905
FXUS02 KWBC 142135
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
534 PM EDT FRI JUL 14 2023
VALID 12Z MON JUL 17 2023 - 12Z FRI JUL 21 2023
...HEAT WAVE PERSISTS ACROSS THE SOUTHERN TIER NEXT WEEK, WITH
RISING HEAT INDICES IN THE EAST AS THE WEEK PROGRESSES...
..OVERVIEW
A PERSISTENT AND ANOMALOUSLY STRONG RIDGE WILL CONTINUE TO CAUSE
EXCESSIVE TO RECORD-BREAKING HEAT ACROSS MUCH OF THE SOUTHERN TIER
OF THE COUNTRY THROUGH NEXT WEEK. THE DESERT SOUTHWEST CAN EXPECT
UNRELENTING HEAT WITH HIGHS IN THE 110S LIKELY TO BREAK RECORDS,
WHILE AREAS OF THE SOUTHEAST ARE LIKELY TO SEE HEAT INDICES CLIMB
UPWARDS TO DANGEROUS LEVELS AGAIN TUESDAY-FRIDAY. FARTHER NORTH, A
MORE PROGRESSIVE PATTERN IS EXPECTED, WITH SHORTWAVES AND TROUGHS
ALOFT PROMOTING SURFACE FRONTS AND SHOWERS/STORMS ACROSS PARTS OF
THE CENTRAL AND EASTERN LOWER 48.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO BE LOCKED IN ON SHOWING AN UPPER HIGH
OF 594+ DM OVER THE FOUR CORNERS STATES AS THE PERIOD BEGINS
MONDAY, WITH RIDGING EXPANDING EAST ACROSS THE SOUTHEAST ON
WEDNESDAY-THURSDAY AS UPPER TROUGHING LIFTS OUT OF THE
EAST-CENTRAL CONUS. MODELS ALSO ARE WELL CLUSTERED FOR THE LEAD
TIME WITH A SHORTWAVE AND ASSOCIATED SURFACE LOW MOVING EAST
ACROSS SOUTHERN CANADA NEAR THE U.S. BORDER THROUGH MUCH OF THE
WEEK, THOUGH WITH SOME TIMING DIFFERENCES WITH THIS AND THE FRONT
BY THURSDAY AND BEYOND. THE EASTERN PACIFIC STARTS TO SHOW SOME
PLACEMENT DIFFERENCES WITH AN UPPER LOW, ESPECIALLY WITH THE NEW
12Z GFS COMING IN WITH A SOUTHERN POSITION COMPARED TO OTHER
MODELS. BUT OVERALL MODEL AGREEMENT IS RATHER GOOD. THE EARLY PART
OF THE WPC MODEL BLEND CONSISTED OF A BLEND FAVORING THE 00/06Z
GFS AND 00Z ECMWF WITH SMALLER PROPORTIONS OF THE CMC AND UKMET,
GRADUALLY TRANSITIONING THE BLEND TO ABOUT HALF ENSEMBLE MEANS
WITH TIME. CHANGES TO THE NBM IN TERMS OF QPF INCLUDED INCREASING
COVERAGE OF LIGHT AMOUNTS IN THE INTERMOUNTAIN WEST, AND TRYING TO
REDUCE A DOUBLE AXIS OF ENHANCED RAIN TOTALS IN THE OHIO VALLEY ON
TUESDAY-WEDNESDAY THAT SEEMED TO BE FROM MODEL DIFFERENCES
CLUSTERING WITH TWO AXES RATHER THAN LEGITIMATE.
