063
FXUS02 KWBC 141821
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 PM EDT SUN JUL 14 2024
VALID 12Z WED JUL 17 2024 - 12Z SUN JUL 21 2024
...HAZARDOUS HEAT LINGERING OVER THE SOUTH AND EAST MIDWEEK THEN
EASES WITH HEAVY RAIN/CONVECTIVE FRONTAL PASSAGE. HEATWAVE TO
ROBUSTLY REBUILD AND PERSIST THIS WEEK OVER THE WEST...
..OVERVIEW
UPPER TROUGH DEVELOPMENT OVER THE EASTERN/NORTHEASTERN PACIFIC
THIS WEEK WILL LEAD TO THE BUILDING OF AN AMPLIFIED UPPER RIDGE
OVER WESTERN NORTH AMERICA. THIS SETS THE STAGE FOR A PROTRACTED
PERIOD WITH WIDESPREAD HAZARDOUS HEAT TO INCLUDE VARIED RECORD
VALUES AS THE SUPPORTING RIDGE SHOULD PROVE SLOW TO ERODE.
AMPLE ENERGIES DIGGING TO THE LEE OF THE WESTERN RIDGE WILL CARVE
OUT A MEAN UPPER TROUGH POSITION OVER THE EAST-CENTRAL U.S. AS A
WELL DEFINED AND WAVY COLD FRONT ACTS AS A ELONGATED FOCUS FOR
HEAVY RAINFALL/RUNOFF THREATS THROUGH THE CENTRAL U.S. WITH SOME
SLOWING OF THE BOUNDARY LIKELY ACROSS THE EAST. THE LAST VESTIGES
OF ONGOING WIDESPREAD ABOVE NORMAL TO HAZARDOUS TEMPERATURES WILL
SIGNIFICANTLY MODERATE OVER THE SOUTH AND EAST AFTER MIDWEEK TO END
THE HEATWAVE WITH FRONTAL PASSAGE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST MODEL AND ENSEMBLE GUIDANCE CONTINUES TO SHOW ABOVE
NORMAL CLUSTERING THROUGH THE FORECAST PERIOD WITH THE OVERALL
LARGE SCALE PATTERN. THERE REMAIN SOME DETAIL DIFFERENCES, MAINLY
LATE PERIOD, WITH AN UPPER LOW OFF BRITISH COLUMBIA WHICH MAY BRING
SOME SHORTWAVE ENERGY INTO THE PACIFIC NORTHWEST, AND ALSO
SHORTWAVE ENERGY THROUGH THE BROADER TROUGH OVER EASTERN CANADA
WHICH MAY SKIRT THE GREAT LAKES/NORTHEAST. THESE ARE DETAILS THAT
WILL NEED MORE TIME TO RESOLVE. THE WPC FORECAST FOR TODAY USED A
BLEND OF THE DETERMINISTIC GUIDANCE THE FIRST HALF OF THE PERIOD,
INCREASING TO FIFTY PERCENT OF THE ENSEMBLE MEANS LATE PERIOD TO
MITIGATE THE ABOVE DIFFERENCES. OVERALL, MAINTAINED GOOD
CONSISTENCY WITH THE PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
MONSOONAL MOISTURE WILL LINGER OVER THE FOUR CORNERS REGION, WHICH
WILL ALLOW FOR DAILY ROUNDS OF PRECIPITATION THAT COULD RESULT IN
FLASH FLOODING, ESPECIALLY NEAR STEEP TERRAIN AND BURN SCARS. A
MARGINAL RISK OF EXCESSIVE RAINFALL (ERO) REMAINS PLANNED FOR DAY 4
(WEDNESDAY) AND DAY 5 (THURSDAY) FROM ARIZONA TO THE SOUTHERN
ROCKIES/HIGH PLAINS IN A REGION WITH FAVORABLE UPPER DIFFLUENCE.
FAVORABLE UPPER LEVEL SUPPORT AND A WELL DEFINED/WAVY SURFACE
FRONT WILL SHIFT SOUTH AND EASTWARD ACROSS MUCH OF THE CENTRAL AND
EASTERN U.S. LEADING TO MULTIPLE ROUNDS OF HEAVY
SHOWERS/THUNDERSTORMS. WITH AMPLE MOISTURE AND INSTABILITY IN
PLACE, LOCALLY HEAVY RAINFALL WILL BE POSSIBLE AND MAY LEAD TO
INSTANCES OF FLASH FLOODING. A DAY 4/WEDNESDAY ERO MARGINAL THREAT
EXTENDS FROM THE CENTRAL PLAINS/MID-SOUTH TO THE OHIO VALLEY AND
THE NORTHEAST BUT THE FRONT SHOULD BE FAIRLY PROGRESSIVE LIMITING
THE OVERALL FLASH FLOOD RISK . A MARGINAL RISK CONTINUES DAY
5/THURSDAY INTO THE LOWER MISSISSIPPI/TENNESSEE VALLEYS AND INTO
PARTS OF THE SOUTHEAST AND MID-ATLANTIC. AN EMBEDDED SLIGHT RISK
WAS INCLUDED IN THE UPDATE THIS AFTERNOON ACROSS SOUTHEAST VIRGINIA
AND EASTERN NORTH CAROLINA WHERE THE FRONTAL BOUNDARY WILL BE
SLOWER. THE BOUNDARY MAY EVENTUALLY STALL ACROSS THE REGION INTO
THE WEEKEND PROVIDING FOCUS FOR DAILY SUMMERTIME CONVECTION AND
LOCAL HEAVY RAIN THREATS ACROSS THE SOUTHEAST AND FLORIDA.
THE ONGOING HEATWAVE WITH RECORD VALUES SHOULD FINALLY MODERATE
OVER THE SOUTH AND EAST AFTER MIDWEEK. HAZARDOUS HEAT SHOULD SLOWLY
SUPPRESS SOUTH AND EASTWARD WITH TIME AS AMPLIFIED TROUGHING
SETTLES INTO THE EAST-CENTRAL U.S.. MEANWHILE UPSTREAM, THE
BUILDING OF AN AMPLIFIED UPPER RIDGE OVER WESTERN NORTH AMERICA
WILL LEAD INTO AN EPISODE WITH WIDESPREAD HAZARDOUS HEAT OVER MUCH
OF THE WEST NEXT WEEK TO INCLUDE VARIED RECORD VALUES AS THE
SUPPORTING RIDGE SHOULD PROVE SLOW TO ERODE.
SANTORELLI/SCHICHTEL
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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