833
FXUS02 KWBC 171903
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SAT JUN 17 2023
VALID 12Z TUE JUN 20 2023 - 12Z SAT JUN 24 2023
...WATCHING THE POTENTIAL OF HEAVY RAIN DEVELOPING 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 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 SURFACE LOW PRESSURE
WAVE FORMING ALONG A COASTAL FRONT. 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. NO SIGNIFICANT
CHANGES WERE MADE TO THE DAY 4 ERO, WHILE THE INTRODUCED DAY 5 ERO
CONTINUES THE GRADUAL SHIFT EAST OF THE SLIGHT RISK AREA WITH EACH
DAY EARLY TO MID-NEXT WEEK. AS THE WEEK PROGRESSES, THE TRACK OF
THE UPPER LOW WILL AFFECT WHERE RAINFALL SPREADS, BUT THE TREND
HAS BEEN TO FOCUS ON THE SOUTHEAST WITH POSSIBLY SOME EXTENSION
INTO THE MID-ATLANTIC, AS WELL AS LIKELY INCREASING AMOUNTS INTO
SOUTH FLORIDA. MEANWHILE, TEMPERATURES ACROSS THE REGION ARE
LIKELY TO BE BELOW AVERAGE ESPECIALLY IN TERMS OF HIGHS WITH THE
CLOSED LOW OVERHEAD, INFLUENCE OF CLOUDS/PRECIPITATION, AND
COLD-AIR DAMMING SETTING UP ALONG THE APPALACHIANS.
AS ANOTHER UPPER LOW COMES INTO THE NORTHWEST AND PIVOTS NEXT
WEEK, SOME PRECIPITATION IS POSSIBLE ALONG AND BEHIND A FRONT ON
TUESDAY. GIVEN THE BELOW NORMAL HEIGHTS AND THUS TEMPERATURES, THE
HIGHEST ELEVATIONS OF THE CASCADES AND NORTHERN ROCKIES COULD SEE
SOME SNOW. FARTHER EAST, RAIN AND THUNDERSTORM CHANCES SHOULD BE
INCREASINGLY COMMON OVER PORTIONS OF THE THE NORTHERN AND CENTRAL
PLAINS AS THE LOW PRESSURE/FRONTAL SYSTEM STALLS AND FOCUSES
MOISTURE, WITH THE GREATEST POTENTIAL FOR SOME LOCALLY HEAVY
RAINFALL WEDNESDAY-THURSDAY. A MARGINAL RISK IS IN PLACE FOR DAY
5/WEDNESDAY, BUT EVEN GLOBAL MODELS ARE SHOWING THAT POTENTIAL
RAIN RATES COULD EXCEED 1-3 INCHES PER HOUR IN AN ENVIRONMENT WITH
PLENTY OF INSTABILITY AND UPPER DIFLUENCE. IF MODEL GUIDANCE
CONVERGES ON AN AREA FOR RAINFALL TO FOCUS, THERE WILL LIKELY BE A
SLIGHT RISK EMBEDDED AT SOME POINT. THE TROUGHING IN THE WEST WILL
ALSO LEAD TO WELL BELOW NORMAL TEMPERATURES BY AROUND 15-20F FOR
HIGHS AND 10-15F FOR LOWS ON TUESDAY, WITH A FEW RECORD COOL
TEMPERATURES POSSIBLE. TEMPERATURES LOOK TO GRADUALLY MODERATE
CLOSER TO, BUT STILL REMAINING BELOW, NORMAL FOR THE LATTER HALF
OF THE WEEK ACROSS THE WEST.
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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