550
FXUS02 KWBC 151856
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 PM EDT MON JUL 15 2024
VALID 12Z THU JUL 18 2024 - 12Z MON JUL 22 2024
...DANGEROUS HEAT AND WILDFIRE THREATS WILL BUILD OVER MUCH OF THE
WEST THIS WEEK AND INTO NEXT WEEK...
...MONSOON CONDITIONS CONTINUE FOR THE FOUR CORNERS STATES; HEAVY
RAIN WILL DEVELOP IN THE SOUTH, SOUTHEAST, AND SOUTHERN MID-
ATLANTIC...
..OVERVIEW
AN AMPLIFIED UPPER PATTERN WILL RESULT IN A STRONG RIDGE ACROSS
THE WESTERN U.S. AND TROUGH ACROSS THE EASTERN U.S. THROUGH MOST OF
THE MEDIUM RANGE PERIOD. AN UPPER TROUGH WILL ATTEMPT TO MOVE INTO
THE PACIFIC NORTHWEST LATE IN THE PERIOD, BUT PROGRESS WILL BE SLOW
DUE TO THE STRONG RIDGE OVER MUCH OF THE WEST. DANGEROUS HEAT WILL
DEVELOP UNDERNEATH THE RIDGE, AND TEMPERATURES MAY REACH NEAR
RECORD VALUES OVER THE WEEKEND. IN ADDITION TO DANGEROUS HEAT, HOT
TEMPERATURES, LOW HUMIDITY/DRY FUELS, AND BREEZY WINDS WILL RESULT
IN AN INCREASED THREAT OF WILDFIRES IN PORTIONS OF THE PACIFIC
NORTHWEST ON THURSDAY. BETTER MOISTURE WILL BE LOCATED TO THE SOUTH
ACROSS THE FOUR CORNERS REGION AND SOUTHERN ROCKIES WHERE MONSOON
CONDITIONS WILL LIKELY CONTINUE THROUGH THIS WEEK INTO NEXT WEEK.
UNDERNEATH THE TROUGH IN THE EAST, A SLOW MOVING FRONTAL BOUNDARY
WILL SAG INTO THE SOUTH-CENTRAL U.S., SOUTHEAST, AND MID-ATLANTIC.
THIS BOUNDARY IS FORECAST TO STALL AND CREATE A PROLONGED PERIOD
OF HEAVY RAIN THAT COULD RESULT IN FLOODING CONCERNS. AREAS NORTH
OF THE BOUNDARY WILL FINALLY SEE A BREAK IN THE HEAT AS COOLER AIR
MOVES IN FROM CANADA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS ARE IN GOOD AGREEMENT ON THE LARGE SCALE UPPER LEVEL
PATTERN, AND THERE IS AN EXPECTED AMOUNT OF UNCERTAINTY IN THE
FINER SCALE DETAILS FOR THE MEDIUM RANGE PERIOD. THE MAIN MODEL
DIFFERENCES CONCERN HOW THE MODELS ARE HANDLING ENERGY IN THE
UPPER LEVEL TROUGHS IN THE PACIFIC NORTHWEST AND EASTERN CANADA,
WHICH WILL AFFECT LOCATION AND TIMING OF SURFACE FRONTS AND
SENSIBLE WEATHER. THE WPC BLEND WAS COMPRISED OF A GENERAL BLEND OF
DETERMINISTIC GUIDANCE FROM THE GFS/ECMWF/CMC/UKMET FOR THE FIRST
HALF OF THE PERIOD, AND ENSEMBLE MEANS FROM THE GEFS/CMCE WERE
ADDED TO THE BLEND FOR THE SECOND HALF OF THE PERIOD TO IRON OUT
SOME MODEL DIFFERENCES. THE AFTERNOON FORECAST PUT SLIGHTLY LESS
WEIGHT ON THE 00Z UKMET AND ECMWF SINCE THESE DETERMINISTIC
SOLUTIONS STRAYED FARTHER AWAY FROM THE OTHER SOLUTIONS AND
ENSEMBLE MEANS.
..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.
THE NWS HEATRISK PRODUCT IS SHOWING WIDESPREAD MODERATE TO LOCALLY
MAJOR TO EXTREME HEATRISK VALUES DEVELOPING MID-WEEK AND
STRENGTHENING THIS WEEKEND, AND RECORD-SETTING TEMPERATURES WILL
BE POSSIBLE. THIS HEAT WAVE IS FORECAST TO CONTINUE INTO THE WEEK
TWO PERIOD, PER THE CLIMATE PREDICTION CENTER OUTLOOK, AND HOT
TEMPERATURES COULD RESULT IN A PROLONGED PERIOD OF ENHANCED
WILDFIRE DANGER AS WELL.
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 REMAINS IN THE EXCESSIVE RAINFALL
OUTLOOK (ERO) FOR DAY 4/THURSDAY AND DAY 5/FRIDAY FROM THE FOUR
CORNERS REGION TO THE SOUTH-CENTRAL ROCKIES/HIGH PLAINS WITH
FAVORABLE UPPER DIFFLUENCE, INSTABILITY, AND MOISTURE.
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. THE
DAY 4/THURSDAY AND DAY 5/FRIDAY 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, FAR
SOUTHEASTERN VIRGINIA, AND FAR NORTHEASTERN SOUTH 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.
THE FRONTAL SYSTEM MOVING SOUTH ACROSS THE CENTRAL AND EASTERN
U.S. WILL FINALLY BRING RELIEF FROM THE HEAT THAT HAS BEEN
PLAGUING THE EASTERN TWO-THIRDS OF THE NATION SINCE EARLY JULY.
THIS FRONT WILL USHER IN COOLER AIR FROM CANADA, AND TEMPERATURES
WILL DROP TO NEAR OR BELOW AVERAGE MID-WEEK THROUGH THE WEEKEND.
DOLAN/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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