513
FXUS02 KWBC 082031
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
431 PM EDT FRI SEP 08 2023
VALID 12Z MON SEP 11 2023 - 12Z FRI SEP 15 2023
...HAZARDOUS HEAT FROM THE SOUTH-CENTRAL U.S TO THE SOUTHWEST TO
MODERATE NEXT WEEK...
..OVERVIEW
THE GUIDANCE FOR NEXT WEEK EXPECTS MEAN TROUGHING ALOFT OVER THE
EASTERN HALF OF THE COUNTRY TO BECOME SOMEWHAT DEEPER THAN IN THE
SHORT RANGE PERIOD, WHILE A FLAT RIDGE OVER THE WEST EARLY-MID
WEEK COULD STRENGTHEN BY THURSDAY OR FRIDAY AS NORTHEASTERN
PACIFIC SHORTWAVE ENERGY PROGRESSING INTO/THROUGH THE NORTHWESTERN
U.S./WESTERN CANADA EVENTUALLY STARTS FEEDING INTO THE DOWNSTREAM
MEAN TROUGH. IN ASSOCIATION WITH THE DEEPENING EASTERN TROUGH,
GREAT LAKES INTO NEW ENGLAND/SOUTHEASTERN CANADA LOW PRESSURE AND
FRONTAL SYSTEM WILL PROMOTE AN ORGANIZED AREA OF RAINFALL WITH
HIGHEST AMOUNTS TENDING TO BE OVER THE NORTHEAST. MEANWHILE A
COUPLE FRONTS OVER THE SOUTHERN ROCKIES AND PLAINS WILL PROVIDE
SOME FOCUS FOR WHAT COULD BE A FAIRLY WET PERIOD OVER THAT REGION.
SOUTHERN TIER HEAT SHOULD GET SUPPRESSED AFTER EARLY IN THE WEEK
WHILE COOL DAYTIME TEMPERATURES WILL LIKELY SPREAD EASTWARD FROM
THE CENTRAL U.S. OVER THE COURSE OF NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
GUIDANCE TODAY CONTINUES TO SHOW GOOD AGREEMENT ON THE LARGE SCALE
WITH THE FORECAST EVOLUTION NEXT WEEK. A POSITIVELY TILTED
SHORTWAVE DROPPING INTO THE UPPER MIDWEST EARLY NEXT WEEK SHOULD
CLOSE OFF AN UPPER LOW AROUND MIDWEEK, WITH THIS UPPER LOW OPENING
UP AND EJECTING NORTHEASTWARD WITH THE APPROACH OF NORTHEAST
PACIFIC ENERGY CROSSING THE NORTHERN TIER U.S. AND SOUTHERN
CANADA. UKMET RUNS CONTINUE TO BE DEEPER WITH THE UPPER LOW,
LEADING A MUCH FARTHER NORTH SURFACE LOW BY NEXT WEDNESDAY. THE
GFS IS ALSO SOMEWHAT DEEPER WITH THE SHORTWAVE (NEW 12Z RUN MUCH
FASTER TOO) LATER NEXT WEEK, WHICH SEEMS TO HAVE INFLUENCE ON THE
LATE PERIOD SPEED OF HURRICANE LEE, CURRENTLY FORECAST TO TRACK
NORTHWARD BETWEEN THE EAST COAST AND BERMUDA NEXT WEEK. THE GFS IS
MUCH FASTER TO PULL LEE NORTH BECOMING ABSORBED INTO THE EXITING
NORTHEAST SHORTWAVE, AS EARLY AS NEXT FRIDAY. THE ENSEMBLE MEANS
AND THE ECMWF/CMC ARE SLOWER WITH LEE, SUGGESTING THAT ANY
POSSIBLE IMPACTS ON NEW ENGLAND AND THE CANADIAN MARITIMES ARE
LIKELY TO HOLD OFF UNTIL JUST PAST THE END OF THE PERIOD. THIS
WILL NEED TO BE MONITORED CLOSELY. REFER TO FORECASTS FROM THE
NATIONAL HURRICANE CENTER FOR THE LATEST INFORMATION ON THE
STRENGTH AND TRACK OF LEE.
