272
FXUS02 KWBC 181859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT SUN AUG 18 2024
VALID 12Z WED AUG 21 2024 - 12Z SUN AUG 25 2024
..HAZARDOUS HEAT TO PERSIST FOR THE SOUTHERN PLAINS THIS WEEK
..OVERVIEW
THE PREVAILING AMPLIFIED UPPER PATTERN ACROSS MUCH OF OUR COUNTRY
IS FORECAST TO PERSIST THROUGH THE END OF THIS WEEK. THIS PATTERN WILL
BE HIGHLIGHTED BY AN UPPER HIGH CENTERED OVER THE SOUTHERN PLAINS
TO SUSTAIN HAZARDOUS HEAT. THE NORTHWARD BUILDING RIDGE OVER TIME
WILL BE SANDWICHED BY AN AMPLIFIED UPPER TROUGH UPSTREAM NEAR THE
WEST COAST AND AN AMPLIFIED UPPER TROUGH DOWNSTREAM OVER THE EAST
WITH A COOL HIGH PRESSURE SYSTEM AT THE SURFACE WHILE TROPICAL
MOISTURE WILL BE LURKING NEAR THE GULF COAST AND ACROSS FLORIDA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
FORECAST SPREAD REMAINS THE MAIN CONCERN IN THE WESTERN U.S.
THROUGH THE MEDIUM-RANGE FORECAST PERIOD, PRIMARILY AS ATTRIBUTED
TO DIFFERENCES WITH THE HANDLING OF DEEP EASTERN PACIFIC UPPER
TROUGH/LOW ENERGIES INLAND INTO THE WEST/NORTHWEST STARTING LATE
THIS WEEK. THE ECMWF HAS SWITCHED TO THE FASTEST SIDE OF THE
GUIDANCE ENVELOP SINCE YESTERDAY WHILE THE GFS AND UKMET ARE
SLOWER, WITH THE CMC THE SLOWEST SOLUTION. THEIR ENSEMBLE MEANS
ALSO DEPICT THE SAME KIND OF TIMING DIFFERENCES ALTHOUGH NOT AS
PRONOUNCED AS THEIR DETERMINISTIC COUNTERPART. THE LATEST EC-AIFS
ALSO FAVORED A MORE PROGRESSIVE AND LESS AMPLIFIED SOLUTION. THE
FASTER SOLUTION AFFECTS HOW MUCH DOWNSTREAM CYCLOGENESIS WILL OCCUR
ON THE LEE OF THE NORTHERN ROCKIES AND CANADIAN ROCKIES. MODEL
SPREAD REMAINS MODEST REGARDING THE TIMINGS AND AMPLITUDES OF THE
DOWNSTREAM RIDGE OVER THE MID-SECTION OF THE COUNTRY AND NEAR THE
EAST COAST.
THE WPC MORNING FORECAST PACKAGE WAS BASED ON A COMPOSITE BLEND OF
THE 06Z GFS/GEFS, 00Z ECMWF/EC MEAN, AS WELL AS THE 00Z CMC/CMC
MEAN. AGAIN, MORE NOTICEABLE DESCREPANCY FROM YESTERDAY'S FORECAST
PACKAGE WAS ACROSS THE NORTHWESTERN U.S. WITH THE FORMATION OF AN
OCCLUDED LOW PRESSURE SYSTEM DURING THE WEEKEND ON THE LEE OF THE
SOUTHERN CANADIAN ROCKIES.
