715
FXUS02 KWBC 140659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT FRI JUL 14 2023
VALID 12Z MON JUL 17 2023 - 12Z FRI JUL 21 2023
***DANGEROUS HEATWAVE TO PERSISTENT FROM THE DESERT
SOUTHWEST/INTERMOUNTAIN WEST TO THE GULF COAST STATES ALL WEEK***
..SYNOPTIC OVERVIEW
THE MAIN THING THAT WILL MAKE WEATHER HEADLINES NEXT WEEK 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 BASICALLY
NO ABATEMENT THROUGH FRIDAY 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 WITH ABOVE AVERAGE
FORECAST CONFIDENCE. THERE ARE SOME MINOR DIFFERENCES WITH THE
UKMET CONCERNING A SLIGHTLY LESS AMPLIFIED TROUGH OVER THE MIDWEST
AND OHIO VALLEY EARLY IN THE 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 WEDNESDAY. EVEN BY
FRIDAY, 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 30% BY FRIDAY.
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
THE BEST PROSPECTS FOR 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 MCS EVENTS 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 WILL FEATURE MARGINAL RISK AREAS FOR THE REGIONS
MENTIONED, AND ALSO A PORTION OF EASTERN ARIZONA ON DAY 4 WHERE A
GREATER CONCENTRATION OF MONSOONAL MOISTURE COULD LEAD TO A FEW
ISOLATED INSTANCES OF FLOODING. THERE IS ALSO A MARGINAL RISK
AREA PLANNED FOR PORTIONS OF THE NORTHEAST U.S. FOR 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. GOING BEYOND
TO THE DAY 6 AND 7 TIME PERIOD, THERE WILL LIKELY BE IN INCREASE
IN CONVECTION ACROSS PORTIONS OF THE WESTERN HIGH PLAINS AND ALSO
ACROSS THE CENTRAL APPALACHIANS, POTENTIALLY REACHING THE
NORTHEAST ONCE AGAIN BY FRIDAY.
THE MAIN HEADLINE WILL CONTINUE TO BE THE WIDESPREAD OPPRESSIVE
HEAT AND HUMIDITY THAT WILL AFFECT MUCH OF THE SOUTH-CENTRAL 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.
FARTHER EAST, DOWNRIGHT OPPRESSIVE HUMIDITY WITH DEWPOINTS IN THE
MID 70S TO LOW 80S WILL LEAD TO DANGEROUS HEAT INDICES OF 105-115+
FOR A LARGE PORTION OF THE GULF COAST REGION FROM EASTERN TEXAS
INTO THE DEEP SOUTH AND FLORIDA. AGAIN, SOME DAILY TEMPERATURE
RECORDS ARE POSSIBLE. SEE KEY MESSAGES ISSUED BY WPC FOR
ADDITIONAL INFORMATION AND GRAPHICS RELATED TO THIS HEAT WAVE.
ABOVE NORMAL TEMPERATURES MAY ALSO EXPAND NORTHWARD INTO PARTS OF
THE CENTRAL PLAINS AND MIDWEST EARLY NEXT WEEK.
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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