083
FXUS02 KWBC 221905
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
305 PM EDT THU JUN 22 2023
VALID 12Z SUN JUN 25 2023 - 12Z THU JUN 29 2023
...PROLONGED HEAT WAVE CONTINUES ACROSS TEXAS AND SOUTHEASTERN NEW
MEXICO AND WILL EXPAND NORTHEAST NEXT WEEK...
..OVERVIEW
THE GENERAL UPPER LEVEL PATTERN WILL REMAIN FAIRLY STAGNANT
THROUGH THE PERIOD WITH A STRONG RIDGE OVER THE SOUTH-CENTRAL U.S.
AND TROUGHING OVER THE EAST AND WEST COASTS. THE RIDGE IS
RESPONSIBLE FOR EXCESSIVE HEAT IN THE SOUTHERN PLAINS, AND HEAT
WILL GRADUALLY EXPAND EAST AND NORTH INTO THE LOWER MISSISSIPPI
VALLEY AND PARTS OF THE MIDDLE MISSISSIPPI VALLEY AND CENTRAL
PLAINS BY MID-NEXT WEEK. ADDITIONAL SHOWERS AND THUNDERSTORMS ARE
EXPECTED IN THE EASTERN THIRD OF THE COUNTRY AS A FEW SURFACE LOW
PRESSURE SYSTEMS MOVE ACROSS THE REGION.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
EARLY IN THE PERIOD, MODELS WERE IN GOOD AGREEMENT ON THE UPPER
LEVEL PATTERN WITH TWO SHORTWAVE TROUGHS COMBINING OVER THE EAST
TO FORM A DEEPER TROUGH BY LATE MONDAY INTO TUESDAY. THE RESULTING
TROUGH AND THE SOUTHERN RIDGE ARE FORECAST TO SLOWLY DRIFT EAST
THROUGH THE PERIOD AS THROUGHING STRENGTHENS OVER THE WEST COAST.
THE GFS WAS THE MOST PROGRESSIVE WITH THIS WHILE THE CMC AND ECMWF
TENDED TO FAVOR SLOWER EASTWARD MOVEMENT. A MODEL BLEND OF
DETERMINISTIC AND ENSEMBLE GUIDANCE WAS USED TO CREATE A MIDDLE
GROUND SOLUTION WITH THE EASTERN TROUGH AXIS OVER THE NORTHEAST
AND THE CENTER OF THE RIDGE OVER EAST TEXAS BY THE END OF THE
PERIOD.
ANOTHER SHORTWAVE TROUGH IS FORECAST TO MOVE NORTHEAST ACROSS THE
WEST AND ROUND THE TOP OF THE RIDGE LATE IN THE PERIOD. MODELS ARE
IN GOOD AGREEMENT THAT THE ENERGY ASSOCIATED WITH THIS FEATURE
WILL SWING THROUGH THE WESTERN TROUGH BY LATE TUESDAY, LEAVING A
WEAKENED TROUGH OVER THE WEST. HOWEVER, MODELS DIFFER ON THE EXACT
POSITION, TIMING, AND MAGNITUDE OF THE SHORTWAVE AS IT MOVES OVER
AND EAST OF THE RIDGE. A MODEL BLEND OF DETERMINISTIC GFS AND
ECMWF, AND ENSEMBLE MEANS WAS USED TO CREATE A MIDDLE OF THE ROAD
SOLUTION, WHICH WORKS WELL FOR THIS FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
AT THE START OF THE PERIOD SUNDAY, A LOW PRESSURE SYSTEM ALOFT AND
AT THE SURFACE COULD CAUSE SOME RAIN TO LINGER ACROSS THE UPPER
MIDWEST, WITH LOCALLY HEAVY AMOUNTS POSSIBLE GIVEN THE GOOD
DYNAMICAL SUPPORT. FARTHER SOUTH IN THE LOWER MISSISSIPPI VALLEY
AND MID-SOUTH, AMPLE MOISTURE AND INSTABILITY AHEAD OF THE COLD
FRONT WILL SUPPORT CONVECTIVE DEVELOPMENT, AND SOME AREAS MAY SEE
SOME HEAVY RAIN RATES IN POTENTIAL MESOSCALE CONVECTIVE SYSTEMS.
