285
FXUS02 KWBC 180653
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 AM EDT TUE JUL 18 2023
VALID 12Z FRI JUL 21 2023 - 12Z TUE JUL 25 2023
***DANGEROUS HEAT WAVE PERSISTS ACROSS THE SOUTHWESTERN U.S.
THROUGH EARLY NEXT WEEK, AND HEAT BUILDS FARTHER NORTH ACROSS THE
NORTHWESTERN HIGH PLAINS***
..GENERAL OVERVIEW
THE MAIN STORY THAT WILL MAKE WEATHER HEADLINES WILL BE THE
CONTINUATION OF THE HEAT WAVE OVER THE DESERT SOUTHWEST AND
BUILDING NORTHWARD TOWARDS MONTANA AND THE WESTERN DAKOTAS IN
ASSOCIATION WITH AN ANOMALOUS UPPER RIDGE ANCHORED OVER THE FOUR
CORNERS REGION. THE RIDGE AXIS WILL INITIALLY BE ELONGATED
EASTWARD ACROSS INTERIOR PORTIONS OF THE GULF COAST REGION THROUGH
EARLY FRIDAY BEFORE RETRACTING BACK TO THE WEST, AND BUILDING
NORTHWARD TO INCLUDE MORE OF THE NORTHWESTERN HIGH PLAINS, AND A
BROAD TROUGH BUILDS FROM THE GREAT LAKES TO THE EAST COAST.
MEANWHILE, A FRONTAL BOUNDARY DROPPING SOUTH FROM THE OHIO VALLEY
TO THE DEEP SOUTH WILL BRING EPISODES OF POTENTIALLY HEAVY
RAINFALL AND STRONG STORMS ACROSS MUCH OF THE SOUTHEAST U.S.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
SIMILAR TO THE PAST SEVERAL DAYS, THE 00Z MODEL GUIDANCE SUITE
STARTS OFF WITH VERY GOOD AGREEMENT AND ABOVE AVERAGE CONFIDENCE
ON THE SYNOPTIC SCALE THROUGH SUNDAY, AND ALL OF THE GUIDANCE
SUGGESTS THE UPPER RIDGE AXIS WILL CONTRACT TO THE WEST AS A BROAD
TROUGH AXIS BUILDS IN ACROSS THE EASTERN HALF OF THE NATION. THE
GFS IS A LITTLE STRONGER WITH A SHORTWAVE CROSSING THE OHIO VALLEY
THIS WEEKEND COMPARED TO THE OTHER GUIDANCE, BUT OTHERWISE FITS IN
WELL ELSEWHERE. THE LATEST 00Z GFS FITS IN MUCH BETTER WITH THE
OVERALL CONSENSUS COMPARED TO EARLIER RUNS ACROSS SOUTHERN CANADA
EARLY NEXT WEEK. THE BIGGEST DIFFERENCE BY THE END OF THE
FORECAST PERIOD IS A STRONGER SOLUTION WITH THE 00Z CMC REGARDING
A TROUGH BUILDING OVER THE PACIFIC NORTHWEST, WHEREAS THE ENSEMBLE
MEANS FAVOR THIS TROUGH TO BE MORE OFFSHORE. OVERALL, THE DEGREE
OF MODEL UNCERTAINTY ACROSS SOUTHERN CANADA HAS IMPROVED COMPARED
TO THE 12/18Z MODEL RUNS. A MULTI-DETERMINISTIC MODEL BLEND
SUFFICES AS A STARTING POINT IN THE FORECAST PROCESS THROUGH
SUNDAY, FOLLOWED BY GRADUAL INCLUSION OF THE ENSEMBLE MEANS TO
ABOUT HALF BY TUESDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE FRONTAL BOUNDARY THAT DROPS SOUTHWARD TOWARD THE GENERAL
VICINITY OF THE INTERSTATE 20 CORRIDOR ACROSS THE DEEP SOUTH BY
THIS WEEKEND IS EXPECTED TO BE A FOCUS FOR SCATTERED TO PERHAPS
NUMEROUS SHOWERS AND STORMS, PARTICULARLY NEAR ANY SURFACE LOWS
THAT DEVELOP ALONG THE BOUNDARY. THERE IS A MARGINAL RISK AREA
