939
FXUS02 KWBC 130655
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EDT TUE JUN 13 2023
VALID 12Z FRI JUN 16 2023 - 12Z TUE JUN 20 2023
***EARLY SEASON HEATWAVE TO PERSIST ACROSS MUCH OF THE
SOUTH-CENTRAL U.S. INTO EARLY NEXT WEEK AND BEYOND***
..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 END OF THIS
WEEK, WITH A BROAD UPPER LOW SITUATED OVER SOUTHERN QUEBEC/NEW
ENGLAND, A RIDGE ACROSS WESTERN ONTARIO/UPPER MIDWEST, AND A
TROUGH OVER SASKATCHEWAN AND INTO MONTANA. THIS BREAKS DOWN SOME
GOING INTO THE WEEKEND AND MORE OF A QUASI-ZONAL FLOW PATTERN
DEVELOPS ACROSS THE SOUTH-CENTRAL STATES. A MUCH STRONGER TROUGH
BEGINS TO BUILD SOUTHWARD ACROSS THE PACIFIC NORTHWEST AND INTO
THE NORTHERN ROCKIES AND INTERMOUNTAIN WEST FOR THE BEGINNING OF
NEXT WEEK, AND THE EAST COAST TROUGH ALSO BUILDS BACK IN WITH
RIDGING FROM TEXAS TO THE GREAT LAKES. MEANWHILE, THE CORE OF THE
UPPER RIDGE OVER TEXAS AND THE WESTERN GULF OF MEXICO WILL
CONTINUE WITH THE ONGOING HEATWAVE UNABATED THROUGH THE FORECAST
PERIOD, AND EVEN BEYOND NEXT TUESDAY BASED ON RECENT CLIMATE
PREDICTION CENTER OUTLOOKS.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE CONTINUES TO INDICATE GOOD OVERALL
SYNOPTIC SCALE AGREEMENT THROUGH THE MAJORITY OF THE FORECAST
PERIOD FOR THE UPPER LEVEL PATTERN, BUT THERE IS SOME VARIABILITY
IN THE MESOSCALE DETAILS. SOME OF THE GREATEST MODEL DIFFERENCES
CONTINUE WITH SOME WEAK SHORTWAVE ENERGY CROSSING FROM THE UPPER
MIDWEST TO THE OHIO VALLEY THIS WEEKEND, ADDING TO UNCERTAINTIES
IN THE RAINFALL FORECAST ACROSS THESE REGIONS AS WELL. THE UKMET
DIFFERED THE MOST WITH A STRONGER LOW CROSSING THE CAROLINAS BY
THE WEEKEND. THERE ARE ALSO TIMING UNCERTAINTIES OF WAVES
CROSSING THE NORTHEAST AHEAD OF THE AFOREMENTIONED FEATURE, AND
THE PLACEMENT OF A DEEPER UPPER LOW OVER SOUTHWEST CANADA OR THE
PACIFIC NORTHWEST FOR EARLY NEXT WEEK. THE CMC IS FARTHER SOUTH
WITH THE PLACEMENT OF THE UPPER LOW ACROSS THE WEST BY TUESDAY
WHEN COMPARED TO THE MODEL CONSENSUS. MOST OF THE OTHER
DIFFERENCES ARE SMALLER IN SCALE AND MAY TAKE UNTIL THE SHORT
RANGE PERIOD TO FULLY RESOLVE. A GENERAL MODEL BLEND OF THE
DETERMINISTIC MODELS WORKED WELL FOR FRIDAY AND THEN DROPPING THE
UKMET BY SATURDAY, BUT THE SECOND HALF TRANSITIONED TOWARDS ABOUT
40% OF THE ENSEMBLE MEANS, WITH SOME CONTRIBUTIONS FROM THE
DETERMINISTIC ECMWF AND GFS FOR ADDED SYSTEM DEFINITION. THIS
APPROACH FITS WELL WITH PREVIOUS SHIFT WPC CONTINUITY.