MEANWHILE, THERE MAY AGAIN BE A SOMEWHAT FOCUSED AXIS OF RAINFALL
ACROSS THE NORTHERN MID-ATLANTIC REGION INTO THE INTERIOR
NORTHEAST ON SUNDAY, WITH SOME FLOODING CONCERNS OVER AREAS WITH
LOW FLASH FLOOD GUIDANCE. ALL THESE AREAS HAVE MARGINAL RISKS OF
EXCESSIVE RAINFALL IN PLACE FOR SUNDAY-SUNDAY NIGHT. CONVECTION
LOOKS TO OVERSPREAD MUCH OF THE EAST ON MONDAY, WITH SEVERE
WEATHER A POSSIBILITY TOO. A LARGE MARGINAL RISK HAS BEEN
MAINTAINED FOR MUCH OF THE EAST AS THERE MAY BE LOCALLY HEAVY RAIN
WITH THESE SCATTERED TO WIDESPREAD STORMS IN AN UNSTABLE
ENVIRONMENT. EMBEDDED SLIGHT RISK(S) ARE POSSIBLE AS WELL IN
FUTURE CYCLES IF MODEL GUIDANCE AGREES ON AREAS OF FOCUS FOR HEAVY
RAIN, BUT AS OF NOW, UNCERTAINTY IS TOO LARGE TO HIGHLIGHT
SPECIFIC AREAS. BY TUESDAY AND WEDNESDAY, THE FRONT SHOULD PUSH
SLOWLY EASTWARD WITH DRYING BEHIND THE FRONT, WHILE ADDITIONAL
ROUNDS OF RAIN AND THUNDERSTORMS CONTINUE FOR THE EASTERN SEABOARD
AHEAD OF IT. THE NEXT SYSTEM MOVING ACROSS THE WEST WILL ALSO
ALLOW SCATTERED SHOWERS AND STORM CHANCES TO RETURN ACROSS PARTS
OF THE NORTHWEST AND INTO THE NORTHERN ROCKIES AND PLAINS NEXT
MONDAY-WEDNESDAY.
IN TERMS OF TEMPERATURES, THERE IS REALLY NO END IN SIGHT FOR THE
EXCESSIVE HEAT THAT HAS PLAGUED PARTICULARLY TEXAS/SOUTHEASTERN
NEW MEXICO IN RECENT DAYS. TEMPERATURES OVER 100F AND HEAT INDICES
MUCH HIGHER WILL CONTINUE EXPANDING EAST INTO THE LOWER
MISSISSIPPI VALLEY AND NORTH TOWARD THE CENTRAL PLAINS NEXT WEEK.
THE CURRENT FORECAST CALLS FOR TEMPERATURES EXCEEDING NEAR TO JUST
ABOVE 100F IN OKLAHOMA/KANSAS/ARKANSAS BY WEDNESDAY-THURSDAY.
SEVERAL RECORD TEMPERATURES COULD BE SET OR TIED, AS TEMPERATURES
NEARING OR EXCEEDING 110 DEGREES COULD AGAIN OCCUR IN WESTERN AND
SOUTHERN TEXAS. THE DESERT SOUTHWEST STARTS TO SEE TEMPERATURES
WELL OVER 100F NEXT WEEK TOO, THOUGH NOT REALLY ANOMALOUS FOR THIS
TYPICALLY HOTTEST TIME OF THE YEAR THERE. MEANWHILE THE WEST
SHOULD SEE SLIGHTLY COOLER THAN NORMAL TEMPERATURES PARTICULARLY
FOR HIGHS WITH THE BOUTS OF UPPER TROUGHING ALOFT. THE EAST LOOKS
TO BE WITHIN A FEW DEGREES OF AVERAGE FOR EARLY SUMMER, WITH A
TREND TOWARD BELOW AVERAGE BY AROUND 5-10 DEGREES FOR THE GREAT
LAKES REGION.
DOLAN/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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