609
FXUS02 KWBC 150659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT THU JUN 15 2023
VALID 12Z SUN JUN 18 2023 - 12Z THU JUN 22 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 SUNDAY, A WELL DEFINED
NORTHEASTERN PACIFIC/GULF OF ALASKA TROUGH WITH EMBEDDED UPPER LOW
WILL BUILD SOUTHEASTWARD ACROSS THE WESTERN U.S. AND SOUTHWESTERN
CANADA, AND A WEAK COASTAL LOW PRESSURE SYSTEM WILL LIKELY BE
EXITING NEW ENGLAND. THE CORE OF THE UPPER RIDGE OVER SOUTHERN
TEXAS AND NORTHEASTERN MEXICO WILL PERSIST THROUGH THE FORECAST
PERIOD, MAINTAINING A SOUTH-CENTRAL U.S. HEAT WAVE THAT SHOULD
EXTEND THROUGH NEXT WEEK. MEANWHILE, THE PATTERN EVOLUTION SHOULD
FAVOR AN AREA OF ENHANCED RAINFALL FROM THE MIDWEST STATES INTO
THE SOUTHEAST U.S., 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 IS GENERALLY IN ABOVE AVERAGE
AGREEMENT ON MOST ASPECTS OF THE SYNOPTIC SCALE PATTERN, EVEN
GOING INTO NEXT WEDNESDAY AND THURSDAY OWING TO THE AMPLIFIED FLOW
ACROSS MUCH OF THE FORECAST DOMAIN. 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, BUT THE LATEST RUN HAS THE
LOW WELL AWAY FROM THE COAST AND IT LOOKS REASONABLE ELSEWHERE, SO
IT WAS PART OF THE DETERMINISTIC BLEND THROUGH MONDAY NIGHT.
SIMILAR TO YESTERDAY, THE GFS IS A LITTLE FASTER WITH THE
SHORTWAVE ACROSS THE MIDWEST ON SUNDAY, BUT IT ALIGNS CLOSER TO
THE OTHER GUIDANCE BY TUESDAY. 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. THE USE OF THE ENSEMBLE MEANS FOR MASS FIELDS
INCREASED TO ABOUT 35% BY NEXT THURSDAY.
..WEATHER/HAZARDS HIGHLIGHTS
FOR THE DAY 4 PERIOD SUNDAY-SUNDAY NIGHT, THERE IS A BROAD SIGNAL
FOR SCATTERED HEAVY SHOWERS AND STORMS FROM MISSOURI INTO THE DEEP
SOUTH NEAR A FRONTAL BOUNDARY AND SHORTWAVE ALOFT. THE OUTLOOK
NOW INCLUDES A PLANNED SLIGHT RISK AREA ACROSS PORTIONS OF
MISSISSIPPI AND ALABAMA, WHERE HEAVY RAINFALL THROUGH TOMORROW
WILL RESULT IN MORE SATURATED GROUND CONDITIONS LEADING UP TO THIS
EVENT. THE EASTERN PORTION OF THE OLD DAY 5 MARGINAL RISK HAS
BEEN TRIMMED BACK ON THE NORTHEAST SIDE TO ACCOUNT FOR A SLIGHT
SOUTHWESTERN TREND IN THE GUIDANCE. GOING INTO THE DAY 5 PERIOD
MONDAY-MONDAY NIGHT, THE GUIDANCE SUGGEST THE CORE OF THE HEAVIEST
RAINFALL MAY EXHIBIT MORE OF A BI-MODAL DISTRIBUTION ACROSS THE
SOUTHEASTERN U.S., WITH ONE MAXIMA OVER NORTHERN GEORGIA AND THE
SOUTHERN APPALACHIANS, AND ANOTHER MAXIMA NEAR THE GA/FL BORDER.
A SLIGHT RISK FOR DAY 5 IS NOW PLANNED FOR THE NORTHERN MAXIMA
WHERE A SLIGHTLY BETTER CONCENTRATION OF MODEL GUIDANCE CURRENTLY
EXISTS.
ELSEWHERE ACROSS THE U.S., LIGHTER RAINFALL WILL LIKELY EXTEND
FARTHER NORTHEAST INTO THE OHIO VALLEY/MID-ATLANTIC/NORTHEAST U.S.
GOING INTO EARLY NEXT WEEK. 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 TUESDAY. SOME
LOCALLY HEAVY RAIN MAY FALL OVER AREAS IN THE NORTHERN ROCKIES
THAT COULD BE SENSITIVE DUE TO WELL ABOVE NORMAL RAINFALL OVER THE
PAST FEW WEEKS. THE DEPTH AND TRACK OF THE UPPER SYSTEM COULD
ALSO SUPPORT SOME SNOW AT THE HIGHEST ELEVATIONS, MAINLY FOR THE
CASCADES AND WESTERN MONTANA.
THE EXCESSIVE HEAT WILL CONTINUE INTO NEXT WEEK ACROSS MUCH OF
TEXAS AND INTO PORTIONS 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 CENTRAL/SOUTHERN TEXAS, AND SOME INSTANCES OF HEAT INDICES
OVER 115 DEGREES ARE POSSIBLE FOR PARTS OF DEEP SOUTH TEXAS WHERE
THE GREATEST COMBINATION OF HIGH DEWPOINTS AND THE HEAT WILL
LIKELY EXIST. 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 WHERE HIGHS COULD BE UP TO 20 DEGREES BELOW AVERAGE. A FEW
PLACES COULD CHALLENGE DAILY RECORDS FOR COOL HIGHS. MOST OF THE
EAST COAST REGION SHOULD BE NEAR OR SLIGHTLY BELOW CLIMATOLOGICAL
MID-JUNE LEVELS, AND PLEASANT BY EARLY SUMMER STANDARDS.
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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