..WEATHER/HAZARDS HIGHLIGHTS
THERE WILL LIKELY BE TWO MAIN AREAS FOR HEAVY RAINFALL POTENTIAL
FOR THE FRIDAY TO SATURDAY TIME PERIOD. THE FIRST AREA IS
EXPECTED ACROSS PORTIONS OF MISSISSIPPI AND ALABAMA WHERE THE
DETERMINISTIC GUIDANCE INDICATES A CORRIDOR OF ENHANCED QPF,
LIKELY AS THE RESULT OF MCS ACTIVITY WITH NORTHWEST FLOW ALOFT.
THE POTENTIAL EXISTS FOR 2-4 INCH TOTALS DURING THE DAY 4 PERIOD
FRIDAY-FRIDAY NIGHT, BUT THE MODELS ARE NOT YET LOCKED IN ON THE
PLACEMENT OF THE MAIN QPF AXIS, SO THIS PRECLUDES ANYTHING HIGHER
THAN A MARGINAL RISK AT THIS TIME. THE SECOND AREA OF POTENTIAL
CONCERN WILL BE JUST EAST OF THE FRONT RANGE OF THE ROCKIES WHERE
ADDITIONAL HEAVY SHOWERS AND STORMS ARE FORECAST OVER AREAS THAT
HAVE RECEIVED COPIOUS RAINFALL OVER THE PAST WEEK, AND THIS MAY
EVENTUALLY RESULT IN A SLIGHT RISK AS THE EVENT GETS CLOSER IN
TIME, HOWEVER A MARGINAL RISK AREA IS PLANNED FOR NOW. FOR THE
DAY 5 PERIOD SATURDAY-SATURDAY NIGHT, A BROADER SIGNAL FOR
SCATTERED HEAVY SHOWERS AND STORMS EXISTS FROM MINNESOTA TO THE
DEEP SOUTH NEAR A FRONTAL BOUNDARY AND SHORTWAVE ALOFT, AND A
MARGINAL RISK IS WARRANTED FOR NOW. ADDITIONAL SHOWERS AND STORMS
ARE LIKELY ACROSS THE SOUTHEAST AND PORTIONS OF THE EAST COAST
REGION GOING INTO EARLY NEXT WEEK AS WELL, AND THE AMPLIFYING
TROUGH ACROSS THE NORTHERN ROCKIES AND PACIFIC NORTHWEST IS ALSO
EXPECTED TO RESULT IN SCATTERED TO NUMEROUS SHOWERS LATE IN THE
FORECAST PERIOD.
THE EXCESSIVE HEAT CONTINUES GOING THROUGH THE REMAINDER OF THE
WEEK AND INTO THE WEEKEND ACROSS MUCH OF TEXAS AND INTO MUCH OF
LOUISIANA AND OKLAHOMA, WITH WIDESPREAD 100S ACROSS CENTRAL AND
SOUTHERN PORTIONS OF TEXAS, AND 90S COVERING MUCH OF THE DEEP
SOUTH AND THE CENTRAL PLAINS. SOME DAILY RECORD HIGH TEMPERATURES
AND 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.
THERE IS STRONG MODEL SUPPORT FOR THIS EVENT TO HAVE ADDITIONAL
STAYING POWER INTO MUCH OF NEXT WEEK AS WELL. ON THE OTHER END OF
THE SPECTRUM, THE BUILDING UPPER TROUGH ACROSS THE NORTHWESTERN
U.S. WILL HERALD THE ARRIVAL OF NOTICEABLY COOLER TEMPERATURES BY
SUNDAY AND ESPECIALLY INTO EARLY NEXT WEEK ACROSS MUCH OF
CALIFORNIA, NEVADA, WASHINGTON, OREGON, AND IDAHO. AFTERNOON
HIGHS SHOULD GENERALLY 5 TO 15 DEGREES BELOW AVERAGE, WITH THE
GREATEST ANOMALIES OVER THE NORTHERN GREAT BASIN. SNOW SHOWERS
ARE EVEN WITHIN THE REALM OF POSSIBILITY FOR THE HIGHEST MOUNTAIN
PEAKS. MOST OF THE EAST COAST REGION SHOULD BE NEAR OR SLIGHTLY
BELOW 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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