..WEATHER/HAZARDS HIGHLIGHTS
THE BEST PROSPECTS FOR MODERATE TO HEAVY RAINFALL NEXT WEEK ARE
EXPECTED IN A GENERAL CORRIDOR FROM THE EASTERN DAKOTAS/MINNESOTA
SOUTHEASTWARD ACROSS THE MIDWEST/OHIO VALLEY AND CENTRAL
APPALACHIANS. THE COMBINATION OF A QUASI-STATIONARY FRONT
LINGERING ACROSS THE OHIO VALLEY AND A COUPLE OF SURFACE LOWS
PASSING ACROSS THE GREAT LAKES IN TANDEM WITH SHORTWAVE
PERTURBATIONS IN NORTHWEST FLOW ALOFT WILL SUPPORT THE DEVELOPMENT
OF MULTIPLE MESOSCALE CONVECTIVE SYSTEMS THAT SHOULD OVERALL BE
FAIRLY PROGRESSIVE IN NATURE, BUT THERE COULD ALSO BE SOME
INSTANCES OF TRAINING CONVECTION THAT COULD LEAD TO HEAVIER
RAINFALL TOTALS. FOR NOW, BOTH THE DAY 4 AND DAY 5 EXCESSIVE
RAINFALL OUTLOOKS FEATURE MARGINAL RISK AREAS FOR THE REGIONS
MENTIONED. ADDITIONALLY, A MARGINAL RISK REMAINS IN PLACE FOR
PARTS OF THE NORTHEAST FOR POSSIBLY HEAVY SHOWERS AND STORMS THAT
DEVELOP AHEAD OF A COLD FRONT ON TUESDAY, AND IT IS POSSIBLE PARTS
OF THIS REGION COULD EVENTUALLY NEED A SLIGHT RISK IN FUTURE
UPDATES, ESPECIALLY IF THE MAIN AXIS SETS UP OVER AREAS THAT HAVE
BEEN HAMMERED BY RECENT DOWNPOURS. MEANWHILE, THIS UPDATE ADDS
MARGINAL RISKS TO PARTS OF THE FLORIDA PENINSULA FOR MONDAY AND
TUESDAY SINCE THERE COULD BE HIGH RAIN RATES WITH CONVECTION IN A
MOIST (2+ STANDARD DEVIATIONS ABOVE AVERAGE PRECIPITABLE WATER
VALUES) AND UNSTABLE ENVIRONMENT. THERE IS SOME CHANCE FOR
MONSOONAL MOISTURE TO COME INTO THE SOUTHWEST BY MONDAY, WHICH WPC
HAS BEEN CARRYING A MARGINAL RISK FOR, AND SCATTERED SHOWERS COULD
SPREAD FARTHER NORTHEAST ON TUESDAY AND INCREASE IN
COVERAGE/AMOUNTS IN THE HIGH PLAINS INTO MID-LATE NEXT WEEK.
ADDITIONAL ROUNDS OF CONVECTION ARE POSSIBLE FOR THE OHIO VALLEY
INTO THE EAST FOR THE LATTER HALF OF NEXT WEEK AS WELL.
THE MAIN HEADLINE WILL CONTINUE TO BE THE WIDESPREAD OPPRESSIVE
HEAT AND HUMIDITY THAT WILL AFFECT THE SOUTH-CENTRAL TO
SOUTHEASTERN U.S. AND ALSO EXTREME HEAT FOR THE DESERT SOUTHWEST
THROUGH THE END OF THE WEEK (AND LIKELY BEYOND PER LATEST CPC
FORECASTS). NUMEROUS DAILY RECORD HIGH TEMPERATURES ARE LIKELY,
PERHAPS CHALLENGING A FEW ALL-TIME RECORDS IN A FEW INSTANCES
ACROSS THE SOUTHWEST. AREAS OF THE GREAT BASIN MAY BE MORE
FORTUNATE TO SEE DECREASING COVERAGE OF HIGHS OVER 100F AFTER
MONDAY, BUT MAY WARM UP AGAIN INTO LATE WEEK. FARTHER EAST,
OPPRESSIVE HUMIDITY WITH DEWPOINTS IN THE MID 70S TO LOW 80S WILL
LEAD TO DANGEROUS HEAT INDICES OF 105-115+ FOR EASTERN TEXAS INTO
THE LOWER MISSISSIPPI VALLEY ON MONDAY AND EXTENDING EAST INTO THE
DEEP SOUTH/FLORIDA AND PORTIONS OF THE CAROLINAS AS THE WEEK
PROGRESSES. SEE KEY MESSAGES ISSUED BY WPC FOR ADDITIONAL
INFORMATION AND GRAPHICS RELATED TO THIS HEAT WAVE.
TATE/HAMRICK
HAZARDS:
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHEAST.
- HAZARDOUS HEAT ACROSS MUCH OF THE DESERT SOUTHWEST INTO PORTIONS
OF SOUTHEASTERN UTAH, ACROSS THE SOUTHERN ROCKIES, THROUGH THE
SOUTHERN PLAINS, DEEP SOUTH, AND MUCH OF THE SOUTHEASTERN U.S.
INCLUDING FLORIDA AND INTO THE MID-ATLANTIC, MON-FRI, JUL 17-JUL
21.
- HAZARDOUS HEAT ACROSS THE SOUTHERN PORTION OF THE INTERIOR
VALLEY IN CALIFORNIA, MON-TUE, JUL 17-JUL 18.
- HAZARDOUS HEAT ACROSS CENTRAL GREAT BASIN, MON, JUL 17.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHERN ROCKIES, SOUTHERN
HIGH PLAINS, AND FROM THE CENTRAL PLAINS TO THE MID-MISSISSIPPI
VALLEY, MON-WED, JUL 17-JUL 19.
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
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