584
FXUS02 KWBC 081844
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 PM EDT SUN SEP 8 2024
VALID 12Z WED SEP 11 2024 - 12Z SUN SEP 15 2024
...CENTRAL GULF COAST TO LOWER MISSISSIPPI/TENNESSEE VALLEY HEAVY
RAINFALL/FLOODING THREAT INTO MID-LATER WEEK, WITH POSSIBLE
TROPICAL SYSTEM DEVELOPMENT AND LANDFALL AS MONITORED BY NHC...
..OVERVIEW
WIDESPREAD AND INTENSE RAIN/THUNDERSTORMS WITH FLOODING ISSUES
WILL MAKE CONTINUED MAJOR WEATHER HEADLINES WITH SPREAD ACROSS FOR
THE CENTRAL GULF COAST STATES AND LOWER MISSISSIPPI/TENNESSEE
VALLEY AND VICINITY WITH INLAND RETURN RESURGENCE OF DEEP GULF
MOISTURE WITH A LEADING LIFTING WARM FRONT MID-LATER THIS WEEK. THE
THREAT COULD BE SIGNIFICANTLY ENHANCED WITH POSSIBLE TROPICAL
SYSTEM DEVELOPMENT AND APPROACH/LANDFALL AS CURRENTLY MONITORED BY
NHC. RAIN FROM THIS SYSTEM WILL LIKELY LIFT NORTHWARD TOWARDS THE
OHIO VALLEY AS IT WEAKENS THROUGH NEXT WEEKEND IN SLOWED FLOW.
OUT WEST, THE PERSISTENT UPPER RIDGE AND WIDESPREAD ANOMALOUS
WARMTH IS FORECAST TO ABATE BY THE SECOND HALF OF THE WEEK AS AN
UPPER TROUGH WORKS ACROSS THE WEST COAST, THE INTERMOUNTAIN WEST
AND EVENTUALLY THROUGH THE NORTHERN ROCKIES/PLAINS IN AN ORGANIZED
RAIN PATTERN WITH SOME POTENTIAL FOR LOCAL/TERRAIN ENHANCED RAINS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODEL GUIDANCE FEATURES GOOD OVERALL SYNOPTIC SCALE
AGREEMENT ACROSS THE NATION, WITH DIFFERENCES ONLY SLOWLY
INCREASING THROUGH LONGER TIME FRAMES. IMPORTANTLY, THE FORECAST
SIGNAL CONTINUES TO INCREASE IN FAVOR OF POSSIBLE TROPICAL SYSTEM
DEVELOPMENT OVER THE GULF OF MEXICO WITH LIKELY IMPACTS FOR THE
WESTERN TO CENTRAL GULF COAST AND INLAND OVER THE EAST-CENTRAL U.S..
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A
BROAD MODEL AND ENSEMBLE BLEND ALONG WITH THE 13 UTC NATIONAL
BLEND OF MODELS AND WPC OVERNIGHT CONTINUITY. BLEND WEIGHT FOCUS
GRADUALLY TRANSITIONS FROM THE MODELS TO THE ENSEMBLE MEANS TO
ADDRESS SLOWLY GROWING FORECAST SPREAD. THIS SOLUTION WORKS WELL
WITH LATEST NHC GUIDANCE, BUT REMAINS DEPENDENT ON UPDATED INFO.
..WEATHER/HAZARDS HIGHLIGHTS
HEAVY RAINFALL, WIND/COASTAL AFFECTS 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 SOUTH AND NORTHWARD. THIS WOULD OCCUR AS
A POTENTIAL WESTERN GULF TROPICAL LOW LIFTS; LEADING TO POSSIBLE
LANDFALL AND NORTHWARD INLAND TRACK WITH EXTRATROPCIAL
TRANSITION AND WEAKENING OVER TIME. A WPC EXCESSIVE RAINFALL
OUTLOOK SLIGHT RISK AREA HAS BEEN DEPICTED FROM THE GREATER
HOUSTON METRO AREA TO THE CENTRAL GULF COAST, WHERE THE OVERALL
MODEL SIGNAL IS GREATEST FOR 2-4+ INCH TOTALS, AND POTENTIALLY
DOUBLE THAT FOR AREAS WHERE CONVECTION REPEATEDLY TRAINS. 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. 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. THE HEAVIEST QPF FROM THIS WILL
LIKELY BE OVER NORTHERN WYOMING AND INTO MONTANA, WITH SNOW FOR THE
HIGHEST MOUNTAIN RIDGES. CLOSED LOW PASSAGE AND INCREASED ENSEMBLE
ENHANCED QPF PROBS SEEMS TO ALSO SUPPORT A MARGINAL RISK ERO AREA.
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/SCHICHTEL
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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