236
FXUS02 KWBC 140653
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 AM EDT WED JUN 14 2023
VALID 12Z SAT JUN 17 2023 - 12Z WED JUN 21 2023
***EARLY SEASON HEAT WAVE TO PERSIST ACROSS MUCH OF THE
SOUTH-CENTRAL U.S. INTO EARLY NEXT WEEK AND BEYOND***
..SYNOPTIC OVERVIEW
FOR THE BEGINNING OF THE FORECAST PERIOD THIS WEEKEND, A WELL
DEFINED NORTHEASTERN PACIFIC/GULF OF ALASKA TROUGH WITH EMBEDDED
UPPER LOW WILL BUILD SOUTHEASTWARD ACROSS THE WESTERN U.S. AND
SOUTHWESTERN CANADA, WHILE CENTRAL U.S. INTO CANADA RIDGING
EVENTUALLY REBUILDS AFTER INITIAL WESTERN U.S. SHORTWAVE ENERGY
PROGRESSES THROUGH THE PLAINS AND SETTLES INTO THE LONG-TERM
EASTERN U.S. MEAN TROUGH. THE CORE OF THE UPPER RIDGE OVER TEXAS
AND THE WESTERN GULF OF MEXICO WILL PERSIST THROUGH THE FORECAST
PERIOD, MAINTAINING A SOUTH-CENTRAL U.S. HEAT WAVE THAT SHOULD
EXTEND BEYOND NEXT TUESDAY BASED ON CLIMATE PREDICTION CENTER
OUTLOOKS. MEANWHILE, THE PATTERN EVOLUTION SHOULD FAVOR AN AREA
OF ENHANCED RAINFALL FROM THE NORTHERN-CENTRAL PLAINS INTO
SOUTHEAST/MID-ATLANTIC, WITH PORTIONS OF THE DEEP SOUTH LIKELY
HAVING THE HIGHEST TOTALS OVERALL. THE NORTHWESTERN U.S./NORTHERN
ROCKIES SHOULD SEE PRECIPITATION INCREASE EARLY NEXT WEEK AS THE
WESTERN SYSTEM MOVES IN, AND THE INITIAL UPPER TROUGH/LOW OVER THE
NORTHEAST WILL ALSO SUPPORT PERIODS OF RAINFALL THERE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE AT THE BEGINNING OF THE FORECAST
PERIOD SATURDAY IS IN GOOD SYNOPTIC SCALE AGREEMENT FOR MOST
AREAS. THE GFS IS A LITTLE FASTER IN EJECTING THE LEAD SHORTWAVE
TROUGH ACROSS THE WESTERN HIGH PLAINS AND THE CMC IS MORE
AMPLIFIED WITH THE TROUGH OVER THE EAST COAST REGION, BUT ARE
WITHIN THE MARGIN OF ERROR AND A BLEND OF THE ECMWF/GFS/CMC WORKS
WELL AS A STARTING POINT IN THE FORECAST PROCESS FOR THE WEEKEND.
THE PAST COUPLE OF UKMET RUNS HAD A STRONGER LOW NEAR THE
SOUTHEAST U.S. COAST THAT DID NOT ALIGN WELL WITH THE MODEL
CONSENSUS. GOING INTO NEXT MONDAY, THE CMC IS A BIT WEAKER WITH
THE SHORTWAVE TROUGH OVER THE OHIO VALLEY COMPARED TO THE MORE
AMPLIFIED ECMWF/GFS SOLUTIONS, BUT THE MODEL AGREEMENT REMAINS
GOOD FOR THE MAJOR TROUGH BUILDING IN ACROSS THE NORTHWESTERN
STATES. LOOKING AHEAD TO THE MIDDLE OF THE WEEK, THERE IS STRONG
CONSENSUS FOR A DEVELOPING OMEGA BLOCK PATTERN WITH AN UPPER RIDGE
AXIS EXTENDING WELL INTO CENTRAL CANADA AND A TROUGH AND POTENTIAL
UPPER LOW SITUATED NEAR THE APPALACHIANS, WITH THE CMC REMAINING
ON THE WEAKER SIDE OF THE GUIDANCE. THERE ARE MORE IN THE WAY OF
QPF DIFFERENCES REGARDING PLACEMENTS OF HEAVY RAINFALL SWATHS THAT
WILL BE HEAVILY DEPENDENT ON SMALLER SCALE SHORTWAVE AND MCS
TRACKS, SO THE 1Z NBM WAS THE MAIN SOLUTION OF CHOICE WITH SOME
GFS/ECMWF INCLUDED. THE USE OF THE ENSEMBLE MEANS FOR MASS FIELDS
INCREASED TO ABOUT 40-50% BY NEXT WEDNESDAY.
