991
FXUS02 KWBC 170701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SAT JUN 17 2023
VALID 12Z TUE JUN 20 2023 - 12Z SAT JUN 24 2023
...DANGEROUS HEAT EXPECTED ACROSS TEXAS, LOUISIANA, AND SOUTHEAST
NEW MEXICO WITH SOME RECORD TEMPERATURES POSSIBLE THROUGH NEXT
WEEK...
..OVERVIEW
A BLOCKY PATTERN WILL CONTINUE TO BE IN PLACE FOR THE MEDIUM RANGE
PERIOD NEXT WEEK, WITH AN UPPER RIDGE/HIGH NEAR THE RIO GRANDE
THAT WILL PRODUCE EXCESSIVE HEAT ACROSS THE SOUTH-CENTRAL CONUS.
THE UPPER RIDGE SHOULD EXTEND TO THE NORTHEAST NEAR THE
MIDWEST/GREAT LAKES, WHILE AN UPPER LOW LOOKS TO BE ATOP THE
SOUTHEAST/TENNESSEE VALLEY FOR A POTENTIAL REX BLOCK PATTERN. THE
UPPER LOW ALONG WITH AMPLE MOISTURE IS LIKELY TO PRODUCE HEAVY TO
EXCESSIVE RAIN ACROSS THOSE REGIONS. MEANWHILE IN THE WEST,
PERSISTENT TROUGHING WILL LEAD TO COOLER THAN NORMAL TEMPERATURES
AND SOME PRECIPITATION IN THE NORTHWEST SHIFTING INTO THE PLAINS
WITH TIME, WITH AN EVENTUAL HEAVY RAINFALL THREAT POSSIBLE THERE
AS WELL.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE OVERALL PATTERN CONSISTING OF AN INITIALLY ANOMALOUSLY DEEP
LOW/TROUGH OVER THE NORTHWEST, RIDGING OVER THE SOUTH-CENTRAL U.S.
WITH A RIDGY COMPONENT STRETCHING NORTH THAT DRIFTS EAST WITH
TIME, AND AN UPPER LOW MEANDERING OVER THE TENNESSEE
VALLEY/SOUTHEAST LOOKS REASONABLY WELL HANDLED BY THE MODELS FOR
MUCH OF THE PERIOD, BUT WITH CONTINUED DIFFERENCES IN THE DETAILS.
ONE ASPECT THAT MODELS HAVE BEEN WAFFLING WITH IS WITH THE
POSITION OF THE SOUTHEASTERN U.S. UPPER LOW. THE 12/18Z MODEL
CYCLE SPANNED FROM THE FARTHEST SOUTHWEST GFS RUNS (ESPECIALLY THE
12Z RUN, THAT DRIFTED THE UPPER LOW INTO THE WESTERN GULF BY DAY
7/SATURDAY WHICH WAS FARTHER SOUTH THAN ANY ENSEMBLE MEMBER) TO
THE FARTHEST NORTH UKMET RUN THROUGH ITS TIMEFRAME. THE ECMWF AND
CMC SEEMED TO HAVE THE BEST MIDDLE GROUND THAT WAS IN BETWEEN BOTH
THE SOUTH/NORTH EXTREMES AND ALSO IN THE MIDDLE OF THE GUIDANCE
CONSENSUS FROM THE PAST COUPLE OF DAYS. THE INCOMING 00Z MODEL
CYCLE MAY BE A LITTLE MORE AGREEABLE WITH THE POSITIONING OF THE
LOW. THE 00Z GUIDANCE WAS A LITTLE SLOWER TO BRING THE LOW SOUTH
TUESDAY-WEDNESDAY COMPARED TO THE EARLIER CYCLE. THE 00Z GFS
TRENDED AWAY FROM A GULF COAST TYPE OF SOLUTION, PUTTING IT MORE
IN LINE WITH OTHER GUIDANCE. THERE MAY BE SOME PHASING BACK WITH
THE NORTHERN STREAM BY LATE NEXT WEEK, THE DETAILS OF WHICH REMAIN
TO BE SEEN.
FARTHER WEST, MODELS REMAINED QUITE AGREEABLE WITH THE HOT UPPER
RIDGE IN THE SOUTH-CENTRAL U.S., WHILE ITS EXTENT NORTH AND EAST
WILL VARY SOMEWHAT DEPENDENT ON THE UPPER LOW'S POSITION. THEN
GUIDANCE ALSO SHOWS GOOD CONSENSUS FOR THE EARLY PART OF THE
PERIOD WITH THE WESTERN TROUGH WITH THE EMBEDDED UPPER LOW
TRACKING FROM THE U.S. NORTHWEST TUESDAY INTO CANADA MIDWEEK. THE
PATTERN THERE GETS MORE MESSY BY LATE WEEK AS THERE IS POTENTIAL
FOR ADDITIONAL PACIFIC ENERGY TO COME IN, AND THIS IS OFTEN A LOW
PREDICTABILITY PART OF THE FORECAST THAT WILL PROBABLY CHANGE WITH
TIME.
THUS THE WPC FORECAST USED A MULTI-MODEL BLEND OF THE 12/18Z
GUIDANCE FAVORING THE ECMWF AND CMC EARLY ON. WITH TIME, PHASED
OUT THE UKMET AND THEN THE GFS WHILE INCREASING THE PROPORTION OF
ENSEMBLE MEANS TO OVER HALF BY DAY 7 AMID THE INCREASING
UNCERTAINTY. THIS WAS FAIRLY CONSISTENT WITH THE PREVIOUS FORECAST
THOUGH WITH A BIT OF A NORTHEASTERN TREND TO THE EASTERN UPPER
LOW, GIVEN THAT MOST MODELS HAD TRENDED AWAY FROM A GULF COAST
CENTROID SOLUTION.
..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.
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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