786
FXUS02 KWBC 150700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT SAT JUL 15 2023
VALID 12Z TUE JUL 18 2023 - 12Z SAT JUL 22 2023
***DANGEROUS HEAT WAVE PERSISTS ACROSS THE SOUTHERN TIER NEXT
WEEK, WITH RISING HEAT INDICES IN THE EAST AS THE WEEK
PROGRESSES***
..OVERVIEW
THE MAIN THING THAT WILL MAKE WEATHER HEADLINES TUESDAY THROUGH
SATURDAY WILL BE THE CONTINUED PERSISTENCE OF AN ANOMALOUS UPPER
RIDGE THAT WILL BE ANCHORED IN PLACE ACROSS THE DESERT SOUTHWEST
AND EXTENDING EASTWARD ACROSS TEXAS AND THE CENTRAL GULF COAST,
WITH LITTLE TO NO ABATEMENT THROUGH THE END OF THE WEEK WITH
UNRELENTING HEAT AND HUMIDITY LIKELY SETTING SOME RECORD HIGHS.
THIS IN TURN WILL FAVOR A SERIES OF DOWNSTREAM UPPER SHORTWAVES
AND TROUGHS FROM THE UPPER MIDWEST TO THE EAST COAST THAT WILL
SUSTAIN A SERIES OF MESOSCALE CONVECTIVE COMPLEXES WITHIN
NORTHWEST FLOW ALOFT, ESPECIALLY FROM MINNESOTA TO THE OHIO VALLEY
AND CENTRAL APPALACHIANS, AND SHOWERS AND STORMS FOR THE NORTHEAST
AHEAD OF A COLD FRONT ON TUESDAY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE HAS AN EXCELLENT OVERALL DEPICTION OF
THE SYNOPTIC SCALE PATTERN FOR NEXT WEEK AND INTO SATURDAY WITH
ABOVE AVERAGE FORECAST CONFIDENCE. THERE ARE SOME MINOR
DIFFERENCES WITH THE UKMET CONCERNING A SLIGHTLY FASTER SURFACE
LOW/WAVE OVER THE OHIO VALLEY EARLY-MID WEEK, BUT CERTAINLY WITHIN
THE MARGIN OF ERROR, SO A DETERMINISTIC MODEL BLEND WORKS WELL AS
A STARTING POINT IN THE FORECAST PROCESS THROUGH EARLY THURSDAY.
EVEN BY FRIDAY/SATURDAY, THE MODELS STILL ARE VERY CLOSE OVERALL
WITH THE RIDGE CENTERED OVER EASTERN AZ/WESTERN NM, AND A WELL
DEVELOPED TROUGH CROSSING THE GREAT LAKES, WITH ABOVE AVERAGE
CONFIDENCE CONTINUING AND INCLUSION OF THE ENSEMBLE MEANS CAPPED
AT JUST 35% BY SATURDAY. IN TERMS OF QPF, VALUES WERE RAISED
ABOVE THE NBM TO MORE CLOSELY MATCH THE QPF PATTERN PORTRAYED BY
THE ECMWF FOR THE ROCKIES AND DESERT SOUTHWEST TO ACCOUNT FOR A
GRADUAL INCREASE IN MONSOONAL MOISTURE ACROSS THIS REGION.
RAINFALL TOTALS WERE ALSO INCREASED BY ABOUT 30% FOR THE FLORIDA
PENINSULA OWING TO A LOW BIAS NOTED IN THE NBM. ELSEWHERE, THE
BASELINE FOR QPF WAS ABOUT 60% NBM, AND 20% EACH OF THE GFS AND
ECMWF.
..WEATHER/HAZARDS HIGHLIGHTS
MULTIPLE ROUNDS OF SHOWERS AND THUNDERSTORMS, SOME OF WHICH MAY BE
ASSOCIATED WITH MESOSCALE CONVECTIVE COMPLEXES, ARE EXPECTED TO
CROSS THE MIDWEST AND THE OHIO VALLEY ON THURSDAY AROUND THE
NORTHEASTERN PERIPHERY OF THE BIG UPPER RIDGE SITUATED OVER TEXAS.
THE QPF SIGNAL IN THE 00Z MODEL GUIDANCE SUITE HAS INCREASED OVER
THE PAST FEW RUNS AND ALSO AGREES BETTER IN THE PLACEMENT OF THE
MAIN QPF AXIS, AND THEREFORE A SLIGHT RISK AREA IS PLANNED FOR THE
NEW DAY 4 EXCESSIVE RAINFALL OUTLOOK FROM CENTRAL ILLINOIS TO
CENTRAL KENTUCKY. THE POTENTIAL EXISTS FOR SOME SCATTERED 2+ INCH
RAINFALL TOTALS HERE DURING THIS TIME, WHICH MAY FALL IN A
RELATIVELY SHORT PERIOD OF TIME. FOR THE NORTHEAST U.S., SHOWERS
AND STORMS AHEAD OF AN APPROACHING COLD FRONT ARE EXPECTED TO
RESULT IN AREAL RAINFALL AVERAGES OF 0.5 TO 1 INCH ON TUESDAY.
EVEN THOUGH THIS TYPE OF RAINFALL IS NORMALLY NOT ALL THAT
NOTEWORTHY, THE ANTECEDENT CONDITIONS OWING TO POTENTIALLY
EXCESSIVE RAINFALL OVER THE WEEKEND WILL TEND TO MAKE THE NORTHERN
APPALACHIANS MORE VULNERABLE TO ADDITIONAL RAIN, SO A SLIGHT RISK
AREA WAS ADDED FOR THIS REGION AS WELL ON DAY 4 TO ACCOUNT FOR
THIS. THE EXISTING MARGINAL RISK REMAINS FOR SOUTH FLORIDA WITH
ANOMALOUS MOISTURE IN PLACE. GOING INTO THE DAY 5 PERIOD
WEDNESDAY, PORTIONS OF THE OHIO VALLEY AND INTO THE CENTRAL
APPALACHIANS MAY CONTINUE TO HAVE LINGERING SHOWERS AND STORMS,
AND SOME OF THESE COULD ALSO BE LOCALLY HEAVY, SO A MARGINAL RISK
IS PLANNED HERE. THE SAME HOLDS TRUE FOR NORTHERN PARTS OF THE
UPPER MIDWEST WHERE AN ORGANIZED CONVECTIVE COMPLEX MAY DEVELOP,
WITH A MARGINAL RISK AREA PLANNED. ANOTHER COMPLEX OF HEAVY
SHOWERS AND STORMS MAY FORM OVER PORTIONS OF THE WESTERN HIGH
PLAINS BY MIDWEEK, SO THAT WILL CONTINUE TO BE MONITORED.
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 PROBABLY INTO NEXT WEEKEND AS
WELL. 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. 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
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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