANCE EXCEPT THE
GFS, WHICH REMAINS AN OUTLIER. BOTH THE MOST RECENT 00Z/06Z RUNS
DEPICT A WEAKER AND MORE PROGRESSIVE OPEN WAVE, AND CONTINUOUSLY
VARIABLE SOLUTIONS IN PREVIOUS RUNS DECREASES CONFIDENCE IN THE
GFS. NATURALLY THERE IS MORE DISAGREEMENT BOTH AMONGST THE LATEST
RUNS AND PREVIOUS RUNS ON THE TIMING/PHASING OF THE SHORTWAVE
APPROACHING THE WEST CONSIDERING THE SCALE, BUT THE FACT IT IS AT
LEAST CAPTURED IN SOME RESPECT BY ALL OF THE GUIDANCE EARLY IN THE
PERIOD, INCLUDING THE ENSEMBLE MEANS, HELPS BOLSTER SOME
CONFIDENCE THAT THE GUIDANCE HAS A REASONABLE HANDLE ON ITS
EVOLUTION. THIS WAVE ALONG WITH ADDITIONAL UPPER-LEVEL ENERGY
EVENTUALLY HELPS TO DEVELOP WEAK MEAN TROUGHING OVER THE CENTRAL
U.S. FOLLOWING THE DEPARTURE OF THE UPPER LOW OVER THE MIDWEST IN
MOST OF THE GUIDANCE WITH THE EXCEPTION OF THE 12Z CMC, WHICH HAS
A SLOWER WAVE THAT DIVES FURTHER SOUTHWARD INTO THE SOUTHWEST.
THIS SHOULD LEAD TO SEVERAL DAYS OF ENERGETIC NORTHWEST FLOW OVER
THE PLAINS. MEAN RIDGING LOOKS TO EVOLVE OVER THE WEST IN TANDEM
WITH THE TROUGHING TOWARDS THE CENTRAL/EASTERN U.S. THE LAST, AND
POTENTIALLY BIGGEST CHALLENGE OF THE FORECAST IS THE TRACK OF
HURRICANE LEE AND HOW IT MAY OR MAY NOT COME CLOSE ENOUGH TO THE
EAST COAST TO INTERACT WITH THE WEATHER PATTERN OVER THE CONUS.
THE GFS HAS REMAINED FASTER AND FURTHER NORTHWEST WITH THE TRACK,
WITH THE SYSTEM EVENTUALLY BEING ABSORBED INTO THE UPPER
TROUGH/LOW LIFTING THROUGH THE NORTHEAST. THE ECMWF AND CMC ARE
SLOWER AND FURTHER SOUTH, ALLOWING THIS TROUGH TO DEPART
NORTHEASTWARD INTO CANADA AS THE STORM REMAINS FURTHER SOUTH OVER
THE WESTERN ATLANTIC, AND ANY SUBSEQUENT INTERACTION WITH
TROUGHING OVER THE NORTHEAST OCCURRING BEYOND THE CURRENT FORECAST
PERIOD. FOR NOW, HAVE REMAINED WITH THE SLOWER SOLUTIONS, WITH ANY
ADDITIONAL UPDATES AND MORE SPECIFIC TRACK INFORMATION AVAILABLE
FROM THE NATIONAL HURRICANE CENTER. THE UPDATED WPC FORECAST
BEGINS WITH A COMPOSITE BLEND OF THE DETERMINISTIC GUIDANCE GIVEN
GOOD AGREEMENT IN THE EARLY PERIOD. THE MEANS ARE GRADUALLY
INCREASED IN THE MID- TO LATE PERIOD AS FORECAST UNCERTAINTY
INCREASES AND THE CONTRIBUTION FROM THE GFS IS REMOVED GIVEN THE
NOTED OUTLIER NATURE OF THE SOLUTION WITH REGARDS TO THE UPPER
TROUGH/CUTOFF LOW AND HANDLING OF HURRICANE LEE. THE LATEST UPDATE
FROM THE 12Z GFS CONTINUED THESE NOTED TRENDS.
