915
FXUS02 KWBC 111858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM EDT FRI AUG 11 2023
VALID 12Z MON AUG 14 2023 - 12Z FRI AUG 18 2023
...SEVERE WEATHER AND FLASH FLOODING POSSIBLE ACROSS PARTS OF THE
UPPER MIDWEST TO EASTERN U.S. EARLY NEXT WEEK...
...HEAT WAVE TO PREVAIL FROM THE CENTRAL GULF COAST WESTWARD INTO
THE SOUTHWEST...
...HAZARDOUS HEAT ACROSS THE PACIFIC NORTHWEST INTO MID NEXT
WEEK...
..OVERVIEW
RIDGING IS MOST PERSISTENT ACROSS THE SOUTHWEST THIS PERIOD AS A
TROUGH TRIES TO TAKE OVER THE FLOW PATTERN AS MUCH AS IS FEASIBLE
IN MID TO LATE AUGUST. THE WESTERN AND CENTRAL GULF COAST WILL BE
MOSTLY LEFT OUT OF THE TROUGHING ALOFT THIS PERIOD AS A FRONT
TRIES TO NEAR THE REGION WHILE THE NORTHWEST SLOWLY BACKS OUT OFF
HEATWISE AS WARM CORE RIDGING RELENTS AND FRONTS ATTEMPT TO MAKE
PROGRESS INTO THE AREA. THE FIRST SYSTEM MOVING THROUGH THE BASE
OF THE TROUGH SHOULD BE THE MOST ROBUST, MOVING FROM THE UPPER
MIDWEST, ACROSS THE GREAT LAKES, AND INTO THE NORTHEAST THE FIRST
HALF OF NEXT WEEK, POSSIBLY GENERATING EPISODES OF STRONG TO
SEVERE CONVECTION AND HEAVY RAINFALL.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
OUTSIDE OF THE 00Z CANADIAN, THE OTHER GUIDANCE WAS REASONABLY
AGREEABLE. THIS LED TO A EQUAL BLEND OF THE 00Z UKMET, 00Z
CANADIAN, 00Z GFS, AND 00Z ECMWF FOR MONDAY INTO TUESDAY, BEFORE
SLOWLY REPLACING THE CANADIAN/UKMET WITH THE 00Z NAEFS/ECMWF
ENSEMBLE MEANS FOR THE BLEND USED IN THE PRESSURES, QPF, 500 HPA
HEIGHTS, AND WINDS. THE 13Z NBM WAS THE BASIS FOR THE REST OF THE
GRIDS, WITH SOME ADJUSTMENT IN THE POPS MADE FOR THE QPF.
..WEATHER/HAZARDS HIGHLIGHTS
THE MOST PROMINENT FOCUS FOR ACTIVE WEATHER DURING THE PERIOD WILL
BE FROM THE MIDWEST/GREAT LAKES INTO THE NORTHEAST NEXT
MONDAY-TUESDAY. STRONG COLD FRONT SWEEPING THROUGH THE REGION
SHOULD SUPPORT AREAS OF STRONG TO SEVERE THUNDERSTORMS AND HEAVY
RAINFALL ALONG AND AHEAD OF THE BOUNDARY. THIS IS REFLECTED IN THE
DAY 4 WPC EXCESSIVE RAINFALL OUTLOOK HIGHLIGHTING SLIGHT RISKS
NEAR THE GREAT LAKES/MICHIGAN, WHERE LOCAL 2-4" AMOUNTS ARE
EXPECTED NEAR AND ALONG THE TRACK OF THE SURFACE LOW, WITH A
SECOND RISK AREA ACROSS THE CENTRAL APPALACHIANS WHICH HAS SIMILAR
RAINFALL POTENTIAL. BOTH SAW SOME CHANGES IN THE AFTERNOON
UPDATE. THE STORM PREDICTION CENTER ALSO HIGHLIGHTS A RISK FOR
