125
FXUS02 KWBC 171901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MON JUL 17 2023
VALID 12Z THU JUL 20 2023 - 12Z MON JUL 24 2023
***DANGEROUS HEAT WAVE PERSISTS ACROSS THE SOUTHERN TIER, WITH
HAZARDOUS HEAT IN THE SOUTHWEST EVEN INTO NEXT WEEK AND OPPRESSIVE
HEAT INDICES IN THE SOUTHEAST THROUGH THE END OF THE WORKWEEK***
..GENERAL OVERVIEW
THE MAIN STORY THAT WILL MAKE WEATHER HEADLINES WILL BE THE
CONTINUATION OF THE HEAT WAVE FROM THE INTERMOUNTAIN WEST TO THE
CENTRAL GULF COAST IN ASSOCIATION WITH AN ANOMALOUS UPPER RIDGE
ANCHORED OVER THE SOUTHERN ROCKIES AND DESERT SOUTHWEST. THE
RIDGE AXIS WILL INITIALLY BE ELONGATED EASTWARD ACROSS INTERIOR
PORTIONS OF THE GULF COAST REGION THROUGH THURSDAY BEFORE
RETRACTING BACK TO THE WEST, AND BUILDING NORTHWARD TO INCLUDE
MORE OF THE NORTHWESTERN HIGH PLAINS, AND A TROUGH BUILDS FROM THE
GREAT LAKES TO THE EAST COAST. MEANWHILE, SHORTWAVE DISTURBANCES
IN NORTHWEST FLOW ALOFT AROUND THE NORTHERN PERIPHERY OF THE RIDGE
WILL LIKELY SUPPORT THE DEVELOPMENT OF MULTIPLE MESOSCALE
CONVECTIVE SYSTEMS THAT WILL BRING EPISODES OF HEAVY RAINFALL AND
STRONG STORMS FROM THE UPPER MIDWEST TO THE NORTHEAST/MID-ATLANTIC
STATES.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE IS IN REASONABLE AGREEMENT WITH REGARDS TO THE
EVOLUTION OF THE SYNOPTIC PATTERN DURING THE MEDIUM RANGE PERIOD.
A GENERAL MODEL BLEND CONSISTING OF THE 00Z EC/UKMET/CMC AND 06Z
GFS WAS USED THROUGH DAY 4. THE 00Z ECE AND 06Z GEFS WERE
INTRODUCED ON DAY 5 WHILE THE 00Z UKMET WAS REMOVED FROM THE BLEND
DUE TO DISCREPANCIES WITH RESPECT TO THE SOUTHERN RIDGE. THE 00Z
CMCE WAS INTRODUCED ON DAY 6 AND BY DAY 7 THE ENSEMBLES MAKE UP
90% OF THE BLEND AND THE 06Z GFS IS REMOVED.
..WEATHER/HAZARDS HIGHLIGHTS
A SURFACE LOW IS FORECAST TO DEVELOP AND INTENSIFY ACROSS THE
GREAT LAKES DURING THE DAY ON THURSDAY, WITH A TRAILING COLD FRONT
EXTENDING SOUTH ACROSS THE CENTRAL APPALACHIANS AND A MOIST
CONVEYOR AHEAD OF IT. WIDESPREAD SHOWERS AND THUNDERSTORMS ARE
EXPECTED TO DEVELOP AHEAD OF THIS FRONT FROM THE CENTRAL
APPALACHIANS TO THE INTERIOR NORTHEAST THROUGH EARLY FRIDAY
MORNING. NOW THAT THE MODEL SIGNAL IS MORE CONCENTRATED WITH THE
00Z GUIDANCE, A SLIGHT RISK AREA IS IN EFFECT FROM SOUTHWEST
PENNSYLVANIA TO THE SOUTHERN ADIRONDACKS FOR THE DAY 4 PERIOD, AND
THIS IS ALSO OWING TO WET ANTECEDENT CONDITIONS FROM MULTIPLE
ROUNDS OF RECENT HEAVY RAINFALL IN THIS REGION. THE POTENTIAL NOW
EXISTS FOR SCATTERED ONE INCH RAINFALL TOTALS, AND ISOLATED 2+
INCH TOTALS WHERE STORMS PERSIST THE LONGEST. FARTHER WEST, SOME
MONSOONAL MOISTURE LOOKS TO ADVECT NORTHWARD INTO PORTIONS OF THE
SOUTHERN ROCKIES, AND AS IT MEETS WITH A FRONTAL SYSTEM IN THE
CENTRAL HIGH PLAINS, THIS WILL BECOME A FOCUS FOR CONVECTION AS
WELL. THURSDAY INTO THURSDAY NIGHT LOOKS TO BE THE MAIN DAY FOR
POTENTIAL FLASH FLOODING AS CONVECTION IS LIKELY TO CONGEAL
OVERNIGHT INTO A LARGE MCS WITH POTENTIALLY HIGH RAIN RATES, AND
THIS IS WHERE THE DAY 4 SLIGHT RISK EXTENDS FROM EASTERN COLORADO
TO CENTRAL KANSAS FOR THIS POTENTIAL. ADDITIONAL SHOWERS AND
STORMS ARE POSSIBLE INTO FRIDAY AND BEYOND IN THIS REGION AS WELL.
WIDESPREAD OPPRESSIVE HEAT UNFORTUNATELY LOOKS TO CONTINUE
THROUGHOUT THE WEEK ACROSS THE SOUTHERN TIER OF THE COUNTRY. THE
DESERT SOUTHWEST WILL CONTINUE TO SEE THE CORE OF THE HOTTEST
OVERALL TEMPERATURES, WITH HIGHS WELL INTO THE 110S FOR THE LOWER
ELEVATIONS, AND LOWS ONLY IN THE 80S TO LOWER 90S PROVIDING
PRACTICALLY NO RELIEF FROM THE PERSISTENT HEAT, WITH MORE DAILY
RECORD HIGHS LIKELY. FARTHER EAST, THE CONCERN WILL BE FOR
OPPRESSIVE HUMIDITY WITH DEWPOINTS IN THE MID 70S TO NEAR 80 TO
COMBINE WITH THE HEAT AND PRODUCE HEAT INDICES OF 105-115+ FOR
EASTERN TEXAS INTO THE LOWER MISSISSIPPI VALLEY, THE DEEP SOUTH,
FLORIDA, AND PARTS OF THE CAROLINAS. FAR SOUTHERN TEXAS COULD
APPROACH HEAT INDICES OF 120 DEGREES. THESE ARE LIKELY TO PEAK
THURSDAY AND FRIDAY, BUT AS THE UPPER RIDGE RETRACTS BACK WEST BY
NEXT WEEKEND, THESE AREAS SHOULD MODERATE CLOSER TO TYPICAL SUMMER
HEAT. INTERIOR AREAS OF THE NORTHWEST AND THE NORTHWESTERN HIGH
PLAINS ARE LIKELY TO SEE TEMPERATURES WARMING TO ABOVE AVERAGE FOR
THE LATTER HALF OF THE WEEK INTO NEXT WEEKEND. SEE KEY MESSAGES
ISSUED BY WPC FOR ADDITIONAL INFORMATION AND GRAPHICS RELATED TO
THIS HEAT WAVE. DOWNSTREAM, THE NORTHERN PLAINS AND MIDWEST ARE
LIKELY TO BE PLEASANT TEMPERATURE WISE, WITH HIGHS IN PARTICULAR
FORECAST TO BE BELOW AVERAGE, WHILE THE NORTHEASTERN U.S. CAN
EXPECT NEAR NORMAL TEMPERATURES.
KEBEDE/HAMRICK
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
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