300
FXUS02 KWBC 181857
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM EDT THU JUL 18 2024
VALID 12Z SUN JUL 21 2024 - 12Z THU JUL 25 2024
***HEAT WAVE CONTINUES ACROSS THE WEST, AND SHOWERS AND STORMS WITH
HEAVY RAINFALL EXPECTED FROM THE FOUR CORNERS TO THE SOUTHEAST***
..GENERAL OVERVIEW
IT REMAINS THE CASE THAT AN AMPLIFIED UPPER PATTERN WITH A STRONG
RIDGE OVER THE WESTERN U.S. AND A BROAD UPPER TROUGH OVER THE
PLAINS AND MIDWEST WILL PERSIST THROUGH NEXT THURSDAY. DANGEROUS,
POTENTIALLY RECORD-SETTING, HEAT WILL DEVELOP UNDERNEATH THE
WESTERN RIDGE AND PERSIST THROUGH THE WEEKEND AND INTO NEXT WEEK.
MONSOON CONDITIONS WILL PERSIST ACROSS THE SOUTHERN ROCKIES, AND A
QUASI-STATIONARY FRONT WILL LIKELY PERSIST ACROSS THE SOUTH-
CENTRAL U.S. TO THE SOUTHERN MID-ATLANTIC. A MULTI-DAY PATTERN
WITH SCATTERED STORMS WITH HEAVY RAINFALL IS FORECAST FOR MUCH OF
THE SOUTHERN TIER OF THE NATION AS A RESULT. TROPICAL MOISTURE
WILL ALSO WORK INTO FLORIDA EARLY NEXT WEEK TO ENHANCE DAILY
SHOWER/THUNDERSTORM ACTIVITY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 12Z MODEL GUIDANCE SUITE MAINTAINS GENERALLY ABOVE AVERAGE
MODEL AGREEMENT FOR THE SUNDAY THROUGH THURSDAY TIME PERIOD, WITH A
GENERAL DETERMINISTIC MODEL BLEND SUFFICING AS A STARTING POINT IN
THE FORECAST PROCESS. THERE ARE SOME MODEST DIFFERENCES THAT EMERGE
TOWARDS THE MIDDLE OF NEXT WEEK, WITH THE ECMWF DISPLACED SOME TO
THE NORTHWEST WITH THE TROUGH AXIS ACROSS THE MIDWEST AND THE CMC
SLIGHTLY MORE AMPLIFIED, BUT STILL GOOD ENOUGH TO HAVE ABOUT 20%
EACH OF THE ECMWF/CMC/GFS AND ABOUT 30-40% OF THE ENSEMBLE MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
DANGEROUS HEAT WILL RAMP UP THIS WEEKEND OVER MUCH OF THE WEST,
WITH MAJOR TO EXTREME HEAT RISK 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
BY 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 NEXT WEEK. THIS PROLONGED
PERIOD OF DRY HEAT COULD ALSO RESULT IN ENHANCED WILDFIRE DANGER.
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 (SUNDAY AND MONDAY)
EXCESSIVE RAINFALL OUTLOOKS. A SLIGHT RISK AREA IS NOW PLANNED FOR
THE NORTHERN NEW MEXICO ROCKIES FOR DAY 4 (12Z SUNDAY-12Z MONDAY)
OWING TO HEAVY RAINFALL EXPECTED IN THE 72-HOUR TIME PERIOD PRIOR,
AND BETTER MODEL AGREEMENT FOR HIGHER TOTALS ACROSS THIS REGION.
THE MARGINAL RISK AREA ALSO INCLUDES PORTIONS OF THE SOUTHERN AND
CENTRAL ROCKIES AND ADJACENT HIGH 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 AND
WELL INTO 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 REPEATED/TRAINING CONVECTION. MARGINAL RISK AREAS
REMAIN IN PLACE FROM THE CENTRAL/SOUTHERN PLAINS THROUGH THE
SOUTHEAST TO THE SOUTHERN MID-ATLANTIC IN BOTH THE DAY 4 AND 5
(SUNDAY THROUGH MONDAY NIGHT) EXCESSIVE RAINFALL OUTLOOKS. A SLIGHT
RISK AREA IS NOW PLANNED FOR THE DAY 5 PERIOD ACROSS PORTIONS OF
CENTRAL TEXAS WHERE THE 12Z DETERMINISTIC MODEL SIGNAL IS NOW IN
BETTER AGREEMENT ON AN AXIS OF ENHANCED 2-4+ INCH TOTALS, AND
THERE WILL LIKELY BE SOME NOTEWORTHY RAINFALL IN THE SAME GENERAL
AREA THE DAY PRIOR. ADDITIONALLY, AN INFLUX OF TROPICAL MOISTURE
INTO FLORIDA EARLY NEXT WEEK MAY ENHANCE DAILY SHOWERS AND
THUNDERSTORMS IN THE SOUTHEAST.
HAMRICK/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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