555
FXUS02 KWBC 161901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SUN JUL 16 2023
VALID 12Z WED JUL 19 2023 - 12Z SUN JUL 23 2023
...DANGEROUS HEAT WAVE PERSISTS ACROSS THE SOUTHERN TIER, WITH
HAZARDOUS HEAT IN THE SOUTHWEST EVEN INTO NEXT WEEK 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 THIS WEEK. AS THE MEDIUM
RANGE PERIOD BEGINS WEDNESDAY, THE RIDGE WILL BE ELONGATED FROM
THE SOUTHWEST EASTWARD INTO THE SOUTHEAST, CAUSING HEAT INDICES TO
CLIMB UPWARD TO DANGEROUS LEVELS WEDNESDAY-FRIDAY THERE, BEFORE AN
AMPLIFYING TROUGH AND COOL FRONT SHOULD DROP TEMPERATURES IN THESE
AREAS NEAR TYPICAL SUMMERTIME VALUES. MEANWHILE, THE DESERT
SOUTHWEST CAN EXPECT UNRELENTING HEAT WITH HIGHS IN THE 110S
LIKELY TO BREAK RECORDS AS THE RIDGE IS ANCHORED THERE. IN TERMS
OF RAINFALL, SHORTWAVES ROUNDING THE NORTHERN PERIPHERY OF THE
RIDGE AS WELL AS SURFACE FRONT/LOW PRESSURE SYSTEMS COULD PRODUCE
SHOWERS AND 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 RIDGE
OF 594+ DM STRETCHING ACROSS THE SOUTHWEST TO SOUTHERN PLAINS TO
SOUTHEAST AS THE PERIOD BEGINS WEDNESDAY-THURSDAY, WITH THE 00Z EC
ENSEMBLE MEMBERS EVEN INDICATING AN 80 PERCENT CHANCE OF A 600DM
RIDGE IN THE SOUTHERN HIGH PLAINS. MODELS THEN AGREE FAIRLY WELL
THAT TROUGHING SHOULD AMPLIFY A BIT INTO THE SOUTHEAST LATE
WEEK/WEEKEND 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 INITIALLY
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. BY LATE WEEK HOWEVER, MORE
NOTABLE DIFFERENCES SHOW UP WITH THIS SHORTWAVE WITH SOME GUIDANCE
LIKE THE 00Z ECMWF CLOSING OFF A LOW THAT BECOMES SLOW-MOVING OVER
THE GREAT LAKES, WHILE MODELS LIKE THE GFS AND CMC SHOW IT TO BE
MORE PROGRESSIVE WHILE ANOTHER SHORTWAVE COMES IN BEHIND. THE
NEWER 12Z ECMWF DOES NOT SHOW THE LOW CLOSING OFF ANYMORE. AN
APPROACH BLENDING THE MODELS WITH THE ENSEMBLE MEANS SEEMED TO
CREATE A GOOD MIDDLE GROUND FOR HANDLING THIS TROUGH. MEANWHILE
MODELS ALSO AGREE IN SHOWING AN UPPER LOW IN THE EASTERN PACIFIC
DRIFTING GRADUALLY SOUTHEAST WITH TIME.
OVERALL MODEL AGREEMENT IS RATHER GOOD AND THUS CONFIDENCE IN THE
PATTERN IS ABOVE AVERAGE. THE FORECAST BLEND FAVORED THE 00Z ECMWF
AND 06Z GFS WITH SMALLER PROPORTIONS OF THE
CMC AND UKMET EARLY ON AND INCLUDED SOME ENSEMBLE MEANS BY DAYS
5-7, THOUGH WAS ABLE TO KEEP A MAJORITY DETERMINISTIC MODEL BLEND.
