625
FXUS02 KWBC 151900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM 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 HAZARDOUS HEAT IN THE SOUTHWEST THROUGH THE PERIOD AND
OPPRESSIVE HEAT INDICES IN THE SOUTHEAST THROUGH THE END OF THE
WORKWEEK...
..OVERVIEW
A PERSISTENT AND ANOMALOUSLY STRONG UPPER RIDGE WILL CONTINUE TO
CAUSE EXCESSIVE TO RECORD-BREAKING HEAT ACROSS MUCH OF THE
SOUTHERN TIER OF THE COUNTRY THROUGH NEXT WEEK. THE DESERT
SOUTHWEST CAN EXPECT UNRELENTING HEAT WITH HIGHS IN THE 110S
LIKELY TO BREAK RECORDS, WHILE AREAS OF THE SOUTHEAST ARE LIKELY
TO SEE HEAT INDICES CLIMB UPWARDS TO DANGEROUS LEVELS AGAIN
TUESDAY-FRIDAY AS THE RIDGE BUILDS EASTWARD, BEFORE POSSIBLY
RETRACTING BY NEXT SATURDAY AND ALLOWING FOR MORE TYPICAL SUMMER
HEAT IN THOSE EASTERN AREAS. FARTHER NORTH, A MORE PROGRESSIVE
PATTERN IS EXPECTED, WITH SHORTWAVES AND TROUGHS ALOFT PROMOTING
SURFACE FRONTS AND SHOWERS/STORMS ACROSS PARTS OF THE CENTRAL AND
EASTERN LOWER 48.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO BE LOCKED IN ON SHOWING AN UPPER HIGH
OF 594+ DM OVER THE FOUR CORNERS STATES AND INTO TEXAS AS THE
PERIOD BEGINS TUESDAY, WITH THE 00Z EC ENSEMBLE MEMBERS EVEN
INDICATING AN 80 PERCENT CHANCE OF A 600DM RIDGE IN THE SOUTHERN
HIGH PLAINS ON WEDNESDAY AS RIDGING EXPANDS EASTWARD TEMPORARILY
INTO THE SOUTHEAST ESPECIALLY WEDNESDAY-THURSDAY. MODELS THEN
AGREE FAIRLY WELL THAT TROUGHING SHOULD AMPLIFY A BIT INTO THE
SOUTHEAST LATE WEEK AND SERVE TO RETRACT THE RIDGE/HIGH FARTHER
WEST, FOCUSING IN THE FOUR CORNERS REGION AGAIN AND PERHAPS
EXPANDING NORTH ACROSS THE INTERMOUNTAIN WEST.
NORTH OF THE PERSISTENT RIDGE, MOST MODEL GUIDANCE IS WELL
CLUSTERED FOR THE LEAD TIME WITH A SHORTWAVE AND ASSOCIATED
SURFACE LOW MOVING EAST ACROSS SOUTHERN CANADA NEAR THE U.S.
BORDER THROUGH MUCH OF THE WEEK. HOWEVER, THE 00Z CMC DID NOT HAVE
AS CONSOLIDATED A SHORTWAVE AS OTHER MODELS AND SPLIT, SO IT WAS
NOT PREFERRED BY LATE WEEK. MODELS ALSO AGREE IN SHOWING AN UPPER
LOW IN THE EASTERN PACIFIC DRIFTING GRADUALLY SOUTHEAST WITH TIME.
THIS FEATURE'S POSITION IS PRETTY WELL CLUSTERED IN THE
MODELS/ENSEMBLE MEANS, THOUGH THE 00Z GFS WAS DISPLACED SOMEWHAT
SOUTHEAST OF OTHER GUIDANCE.
OVERALL MODEL AGREEMENT IS RATHER GOOD AND THUS CONFIDENCE IN THE
PATTERN IS ABOVE AVERAGE. THE FORECAST BLEND CONSISTED OF A BLEND
FAVORING THE 00Z ECMWF AND 06Z GFS WITH SMALLER PROPORTIONS OF THE
CMC AND UKMET, INCLUDING SOME ENSEMBLE MEANS BY DAYS 5-7 THOUGH
WAS ABLE TO KEEP A MAJORITY DETERMINISTIC MODEL BLEND. PREFERRED
THE ECENS MEAN OVER THE GEFS MEANS AS THE FORMER SHOWED SOME
SLIGHT STREAM SEPARATION NEAR THE GREAT LAKES REGION TO INDICATED
A SHORTWAVE, MORE LIKE MOST DETERMINISTIC MODELS.
