637
FXUS02 KWBC 200700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT TUE JUN 20 2023
VALID 12Z FRI JUN 23 2023 - 12Z TUE JUN 27 2023
...PROLONGED HEAT WAVE CONTINUES ACROSS TEXAS AND SOUTHEASTERN NEW
MEXICO THROUGHOUT THIS WEEK WITH SOME SPREAD INTO THE LOWER
MISSISSIPPI VALLEY EARLY NEXT WEEK...
...HEAVY RAIN AND FLOODING ARE POSSIBLE ACROSS THE NORTH-CENTRAL
U.S. LATE THIS WEEK WITH A LOW PRESSURE SYSTEM...
..OVERVIEW
THE MEDIUM RANGE PERIOD WILL BEGIN FRIDAY WITH AN UPPER LOW
FINALLY LIFTING NORTH OUT OF THE TENNESSEE VALLEY, THOUGH WITH
SOME REMAINING SHOWERS AND THUNDERSTORMS ACROSS THE EAST WITH A
LOW PRESSURE/FRONTAL SYSTEM AT THE SURFACE. FARTHER WEST, ANOTHER
UPPER LOW IS FORECAST TO PRESS ACROSS THE WEST INTO THE NORTHERN
PLAINS THROUGH THE WEEKEND AND THEN INTO THE GREAT LAKES REGION,
SPREADING RAIN WITH IT THAT COULD BE HEAVY AND CAUSE FLASH
FLOODING CONCERNS PARTICULARLY IN THE NORTHERN PLAINS. MEANWHILE,
A STRONG UPPER HIGH WILL CONTINUE TO MEANDER AROUND THE RIO GRANDE
THROUGH THE WEEK AND INTO NEXT WEEK, CAUSING PERSISTENT HEAT
ACROSS MUCH OF TEXAS AND SOUTHEASTERN NEW MEXICO, AND HIGH HEAT
INDICES ARE LIKELY TO SPREAD INTO THE LOWER MISSISSIPPI VALLEY AS
WELL BY EARLY NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
FOR LATE WEEK, MODEL GUIDANCE CONTINUES TO SHOW FAIRLY GOOD
AGREEMENT WITH THE OVERALL INITIALLY BLOCKY SYNOPTIC PATTERN, WITH
TROUGHING ACROSS THE WEST INCLUDING A SMALL UPPER LOW CLOSING OFF
ATOP THE NORTHERN HIGH PLAINS BY EARLY SATURDAY, RIDGING EXTENDING
FROM TEXAS NORTHWARD, AND THE UPPER LOW/TROUGH GRADUALLY LIFTING
OUT OF THE EAST-CENTRAL CONUS. FOR THE EARLY PART OF THE FORECAST
PERIOD, UTILIZED A BLEND OF THE 12/18Z DETERMINISTIC GUIDANCE
FAVORING THE ECMWF AND GFS.
BY EARLY NEXT WEEK, THE NORTH-CENTRAL U.S. UPPER AND SURFACE LOWS
LOOK TO CONTINUE THEIR TREK EASTWARD AND MOVE ATOP THE UPPER GREAT
LAKES REGION FOR RENEWED TROUGHING ACROSS THE EAST, WITH
REASONABLE MODEL AGREEMENT GIVEN THE LEAD TIME. THE 12Z ECMWF WAS
ON THE SLOW SIDE WITH THE TROUGH BY DAY 7/TUESDAY BUT THE NEWER
00Z MODELS SEEM TO HAVE SPED UP IN GENERAL. MORE DIFFERENCES IN
TERMS OF PLACEMENT AND TIMING ARISE WITH AN UPPER TROUGH/LOW IN
THE EASTERN PACIFIC SUNDAY-MONDAY THAT COULD PUSH INTO THE WEST BY
TUESDAY. THE 18Z GFS WAS ON THE FAST SIDE, SO STARTED TO FAVOR THE
12Z GFS THAT WAS BETTER ALIGNED WITH THE AXIS OF THE ENSEMBLE
MEANS. ON THE OTHER HAND THE 12Z ECMWF SLOWED FARTHER WEST THAN
THE OTHER GUIDANCE, INCLUDING THE NEWER 00Z GUIDANCE SUITE.
MEANWHILE MODELS SHOW GOOD AGREEMENT THAT THE UPPER HIGH OVER
WESTERN TEXAS/NORTHERN MEXICO WILL CONTINUE TO HOLD ON, WHILE
RIDGING MAY POKE NORTHWARD INTO THE FOUR CORNERS STATES AND
BEYOND, BUILDING AHEAD OF THE EASTERN PACIFIC TO WESTERN U.S.
