530
FXUS02 KWBC 172004
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 PM EDT SAT JUN 17 2023
VALID 12Z TUE JUN 20 2023 - 12Z SAT JUN 24 2023
...WATCHING THE POTENTIAL OF HEAVY RAIN EXPANDING OVER PARTS OF
THE SOUTHEAST AS A PROLONGED HEAT WAVE CONTINUES ACROSS THE
SOUTHERN PLAINS THROUGH NEXT WEEK...
..OVERVIEW
A SIMILARLY BLOCKY PATTERN IS FORECAST TO CONTINUE THROUGH MUCH OF
NEXT WEEK ACROSS THE MAINLAND U.S. THIS PATTERN WILL FEATURE (1)
A DEEP POSITIVELY-TILTED TROUGH ACROSS THE NORTHWESTERN U.S., (2)
ANOTHER LONGWAVE TROUGH DOWN THE EAST COAST TOGETHER WITH AN
EXPANSIVE COOL SURFACE ANTICYCLONE, (3) A WARM RIDGE REMAINED
ANCHORED OVER TEXAS, AND (4) AN UPPER LOW THAT WILL LIKELY BRING
HEAVY RAIN INTO THE SOUTHEAST AND PARTS OF THE MID-ATLANTIC WITH
MODELS TRENDING TOWARD HIGH RAINFALL AMOUNTS ACROSS THE SOUTHERN
MID-ATLANTIC INTO THE SOUTHERN APPALACHIANS. MEANWHILE, THE
POTENTIAL FOR HEAVY RAIN EXISTS FROM THE CENTRAL HIGH PLAINS TO
THE NORTHERN PLAINS AS A FRONT IS FORECAST TO BECOME STATIONARY IN
THE VICINITY MIDWEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
DESPITE THE PREVAILING BLOCKY AND AMPLIFIED SYNOPTIC PATTERN
ACROSS THE U.S., MODELS AND ENSEMBLES HAVE DISPLAYED RELATIVELY
MINIMAL SPREAD THROUGH THE MEDIUM-RANGE PERIOD. THE MOST
UNCERTAIN FEATURE CONTINUES TO BE THE POTENTIAL FOR A CLOSED UPPER
LOW TO FORM OVER THE SOUTHEAST WHICH MAY LINGER FURTHER IN THE
VICINITY IF THE FEATURE ENDS UP STRONGER THAN PREDICTED. THIS
UPPER LOW WILL HAVE IMPORTANT IMPLICATIONS TO WHERE AND HOW MUCH
HEAVY RAIN WILL IMPACT THE SOUTHEAST. MODELS HAVE BEEN TRENDING
TOWARD DEVELOPING A BETTER-DEFINED UPPER LOW, LEADING TO A DEEPER
AND STRONGER INFLUX OF MOISTURE TOWARD THE SOUTHERN MID-ATLANTIC
AND SOUTHERN APPALACHIANS, WITH A STRONGER LOW PRESSURE WAVE
FORMING ALONG A COASTAL FRONT. AN AMPLIFIED UPPER RIDGE BUILDING
EAST ACROSS THE THE GREAT LAKES TOWARD NEW ENGLAND WILL ALSO HELP
TO CLOSE OFF THE UPPER LOW OVER THE SOUTHEAST WHILE KEEPING THE
LOW IN PLACE. THIS SITUATION WILL NEED TO BE FURTHER MONITORED AS
IT DOES NOT TAKE MUCH FOR THE DYNAMICS TO BUMP UP QPFS THERE.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER LOW MEANDERING OVER THE SOUTHEAST/TENNESSEE VALLEY OR
SO, ALONG WITH A FRONTAL SYSTEM AND AMPLE GULF MOISTURE, WILL
PROVIDE SUPPORT FOR MULTIPLE ROUNDS OF RAIN AND THUNDERSTORMS FOR
THE SOUTHEASTERN QUADRANT OF THE COUNTRY THROUGH MUCH OF NEXT
WEEK. SLIGHT RISKS OF EXCESSIVE RAINFALL ARE IN PLACE FOR BOTH
DAYS 4 AND 5 (TUESDAY AND WEDNESDAY) IN THE SOUTHEAST TO SOUTHERN
APPALACHIANS GIVEN THE POTENTIAL FOR WIDESPREAD 1-3" TOTALS PER
DAY WITH LOCALLY HIGHER AMOUNTS. PORTIONS OF THIS REGION HAVE OR
WILL LIKELY HAVE BY THAT TIME WET ANTECEDENT CONDITIONS GIVEN
RECENT OR UPCOMING EPISODES OF HEAVY RAINFALL. THE SLIGHT HAS
BEEN SPLIT INTO TWO, WITH THE NORTHERN PORTION ASSOCIATED WITH THE
DEVELOPMENT OF A WAVE ALONG THE COASTAL FRONTAL IN CONJUCTION WITH
A STRONGER INFLUX OF ATLANTIC MOISTURE AHEAD OF A STRONGER UPPER
LOW OVER THE SOUTHEAST. THE SOUTHERN PORTION OF THE SLIGHT IS
ASSOCIATED WITH A STATIONARY FRONT NEAR THE EASTERN GULF COAST.
