924
FXUS02 KWBC 150659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT MON JUL 15 2024
VALID 12Z THU JUL 18 2024 - 12Z MON JUL 22 2024
...MAJOR HAZARDOUS HEATWAVE AND WILDFIRE THREATS TO BUILD OVER
MUCH OF THE WEST THIS WEEK AND INTO NEXT WEEK...
...HEAVY RAINFALL THREAT FOR THE FOUR CORNERS STATES AND SOUTH-
CENTRAL ROCKIES/HIGH PLAINS AND ALSO THE SOUTH/SOUTHEAST AND
SOUTHERN MID- ATLANTIC WITH A HEATWAVE BREAKING FRONT...
..OVERVIEW
AMPLIFIED UPPER TROUGH DEVELOPMENT OVER THE EASTERN/NORTHEASTERN
PACIFIC THIS WEEK WILL LEAD TO THE BUILDING OF AN AMPLIFIED UPPER
RIDGE DOWNSTREAM OVER WESTERN NORTH AMERICA. THIS SETS THE STAGE
FOR A PROTRACTED PERIOD WITH WIDESPREAD HAZARDOUS HEAT OVER MUCH OF
THE WEST TO INCLUDE RECORD VALUES AS THE SUPPORTING UPPER RIDGE
SHOULD PROVE SLOW TO ERODE. THERE IS ALSO A LINGERING THREAT FOR
SOME LOCALLY HEAVY MONSOONAL DOWNPOURS FOR THE FOUR CORNERS STATES
AND SOUTH-CENTRAL ROCKIES/HIGH PLAINS.
AMPLE ENERGIES DIGGING TO THE LEE OF THE BUILDING WESTERN U.S. UPPER
RIDGE WILL CARVE OUT A MEAN UPPER TROUGH POSITION OVER THE EAST-
CENTRAL U.S. AS A WELL DEFINED AND WAVY COLD FRONT SAGS SOUTHWARD
AND ACTS AS A FOCUS FOR HEAVY RAINFALL/RUNOFF THREATS FROM THE
SOUTH-CENTRAL U.S. TO THE SOUTHERN MID-ATLANTIC AND SOUTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE FORECAST SPREAD THROUGH MEDIUM RANGE TIME
SCALES REMAINS LOWER THAN NORMAL. A WPC BLEND OF BEST CLUSTERED
GUIDANCE FROM THE 18 UTC GFS/GEFS MEAN, 12 UTC UKMET/CANADIAN AND
ECMWF/CANADIAN ENSEMBLE MEANS ALONG WITH THE 01 UTC NATIONAL BLEND
OF MODELS SEEMS TO OFFER A SOLID FORECAST BASIS THURSDAY INTO NEXT
MONDAY WITH REASONABLE DETAIL CONSISTENT WITH A PATTERN WITH ABOVE
NORMAL PREDICTABILITY. THE 12 UTC ECMWF SEEMED A LESS SUPPORTED
SOLUTION, WITH MAIN TREND DIFFERENCES EMINATING FROM THE
EAST/NORTHEAST PACIFIC. OPTED TO GRADUALLY SHADE BLEND FOCUS FROM
THE DETERMINISTIC MODELS TO THE ENSEMBLE MEANS OVER TIME TO SMOOTH
THE ROUGH FORECAST EDGES 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, INCLUDING
SOME FAVORABLE TRENDS FROM THE 00 UTC ECMWF.
..WEATHER/HAZARDS HIGHLIGHTS
A BIG WEATHER STORY WILL BE THE BUILDING AND PERSISTENCE OF A
MAJOR HEATWAVE OVER MUCH OF THE WEST THIS WEEK AND INTO NEXT WEEK
AS PER THE CLIMATE PREDICTION CENTER. KEY MESSAGES REMAIN ACTIVE
FOR WIDESPREAD MODERATE TO LOCALLY MAJOR TO EXTREME HEAT RISK
VALUES TO INCLUDE SOME RECORD MAXIMUM AND MINIMUM HEAT VALUES.
MEANWHILE, 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 FOR
DAY 4/THURSDAY AND DAY 5/FRIDAY FROM EASTERN ARIZONA TO THE SOUTH-
CENTRAL ROCKIES/HIGH PLAINS WITH FAVORABLE UPPER DIFFLUENCE.
FAVORABLE UPPER LEVEL SUPPORT AND A WELL DEFINED/WAVY SURFACE
FRONT WILL SHIFT SOUTHWARD ACROSS 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. WPC DAY
4/5/EROS SHOW A SLOWLY SOUTHWARD SHIFTING MARGINAL RISK AREA FROM
EAST TEXAS THROUGH THE SOUTH/SOUTHEAST AND SOUTHERN MID-ATLANTIC.
AN EMBEDDED SLIGHT RISK AREA NOW FOCUSES THE THREAT ACROSS EASTERN
NORTH CAROLINA GIVEN LATEST GUIDANCE TRENDS AND CONVECTION BIAS
IN A PATTERN WITH HIGHLY FAVORABLE UPPER JET RIGHT ENTRANCE REGION
SUPPORT. THE WAVY BOUNDARY WILL EVENTUALLY STALL OVER THE REGION
INTO THE WEEKEND, PROVIDING FOCUS FOR DAILY SUMMERTIME CONVECTION
AND LOCAL HEAVY RAIN FOR THE SOUTH/SOUTHEAST AND MID- ATLANTIC.
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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