..WEATHER/HAZARDS HIGHLIGHTS
THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS (EROS) THAT COVER TUESDAY
THROUGH WEDNESDAY NIGHT REFLECT HEAVY RAINFALL/FLASH FLOOD
POTENTIAL OVER TWO GENERAL AREAS, ONE OVER CENTRAL/NORTHERN
PORTIONS OF THE EAST AND THE OTHER OVER/WEST OF THE SOUTHERN
PLAINS. DURING THE DAY 4 TIME FRAME, THE SYSTEM BEGINNING TO
EVOLVE OVER THE GREAT LAKES MAY GENERATE SOME LOCALLY ENHANCED
RAINFALL FROM THE GREAT LAKES/APPALACHIANS INTO THE MID-ATLANTIC
AND INTERIOR NORTHEAST. GUIDANCE IS NOT FULLY AGREEABLE ON THE
EXACT FORECAST SCENARIO QPF-WISE BUT THIS AREA WILL HAVE WET
ANTECEDENT CONDITIONS FROM RECENT AND NEAR-FUTURE RAINFALL. BY
DAY 5 EXPECT A MORE PRONOUNCED POTENTIAL FOR HEAVIER RAINFALL OVER
PORTIONS OF THE NORTHEAST, WHERE THE SLOWER NON-GFS MAJORITY
CLUSTER FOR THE SYSTEM HEADING INTO THE REGION MERITS A SLIGHT
RISK. FROM THE SOUTHERN PLAINS WESTWARD, SHORTWAVE ENERGY WILL
INTERACT WITH ANOMALOUS MOISTURE TO YIELD AREAS OF LOCALLY HEAVY
RAIN AND THUNDERSTORMS. A FRONT PERSISTING OVER THE SOUTHERN
PLAINS WILL PROVIDE ANOTHER RAINFALL FOCUS. THE CORRESPONDING
MARGINAL RISK AREA ON DAY 4 EXTENDS FROM PARTS OF TEXAS INTO THE
FOUR CORNERS REGION, WHILE THE DAY 5 MARGINAL RISK REFLECTS AN
EASTWARD SHIFT IN ACTIVITY INTO COLORADO/NEW MEXICO BUT A DRIER
TREND OVER ARIZONA. A SLIGHT RISK HAS BEEN INTRODUCED FOR PORTIONS
OF THE SOUTHERN PLAINS ON DAY 5 WHERE CONFIDENCE HAS INCREASED IN
THE THREAT FOR HEAVY RAINFALL, PARTICULARLY OVERNIGHT WEDNESDAY
INTO EARLY THURSDAY MORNING. WHILE THERE REMAINS SOME UNCERTAINTY
IN THE SPECIFICS SUCH AS THE TIMING OF UPPER-LEVEL ENERGY,
STRENGTH OF THE LOW-LEVEL JET, THE LOCATION OF A LINGERING SURFACE
BOUNDARY, AND OVERALL AVAILABLE MOISTURE STARTING TO TREND
DOWNWARD, THE GUIDANCE IS RELATIVELY UNANIMOUS IN DEPICTING
LOCALIZED TOTALS OF SEVERAL INCHES OVER THE REGION, WITH AREAL
AVERAGE TOTALS AND HIGH ENSEMBLE PROBABILITIES FOR OVER 1". THE
OVERALL PATTERN HAS BEEN VERY HOT AND DRY OVER THE REGION THIS
SUMMER, BUT MULTIPLE DAYS WITH RAINFALL CHANCES THROUGH MID-WEEK
SHOULD ALSO HELP TO LEAD TO WETTER ANTECEDENT CONDITIONS.
SOME MODERATE TO HEAVY RAINFALL MAY CONTINUE INTO EASTERN NEW
ENGLAND THROUGH LATE NEXT WEEK. RAINFALL AND OTHER SENSIBLE
WEATHER DETAILS FOR NEW ENGLAND BY NEXT WEEKEND WILL DEPEND ON THE
TRACK AND TIMING OF HURRICANE LEE. CONTINUE TO MONITOR NATIONAL
HURRICANE CENTER PRODUCTS FOR THE LATEST INFORMATION ON LEE OVER
THE COMING DAYS. RAIN AND THUNDERSTORM CHANCES LOOK TO SHIFT SOUTH
AND EASTWARD TOWARDS THE LOWER MISSISSIPPI VALLEY/SOUTHEAST AND
GULF COAST LATE WEEK, WHILE CHANCES OVER THE ROCKIES SHOULD TREND
LIGHTER AS UPPER-LEVEL RIDGING SETS IN.
BELOW NORMAL HIGH TEMPERATURES OVER THE CENTRAL U.S. AND
MIDWEST/GREAT LAKES AS OF TUESDAY SHOULD GRADUALLY SPREAD FARTHER
EASTWARD, THOUGH WITH A MODERATING TREND BY FRIDAY-SATURDAY. BEST
POTENTIAL FOR HIGHS 10-15F BELOW NORMAL WILL BE DURING
TUESDAY-THURSDAY OVER THE CENTRAL/SOUTH-CENTRAL PLAINS AS WELL AS
THE GREAT LAKES/OHIO VALLEY AS POST-FRONTAL HIGH PRESSURE SETTLES
IN AND CLOUDS/PRECIPITATION ALSO KEEP TEMPERATURES DOWN. SLIGHTLY
ABOVE NORMAL TEMPERATURES MAY HOLD ON OVER FAR SOUTHERN TEXAS A
LITTLE BEYOND MIDWEEK, WHILE THE PACIFIC NORTHWEST EASTWARD TO THE
FAR NORTHERN PLAINS MAY TREND SOMEWHAT ABOVE NORMAL BY
THURSDAY-SATURDAY.
PUTNAM/RAUSCH
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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