SEVERE THUNDERSTORMS ACROSS PARTS OF THE OHIO VALLEY/CENTRAL
APPALACHIANS ON MONDAY. THIS SYSTEM SHOULD RACE QUICKLY THROUGH
THE NORTHEAST ON TUESDAY, BUT GIVEN ANOMALOUS MOISTURE AND
SENSITIVITY IN SOME REGIONS OF THE NORTHEAST, HEAVY RAINFALL
AND/OR FLASH FLOODING CANNOT BE RULED OUT. A MARGINAL RISK REMAINS
ACROSS THIS REGION TO THE DAY 5 EXCESSIVE RAINFALL OUTLOOK, THOUGH
IT IS ON THE LOW END OF THE MARGINAL RISK AS IT APPEARS THAT THE
GUIDANCE IS SHOWING AMOUNTS WHICH ARE LIGHTER. SOME RISK FOR
HEAVY RAINS NEAR AN AREA OF LOW PRESSURE ALONG THE BOUNDARY FOR
EASTERN NORTH CAROLINA AS WELL ON TUESDAY AND THE LINGERING
PORTION OF THE BOUNDARY NEAR THE GULF COAST. THE BROAD TROUGHING
ACROSS THE GREAT LAKES SHOULD CONTINUE UNSETTLED WEATHER INTO THE
LATTER PART OF NEXT WEEK FOR THIS REGION. ELSEWHERE, MONSOONAL
MOISTURE WILL CONTINUE INTO THE SOUTHWEST/FOUR CORNERS NEXT WEEK,
PEAKING MONDAY INTO TUESDAY. AS SUCH, MARGINAL RISKS WERE CARRIED
ON BOTH DAYS IN THE EXCESSIVE RAINFALL OUTLOOKS, WITH ONLY SMALL
MODIFICATIONS IN THE AFTERNOON UPDATE.
OPPRESSIVE HEAT WILL CONTINUE THROUGH AT LEAST NEXT WEEK FROM THE
CENTRAL GULF COAST WESTWARD. IT WILL BE MOST PERSISTENT FROM
SOUTHERN AND SOUTHEAST TEXAS INTO LOUISIANA, WITH SOME MODERATION
EXPECTED ACROSS THE SOUTHEAST/FLORIDA MID TO LATE NEXT WEEK.
NUMEROUS DAILY RECORD HIGHS AND WARM OVERNIGHT LOWS ARE LIKELY.
THE COMBINATION OF HEAT AND HUMIDITY WILL ALSO RESULT IN EXTREMELY
DANGEROUS HEAT INDICES IN EXCESS OF 110F IN MANY LOCATIONS. HEAT
SHOULD ALSO BUILD BACK INTO THE SOUTHWEST LATER NEXT WEEK AS WELL.
MEANWHILE, A SECOND AREA OF HEAT IS EXPECTED TO BUILD INTO PARTS
OF THE NORTHWEST THIS WEEKEND AND THROUGH MID NEXT WEEK, WITH
DAYTIME HIGHS 10 TO 20 DEGREES ABOVE NORMAL THROUGH THURSDAY. HIGH
TEMPERATURES IN THE 90S, 100S, AND EVEN LOCALIZED 110S POSSIBLE
ARE EXPECTED ACROSS WASHINGTON, OREGON, AND THE INTERIOR VALLEY OF
CALIFORNIA; OREGON SHOULD SEE THE MOST PERSISTENT HEAT. EROSION
OF THE WARM CORE RIDGE ACROSS THE NORTHWEST WITH TIME SHOULD BEGIN
TO MODERATE TEMPERATURES ON THURSDAY, THOUGH MORE SUBSTANTIALLY BY
NEXT FRIDAY. SEE KEY MESSAGES ISSUED BY WPC FOR ADDITIONAL
INFORMATION AND GRAPHICS RELATED TO THESE TWO HEAT WAVES.
ROTH/SANTORELLI
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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