198
FXUS02 KWBC 190714
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
314 AM EDT MON AUG 19 2024
VALID 12Z THU AUG 22 2024 - 12Z MON AUG 26 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 THERE AND MOIST MONSOONAL FLOW ON THE
WESTERN PERIPHERY OVER THE SOUTHWEST/FOUR CORNERS. THE NORTHWARD
BUILDING RIDGE/HEAT OVER TIME WILL BE SANDWICHED BY AN AMPLIFIED
UPPER TROUGH UPSTREAM INTO THE WEST COAST AND AN AMPLIFIED UPPER
TROUGH DOWNSTREAM OVER THE EAST IN A PATTERN WITH A COOL HIGH
PRESSURE SYSTEM AT THE SURFACE. TROPICAL MOISTURE WILL LURK 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 18 UTC GFS HAS BEEN THE LATEST MODEL TO FAVOR A
SOLUTION ON THE MORE PROGRESSIVE SIDE OF GUIDANCE WHILE MOST OTHER
GUIDANCE HAS BEEN TRENDING SLOWER WITH RECENT RUNS THROUGH 12 UTC.
PREFER TO FAVOR A SLOWER SOLUTION AND THAT TREND SEEMS AT LEAST
MODESTLY SUPPORTED BY LATEST 00 UTC GUIDANCE.
A COMPOSITE BLEND OF MORE COMPATIBLE GUIDANCE OF THE 12 UTC
GFS/UKMET/ECMWF/CANADIAN MODELS WAS USED TO DERIVE THE WPC MEDIUM
RANGE PRODUCT SUITE FOR THURSDAY INTO SATURDAY IN CONJUCTURE WITH
THE 01 UTC NATIONAL BLEND OF MODELS. FORECAST UNCERTAINTY GROWS
QUICKLY LATER WEEKEND INTO NEXT WEEK, BUT THE 12 UTC GFS/ECMWF AT
LEAST OFFER A REASONABLY SLOW PATTERN PROGRESSION WHILE MAINTAINING
BETTER SYSTEM CONTINUITY/AMPLITUDE/IDENTITY AND FOCUS OUT THROUGH
THE WEST. THE EVEN SLOWER TRANSLATION OF RECENT CANADIAN RUNS IS
PLAUSIBLE GIVEN THE PATTERN, BUT WAS HESITANT TO FULLY EMBRACE
GIVEN LACKLUSTER ENSEMBLE SUPPORT, EVEN FROM CANADIAN ENSEMBLES.
..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 THROUGH THE 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 WEST-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.
A MONSOONAL CONVECTIVE PATTERN WILL LINGER OVER THE SOUTHWEST/FOUR
CORNERS STATES THIS WEEK WITH MOIST SOUTHERLY FLOW WEST OF A SLOW
TO DISLODGE UPPER RIDGE AXIS. THE WPC DAY 4/5 EXCESSIVE RAINFALL
OUTLOOKS FOR THURSDAY/FRIDAY DEPICT A MARGINAL RISK AREA FOR
PORTIONS OF ARIZONA, UTAH, SOUTHERN NEVADA AND WESTERN COLORADO.
LOCAL STORMS WITH EMBEDDED HEAVY RAIN COULD CAUSE ISOLATED
FLOODING, PARTICULARLY IN VULNERABLE AREAS.
UPPER TROUGH AMPLIFICATION PROXIMITY ALONG THE WEST COAST PORTENDS
A COOLER AND WETTER PATTERN FOR THE NORTHWEST AND VICINITY THROUGH
LATER THIS WEEK. RAINS AND SPOTTY HIGH ELEVATION MOUNTAIN SNOWS
MAY WORK INLAND ACROSS THE NORTH-CENTRAL INTERMOUNTAIN WEST/ROCKIES
THIS WEEKEND INTO NEXT WEEK DEPENDENT ON THE UNCERTAIN TRACK/TIMING
OF SUPPORTING UPPER TROUGH/LOW EJECTION. RAINS/CONVECTION MAY ALSO
CONSOLIDATE DOWNSTREAM OVER THE NORTH-CENTRAL U.S. GIVEN POSSIBLE
MODERATE CYCLOGENESIS/FRONTOGENESIS FOR FOCUS IN THIS SCENARIO.
UPPER RIDGING FOCUS OVER THE SOUTH-CENTRAL U.S. WILL SUPPORT 5-15
DEGREE ABOVE NORMAL TEMPERATURES. HIGHS WELL INTO THE 100S IN MUCH
OF TEXAS IN PARTICULAR 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 INTO THE WEST/NORTHWEST AND OVER THE EASTERN U.S. WHERE
SOME RECORD COOL OVERNIGHT TEMPERATURE VALUES ARE POSSIBLE.
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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