612
FXUS02 KWBC 190658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT SAT AUG 19 2023
VALID 12Z TUE AUG 22 2023 - 12Z SAT AUG 26 2023
***MAJOR HEAT WAVE FOR THE CENTRAL U.S. AND EXTENDING TO THE GULF
COAST REGION FOR MUCH OF NEXT WEEK WITH NUMEROUS RECORD HIGHS
LIKELY***
..SYNOPTIC OVERVIEW
AN IMPRESSIVE 600DM UPPER RIDGE WILL BE ANCHORED IN PLACE ACROSS
THE MIDWEST FOR THE BEGINNING TO MIDDLE OF NEXT WEEK WITH
WIDESPREAD EXCESSIVE HEAT AND HUMIDITY ACCOMPANYING IT. THIS
RIDGE WILL LIKELY START TO DECAY SOME GOING INTO THE END OF THE
WEEK AND THEN GETS DISPLACED TOWARDS THE SOUTH AS SHORTWAVE ENERGY
IMPINGES UPON IT FROM THE NORTH, BUT THE HEAT AND HUMIDITY WILL
LIKELY CONTINUE TO MAKE WEATHER HEADLINES FOR MUCH OF THE
SOUTH-CENTRAL STATES. ACROSS THE NORTHEAST U.S., AN UPPER LEVEL
TROUGH IS EXPECTED TO BE IN PLACE FOR MOST OF THE WEEK AND THIS
WILL SHIELD THE REGION FROM THE EXCESSIVE HEAT THAT IS EXPECTED
ACROSS THE CENTRAL U.S., AND AN INCREASE OF MOISTURE ACROSS THE
NORTHERN GULF WILL FUEL MORE WIDESPREAD COVERAGE OF SHOWERS AND
STORMS ACROSS SOUTHERN TEXAS GOING INTO TUESDAY. SHOWERS ARE ALSO
EXPECTED FROM THE PACIFIC NORTHWEST TO THE NORTHERN ROCKIES
THROUGH MID-WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE INDICATES VERY GOOD OVERALL SYNOPTIC
SCALE AGREEMENT ACROSS THE FORECAST DOMAIN FOR THE MIDDLE OF THE
WEEK, WITH ABOVE AVERAGE CONFIDENCE WITH THE HUGE UPPER RIDGE OVER
THE CENTRAL U.S. EARLY IN THE WEEK, WITH MULTIPLE MODELS
INDICATING A RARE 600DM CONTOUR OVER IOWA AND MISSOURI. THE MAIN
DIFFERENCES NOTED LATER IN THE WEEK INVOLVE THE TIMING AND
MAGNITUDE OF SHORTWAVES TRAVERSING AROUND THE NORTHERN PERIPHERY
OF THE RIDGE, WITH THE CMC/ECMWF SLOWER WITH THE SHORTWAVE
PASSAGES. THE CMC BECOMES A LITTLE TO THE WEST OF THE MODEL
CONSENSUS WITH THE CORE OF THE UPPER HIGH BY NEXT SATURDAY, BUT
THE 00Z RUN IS IN BETTER ALIGNMENT COMPARED TO THE 12Z THAT WAS
NOT FAVORED BEYOND THURSDAY. THE GFS TEMPERATURES WITH THE
UPCOMING HEATWAVE ARE LIKELY TOO HIGH ACROSS MUCH OF THE MIDWEST
AND EVEN ACROSS PARTS OF THE GREAT LAKES AND OHIO VALLEY, WITH THE
ECMWF AND ENSEMBLE MEAN TEMPERATURES CLOSER TO WHAT IS EXPECTED TO
EVOLVE. THE WPC BLEND FOR THE FRONTS/PRESSURES INCORPORATED A
NEARLY DETERMINISTIC MODEL BLEND THROUGH WEDNESDAY, AND THEN
REDUCING THE CMC AND SLOWLY TRANSITIONING TO ABOUT 40-50% OF THE
18Z GEFS/12Z ECENS ENSEMBLE MEANS FOR FRIDAY AND SATURDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE GOOD NEWS HERE IS THE HEAVIEST RAIN ASSOCIATED WITH THE
REMNANTS OF HILARY SHOULD BE OVER BY TUESDAY MORNING WITH JUST
SOME SCATTERED SHOWERS AND STORMS REMAINING IN ITS WAKE ACROSS THE
DESERT SOUTHWEST AND THE INTERMOUNTAIN WEST. HOWEVER, THERE WILL
LIKELY BE A MORE CONCENTRATED CORRIDOR OF MOISTURE CONVERGENCE
FROM EASTERN OREGON TO NORTHERN IDAHO WHERE THE MODELS ARE
DEPICTING LOCAL RAINFALL MAXIMA AROUND AN INCH ON TUESDAY, AND
GIVEN EXPECTED RAINFALL PRIOR TO THIS TIME, A SLIGHT RISK AREA IS
PLANNED FOR DAY 4 ACROSS THIS REGION. ACROSS THE GULF COAST
REGION, A TROPICAL WAVE MOVING UNDERNEATH THE STRONG UPPER RIDGE
IS EXPECTED TO ADVECT WESTWARD ACROSS THE GULF OF MEXICO AND
INLAND ACROSS SOUTHERN TEXAS, SUPPORTING THE DEVELOPMENT OF
WIDESPREAD SHOWERS AND THUNDERSTORMS ON TUESDAY, AND THEN ACROSS
NORTHERN MEXICO BY WEDNESDAY AND BEYOND. A MARGINAL RISK AREA IS
PLANNED FOR THIS REGION AS A RESULT WITH 1-2 INCHES OF RAINFALL
POSSIBLE SOUTH OF THE INTERSTATE 10 CORRIDOR. THERE IS ALSO A
MARGINAL RISK AREA PLANNED FOR PORTIONS OF THE MID-ATLANTIC ON DAY
5 WITH A POTENTIAL MCS TRACKING SOUTHEAST FROM THE GREAT LAKES,
ALTHOUGH CONFIDENCE ON ITS EVOLUTION IS LIMITED FOR NOW.