IT APPEARS THAT THE BIGGEST THREAT OF THE HEAVY RAIN IN THE
SOUTHEAST WILL BE THROUGH MIDWEEK NEXT WEEK BEFORE GRADUAL
DECREASE IN QPFS SETS IN FOR LATER NEXT WEEK AS THE UPPER LOW IS
FORECAST TO WEAKEN. HOWEVER, THE RECENT MODEL TREND FOR A
STRONGER UPPER LOW COULD IMPLY A BETTER-DEFINED LOW TO LINGER IN
THE VICINITY FURTHER INTO NEXT WEEK, WHICH MAY HELP KEEP THE
RAINFALL IN PLACE ACROSS THE SOUTHEAST AND THEN PERHAPS SPREAD
FARTHER UP THE EAST COAST BY NEXT WEEKEND.
AS ANOTHER UPPER LOW COMES INTO THE NORTHWEST AND LIFTS TOWARD
SOUTHERN CANADA NEXT WEEK, SOME PRECIPITATION IS POSSIBLE ALONG
AND BEHIND A FRONT ON TUESDAY. GIVEN THE BELOW NORMAL HEIGHTS AND
TEMPERATURES, THE HIGHEST ELEVATIONS OF THE CASCADES AND NORTHERN
ROCKIES COULD SEE SOME SNOW. FARTHER EAST, RAIN AND THUNDERSTORM
CHANCES SHOULD BE EXPANDING OVER PORTIONS OF THE THE NORTHERN
PLAINS AND DOWN TOWARD THE CENTRAL HIGH PLAINS AS THE LOW
PRESSURE/FRONTAL SYSTEM STALLS AND FOCUSES MOISTURE, WITH THE
GREATEST POTENTIAL FOR SOME LOCALLY HEAVY RAINFALL
WEDNESDAY-THURSDAY. A SLIGHT RISK HAS BEEN INTRODUCED NEAR AND
JUST EAST OF THE FORECASTED FRONTAL POSITION. BEHIND THE FRONT,
WIDESPREAD WELL BELOW NORMAL TEMPERATURES ARE EXPECTED ON TUESDAY,
WITH A FEW RECORD COOL TEMPERATURES POSSIBLE. A SLOW MODERATING
TREND IN TEMPERATURES IS FORECAST THEREAFTER BUT THEY WILL STILL
BE BELOW NORMAL FOR THE LATTER HALF OF THE WEEK ACROSS MUCH OF THE
WEST.
MEANWHILE, THE EXCESSIVE HEAT WILL CONTINUE INTO NEXT WEEK ACROSS
MUCH OF TEXAS AND INTO PORTIONS OF LOUISIANA AND NEW MEXICO, WITH
WIDESPREAD 100S AND EVEN SOME 110S ACROSS CENTRAL AND SOUTHERN
PORTIONS OF TEXAS, AND 90S WITH HEAT INDICES WELL OVER 100F
ELSEWHERE. MANY DAILY RECORD HIGH TEMPERATURES ARE POSSIBLE, AND
SOME MONTHLY RECORDS MAY EVEN BE CHALLENGED. HEAT INDICES AS HIGH
AS 115-120 DEGREES ARE POSSIBLE FOR PARTS OF SOUTHERN AND
SOUTHEASTERN TEXAS WHERE THE GREATEST COMBINATION OF HIGH
DEWPOINTS AND TEMPERATURES WILL LIKELY EXIST. AS MEAN UPPER
RIDGING EXPANDS FARTHER NORTH, HIGHS IN THE 90S ARE LIKELY ACROSS
MUCH OF THE PLAINS AND MISSISSIPPI VALLEY. THIS WILL BE ABOUT
10-20F ABOVE AVERAGE FOR THE NORTHERN PLAINS TUESDAY. AS A REX
BLOCK PATTERN SETS UP OVER THE NORTHERN TIER, THE UPPER MIDWEST
INTO THE INTERIOR NORTHEAST CAN EXPECT 80S TO LOW 90S FOR HIGHS
FOR THE LATTER HALF OF THE WEEK, ABOUT 10F ABOVE AVERAGE.
KONG/TATE
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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