282
FXUS02 KWBC 120647
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 AM EDT SAT AUG 12 2023
VALID 12Z TUE AUG 15 2023 - 12Z SAT AUG 19 2023
...HEAT WAVE TO PREVAIL FROM THE CENTRAL GULF COAST WESTWARD INTO
THE SOUTHWEST...
...HAZARDOUS HEAT ACROSS THE PACIFIC NORTHWEST INTO MID NEXT
WEEK...
..OVERVIEW
THE UPPER FLOW PATTERN SHOULD BE FAIRLY AMPLIFIED ACROSS THE
NORTHERN TIER AND INTO PARTS OF THE EAST NEXT WEEK AS A VIGOROUS
INITIAL SHORTWAVE THROUGH THE NORTHEAST TUESDAY INTO WEDNESDAY
WILL GIVE WAY TO ANOTHER STRONG SYSTEM INTO THE UPPER MIDWEST,
GREAT LAKES, AND THE NORTHEAST LATE WEEK. THIS EASTERN U.S.
TROUGHING SHOULD FINALLY ERODE HEAT ACROSS THE SOUTHEAST, BUT
HAZARDOUS HEAT IS EXPECTED TO PERSIST THROUGH THE SOUTHERN PLAINS
INTO THE SOUTHWEST ALL OF NEXT WEEK. A HEAT WAVE ACROSS THE
PACIFIC NORTHWEST REGION STARTING THIS WEEKEND SHOULD LAST THROUGH
ABOUT MID WEEK BEFORE LOWER HEIGHTS MOVE BACK INTO THE REGION.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
INCREASING MODEL AGREEMENT WITH THE INITIAL SHORTWAVE THROUGH THE
NORTHEAST TUESDAY-WEDNESDAY ALLOWED FOR A EQUAL BLEND OF THE
LATEST DETERMINISTIC GUIDANCE THROUGH DAY 5. BY DAY 5 INTO 6, WITH
THE NEXT SHORTWAVE MOVING ACROSS THE GREAT LAKES REGION, THE
18Z/AUG 11 GFS WAS FASTER THAN THE REST OF THE GUIDANCE, AND THE
NEW 00Z RUN EVEN FASTER. GIVEN THIS IS A TYPICAL BIAS FOR THE GFS,
WPC FAVORED A BLEND OF THE SLOWER ECMWF AND CMC MODELS FOR THIS
SYSTEM (ALONG WITH THE ENSEMBLE MEANS). THE ECMWF AND CMC ARE MORE
CONSISTENT THROUGH DAY 7, BUT WITH PLENTY OF UNCERTAINTY IN THE
DETAILS. TRENDED MORE TOWARDS THE ENSEMBLE MEANS FOR DAY 7. THIS
APPROACH ALSO WORKED WELL LATER IN THE PERIOD ACROSS THE NORTHWEST
WHERE MODELS ARE CONSISTENT IN SHOWING LOWERING HEIGHTS PUSHING
THE RIDGE MORE INTO THE CENTRAL PLAINS, BUT WITH SOME
UNCERTAINTIES IN TIMING.
..WEATHER/HAZARDS HIGHLIGHTS
A QUICK MOVING COLD FRONT THROUGH THE NORTHEAST ON TUESDAY MAY
BRING SOME THREAT FOR SHOWERS AND THUNDERSTORMS AHEAD OF IT. GIVEN
SENSITIVITY TO RAINFALL ACROSS PORTIONS OF THE NORTHEAST, A LOW
END MARGINAL RISK REMAINS IN THAT REGION ON THE DAY 4/TUESDAY
EXCESSIVE RAINFALL OUTLOOK. THIS BOUNDARY SHOULD SLOW/STALL AS IT
WEAKENS ACROSS THE SOUTHEAST INTO THE MIDDLE OF THE WEEK, BUT
ANOMALOUS MOISTURE AND INSTABILITY ALONG THE BOUNDARY AND ACROSS
FLORIDA COULD BRING AT LEAST A LOCALIZED HEAVY RAINFALL/FLASH
FLOOD RISK ACROSS PORTIONS OF THIS AREA TUESDAY INTO WEDNESDAY.
THE NEXT SYSTEM LATER IN THE WEEK SHOULD BRING SHOWERS AND
THUNDERSTORMS BACK TO PARTS OF THE MIDWEST/GREAT LAKES INTO THE
NORTHEAST, WHILE FLORIDA REMAINS UNSETTLED THROUGH THE WEEK WITH
DIURNAL SHOWERS AND STORMS. MONSOONAL MOISTURE WILL CONTINUE INTO
THE SOUTHWEST/FOUR CORNERS THROUGH ABOUT TUESDAY, WITH MARGINAL
RISKS INDICATED ON THE DAY 4 ERO. SHOWERS MAY EXPAND ACROSS PARTS
OF THE GREAT BASIN AND WEST LATER NEXT WEEK AS WEAK UPPER
TROUGHING MOVES NORTHWARD OFF CALIFORNIA.
THE BIG STORY DURING THE MEDIUM RANGE PERIOD WILL CONTINUE TO BE
OPPRESSIVE HEAT LASTING INTO NEXT WEEKEND FROM THE CENTRAL GULF
COAST INTO THE SOUTHERN PLAINS. NUMEROUS DAILY RECORD HIGHS AND
WARM OVERNIGHT LOWS ARE LIKELY, AND THE COMBINATION OF HEAT AND
HUMIDITY WILL ALSO RESULT IN EXTREMELY DANGEROUS HEAT INDICES IN
EXCESS OF 110F IN MANY LOCATIONS. HAZARDOUS HEAT THIS WEEKEND INTO
EARLY NEXT WEEK ACROSS THE SOUTHEAST, SHOULD MODERATE WEDNESDAY AS
TROUGHING DROPS INTO THE REGION. MEANWHILE, A SECOND AREA OF HEAT
WILL BUILD INTO PARTS OF THE NORTHWEST THIS WEEKEND INTO 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. EROSION OF THE WARM CORE RIDGE
ACROSS THE NORTHWEST WITH TIME SHOULD BEGIN TO MODERATE
TEMPERATURES ON THURSDAY AND ESPECIALLY FRIDAY. SEE KEY MESSAGES
ISSUED BY WPC FOR ADDITIONAL INFORMATION AND GRAPHICS RELATED TO
THESE TWO HEAT WAVES. TROUGHING ACROSS THE WESTERN U.S. SHOULD
PUSH THE RIDGE EAST, WITH HEAT BEGINNING TO BUILD BACK INTO THE
CENTRAL PLAINS BY NEXT FRIDAY.
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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