FOR FLOODING POTENTIAL FROM THE GENERAL VICINITY OF THE OZARKS TO
THE SOUTHERN APPALACHIANS ON DAY 4 WHERE THE BEST COMBINATION OF
FORCING AND INSTABILITY WILL EXIST. THIS AXIS THEN REACHES THE
COASTAL PLAIN OF THE GULF COAST REGION FROM LOUISIANA TO NORTHERN
FLORIDA ON DAY 5 WHERE A MARGINAL RISK IS ALSO IN EFFECT WHERE
SOME SLOW MOVING STORMS COULD PRODUCE A QUICK 1-3 INCHES OF
LOCALIZED RAINFALL IN SOME AREAS. ACROSS THE WESTERN U.S., A
MARGINAL RISK AREA IS VALID FOR BOTH DAYS 4 AND 5 FROM
SOUTHEASTERN COLORADO ACROSS MUCH OF NEW MEXICO AND INTO EASTERN
PORTIONS OF ARIZONA. WITH THE CORE OF THE UPPER HIGH EXPECTED TO
BE OVER THE FOUR CORNER REGION, THIS WILL RESULT IN SOME ADVECTION
OF MONSOONAL MOISTURE FROM WESTERN MEXICO NORTHWARD ACROSS THE
SOUTHERN ROCKIES, RESULTING IN ISOLATED TO PERHAPS SCATTERED
COVERAGE OF SLOW MOVING THUNDERSTORMS THAT CAN BE EXPECTED MAINLY
DURING THE AFTERNOON AND EVENING HOURS. LOOKING AHEAD TO SUNDAY
AND BEYOND, SHOWERS AND STORMS WILL LIKELY LINGER ACROSS THE GULF
COAST REGION, AND THERE ARE SIGNS THAT SOME THUNDERSTORM COMPLEXES
COULD DEVELOP ACROSS PORTIONS OF THE MIDWEST, ALTHOUGH CONFIDENCE
IS LIMITED ON EXACTLY WHERE THESE WILL BE. ISOLATED MONSOONAL
SHOWERS/STORMS ARE LIKELY TO CONTINUE ACROSS PARTS OF ARIZONA AND
NEW MEXICO.
THE STUBBORN UPPER RIDGE ACROSS THE INTERMOUNTAIN WEST/DESERT
SOUTHWEST WILL RESULT IN A CONTINUATION OF THE ONGOING EXTREME
HEAT GOING THROUGH NEXT WEEKEND AND EARLY NEXT WEEK, WITH
TEMPERATURES GENERALLY RUNNING 5 TO 15 DEGREES ABOVE AVERAGE FOR
BOTH HIGHS AND LOWS FROM THE DESERT SOUTHWEST TO MONTANA AS THE
HEAT BUILDS FARTHER TO THE NORTH, AND ALSO EXTENDING ACROSS THE
NORTH-CENTRAL U.S. BY MONDAY AND TUESDAY. THIS WILL EQUATE TO
HIGHS WELL INTO THE 110S FOR THE LOWER ELEVATIONS OF EASTERN
CALIFORNIA, SOUTHERN ARIZONA, AND SOUTHERN NEVADA, WITH THE
POTENTIAL FOR ADDITIONAL RECORD HIGH TEMPERATURES BEING
ESTABLISHED. THERE IS SOME GOOD NEWS TO REPORT ACROSS MUCH OF THE
SOUTHERN PLAINS AND INTO THE GULF COAST REGION WHERE SOME
ABATEMENT IN THE INTENSE HEAT IS LIKELY BY THE WEEKEND AS A
FRONTAL BOUNDARY HERALDS THE ARRIVAL OF MORE SEASONAL CONDITIONS
COMPARED TO THE PAST WEEK OF OPPRESSIVE HEAT. IT WILL STILL BE
QUITE HOT AND HUMID FOR SOUTHERN TEXAS WHERE HEAT INDICES MAY
EXCEED 110 DEGREES DURING PEAK AFTERNOON HEATING. MUCH OF THE
EASTERN U.S. SHOULD GENERALLY BE WITHIN A FEW DEGREES OF LATE JULY
AVERAGES WITH NO MAJOR HEAT WAVES EXPECTED EAST OF THE MISSISSIPPI
RIVER.
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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