670
FXUS02 KWBC 080657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT SUN SEP 8 2024
VALID 12Z WED SEP 11 2024 - 12Z SUN SEP 15 2024
...DETERIORATING CONDITIONS EXPECTED FOR SOUTHEAST TEXAS AND INTO
LOUISIANA AS A TROPICAL SYSTEM LIKELY AFFECTS THE REGION MIDWEEK...
..OVERVIEW
THE MAIN THING THAT WILL MAKE WEATHER HEADLINES FOR THE MIDDLE OF
NEXT WEEK WILL BE THE INCREASING THREAT OF AN ORGANIZED TROPICAL
SYSTEM, WHICH IS BEING CLOSELY MONITORED BY THE NATIONAL HURRICANE
CENTER WITH A HIGH CHANCE OF DEVELOPMENT. THE RESULT WILL LIKELY
BE HEAVY RAINFALL THAT COULD PRODUCE FLOODING AND GUSTY WINDS FOR
PORTIONS OF THE CENTRAL AND WESTERN GULF COAST, AND THE RAIN FROM
THIS SYSTEM WILL LIKELY LIFT NORTHWARD TOWARDS THE OHIO VALLEY AS
IT WEAKENS LATE IN THE FORECAST PERIOD. ELSEWHERE, A PATTERN CHANGE
WILL BE ARRIVING TO THE WEST COAST AND INTERMOUNTAIN WEST AS AN
UPPER TROUGH AMPLIFIED OVER THE REGION AND HERALDS THE ARRIVAL OF
COOLER TEMPERATURES. MEANWHILE, A GENERALLY WARMER TREND IS
EXPECTED FOR THE EAST COAST REGION AS UPPER LEVEL RIDGING DEVELOPS
IN THE WAKE OF THE RECENT TROUGH ACROSS THE NORTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE FEATURES GOOD OVERALL SYNOPTIC SCALE
AGREEMENT ACROSS THE NATION ON WEDNESDAY AND CONTINUING INTO
THURSDAY, ESPECIALLY WITH THE DEVELOPMENT AND EVOLUTION OF THE
TROUGH ACROSS THE WEST. FOR THE TROPICAL LOW APPROACHING THE
WESTERN GULF COAST, THE UKMET IS A NORTHEASTERN OUTLIER COMPARED TO
THE OTHER GUIDANCE AND THE ENSEMBLE MEANS, AND THE GFS SLIGHTLY
EAST OF THE CMC/ECMWF TRACKS. LOOKING AT INDIVIDUAL ENSEMBLE
MEMBERS, THERE IS STILL A BIG SOUTHWEST TO NORTHEAST SPREAD WITH
THE POSITION OF THE LOW, AND INTENSITY VARIES FROM ABOUT 980-1000
MB AS IT APPROACHES THE COAST.
FOR THE WPC OVERNIGHT FORECAST, A BLEND OF THE DETERMINISTIC
GFS/CMC/ECMWF WAS USED AS A BASELINE THROUGH THE END OF THE WEEK,
AND LESS OF THE UKMET OWING TO ITS EASTERN SOLUTION WITH THE
TROPICAL SYSTEM. ENSEMBLE MEANS WERE ADDED GRADUALLY TO MAKE UP
ABOUT 40% OF THE BLEND BY SUNDAY, WHICH HELPED TO SMOOTH OUT
INCREASING MESOSCALE DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
HEAVY RAINFALL, WIND, AND THE POTENTIAL FOR FLOODING WILL INDEED
BE THE MOST IMPORTANT FACET OF THE MEDIUM RANGE FORECAST ACROSS THE
GULF COAST REGION, AND THEN ACROSS INTERIOR PORTIONS OF THE DEEP
SOUTH AS THE WESTERN GULF TROPICAL LOW LIFTS SLOWLY TOWARDS THE
NORTHEAST. THE CORE OF THE HEAVIEST RAINFALL FROM THE LOW WILL
LIKELY BE JUST APPROACHING THE SOUTHWEST LOUISIANA/SOUTHEAST TEXAS
COAST BY LATE WEDNESDAY, WITH OUTER FEEDER BANDS LIKELY REACHING
NORTH OF THE INTERSTATE 20 CORRIDOR BY EARLY THURSDAY. A SLIGHT
RISK REMAIN VALID FROM THE GREATER HOUSTON METRO AREA TO CENTRAL
LOUISIANA, WHERE THE OVERALL MODEL SIGNAL IS GREATEST FOR 2-4+ INCH
TOTALS, AND POTENTIALLY DOUBLE THAT FOR AREAS WHERE CONVECTION
REPEATEDLY TRAINS OVER THE SAME AREAS. THE SAME GENERAL THINKING
HOLDS TRUE FOR THE NEW DAY 5 PERIOD THURSDAY AS THE MAIN QPF AXIS
LIFTS NORTH ACROSS MISSISSIPPI AND WESTERN TENNESSEE, BUT THERE
REMAINS NOTEWORTHY LONGITUDINAL DIFFERENCES IN THE TRACK OF THE
INLAND LOW, WITH THE UKMET ON THE EASTERN SIDE OF THE GUIDANCE AND
THE GFS TRENDING A LITTLE SLOWER WITH ARRIVAL OF HEAVIEST RAINFALL.
ALTHOUGH A MODERATE RISK MAY EVENTUALLY BE NEEDED FOR PARTS OF
THESE REGIONS, THERE IS STILL NOT ENOUGH CONFIDENCE TO PLACE ONE AT
THIS TIME, ESPECIALLY SINCE THE LOW HAS NOT FULLY DEVELOPED YET.
OTHERWISE, THE TROUGH ARRIVING OVER THE WEST WILL LIKELY PRODUCE
MAINLY LIGHT TO MODERATE SHOWERS ACROSS PORTIONS OF THE PACIFIC
NORTHWEST AND INTO THE ROCKIES THROUGH THURSDAY NIGHT. THE HEAVIEST
QPF FROM THIS WILL LIKELY BE OVER NORTHERN WYOMING AND INTO
MONTANA, WITH SNOW FOR THE HIGHEST MOUNTAIN RIDGES. SHOWERS AND
SOME STORMS THEN REACH THE CENTRAL/NORTHERN PLAINS BY FRIDAY, WHILE
THE GREAT LAKES AND THE NORTHEASTERN QUADRANT OF THE NATION
REMAINS MOSTLY DRY.
TEMPERATURES WILL STILL FEEL MORE LIKE AUGUST ACROSS MUCH OF THE
NORTH-CENTRAL U.S. THROUGH THE END OF THE WEEK FOR BOTH HIGHS AND
LOWS, WITH POTENTIAL +20 DEGREE ANOMALIES FOR LOWS ACROSS NORTH
DAKOTA AND NORTHERN MINNESOTA BY FRIDAY MORNING. MEANWHILE ACROSS
THE WEST COAST REGION AND THE INTERMOUNTAIN WEST, A RETURN TO
REFRESHINGLY COOLER TEMPERATURES IS EXPECTED BY MIDWEEK IN RESPONSE
TO THE BUILDING UPPER TROUGH, AND PROVIDING BADLY NEEDED RELIEF
FROM THE RECENT HOT AND DRY WEATHER THIS REGION HAS ENDURED OVER
RECENT DAYS. WIDESPREAD HIGHS IN THE 60S CAN BE EXPECTED FOR THE
LOWER ELEVATIONS BEHIND THE COLD FRONT.
HAMRICK
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 FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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