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   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   245 PM EST Sat Nov 29 2025   
      
   Day 1   
   Valid 16Z Sat Nov 29 2025 - 12Z Sun Nov 30 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF   
   SOUTHEAST TEXAS...   
      
   ...16Z Update...   
   Morning surface observations and 12z Brownsville RAOB depict the   
   return of a modified Gulf airmass ahead of a strong cold front   
   surging into the Southern Plains. As the front approaches Southeast   
   Texas, organized convection is expected to initiate this afternoon   
   in the vicinity of a pre-frontal trough and returning warm front.   
   12Z CAM guidance suggests some training potential with this   
   convection in the 0-6Z timeframe along these boundaries before the   
   front sweeps through. While much of the HREF guidance has trended   
   upward in the magnitude of the rainfall footprint tonight, the   
   modified airmass should limit hourly rainfall rates when combined   
   with 500-1000 J/kg MUCAPE. Thus, maintained the Marginal Risk with   
   an expansion along the I-10 corridor to account for urban heavy   
   rainfall concerns.   
      
   Asherman   
      
      
   A cold front moving south down the Plains will run into a plume of   
   Gulf moisture moving into eastern Texas tonight. The clash of these   
   two air masses is expected to result in some limited thunderstorm   
   development this evening across portions of east central Texas and   
   northern Louisiana. Overnight tonight, the line will press   
   southward. As the line encounters ever increasing amounts of Gulf   
   moisture, convective coverage is likely to also increase across   
   southeastern Texas. Since the plume will continue northeastward up   
   the front, additional convective development is also expected   
   across central Louisiana. However, both due to increased distance   
   from the Gulf and poor instability (values broadly have come down   
   to at most 500 J/kg of MUCAPE), the storms further north and east   
   into Louisiana are likely to remain as a progressive skinny line of   
   convection. Meanwhile, in the Marginal Risk area across southeast   
   Texas, closer proximity to the Gulf should allow for a bit of pre-   
   frontal convection to form before the more organized line of storms   
   moves through. Given the lack of instability, progressive movement   
   of the storms, time of day (overnight tonight), and very dry soils   
   present along the Gulf Coast, the thinking as regards coverage of   
   flooding remains the same... only very isolated flash flooding   
   possible where any prefrontal storms train over urban or other low-   
   lying, flood-sensitive areas. This remains a lower end (near 5%)   
   flood risk. For the most part, the rain expected tonight will be   
   beneficial. The line will move through the Houston metro around   
   midnight local time, then both weaken and move into the Gulf beyond   
   that.   
      
   Wegman   
      
      
   Day 2   
   Valid 12Z Sun Nov 30 2025 - 12Z Mon Dec 01 2025   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 percent.   
      
   Orrison   
      
      
   Day 3   
   Valid 12Z Mon Dec 01 2025 - 12Z Tue Dec 02 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE   
   NORTHWEST AND CENTRAL GULF COAST INTO THE SOUTHEAST...   
      
   2030Z Update...   
      
   The 12Z suite of guidance is generally a bit faster with the   
   ejection of shortwave energy and surface wave activity across the   
   Gulf Coast states and into the Southeast for this period. However,   
   there will still be an expansion area of convection focusing across   
   areas of southeast TX/LA and east-northeastward across the Deep   
   South and interior parts of the Southeast. There remains   
   uncertainty with just how much instability can pool northward away   
   from the Gulf Coast as most of the guidance focuses the stronger   
   instability along and offshore of the Gulf Coast, but there will be   
   plenty of warm air advection, moisture transport and at least some   
   elevated instability to focus an elongated corridor of heavy   
   showers and thunderstorms. Some localized swaths of cell-training   
   will be possible which may result in some 2 to 4 inch rainfall   
   totals. However, given the dry antecedent conditions, this is   
   expected to generally be an isolated flash flood threat and mainly   
   around the more urbanized locations. Therefore, aside from some   
   modest tweaks to account for the latest guidance, the Marginal Risk   
   area is maintained.   
      
   Orrison   
      
   Previous discussion...   
      
   A fast-moving progressive shortwave trough that extends from an=20   
   expansive upper level low over Canada will provide the upper level=20   
   forcing for cyclogenesis along a potent cold front that will=20   
   roughly parallel the Gulf Coast and Eastern Seaboard. The low will=20   
   begin to form along the Texas Gulf coast during the day Monday,=20   
   then track ENE across the Deep South, ending the period near the=20   
   South Carolina/Georgia border. As the low tracks along the Gulf=20   
   Coast, it will continually add Gulf moisture to its circulation,=20   
   while also thriving on the baroclinicity brought on by a=20   
   reinforcing cold air mass moving southeast from the Midwest. PWATs=20   
   in the warm, moist Gulf air mass will exceed 1.75 inches in some=20   
   areas. However, any instability will likely remain along the=20   
   immediate coast, with very little instability inland. This supports   
   an overrunning rainfall scenario, rather than an overly convective   
   one. A prolonged period of light to moderate rain is expected=20   
   across much of the South as a result. The heaviest rain is forecast   
   from near New Orleans northeast to the southern Appalachians. It's   
   in this corridor that the highest probability of flash flooding=20   
   exists. The qualifier to this statement however is that FFGs across   
   the Deep South are quite high as a result of recent dry weather=20   
   and therefore very dry soils. This will favor most of the rainfall=20   
   associated with this low being beneficial to affected areas.=20   
   Isolated flash flooding is most likely in urban or flood-prone=20   
   areas, as well as in the flashier streams that drain the Southern=20   
   Appalachians.   
      
   Wegman   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!6THRugZ-Z7jBVP-upo0Xl9JGe9avG-wcHE2tbGPtdBXD=   
   Kwb1i31ZuO7GEZcaXP165uX1wQzyt5u6X0C3KngbNaAJfZs$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!6THRugZ-Z7jBVP-upo0Xl9JGe9avG-wcHE2tbGPtdBXD=   
   Kwb1i31ZuO7GEZcaXP165uX1wQzyt5u6X0C3Kngbm3cA97E$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!6THRugZ-Z7jBVP-upo0Xl9JGe9avG-wcHE2tbGPtdBXD=   
   Kwb1i31ZuO7GEZcaXP165uX1wQzyt5u6X0C3Kngbq58N5Pw$=20   
      
   =3D =3D =3D   
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