THE UPDATED WPC FORECAST FOR TODAY USED A STARTING BLEND OF THE
OPERATIONAL DETERMINISTIC MODELS THROUGH DAY 4. REMOVED THE UKMET
AFTER DAY 4/TUESDAY PER ISSUES ABOVE, AND TRENDED AWAY FROM THE
GFS IN THE LATER PERIODS DUE TO ITS FASTER TRACK OF LEE. THE BLEND
AFTER MID WEEK TRENDED MOSTLY TOWARDS THE AGREEABLE ENSEMBLE MEANS
WHICH HELPS MITIGATE TIMING DIFFERENCES WITH THE NEXT SHORTWAVE
INTO THE NORTHWEST LATER NEXT WEEK (ECMWF FASTER THAN THE OTHER
GUIDANCE). THIS APPROACH MAINTAINS GOOD CONTINUITY WITH THE
PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
A PRIMARY REGION OF FOCUS IN THE DAYS 4-5 EXCESSIVE RAINFALL
OUTLOOKS (EROS) THAT COVER MONDAY AND TUESDAY WILL BE OVER AND
EVENTUALLY WEST OF THE SOUTHERN PLAINS WHERE MULTIPLE EPISODES OF
CONVECTION ARE POSSIBLE. CONTRIBUTING INGREDIENTS INCLUDE
SHORTWAVE IMPULSES PROGRESSING WEST TO EAST AROUND UPPER RIDGING
CENTERED OVER MEXICO AND A COUPLE SURFACE FRONTS SAGGING SOUTHWARD
OVER THE SOUTHERN PLAINS. A PERIOD OF EASTERLY UPSLOPE FLOW WILL
BE POSSIBLE OVER THE HIGH PLAINS AS WELL. FORECAST RAINFALL
AMOUNTS AND GUIDANCE SCATTER WITHIN A BACKGROUND OF MODERATELY
POSITIVE MOISTURE ANOMALIES AND SOME INSTABILITY, OFFSET SOMEWHAT
BY RELATIVELY DRY ANTECEDENT CONDITIONS, GENERALLY SUPPORT A
MARGINAL RISK AREA EACH DAY. THE DAY 5 AREA DROPS A BIT SOUTHWARD
VERSUS DAY 4 AS WELL AS EXTENDING FARTHER WEST (INTO ARIZONA
VERSUS JUST INTO THE HIGH PLAINS). REFINEMENTS IN FUTURE MODEL
RUNS MAY ULTIMATELY REVEAL AREAS OF MORE PRONOUNCED FLASH FLOOD
POTENTIAL, BUT FOR NOW THERE CONTINUES TO BE ENOUGH DISAGREEMENT
IN THE PLACEMENT OF HIGHER AMOUNTS TO PRECLUDE A SLIGHT RISK.
MEANWHILE, A MARGINAL RISK AREA HAS BEEN MAINTAINED OVER PARTS OF
NEW ENGLAND FOR DAY 4 AS A WAVY FRONT AND ITS ASSOCIATED MOISTURE
SLOWLY MOVE THROUGH. THE DEVELOPING UPPER/SURFACE SYSTEM REACHING
THE GREAT LAKES COULD PRODUCE ONE OR MORE POCKETS OF MODERATE TO
HEAVY RAINFALL BY THE DAY 5 TIME FRAME BUT CURRENT GUIDANCE
SIGNALS APPEAR TOO LOCALIZED/DIFFUSE FOR A RISK AREA AT THIS TIME.
RAIN AND THUNDERSTORMS OVER THE SOUTHERN PLAINS AND FOUR CORNERS
STATES MAY CONTINUE INTO THE LATTER HALF OF THE WEEK, WITH A
LIGHTER AND MORE SCATTERED TREND OVER ARIZONA AND UTAH. THE
SYSTEM REACHING THE GREAT LAKES BY MIDWEEK SHOULD PRODUCE SOME
RAINFALL OVER PARTS OF THE MIDWEST EARLY IN THE WEEK AND THEN
SPREAD AN ORGANIZED AREA OF RAINFALL FROM THE GREAT LAKES INTO THE
NORTHEAST/MID-ATLANTIC, WITH HIGHEST TOTALS CURRENTLY EXPECTED
OVER THE NORTHERN MID-ATLANTIC/APPALACHIANS INTO NEW ENGLAND.
HAZARDOUS LATE SUMMER HEAT MAY LINGER ACROSS FAR SOUTHERN FLORIDA,
TEXAS, AND THE SOUTHWEST INTO MONDAY. HIGH DEWPOINTS AND HUMIDITY
ESPECIALLY NEAR THE WESTERN GULF COAST WILL LEAD TO HEAT INDICES
AS HIGH AS 110-115F WITH ACTUAL AIR TEMPERATURES UP TO 10-15F
ABOVE NORMAL. SOME RECORD HIGH MINIMUM AND MAXIMUM TEMPERATURES
WILL BE POSSIBLE. EXPECT A COOLER TREND AFTER MONDAY AS SUPPORTING
UPPER LEVEL RIDGING GETS SUPPRESSED. BELOW NORMAL HIGH
TEMPERATURES WILL PREVAIL OVER THE REST OF THE CENTRAL U.S.,
SPREADING EASTWARD WITH TIME. SOME HIGHS MAY BE AS COOL AS 10-15F
BELOW NORMAL, ESPECIALLY OVER THE CENTRAL PLAINS EARLY IN THE
WEEK. TEMPERATURES IN THE NORTHWEST MAY TREND MODERATELY ABOVE
NORMAL BY LATE WEEK UNDER STRONGER RIDGING ALOFT.
SANTORELLI/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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE CENTRAL
ROCKIES, THE SOUTHERN PLAINS, AND
THE CENTRAL PLAINS, MON, SEP 11.
- HEAVY RAIN ACROSS PORTIONS OF THE MID-ATLANTIC AND THE
NORTHEAST, WED, SEP 13.
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHEAST, THU-FRI, SEP 14-SEP
15.
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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