322
FXUS02 KWBC 190658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT WED JUL 19 2023
VALID 12Z SAT JUL 22 2023 - 12Z WED JUL 26 2023
***DANGEROUS HEAT WAVE PERSISTS ACROSS THE SOUTHWESTERN U.S.
THROUGH EARLY NEXT WEEK, AND HEAT BUILDS FARTHER NORTH ACROSS THE
NORTHERN HIGH PLAINS***
..GENERAL OVERVIEW
THE MAIN STORY THAT WILL CONTINUE TO MAKE WEATHER HEADLINES WILL
BE THE CONTINUATION OF THE INTENSE HEAT WAVE OVER THE DESERT
SOUTHWEST AND THEN BUILDING NORTHWARD TOWARDS MONTANA AND THE
DAKOTAS IN ASSOCIATION WITH AN ANOMALOUS UPPER RIDGE ANCHORED OVER
THE FOUR CORNERS REGION THROUGH THE MIDDLE OF NEXT WEEK.
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 GULF COAST REGION
AND THE FLORIDA PENINSULA, AND THIS WILL ALSO SERVE TO RETRACT THE
UPPER RIDGE WEST TO THE WEST AND RESULT IN SOME ABATEMENT OF THE
ONGOING HEATWAVE ACROSS THE DEEP SOUTH STATES.
..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 ABOUT TUESDAY ACROSS THE CONTINENTAL
U.S., AND NEAR AVERAGE CONFIDENCE ACROSS SOUTHERN CANADA. 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 AND REMAINS IN PLACE THROUGH EARLY NEXT WEEK. THERE
ARE SOME MODEST MODEL DIFFERENCES BY NEXT WEDNESDAY, WITH THE CMC
A LITTLE STRONGER WITH A SHORTWAVE ACROSS THE MIDWEST, THE ECMWF A
LITTLE MORE SUPPRESSED WITH THE RIDGE AXIS NEAR THE CANADIAN
BORDER, AND THE GFS STRONGER WITH A TROUGH NEAR THE PACIFIC
NORTHWEST COAST. OVERALL, THE DEGREE OF MODEL UNCERTAINTY ACROSS
SOUTHERN CANADA HAS IMPROVED COMPARED TO YESTERDAY'S MODEL RUNS.
A MULTI-DETERMINISTIC MODEL BLEND SUFFICES AS A STARTING POINT IN
THE FORECAST PROCESS THROUGH EARLY MONDAY, FOLLOWED BY GRADUAL
INCLUSION OF THE ENSEMBLE MEANS TO ABOUT 40-50% BY MID-WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
THE FRONTAL BOUNDARY THAT DROPS SOUTHWARD TOWARD THE GENERAL
VICINITY OF THE INTERSTATE 20 CORRIDOR ACROSS THE DEEP SOUTH BY
SATURDAY IS EXPECTED TO BE A FOCUS FOR SCATTERED TO PERHAPS
NUMEROUS SHOWERS AND STORMS, PARTICULARLY NEAR ANY SURFACE LOWS
THAT DEVELOP ALONG THE BOUNDARY AND SEA BREEZE BOUNDARIES. THERE
IS A MARGINAL RISK AREA FOR FLOODING POTENTIAL ACROSS THE COASTAL
PLAIN OF THE GULF COAST REGION FROM LOUISIANA TO NORTHERN FLORIDA
ON DAY 4 WHERE THE BEST COMBINATION OF FORCING AND INSTABILITY
WILL EXIST. SOME SLOW MOVING STORMS COULD PRODUCE A QUICK 1-3
INCHES OF LOCALIZED RAINFALL IN SOME OF THESE 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 CORNERS 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 MONDAY, SCATTERED SHOWERS AND STORMS WILL LIKELY LINGER
ACROSS THE GULF COAST REGION, ALTHOUGH NOT EXPECTED TO BE AS
WIDESPREAD. THERE ARE ALSO SIGNS THAT SOME THUNDERSTORM COMPLEXES
COULD DEVELOP ACROSS PORTIONS OF THE MIDWEST IN THE NORTHWEST FLOW
PATTERN ALOFT, ALTHOUGH CONFIDENCE IS LIMITED ON EXACTLY WHERE
THESE WILL BE. ISOLATED MONSOONAL SHOWERS/STORMS ARE LIKELY TO
CONTINUE ACROSS PARTS OF THE FOUR CORNERS REGION.
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 UNFORTUNATELY
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 AND RECORD LONG STREAKS OF 110+ DEGREE READINGS FOR
SOME ARIZONA LOCATIONS. READINGS MAY BE A FEW DEGREES LOWER BY
TUESDAY-WEDNESDAY ACROSS MUCH OF THE INTERMOUNTAIN. 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
EXPECTED 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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