TROUGH. WITH THE INCREASING MODEL SPREAD ESPECIALLY IN THE WEST,
STARTED TO FAVOR THE ENSEMBLE MEAN GUIDANCE TO ABOUT HALF BY DAYS
6-7.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE UPPER LOW MEANDERING OVER THE SOUTHEAST/TENNESSEE VALLEY IN
THE SHORT RANGE WEAKENS AND LIFTS NORTH, IT WILL STILL PROVIDE
SOME SUPPORT FOR RAIN AND THUNDERSTORMS BUT LIKELY WITH REDUCED
WIDESPREAD AMOUNTS COMPARED TO THE SHORT TERM. THE UPPER AND
SURFACE LOWS LIFTING NORTH SHOULD ALLOW FOR RAIN CHANCES TO SPREAD
NORTH INTO THE MID-ATLANTIC AND NORTHEAST AS WELL. FOR FRIDAY, A
MARGINAL RISK OF EXCESSIVE RAINFALL IS IN PLACE ACROSS THE
SOUTHEAST AND MID-ATLANTIC FOR LINGERING CONVECTION OVER WHAT IS
LIKELY TO BE WET GROUND AFTER MULTIPLE DAYS OF RAIN IN SOME AREAS.
THE INSTABILITY IN PLACE COULD SUPPORT LOCALIZED HEAVY RAIN RATES.
BY SATURDAY FOR THE DAY 5 ERO, THERE MAY BE A SOMEWHAT FOCUSED
AXIS OF RAINFALL ACROSS THE NORTHERN MID-ATLANTIC REGION INTO THE
INTERIOR NORTHEAST, SO A MARGINAL RISK IS IN PLACE FOR THOSE
REGIONS, AND AREAS OF LOW FLASH FLOOD GUIDANCE COULD BE OF
PARTICULAR CONCERN. SCATTERED THUNDERSTORMS MAY REMAIN FARTHER
SOUTH TOO. A WET PATTERN LOOKS TO PERSIST ACROSS THE EAST THROUGH
EARLY NEXT WEEK AS ADDITIONAL TROUGHING COMES IN.
FARTHER WEST, SUPPORT STARTS TO BECOME FAVORABLE FOR HEAVY RAIN IN
THE NORTH-CENTRAL U.S. AS A COUPLED UPPER JET (RIGHT ENTRANCE/LEFT
EXIT REGION COMBINATION) SETS UP AROUND MONTANA ON FRIDAY AND INTO
THE NORTHERN PLAINS BY SATURDAY, WHILE AT THE SURFACE A LOW
PRESSURE/FRONTAL SYSTEM CONSOLIDATES. BROAD SLIGHT RISKS OF
EXCESSIVE RAINFALL ARE IN PLACE FOR THIS POTENTIAL, ACROSS THE
NORTHERN HIGH PLAINS ON FRIDAY AND FOR THE NORTHERN
PLAINS/NORTHERN MINNESOTA ON SATURDAY. ENSEMBLE MEMBERS FROM THE
GEFS/ECENS/CMC MODEL SUITES COMBINED INDICATE ABOUT A 60 PERCENT
CHANCE OF THE 24 HOUR RAINFALL EXCEEDING THE 1 YEAR AVERAGE
RECURRENCE INTERVAL (ARI) ON FRIDAY IN EASTERN MONTANA, WHICH IS
QUITE HIGH FOR THIS LEAD TIME. AS THE LOW PICKS UP SPEED AND MOVES
EAST EARLY NEXT WEEK, AREAS WEST OF THE GREAT LAKES SHOULD DRY
OUT, EXCEPT THAT THERE MAY BE A RENEWED ROUND OF RAIN ACROSS THE
NORTHWEST EARLY NEXT WEEK.
MEANWHILE, THE EXCESSIVE HEAT WILL CONTINUE THROUGH LATE WEEK,
WITH WIDESPREAD 100S ACROSS CENTRAL AND SOUTHERN PORTIONS OF TEXAS
AND SOUTHERN NEW MEXICO, AND 90S WITH HEAT INDICES WELL OVER 100F
ELSEWHERE IN THE SOUTH-CENTRAL CONUS. THE HAZARDOUS HEAT LOOKS TO
ONCE AGAIN BECOME MORE WIDESPREAD INTO NEXT WEEK, STRETCHING INTO
THE LOWER MISSISSIPPI VALLEY AS WELL. MANY DAILY RECORD HIGH
TEMPERATURES ARE POSSIBLE, AND SOME MONTHLY RECORDS MAY EVEN BE
CHALLENGED. THE DESERT SOUTHWEST STARTS TO SEE TEMPERATURES WELL
OVER 100F BY EARLY NEXT WEEK TOO, THOUGH NOT REALLY ANOMALOUS FOR
THIS TYPICALLY HOTTEST TIME OF THE YEAR THERE. AS MEAN UPPER
RIDGING EXPANDS FARTHER NORTH, HIGHS IN THE 90S ARE LIKELY ACROSS
MUCH OF THE PLAINS AND MISSISSIPPI VALLEY, WHILE 80S AND LOW 90S
IN THE UPPER MIDWEST/GREAT LAKES REGION LATE THIS WEEK WILL BE
10-15F ABOVE NORMAL. MEANWHILE THE WEST SHOULD SEE COOLER THAN
NORMAL TEMPERATURES PARTICULARLY FOR HIGHS WITH THE BOUTS OF UPPER
TROUGHING ALOFT, WHILE COOLER THAN AVERAGE TEMPERATURES WILL ALSO
BE PRESENT IN THE SOUTHEASTERN U.S. LATE THIS WEEK GIVEN THE
CLOUDINESS/RAIN CHANCES AND THE UPPER LOW.
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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