ELSEWHERE, VERY LITTLE IN THE WAY OF RAIN IS EXPECTED ACROSS A
WIDE EXPANSE OF THE CENTRAL U.S. AS THE RIDGE SEVERELY RESTRICTS
THE DEVELOPMENT OF ANY SHOWERS OR STORMS.
A MAJOR LATE SUMMER HEATWAVE IS EXPECTED ACROSS MUCH OF THE
MIDWEST AND EXTENDING ACROSS THE CENTRAL PLAINS THROUGH ABOUT
THURSDAY WITH THE MASSIVE UPPER RIDGE IN PLACE AND SUPPRESSING
CLOUD DEVELOPMENT. WIDESPREAD 100+ DEGREE HIGH TEMPERATURES ARE
EXPECTED FROM SOUTHERN SOUTH DAKOTA AND POINTS SOUTHWARD, AND SOME
OVERNIGHT LOWS MAY STAY ABOVE 80 DEGREES, ESPECIALLY FOR LARGER
URBAN AREAS. THESE READINGS ACROSS THE MIDWEST ARE ON THE ORDER
OF 10-20 DEGREES ABOVE LATE AUGUST AVERAGES, WITH THE CORE OF THE
ANOMALIES CENTERED MAINLY OVER IOWA AND PORTIONS OF ADJACENT
STATES THROUGH MID-WEEK. THERE WILL LIKELY BE SOME ABATEMENT TO
THE LATE SUMMER HEATWAVE ACROSS THE MIDWEST BY FRIDAY AND INTO
NEXT WEEKEND AS THE RIDGE IS SUPPRESSED TO THE SOUTH. MEANWHILE,
THE INTENSE HEAT IS EXPECTED TO PERSIST UNABATED ACROSS TEXAS AND
THE DEEP SOUTH STATES THROUGH THE END OF THE FORECAST PERIOD WITH
HIGHS RUNNING 10-15 DEGREES ABOVE AVERAGE, WITH MANY LOCATIONS
ACROSS THE DEEP SOUTH LIKELY HAVING THEIR WARMEST AUGUST ON
RECORD. NUMEROUS DAILY RECORDS AND PERHAPS SOME MONTHLY RECORD
HIGHS ARE EXPECTED.
THE OPPOSITE HOLDS TRUE FROM CALIFORNIA TO INTERIOR PORTIONS OF
THE PACIFIC NORTHWEST WITH TEMPERATURES RUNNING 10 TO 20 DEGREES
BELOW AVERAGE OWING TO EXPANSIVE CLOUD COVER AND WIDESPREAD
RAINFALL, PERHAPS SETTING SOME RECORD LOW MAX TEMPERATURES ACROSS
THIS REGION ON TUESDAY. TEMPERATURES SLOWLY MODERATE GOING INTO
THE SECOND HALF OF THE WEEK ACROSS THIS REGION AND RETURN CLOSER
TO LATE AUGUST AVERAGES BY NEXT WEEKEND. MUCH OF THE NORTHEAST
U.S. SHOULD ALSO AVOID THE BRUTAL HEAT WITH MULTIPLE SHORTWAVE
PASSAGES REINFORCING A COMFORTABLE AIRMASS ACROSS THE REGION.
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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHWESTERN U.S. FROM EASTERN
OREGON INTO CENTRAL IDAHO, MON, AUG 21.
- HEAVY RAIN ACROSS PORTIONS OF SOUTHERN TEXAS, TUE-WED, AUG
22-AUG 23.
- HAZARDOUS HEAT ACROSS MUCH OF THE MID-SECTION OF THE COUNTRY
INCLUDING THE LOWER AND MID-MISSISSIPPI VALLEY, PORTIONS OF THE
OHIO VALLEY, THE SOUTHEAST, AND INTO NORTHERN FLORIDA, MON-FRI,
AUG 21-AUG 25.
- HAZARDOUS HEAT ACROSS THE INNER COASTAL PLAIN OF THE CAROLINAS,
TUE, AUG 22 AND FRI, AUG 25.
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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