..WEATHER/HAZARDS HIGHLIGHTS
FOR TUESDAY-WEDNESDAY, CONVECTION IS LIKELY ALONG THE BASE OF A
TROUGH FROM THE DAKOTAS/MIDWEST SOUTHEASTWARD ACROSS THE
MIDWEST/OHIO VALLEY. MESOSCALE CONVECTIVE SYSTEMS ARE POSSIBLE
WITHIN THIS NORTHWESTERLY TO WESTERLY FLOW IN CONJUNCTION WITH LOW
PRESSURE/FRONTAL SYSTEMS AT THE SURFACE. ON TUESDAY NIGHT, GLOBAL
MODELS ARE ALREADY DIRECTLY INDICATING RAIN RATES OF 2+ INCHES OF
RAINFALL WITHIN 3 HOURS OVER PARTS OF THE OHIO VALLEY, AND
LOCALIZED RAIN RATES WILL LIKELY BE HIGHER THAN THAT. ADJUSTED THE
SLIGHT RISK IN THE EXCESSIVE RAINFALL OUTLOOK SOUTHWARD A BIT PER
MODEL TRENDS. SIMILARLY, THE MARGINAL RISK ON WEDNESDAY WAS
ADJUSTED SOUTH IN THE OHIO VALLEY WHILE ONE IN THE UPPER MIDWEST
WAS MAINTAINED. MEANWHILE IN THE NORTHEAST, INCREASED MOISTURE
AHEAD OF A FRONT COULD LEAD TO SOME LOCALLY HEAVY RAINFALL ON
TUESDAY. GENERALLY AMOUNTS SHOULD STAY ABOUT HALF AN INCH TO AN
INCH, BUT GIVEN THAT ANTECEDENT CONDITIONS IN THE REGION ARE
ALREADY SATURATED DUE TO RECENT RAINFALL, MORE RAINFALL COULD
CAUSE ADDITIONAL FLOODING/FLASH FLOODING ISSUES. ADDITIONAL ROUNDS
OF RAINFALL ARE ALSO LIKELY IN THE EAST INTO THE LATTER PART OF
NEXT WEEK. OVER THE FLORIDA PENINSULA, MARGINAL RISKS ARE IN PLACE
ON TUESDAY AND WEDNESDAY SINCE THERE COULD BE HIGH RAIN RATES WITH
CONVECTION IN A MOIST (2+ STANDARD DEVIATIONS ABOVE AVERAGE
PRECIPITABLE WATER VALUES) AND UNSTABLE ENVIRONMENT. URBAN AREAS
WOULD BE OF MOST CONCERN FOR ANY FLASH FLOODING POSSIBILITIES.
SOME MONSOONAL MOISTURE COULD START TO COME INTO THE SOUTHWEST
NEXT WEEK. RAIN TOTALS SHOULD REMAIN LIGHT TO MODERATE THROUGH
TUESDAY-WEDNESDAY BUT MAY INCREASE IN AMOUNTS OVER THE CENTRAL
HIGH PLAINS BY THURSDAY-FRIDAY WITH A FRONT IN THE VICINITY.
WIDESPREAD OPPRESSIVE HEAT UNFORTUNATELY LOOKS TO CONTINUE INTO
NEXT WEEK ACROSS THE SOUTHERN TIER OF THE COUNTRY. THE DESERT
SOUTHWEST WILL CONTINUE TO SEE THE CORE OF THE HOTTEST ABSOLUTE
TEMPERATURES, WITH HIGHS WELL INTO THE 110S AND LOWS PERHAPS ONLY
DROPPING INTO THE 80S OR EVEN 90S IN SOME LOCATIONS. THE SOUTHERN
PLAINS CAN EXPECT HIGHS NEARING OR EXCEEDING 100F THAT SHOULD BE
UNRELENTING THROUGH NEXT WEEK. NUMEROUS DAILY RECORDS ARE LIKELY
TO BE SET. FARTHER EAST, THE CONCERN WILL BE FOR OPPRESSIVE
HUMIDITY WITH DEWPOINTS IN THE MID 70S TO LOW 80S TO COMBINE WITH
THE HEAT AND PRODUCE HEAT INDICES OF 105-115+ FOR EASTERN TEXAS
INTO THE LOWER MISSISSIPPI VALLEY, THE DEEP SOUTH, FLORIDA, AND
THE CAROLINAS. FAR SOUTHERN TEXAS COULD APPROACH HEAT INDICES OF
120. THESE ARE LIKELY TO PEAK TUESDAY-FRIDAY, BUT AS THE UPPER
RIDGE RETRACTS BACK WEST BY NEXT WEEKEND, THESE AREAS COULD
MODERATE CLOSER TO TYPICAL SUMMER HEAT. SEE KEY MESSAGES ISSUED BY
WPC FOR ADDITIONAL INFORMATION AND GRAPHICS RELATED TO THIS HEAT
WAVE. INTERIOR AREAS OF THE NORTHWEST ARE LIKELY TO SEE AROUND
AVERAGE TEMPERATURES AS THE PERIOD BEGINS TUESDAY BUT WARM TO
ABOVE AVERAGE FOR THE LATTER HALF OF THE WEEK, WHILE THE
NORTH-CENTRAL TO NORTHEASTERN U.S. SHOULD SEE NEAR TO SLIGHTLY
BELOW AVERAGE CONDITIONS NEXT WEEK
TATE
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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