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   FOUS30 KWBC 251554   
   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   1054 AM EST Tue Nov 25 2025   
      
   Day 1   
   Valid 16Z Tue Nov 25 2025 - 12Z Wed Nov 26 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF   
   THE SOUTHEAST AND SOUTHERN APPALACHIANS, SOUTH TEXAS, AND ALSO FOR   
   THE COASTAL PACIFIC NORTHWEST...   
      
   ...16Z Outlook Update...   
   The ongoing forecast is generally on track with only minimal   
   changes needed based on latest short-term convective evolution.   
   Reference Mesoscale Precipitation Discussion #1250 for short-term   
   flash flood risk evolution across Alabama and vicinity.   
      
   Later today, convection will increase in coverage and intensity   
   across eastern Mississippi and migrate quickly eastward across   
   Alabama into Georgia and southeastern Tennessee through the   
   overnight hours. CAMs depict a mix of cellular and linear   
   convective models with little opportunity for convective training   
   that would enhance local flash flood risk. Marginal Risk and   
   attendant probabilities remain appropriate for today's flash flood   
   threat, with urban areas, sensitive/low-lying areas, and areas that   
   have wet soils from prior rainfall (i.e., western/northern Alabama)   
   experiencing a locally higher (but still isolated) threat of   
   excessive runoff.   
      
   A small Marginal Risk area was drawn for Deep South Texas primarily   
   for the overnight (03Z-12Z) period. A stalling front should drift   
   toward that area during that timeframe. Meanwhile, weak mid-level   
   waves should initiate convection along and south of the front where   
   moderate instability and very moist thermodynamics reside (PW   
   values ~ 1.75 inch). While sufficient steering flow aloft exist for   
   appreciable cell movement, any localized backbuilding near the   
   front could prompt local 3 inch rainfall amounts that could cause   
   excessive runoff especially near urban/sensitive locales.   
      
   The remainder of the forecast (with Marginal Risk/probabilities for   
   excessive runoff across the Pacific Northwest) is on track.   
      
   See the prior forecast below for more information.   
      
   Cook   
      
   ...Previous Discussion...   
      
   ...Southeast states...   
      
   The storm system crossing the southern tier states will continue   
   to have a plume of Gulf moisture surging north ahead of the cold   
   front through Tuesday afternoon, mainly from southeastern   
   Mississippi to the southern Appalachians. The magnitude of the   
   rainfall and also the coverage is expected to wane compared to   
   yesterday as the storm system becomes more elongated and   
   progressive. Recent CAM guidance has swaths of QPF maxima on the   
   order of 1.5 to 3 inches from central Alabama to eastern Tennessee   
   and western North Carolina, with the RRFS taking some of the   
   heavier rains as far north as the Kentucky state line. Only small   
   changes were necessary to the inherited Marginal Risk area, with a   
   modest extension northward to include more of the southern   
   Appalachians, and a little farther westward to areas closer to the   
   Mississippi border.   
      
   ...Pacific Northwest...   
      
   A marginal atmospheric river event will affect the coastal ranges   
   and the Cascades from central Oregon northward through Tuesday   
   night, followed by lighter precipitation going into Wednesday.   
   There will not be much instability to work with, so this will tend   
   to keep rainfall rates in check, but the duration of moderate   
   rainfall with rates near 0.25 inches per hour leading to areas of   
   1-2 inch daily rainfall totals may just be enough to lead to some   
   localized instances of minor flooding from the northern coastal   
   ranges of Oregon to the Olympic Peninsula. The timing for this has   
   also sped up some, to the point where the majority of the rainfall   
   is now expected in the Day 1 period instead of the Day 2 period,   
   so no areas are necessary at this time beyond 12Z Wednesday for   
   this region.   
      
   Hamrick   
      
      
   Day 2   
   Valid 12Z Wed Nov 26 2025 - 12Z Thu Nov 27 2025   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 percent.   
      
   Hamrick   
      
      
   Day 3   
   Valid 12Z Thu Nov 27 2025 - 12Z Fri Nov 28 2025   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 percent.   
      
   Hamrick   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!8gbjXvc5qqBSTfZh-D0BZxilKW_Y7clGkhLZ8eeMyx5g=   
   IQhpX4tYbu4YrUxif8tuJaC7uWJgr-3pNWAknwDGNWwG6l0$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!8gbjXvc5qqBSTfZh-D0BZxilKW_Y7clGkhLZ8eeMyx5g=   
   IQhpX4tYbu4YrUxif8tuJaC7uWJgr-3pNWAknwDGRG23JP0$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!8gbjXvc5qqBSTfZh-D0BZxilKW_Y7clGkhLZ8eeMyx5g=   
   IQhpX4tYbu4YrUxif8tuJaC7uWJgr-3pNWAknwDGDdY0qxk$=20   
      
   =3D =3D =3D   
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