236
FXUS02 KWBC 120659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT MON JUN 12 2023
VALID 12Z THU JUN 15 2023 - 12Z MON JUN 19 2023
***EARLY SEASON HEATWAVE TO PERSIST ACROSS MUCH OF THE
SOUTH-CENTRAL U.S. GOING INTO NEXT WEEKEND***
..SYNOPTIC OVERVIEW
A WEAK OMEGA BLOCK PATTERN ACROSS SOUTHERN CANADA AND THE NORTHERN
TIER OF THE U.S. IS EXPECTED TO BE IN PLACE FOR THE MIDDLE TO END
OF THIS WEEK, WITH A BROAD UPPER LOW SITUATED OVER SOUTHERN
QUEBEC, A RIDGE ACROSS MANITOBA, AND A TROUGH OVER SOUTHWESTERN
CANADA AND INTO MONTANA. THIS BREAKS DOWN SOME GOING INTO NEXT
WEEKEND WITH THE RIDGE DECAYING DOWN AND MORE OF A QUASI-ZONAL
FLOW PATTERN DEVELOPS ACROSS THE CENTRAL STATES. A STRONGER
TROUGH BEGINS TO BUILD SOUTHWARD ACROSS THE PACIFIC NORTHWEST AND
INTO THE NORTHERN ROCKIES BY SUNDAY AND NEXT MONDAY. MEANWHILE,
THE UPPER RIDGE OVER TEXAS AND THE WESTERN GULF OF MEXICO WILL
CONTINUE WITH THE ONGOING HEATWAVE UNABATED THROUGH THE FORECAST
PERIOD, WHILE ANOTHER TROUGH AND SURFACE LOW WILL LIKELY DEVELOP
ACROSS THE EAST COAST REGION BY SUNDAY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE INITIALLY HAS A GOOD OVERALL
DEPICTION OF THE SYNOPTIC SCALE PATTERN ACROSS THE CONTINENTAL
U.S. FOR THE END OF THE WEEK, AND THEREFORE A MULTI-DETERMINISTIC
MODEL BLEND SUFFICES AS A STARTING POINT IN THE FORECAST PROCESS.
THE MODELS HAVE A GOOD SIGNAL FOR A DAY 7 FORECAST WITH THE
AMPLIFYING TROUGH ACROSS THE NORTHWESTERN U.S., ALTHOUGH THERE ARE
MORE PLACEMENT DIFFERENCES WITH THE TROUGH CENTERED NEAR THE EAST
COAST DURING THE SAME TIME. THE GREATEST MODEL DIFFERENCES RESIDE
WITH WEAK SHORTWAVE ENERGY CROSSING THE MIDWEST AND INTO THE OHIO
VALLEY SOUTH OF THE UPPER RIDGE. THE LEVEL OF MODEL SPREAD HAS
DECREASED COMPARED TO THIS TIME YESTERDAY, AND THUS FORECAST
CONFIDENCE HAS IMPROVED FOR THE SECOND HALF OF THE FORECAST
PERIOD. THE ENSEMBLE MEANS ACCOUNTED FOR ABOUT 40-50% OF THE
FORECAST BLEND BY SUNDAY/MONDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE MAIN FOCUS FOR HEAVY RAINFALL IS EXPECTED ACROSS PORTIONS OF
THE DEEP SOUTH/SOUTHEAST MID-LATE WEEK, WHERE AN AXIS OF 1-2 INCH
RAINFALL TOTALS WITH ISOLATED HIGHER AMOUNTS IS EXPECTED, MAINLY
FROM THE FLORIDA PANHANDLE TO SOUTHERN GEORGIA. MOST OF THE
SHOWERS AND STORMS THAT DEVELOP WILL BE SOUTH OF THE WARM FRONT
AND REACH PEAK INTENSITY DURING THE AFTERNOON HOURS, AND SOME
STORMS MAY BE STRONG ENOUGH TO PRODUCE INSTANCES OF FLOODING.
HOWEVER, THE COVERAGE OF THIS SHOULD BE FAIRLY ISOLATED IN MOST
CASES, SO THIS ONLY WARRANTS A MARGINAL RISK AREA AT THIS TIME.
ADDITIONAL HEAVY RAINFALL MAY ALSO AFFECT THE SOUTHEAST U.S. GOING
INTO SUNDAY AND MONDAY AS THE NEXT SYNOPTIC SCALE DISTURBANCE
APPROACHES. ANOTHER AREA TO MONITOR FOR HEAVY RAINFALL POTENTIAL
WILL BE ACROSS THE CENTRAL PLAINS AND EXTENDING INTO THE UPPER
MIDWEST WHERE A FEW MESOSCALE CONVECTIVE SYSTEMS WILL BE POSSIBLE
AHEAD OF A FRONTAL BOUNDARY THAT WILL INTERCEPT INCREASING
MOISTURE ADVECTION, AND A MARGINAL RISK AREA FOR EXCESSIVE
RAINFALL IS IN EFFECT FOR THIS REGION AS WELL. ELSEWHERE, SOME
SHOWERS ARE LIKELY FROM THE GREAT LAKES TO THE NORTHEAST AS
MOISTURE PIVOTS AROUND THE UPPER LEVEL LOW.
THE EXCESSIVE HEAT CONTINUES GOING INTO THE END OF THE WEEK AND
BEYOND ACROSS MUCH OF TEXAS AND INTO LOUISIANA AND OKLAHOMA, WITH
WIDESPREAD 100S ACROSS CENTRAL AND SOUTHERN PORTIONS OF TEXAS.
HEAT INDICES ON THE ORDER OF 105 TO 115 DEGREES ARE LIKELY DURING
THE HOTTEST PARTS OF THE DAY FOR MANY OF THESE AREAS, AND SOME
ISOLATED INSTANCES OF HEAT INDICES UP TO 120 DEGREES ARE POSSIBLE
FOR PARTS OF DEEP SOUTH TEXAS WHERE THE GREATEST COMBINATION OF
HIGH DEWPOINTS AND THE HEAT WILL LIKELY EXIST. IT WILL ALSO BE
QUITE WARM ACROSS THE MIDWEST STATES TO CLOSE OUT THE WEEK WITH
WIDESPREAD UPPER 80S AND LOWER 90S EXPECTED BEFORE A MODEST COOL
DOWN ARRIVES BY SATURDAY, AND THEN ANOTHER WARM-UP LIKELY ENSUES
BY SUNDAY AND INTO MONDAY. THE BUILDING UPPER TROUGH ACROSS THE
NORTHEASTERN U.S. WILL HERALD THE ARRIVAL OF COOLER TEMPERATURES
BY SUNDAY FROM CALIFORNIA TO WASHINGTON STATE, WITH HIGHS
GENERALLY UP TO 10 DEGREES BELOW AVERAGE BY MONDAY. MOST OF THE
EAST COAST REGION SHOULD BE NEAR CLIMATOLOGICAL MID-JUNE LEVELS.
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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