147
FXUS02 KWBC 140718
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
318 AM 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 SINKS DOWN THROUGH THE REGION. 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
MODEL AND ENSEMBLE FORECAST CLUSTERING THROUGH MEDIUM RANGE TIME
SCALES IS BETTER THAN NORMAL, BOLSTERING FORECAST CONFIDENCE. A
COMPOSITE OF THE 18 UTC GFS AND 12 UTC ECMWF/UKMET/CANADIAN ALONG
WITH THE 01 UTC NATIONAL BLEND OF MODELS SEEMS TO OFFER A SOLID
FORECAST BASIS WEDNESDAY-FRIDAY WITH DETAIL CONSISTENT WITH A
PATTERN WITH ABOVE NORMAL PREDICTABILITY. OPTED TO INTRODUCE
SOME GEFS/ECMWF/CANADIAN ENSEMBLE INPUT INTO THE BLEND AT LONGER
TIME FRAMES THROUGH NEXT WEEKEND AMID SLOWLY GROWING FORECAST
SPREAD. THIS STRATEGY MAINTAINS EXCELLENT WPC PRODUCT CONTINUITY
AND IS IN LINE WITH A COMPOSITE OF NEWER 00 UTC CYCLE GUIDANCE.
..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
FRONTS REMAIN SET TO SHIFT SOUTHWARD AND EASTWARD ACROSS MUCH OF
THE CENTRAL AND EASTERN U.S. WILL LEAD 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
MID-ATLANTIC/NORTHEAST AS THE MAIN FRONT SHIFTS SOUTHEASTWARD. A
MARGINAL RISK CONTINUES DAY 5/THURSDAY INTO THE LOWER
MISSISSIPPI/TENNESSEE VALLEYS AND DOWN ACROSS THE MID-ATLANTIC AND
TOWARD THE SOUTHEAST. HEAVY PRECIPITATION CHANCES WILL FURTHER
PROGRESS SOUTHWARD LATER WEEK AS THIS FRONT SETTLES SOUTH, AND
DAILY PRECIPITATION CHANCES WILL PERSIST IN FLORIDA WITH SUMMERTIME
CONVECTION FROM SEA BREEZE CONVERGENCE. LOCALLY HEAVY RAIN WILL BE
POSSIBLE IN THESE AREAS WITH HEAVY THUNDERSTORM ACTIVITY.
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. AND LEADS TO FRONTAL PASSAGE.
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.
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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