CHANGES TO THE NBM QPF WERE MINOR TO MODERATE AND FOCUSED ON
BROADENING LIGHT AMOUNTS WHERE THE NBM HAD ZERO BUT OTHER GUIDANCE
HAD AMOUNTS, AND REDUCING HIGH MAXIMA BY THE LATTER FORECAST DAYS
DUE TO UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
INTO WEDNESDAY, CONVECTION IS LIKELY IN WESTERLY FLOW ALONG THE
BASE OF A TROUGH ALOFT IN PARTS OF THE LOWER OHIO/TENNESSEE
VALLEY, LIKELY PERSISTING FROM A MESOSCALE CONVECTIVE SYSTEM (MCS)
OVERNIGHT TUESDAY. A SLIGHT RISK HAS BEEN MAINTAINED IN THE
EXCESSIVE RAINFALL OUTLOOK FOR THIS AREA WITH A BIT OF BROADENING
TO ACCOUNT FOR MODEL UNCERTAINTY. FARTHER NORTH INTO THE UPPER
MIDWEST/UPPER GREAT LAKES REGION, A SURFACE LOW PASSING THROUGH
SHOULD PRODUCE SOME SHOWERS AND THUNDERSTORMS. WHILE RAIN RATES DO
NOT LOOK TO BE TOO HIGH, THERE IS A TONGUE OF INSTABILITY AND THE
LEFT EXIT REGION OF THE JET MAY BE OVERHEAD TO LOCALLY ENHANCE
TOTALS, AND A MARGINAL RISK REMAINS IN PLACE HERE. AS A COLD FRONT
PRESSES EASTWARD, RAIN IS EXPECTED TO SPREAD AHEAD OF IT FROM THE
APPALACHIANS TO THE EASTERN SEABOARD. THERE IS SOME UNCERTAINTY IN
WHERE RAIN AND STORMS SET UP SO THERE IS A BROAD MARGINAL RISK IN
PLACE ACROSS THE GREAT LAKES REGION INTO THE EAST ON THURSDAY,
WITH SOME REFINEMENT LIKELY WITH TIME IF MODEL GUIDANCE STARTS TO
BE MORE AGREEABLE. RAIN COULD PERSIST IN THE NORTHEAST THROUGH
LATE WEEK AND COULD EXACERBATE FLOODING ISSUES FROM THE RECENT
EXTREMELY WET PATTERN. FARTHER SOUTH, CONVECTION IN SOUTHWESTERN
FLORIDA COULD CONTAIN LOCALLY HEAVY RAIN RATES WEDNESDAY WHERE
THERE IS A MARGINAL RISK. AS A FRONT PRESSES SLOWLY SOUTHWARD INTO
THE GULF COAST STATES LATE WEEK INTO THE WEEKEND, IT COULD HELP
TRIGGER SCATTERED THUNDERSTORMS THERE AS WELL.
FARTHER WEST, MONSOONAL MOISTURE LOOKS TO COME INTO PORTIONS OF
THE WEST AND AS IT MEETS WITH A FRONTAL SYSTEM IN THE CENTRAL HIGH
PLAINS, THIS WILL BECOME A FOCUS FOR CONVECTION AS WELL. A
MARGINAL RISK IS IN EFFECT FOR WEDNESDAY FOR THE FIRST DAY OF
STORMS, BUT THURSDAY INTO THURSDAY NIGHT LOOKS TO BE A BIGGER DAY
FOR POTENTIAL FLASH FLOODING AS CONVECTION IS LIKELY TO CONGEAL
OVERNIGHT INTO A LARGE MCS WITH HIGH RAIN RATES (GFS RUNS ARE
ALREADY INDICATING 3-4 INCHES PER 3 HOURS, AND RATES OFTEN END UP
HIGHER THAN GLOBAL MODELS AND CLOSER TO THOSE SHOWN BY
CONVECTION-ALLOWING MODELS IN THE SHORT RANGE). A DAY 5 SLIGHT
RISK COVERS THE CENTRAL HIGH PLAINS FOR THIS POTENTIAL. ADDITIONAL
SHOWERS AND STORMS ARE POSSIBLE INTO LATE WEEK IN THIS REGION AS
WELL.
WIDESPREAD OPPRESSIVE HEAT UNFORTUNATELY LOOKS TO CONTINUE
THROUGHOUT THE 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.
MUCH OF TEXAS CAN EXPECT HIGHS NEARING OR EXCEEDING 100F THAT
SHOULD BE UNRELENTING THROUGH THE WEEK AND INTO NEXT WEEKEND.
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 PARTS OF THE CAROLINAS. FAR SOUTHERN
TEXAS COULD APPROACH HEAT INDICES OF 120. THESE ARE LIKELY TO PEAK
WEDNESDAY-FRIDAY, BUT AS THE UPPER RIDGE RETRACTS BACK WEST BY
NEXT WEEKEND, THESE AREAS SHOULD MODERATE CLOSER TO TYPICAL SUMMER
HEAT. INTERIOR AREAS OF THE NORTHWEST ARE LIKELY TO SEE
TEMPERATURES WARMING TO ABOVE AVERAGE FOR THE LATTER HALF OF THE
WEEK INTO NEXT WEEKEND. SEE KEY MESSAGES ISSUED BY WPC FOR
ADDITIONAL INFORMATION AND GRAPHICS RELATED TO THIS HEAT WAVE.
DOWNSTREAM, THE CENTRAL/NORTHERN PLAINS COULD BE A RELATIVE COOL
SPOT, WITH HIGHS IN PARTICULAR FORECAST TO BE BELOW AVERAGE, WHILE
THE NORTHEASTERN U.S. CAN EXPECT NEAR NORMAL TEMPERATURES.
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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