..WEATHER/HAZARDS HIGHLIGHTS
AN EASTERN U.S. UPPER TROUGH OFFERS SOME LINGERING UNSETTLED
CONDITIONS GIVEN SLOW TRANSLATION, BUT RAINFALL WILL TAPER OFF
MIDWEEK AS SURFACE HIGH PRESSURE BUILDS IN BEHIND A QUITE
REFRESHING COLD FRONTAL PUSH IN THE WAKE OF ERNESTO LIFTING WELL
OFF INTO THE NORTH ATLANTIC. HOWEVER, TRAILING FRONTS SLATED TO
STALL FARTHER SOUTH ACROSS FLORIDA AND VICINITY WILL MAINTAIN
PERIODIC THUNDERSTORM CHANCES THERE OVER A MULTI-DAY PERIOD LATER
WEEK INTO NEXT WEEKEND. FLOODING ISSUES ARE A POSSIBILITY IF HEAVY
RAIN FALLS IN URBAN AREAS. THIS FRONT MOVES SLOWLY AS IT BENDS BACK
TO THE WEST ATOP THE CENTRAL GULF COAST AND BACK NORTH INTO THE
PLAINS. SCATTERED STORMS ARE POSSIBLE NEAR THE FRONT AS IMPULSES
RIDE AND DIG TO THE LEE OF THE UPSTREAM RIDGE ALOFT, BUT WITH
GENERALLY LOW CONFIDENCE IN THE PREDICTED PLACEMENT.
MEANWHILE, A MONSOONAL CONVECTIVE PATTERN WILL CONTINUE TO AFFECT
THE SOUTHWEST/FOUR CORNERS STATES THIS WEEK WITH MOIST SOUTHERLY
FLOW WEST OF THE UPPER RIDGE AXIS. THE WPC DAY 4/5 EXCESSIVE
RAINFALL OUTLOOKS FOR WEDNESDAY/THURSDAY MAINTAIN A MARGINAL RISK
FOR ARIZONA AND PORTIONS OF UTAH, SOUTHEAST CALIFORNIA, SOUTHERN
NEVADA AND WESTERN COLORADO. LOCAL STORMS WITH EMBEDDED HEAVY RAIN
COULD CAUSE ISOLATED FLOODING, PARTICULARLY IN VULNERABLE AREAS.
A SLIGHT RISK MAY BE CONSIDERED WITHIN THE MARGINAL RISK BUT HAS
BEEN HELD OFF DUE TO MODEL DIFFERENCES.
MEANWHILE, UPPER TROUGH AMPLIFICATION PROXIMITY ALONG/OFF THE WEST
COAST PORTENDS A COOLER AND WETTER PATTERN FOR THE NORTHWEST. SOME
RAINS ARE ALSO FORECAST TO BROADLY FOCUS DOWNSTREAM ACROSS THE U.S.
NORTHERN TIER AS THE WEEK PROGRESSES. SOME CONVECTION MAY BREAK OUT
ALONG/AHEAD OF RELATIVELY SLOW MOVING FRONTAL SYSTEMS ACROSS THE
NORTH-CENTRAL U.S. AS THE WEEK PROGRESSES, BUT THE AFOREMENTIONED
FORECAST PLAN DOWNPLAYS FASTER/ORGANIZED ECMWF/UKMET POTENTIAL.
UPPER RIDGING OVER THE SOUTH-CENTRAL U.S. WILL SUPPORT 5-15 DEGREE
ABOVE NORMAL TEMPERATURES. HIGHS WELL INTO THE 100S IN MUCH OF
TEXAS COULD SET DAILY RECORDS AND HIGH DEWPOINTS SHOULD PRODUCE
HEAT INDICES LIKELY ABOVE 110 DEGREES. LOW TEMPERATURES IN THE
UPPER 70S TO LOW 80S WILL EXACERBATE HEAT STRESS AND COULD SET
RECORDS FOR WARM MINIMUM TEMPERATURES. EXPERIMENTAL HEATRISK
CONTINUES TO INDICATE MAJOR TO EXTREME IMPACTS FROM THIS HEAT. THIS
WILL BE IN CONTRAST TO COOLING CONDITIONS TO CREEP INTO THE
WEST/NORTHWEST AND OVER THE EAST TO INCLUDE SOME RECORD VALUES.
KONG/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page