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   FOUS30 KWBC 020043   
   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   743 PM EST Mon Dec 1 2025   
      
   Day 1   
   Valid 01Z Tue Dec 02 2025 - 12Z Tue Dec 02 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF   
   THE GULF COAST AND DEEP SOUTH...   
      
   A negatively- tilted shortwave trough moving through the Southern   
   Plains at the present time is leading to a forming stationary from   
   across the Deep South to the north of a wave of low pressure in the   
   Gulf of Mexico. An area of low-level convergence which started as   
   a frictional convergence zone near the northwest coast of Cuba is   
   curling up towards the MS/AL coast at the present time. Moisture is   
   sufficient for heavy rainfall, but until recently, instability was   
   scant. However, ahead of the shortwave, MU CAPE has risen to 500   
   J/kg near the southeast tip of LA and is surging north towards the   
   AL/MS barrier islands, which should further increase from there=20   
   and spread into nearby areas of the Central Gulf Coast with time,=20   
   as far east as the FL Panhandle. MU CAPE could rise towards 1000=20   
   J/kg along portions of the Central Gulf Coast through early Tuesday   
   morning. Effective bulk shear of 25-45 kts lurks across the=20   
   region, which could lead to cell organization.   
      
   A band of heavy rain with embedded thunderstorms has recently led=20   
   to hourly rain amounts up to 1.75" in southeast LA and southern AL=20   
   thus far. The 18z HREF and 12z RRFS are not exactly in agreement=20   
   regarding the potential for 2"+ by 12z...their overlap is in a=20   
   narrow zone between Dauphin Island AL and Pensacola where=20   
   downstream instability and moisture overlap would be greatest. The   
   18z hi-res NAM is doing the best with the convective evolution   
   thus far. The three hour flash flood guidance values regionally are   
   quite high though they might be reachable. The risk for 1.75"=20   
   amounts in an hour with local totals up to 4" should continue to=20   
   exist overnight, which would be problematic in urban areas, so left   
   much of the Marginal Risk area from continuity intact. The=20   
   Marginal Risk area has been constrained on its west side per radar=20   
   reflectivity trends and trends noted in the 18z HREF/12z RRFS=20   
   guidance.   
      
   Roth   
      
      
   Day 2   
   Valid 12Z Tue Dec 02 2025 - 12Z Wed Dec 03 2025   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 percent.   
      
   Surface/low level convergence associated with a frontal boundary   
   forecast to translate eastward into the western Atlantic after 18Z   
   may allow for a band of SW to NE training heavy rain/thunderstorms   
   early in the period over eastern North Carolina. Weak instability   
   and precipitable water values increasing to over 1.5 inches along   
   the coast could support rain rates over 2 in/hr, however, recent   
   hires guidance maintains the potential for 3 to 6 inch totals   
   offshore/east of the Outer Banks. While the threat is non-zero, it   
   is low enough to not warrant a risk area at this time.   
      
   Otto   
      
      
   Day 3   
   Valid 12Z Wed Dec 03 2025 - 12Z Thu Dec 04 2025   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 percent.   
      
   The very beginning of a multi-day rainfall event will begin to   
   unfold Wednesday night along portions of the Upper Texas and   
   Louisiana Gulf Coasts. Mainly for the 06-12Z time frame Thursday   
   morning, the 12Z guidance continues to suggest most of the   
   heaviest rainfall from heavy showers/thunderstorms will remain   
   offshore. However, at least some of that rain could make its way   
   inland. The threat remains sub- Marginal, but the area will   
   continue to be evaluated for a later introduction of a Marginal   
   Risk with future updates.   
      
   Otto/Wegman   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!4Q0Y28YgbGtc2Flzj_ycOtdl7RjZfSpJ8TCHAhXsoo57=   
   fY_0TF6l9Qg2GdyqOfjmX-jUhnPlSzx81m_Zt1jyDLhJ7R4$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!4Q0Y28YgbGtc2Flzj_ycOtdl7RjZfSpJ8TCHAhXsoo57=   
   fY_0TF6l9Qg2GdyqOfjmX-jUhnPlSzx81m_Zt1jy_teR2Hc$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!4Q0Y28YgbGtc2Flzj_ycOtdl7RjZfSpJ8TCHAhXsoo57=   
   fY_0TF6l9Qg2GdyqOfjmX-jUhnPlSzx81m_Zt1jywah2tiE$=20   
      
   =3D =3D =3D   
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