..WEATHER/HAZARDS HIGHLIGHTS
FOR THE DAY 4 PERIOD SATURDAY-SATURDAY NIGHT, THERE IS A BROAD
SIGNAL FOR SCATTERED HEAVY SHOWERS AND STORMS FROM PARTS OF THE
NORTH-CENTRAL THROUGH SOUTH-CENTRAL PLAINS INTO THE DEEP SOUTH
NEAR A FRONTAL BOUNDARY AND SHORTWAVE ALOFT. THE OUTLOOK AGAIN
MAINTAINS A MARGINAL RISK AREA WITH THE EASTERN PORTION OF THE OLD
DAY 5 OUTLOOK TRIMMED BACK ON THE NORTHEAST SIDE TO ACCOUNT FOR A
SLIGHT SOUTHWESTERN TREND IN THE GUIDANCE, AND PARTS OF THIS
REGION MAY EVENTUALLY QUALIFY FOR A SLIGHT RISK AS FUTURE MODELS
RUNS COME INTO BETTER AGREEMENT ON THE MAIN QPF AXIS. GOING INTO
THE DAY 5 PERIOD SUNDAY, THE GUIDANCE SUGGEST THE CORE OF THE
HEAVIEST RAINFALL WILL LIKELY SETTLE ACROSS INTERIOR PORTIONS OF
THE DEEP SOUTH WITH THE POTENTIAL FOR 2-4 INCH RAINFALL TOTALS ON
A LOCALIZED BASIS, BUT MODELS VARY IN THE PLACEMENT OF THE
HEAVIEST QPF MAXIMA. ALTHOUGH A BROAD MARGINAL RISK AREA IS
CURRENTLY PLANNED FOR THE NEW DAY 5, PARTS OF ALABAMA AND WESTERN
GEORGIA ARE BORDERLINE FOR A SLIGHT RISK AREA SINCE MULTIPLE
ROUNDS OF HEAVY RAINFALL ARE EXPECTED IN THE SHORT RANGE FORECAST
PERIOD FOR THESE AREAS.
ELSEWHERE ACROSS THE U.S., LIGHTER RAINFALL WILL LIKELY EXTEND
FARTHER NORTHEAST INTO THE OHIO VALLEY/MID-ATLANTIC/SOUTHEAST FROM
LATE WEEKEND INTO EARLY NEXT WEEK. THE NORTHEAST SHOULD SEE
PERIODS OF RAINFALL WITH POSSIBLE LATE-DAY THUNDERSTORMS THIS
WEEKEND WITH THE UPPER TROUGH/LOW OVER THE REGION. MEANWHILE, THE
VIGOROUS UPPER TROUGH/LOW REACHING THE WEST WILL LIKELY INCREASE
THE COVERAGE AND INTENSITY OF PRECIPITATION OVER THE PACIFIC
NORTHWEST AND ESPECIALLY THE NORTHERN ROCKIES FROM SUNDAY INTO
EARLY NEXT WEEK. SOME LOCALLY HEAVY RAIN MAY FALL OVER AREAS IN
THE NORTHERN ROCKIES THAT COULD BE SENSITIVE DUE TO WELL ABOVE
NORMAL RAINFALL RECENTLY. THE DEPTH AND TRACK OF THE UPPER SYSTEM
COULD ALSO SUPPORT SOME SNOW AT THE HIGHEST ELEVATIONS.
THE EXCESSIVE HEAT WILL CONTINUE THROUGH THE REMAINDER OF THIS
WEEK AND INTO NEXT WEEK 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 (MAINLY MONDAY-TUESDAY FOR THE
LATTER). 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 UPPER
TROUGH DIGGING INTO 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 BE 5 TO 15
DEGREES BELOW AVERAGE, WITH THE GREATEST ANOMALIES OVER THE
NORTHERN GREAT BASIN. A FEW PLACES COULD CHALLENGE DAILY RECORDS
FOR COOL HIGHS. ELSEWHERE, THE CENTRAL ROCKIES WILL BE ON THE
COOL SIDE FRIDAY-SATURDAY BEFORE MODERATING, WHILE PARTS OF THE
UPPER MIDWEST/NORTHERN PLAINS WILL BE RATHER WARM WITH HIGHS 5 TO
15 DEGREES ABOVE AVERAGE. 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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