295
FXUS02 KWBC 091858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM EDT SUN JUL 09 2023
VALID 12Z WED JUL 12 2023 - 12Z SUN JUL 16 2023
...HAZARDOUS TO EXTREME HEAT WILL BUILD ACROSS MUCH OF THE
SOUTHERN U.S. AND INTO THE WEST COAST STATES THROUGH THIS WEEK AND
BEYOND...
...HEAVY RAIN CONCERNS LIKELY TO FOCUS OVER PARTS OF THE MIDWEST
AND MID-MISSISSIPPI VALLEY...
..OVERVIEW
THE UPPER-LEVEL PATTERN OVER THE CONUS NEXT WEEK REMAINS RATHER
UNCHANGED AS A DEEP UPPER LOW REMAINS ANCHORED NEAR HUDSON BAY,
AND UPPER RIDGING EXPANDS ACROSS THE SOUTHERN TIER STATES AND
EVENTUALLY UP THE WEST COAST. MULTIPLE WAVES OF ENERGY WILL ROTATE
AROUND THE SOUTHERN PERIPHERY OF THE LOW AND DRIVE ROUNDS OF
SHOWERS AND STORMS THAT COULD RESULT IN AREAS OF HEAVY RAINFALL
AND FLOODING ACROSS THE MIDWEST AND NORTHEAST. UNDERNEATH THE
RIDGE, HAZARDOUS HEAT WILL BUILD OVER THE SOUTHWEST AND TEXAS AND
EXPAND EASTWARD TO THE GULF COAST AND FLORIDA, AS WELL AS BACK
INTO CALIFORNIA THROUGH NEXT WEEK. PER THE LATEST INFORMATION FROM
THE CLIMATE PREDICTION CENTER, THIS COULD BE THE START OF A LONG
DURATION AND POSSIBLY INTENSE HEAT WAVE FOR PORTIONS OF THE WEST
AND SOUTHERN U.S..
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z/06Z GUIDANCE CAPTURES THE OVERALL SYNOPTIC EVOLUTION
REASONABLY WELL. THEREFORE, A GENERAL MODEL BLEND CONSISTING OF
THE 00Z EC/CMC/UKMET AND 06Z GFS WERE UTILIZED THROUGH DAY 4, WITH
LESS FAVORABILITY FOR THE GFS ON DAY 4 DUE TO ITS POOR HANDLING OF
THE UPPER HIGH OVER THE SOUTHWEST. THE 00Z ECE AND 06Z GEFS WERE
INTRODUCED ON DAY 5 AND CONTINUED THROUGH THE END OF THE PERIOD.
THE 00Z CMCE WAS INTRODUCED ON DAY 6 AND CONTINUED THROUGH THE END
OF THE PERIOD. THERE'S SOME UNCERTAINTY WITH RESPECT TO THE
SHORTWAVE IMPULSES THAT ARE FORECAST TO MOVE THROUGH THE MIDWEST
AND NORTHEAST AND GENERATE THUNDERSTORMS ON DAYS 4 AND 5. THUS,
THE FOCUS OF THE HEAVIEST/EXCESSIVE RAINFALL THAT WILL CAUSE FLASH
FLOODING IS ALSO NOT VERY CERTAIN.
..WEATHER/HAZARDS HIGHLIGHTS
A FRONTAL BOUNDARY SETTLING FROM THE CENTRAL PLAINS INTO THE
MIDWEST/OHIO VALLEY SHOULD PROVIDE THE BEST FOCUS FOR DAILY ROUNDS
OF SHOWERS AND STORMS LATER THIS WEEK. HEAVY RAINFALL IS LOOKING
INCREASINGLY LIKELY IN SOME PLACES, PARTICULARLY ACROSS PORTIONS
OF THE MIDDLE MISSISSIPPI VALLEY INTO THE MIDWEST WHERE A SLIGHT
RISK HAS BEEN ADDED TO BOTH THE DAY 4 AND DAY 5 EXCESSIVE RAINFALL
OUTLOOKS GIVEN SIGNIFICANT MOISTURE AND INSTABILITY AVAILABLE TO
FUEL CONVECTIVE STORMS. THE NORTHERN PORTION OF THIS FRONT SHOULD
DRIFT INTO THE NORTHEAST ON FRIDAY FUELING ANOTHER ROUND OF
SHOWERS AND STORMS. THERE WAS STILL ENOUGH UNCERTAINTY TO PRECLUDE
A SLIGHT RISK ACROSS THE REGION ON DAY 5, BUT GIVEN HOW
SUSCEPTIBLE PORTIONS OF ESPECIALLY VERMONT/NEW HAMPSHIRE ARE (AND
SIGNIFICANT RAINFALL EXPECTED IN THE SHORT RANGE PERIOD), IT'S
POSSIBLE A TARGETED SLIGHT RISK MAY BE NEEDED IN FUTURE UPDATES.
BY NEXT WEEKEND, RAINFALL SHOULD DRIFT SOUTH WITH THE FRONT MORE
INTO PARTS OF THE SOUTH-CENTRAL PLAINS AND CONTINUE ACROSS THE
NORTHEAST LOCATED ON THE EASTERN EDGE OF THE UPPER LEVEL TROUGH.
HAZARDOUS HEAT IS EXPECTED TO RETURN AND EXPAND ACROSS THE
SOUTHERN TIER THROUGH AT LEAST NEXT WEEKEND (AND LIKELY BEYOND PER
LATEST CPC FORECASTS) AS THE UPPER RIDGE STRENGTHENS OVER THE
SOUTH AND UP THE WEST COAST. MUCH ABOVE NORMAL TEMPERATURES WILL
EXPAND FROM THE SOUTHERN HIGH PLAINS INTO THE SOUTHWEST AND
CALIFORNIA, WITH POTENTIAL FOR NUMEROUS RECORD DAILY DAYTIME HIGHS
AND WARM OVERNIGHT LOWS ARE POSSIBLE. FARTHER EAST, AIR
TEMPERATURES SHOULD BE MORE NEAR NORMAL, BUT THE REAL STORY WILL
BE OPPRESSIVE HUMIDITY LEADING TO HEAT INDICES OF 105-115 FOR A
LARGE PORTION THE SOUTH FROM EASTERN TEXAS INTO THE SOUTHEAST AND
FLORIDA. AGAIN, SOME DAILY TEMPERATURE RECORDS ARE
POSSIBLE.TEMPERATURES INTO THE 90S TO NEAR 100 ARE POSSIBLE
WEDNESDAY AND THURSDAY FARTHER NORTH INTO THE SOUTH-CENTRAL PLAINS
BUT COOL OFF LATER IN THE WEEK AS UPPER LEVEL TROUGHING MOVES
ACROSS THE REGION. ELSEWHERE, A COLD FRONT DROPPING SOUTH FROM
CANADA SHOULD BRING TEMPERATURES DOWN TO 5-15F BELOW AVERAGE OVER
PARTS OF THE NORTHERN AND CENTRAL PLAINS.
KEBEDE/SANTORELLI
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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