196
FXUS02 KWBC 160659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT SUN JUL 16 2023
VALID 12Z WED JUL 19 2023 - 12Z SUN JUL 23 2023
...DANGEROUS HEAT WAVE PERSISTS ACROSS THE SOUTHERN TIER NEXT
WEEK, WITH HAZARDOUS HEAT IN THE SOUTHWEST THROUGH THE PERIOD AND
OPPRESSIVE HEAT INDICES IN THE SOUTHEAST THROUGH THE END OF THE
WORKWEEK...
..GENERAL PATTERN OVERVIEW
THE MAIN STORY THAT WILL MAKE WEATHER HEADLINES WILL BE THE
CONTINUATION OF THE HEAT WAVE FROM THE INTERMOUNTAIN WEST TO THE
DEEP SOUTH STATES 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 FRIDAY BEFORE RETRACTING
BACK TO THE WEST AS 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 00Z MODEL GUIDANCE SUITE CONTINUES TO HAVE AN EXCELLENT
OVERALL DEPICTION OF THE SYNOPTIC SCALE PATTERN FOR THE WEDNESDAY
THROUGH SUNDAY TIME PERIOD WITH ABOVE AVERAGE FORECAST CONFIDENCE.
THERE ARE SOME MINOR DIFFERENCES WITH THE UKMET CONCERNING
SURFACE LOW EVOLUTION OFF THE EAST COAST BY THURSDAY, BUT
CERTAINLY WITHIN THE MARGIN OF ERROR, SO A DETERMINISTIC MODEL
BLEND WORKS WELL AS A STARTING POINT IN THE FORECAST PROCESS
THROUGH FRIDAY, WITH SLIGHTLY MORE WEIGHTING TOWARDS THE ECMWF/GFS
SOLUTIONS. EVEN BY NEXT WEEKEND, THE MODELS STILL ARE VERY CLOSE
OVERALL WITH THE RIDGE CENTERED OVER THE FOUR CORNERS REGION, AND
AN AMPLIFYING TROUGH ACROSS THE EASTERN HALF OF THE U.S. WITH
ABOVE AVERAGE CONFIDENCE CONTINUING AND INCLUSION OF THE ENSEMBLE
MEANS CAPPED AT JUST 35% BY SUNDAY. THE 00Z ECMWF IS A LITTLE
STRONGER WITH THE EASTERN TROUGH AND HINTING AT A WEAK CLOSED LOW
OVER THE GREAT LAKES REGION, AND THE CMC IS A LITTLE STRONGER WITH
A SURFACE LOW NEAR NEW ENGLAND BY SUNDAY, BUT BOTH OF THESE MODELS
ARE STILL REASONABLY CLOSE FOR A DAY 7 FORECAST. IN TERMS OF QPF,
THE BASELINE WAS ABOUT 60% NBM, AND 20% EACH OF THE GFS AND ECMWF.
VALUES WERE RAISED BY ABOUT 30 PERCENT OVER THE FLORIDA PENINSULA
TO BETTER ACCOUNT FOR SEA BREEZE CONVECTION.
..WEATHER/HAZARDS HIGHLIGHTS
MULTIPLE ROUNDS OF SHOWERS AND THUNDERSTORMS, SOME OF WHICH MAY BE
ASSOCIATED WITH MESOSCALE CONVECTIVE COMPLEXES, ARE EXPECTED TO
CROSS THE OHIO VALLEY ON WEDNESDAY AROUND THE NORTHEASTERN
PERIPHERY OF THE BIG UPPER RIDGE SITUATED OVER TEXAS. THE QPF
SIGNAL IN THE 00Z MODEL GUIDANCE SUITE HAS SHIFTED A LITTLE BIT TO
THE SOUTH OVER THE PAST FEW RUNS ACROSS PORTIONS OF KENTUCKY AND
NORTHERN TENNESSEE, AND THEREFORE A SLIGHT RISK AREA IS PLANNED
FOR THE NEW DAY 4 EXCESSIVE RAINFALL OUTLOOK FROM CENTRAL KENTUCKY
TO NORTHEASTERN TENNESSEE. THE POTENTIAL EXISTS FOR SOME
SCATTERED 1-2 INCH RAINFALL TOTALS HERE, WHICH MAY FALL IN A
RELATIVELY SHORT PERIOD OF TIME. THE EXISTING MARGINAL RISK HAS
BEEN TRIMMED BACK SOME ACROSS SOUTH FLORIDA TO ACCOUNT FOR
CONVECTION FAVORED NEAR THE SOUTHWESTERN COAST ON DAY 4. GOING
INTO THE DAY 5 PERIOD THURSDAY, A SLIGHT RISK AREA IS PLANNED FOR
THE WESTERN HIGH PLAINS OF COLORADO AND NORTHEAST NEW MEXICO WHERE
SLOW MOVING STORMS ARE LIKELY TO CONGEAL INTO A LARGE MCS THAT MAY
BRING ENHANCED RAINFALL RATES TO PORTIONS OF THAT REGION.
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 INTO NEXT WEEKEND AS WELL.
NUMEROUS DAILY RECORD HIGH TEMPERATURES ARE LIKELY, PERHAPS
CHALLENGING A FEW MONTHLY RECORDS IN A FEW INSTANCES ACROSS THE
SOUTHWEST. FARTHER EAST, OPPRESSIVE HUMIDITY WITH DEWPOINTS IN
THE MID 70S TO NEAR 80 DEGREES WILL LEAD TO DANGEROUS HEAT INDICES
OF 105-115+ FOR EASTERN TEXAS INTO THE LOWER MISSISSIPPI VALLEY ON
WEDNESDAY AND THURSDAY, AND SOME 120 HEAT INDICES ARE WITHIN THE
REALM OF POSSIBILITY FOR THE NORMALLY MORE HUMID LOCATIONS ACROSS
SOUTHERN TEXAS. SEE KEY MESSAGES ISSUED BY WPC FOR ADDITIONAL
INFORMATION AND GRAPHICS RELATED TO THIS HEAT WAVE.
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
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