139
FXUS02 KWBC 171901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
301 PM EDT WED JUL 17 2024
VALID 12Z SAT JUL 20 2024 - 12Z WED JUL 24 2024
...DANGEROUS HEAT AND WILDFIRE THREATS WILL BUILD OVER MUCH OF THE
WEST...
...MULTIPLE DAYS OF HEAVY RAIN ARE FORECAST FOR THE FOUR CORNERS,
SOUTH-CENTRAL U.S., SOUTHEAST, AND SOUTHERN MID-ATLANTIC...
..OVERVIEW
AN AMPLIFIED UPPER PATTERN WITH A STRONG RIDGE OVER THE WESTERN
U.S. AND A TROUGH OVER THE CENTRAL AND EASTERN U.S. WILL PERSIST
THROUGH THE MEDIUM RANGE PERIOD. DANGEROUS, POTENTIALLY RECORD-
SETTING, HEAT WILL DEVELOP UNDERNEATH THE RIDGE AND PERSIST THROUGH
THE WEEKEND INTO NEXT WEEK. AN UPPER TROUGH WILL GRADUALLY NUDGE
INTO THE PACIFIC NORTHWEST EARLY NEXT WEEK, WHICH SHOULD HELP
REDUCE TEMPERATURES WEST OF THE CASCADES, BUT INTERIOR AREAS WILL
LIKELY REMAIN HOT AND DRY. COOLER TEMPERATURES WILL ALSO DEVELOP
ACROSS MUCH OF THE CENTRAL AND EASTERN U.S. UNDERNEATH THE UPPER
TROUGH AND IN THE WAKE OF A COLD FRONT.
MULTIPLE DAYS OF HEAVY RAIN ARE FORECAST FOR MOST OF THE SOUTHERN
TIER OF THE NATION. MONSOON CONDITIONS WILL PERSIST IN THE FOUR
CORNERS REGION AND SOUTHERN ROCKIES, AND A SLOW-MOVING FRONTAL
BOUNDARY WILL STALL ACROSS THE SOUTH-CENTRAL U.S., SOUTHEAST, AND
SOUTHERN MID-ATLANTIC. THIS PROLONGED PERIOD OF HEAVY RAIN COULD
RESULT IN FLOODING CONCERNS. TROPICAL MOISTURE WILL ALSO WORK UP
INTO FLORIDA EARLY NEXT WEEK, ENHANCING DAILY SHOWER/THUNDERSTORM
ACTIVITY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES REMAIN IN GOOD AGREEMENT THROUGH THE MEDIUM
RANGE PERIOD. THE WPC FORECAST BLEND WAS COMPRISED OF DETERMINISTIC
SOLUTIONS FROM THE 06Z GFS AND THE 00Z ECMWF/UKMET/CMC, WITH
ENSEMBLE MEANS FROM THE GEFS/ECENS ADDED TO THE BLEND FOR DAYS 5
AND 6. EXCELLENT AGREEMENT AMONG THE MODELS ALLOWED FOR THE
MAJORITY OF THE BLEND TO BE DETERMINISTIC GUIDANCE THROUGH THE END
OF THE PERIOD, WHICH HELPED MAINTAIN DETAIL OF INDIVIDUAL FEATURES
IN THE FORECAST. SLIGHTLY HIGHER WEIGHTS WERE APPLIED TO THE ECMWF
TO DEPICT A SLIGHTLY MORE ROBUST AND RESILIENT WESTERN U.S. UPPER
RIDGE AMPLITUDE OVER TIME.
..WEATHER/HAZARDS HIGHLIGHTS
DANGEROUS HEAT WILL RAMP UP THIS WEEKEND OVER MUCH OF THE WEST,
WITH MAJOR TO EXTREME HEATRISK VALUES EXPECTED FOR MANY INTERIOR
LOCATIONS. HIGH TEMPERATURES IN THE 90S AND 100S WILL BE COMMON,
AND WARM OVERNIGHT LOWS WILL ONLY PROVIDE LIMITED RELIEF. IF THE
CURRENT FORECAST HOLDS, TEMPERATURES MAY REACH RECORD HIGH VALUES
THIS WEEKEND. HEAT WILL WANE SLIGHTLY FOR WESTERN PORTIONS OF THE
PACIFIC NORTHWEST AS AN UPPER TROUGH AND SURFACE COLD FRONT MOVE
INTO THE REGION, BUT TEMPERATURES ELSEWHERE IN THE WEST ARE
FORECAST TO REMAIN WELL ABOVE AVERAGE THROUGH AT LEAST MID-WEEK.
THIS PROLONGED PERIOD OF DRY HEAT COULD RESULT IN ENHANCED WILDFIRE
DANGER IN THE WEST AS WELL.
MEANWHILE, MONSOONAL MOISTURE WILL LINGER OVER THE FOUR CORNERS
REGION, PRODUCING DAILY ROUNDS OF PRECIPITATION. ISOLATED TO
SCATTERED INSTANCES OF FLASH FLOODING WILL BE POSSIBLE, ESPECIALLY
NEAR STEEP TERRAIN AND BURN SCARS. A MARGINAL RISK REMAINS IN PLACE
FOR THIS REGION IN THE WPC DAY 4 AND 5 (SATURDAY AND SUNDAY)
EXCESSIVE RAINFALL OUTLOOKS. THE MARGINAL RISK AREA ALSO INCLUDES
PORTIONS OF THE SOUTHERN/CENTRAL ROCKIES AND ADJACENT PLAINS.
IN THE CENTRAL AND EASTERN U.S., A WELL-DEFINED, WAVY SURFACE
FRONT WILL SLOWLY MEANDER, PROVIDING A FOCUS FOR MULTIPLE ROUNDS OF
HEAVY SHOWERS AND THUNDERSTORMS EACH DAY THROUGH THE WEEKEND INTO
EARLY/MID NEXT WEEK. WITH AMPLE MOISTURE AND INSTABILITY IN PLACE,
LOCALLY HEAVY RAINFALL WILL BE POSSIBLE AND MAY CAUSE INSTANCES OF
FLASH FLOODING, ESPECIALLY IN URBAN AND POOR DRAINAGE AREAS AND
AREAS WITH REPEAT/TRAINING CONVECTION. MARGINAL RISK AREAS REMAIN
IN PLACE FROM THE CENTRAL/SOUTHERN PLAINS THROUGH THE SOUTHEAST TO
THE SOUTHERN MID-ATLANTIC IN THE DAY 4 AND 5 (SATURDAY AND SUNDAY)
EXCESSIVE RAINFALL OUTLOOKS. SOILS MAY BE SATURATED IN SOME AREAS
FROM HEAVY RAINFALL IN THE SHORT RANGE PERIOD (DAYS 1-3), WHICH
COULD ENHANCE FLOODING POTENTIAL AS WELL. ADDITIONALLY, AN INFLUX
OF TROPICAL MOISTURE INTO FLORIDA EARLY NEXT WEEK MAY HELP ENHANCE
DAILY SHOWERS AND THUNDERSTORMS IN THE SOUTHEAST.
DOLAN
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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