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   FOUS30 KWBC 091915   
   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   215 PM EST Fri Jan 9 2026   
      
   Day 1   
   Valid 16Z Fri Jan 09 2026 - 12Z Sat Jan 10 2026   
      
   ..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS   
   OF SOUTHERN MISSISSIPPI AND ADJACENT LOUISIANA...   
      
   ...16Z update...   
      
   The OSPO Advected LPW product showed the axis of anomalous moisture   
   in place over the Lower Mississippi Valley (2 to 4 standard   
   deviations above the mean) with origins in the middle and upper   
   levels to the tropical eastern Pacific, while low level moisture   
   was originating from the Gulf. The dual connection of moisture has   
   resulted in higher end rainfall events in the past so several of   
   the 12Z CAMs showing 7+ inches over the 24 hour window ending   
   Saturday morning look believable.   
      
   Ongoing axes of heavy rain were observed along the eastern LA/MS   
   border between Baton Rouge and Hattiesburg early this morning with   
   hourly rainfall of 1 to 2+ inches and 2 to 4 inches through just   
   prior to 16Z. Similar potential will exist over the next 12-24   
   hours with the likelihood for several training axes to develop   
   across the Lower Mississippi Valley. The greatest probability of   
   overlap of heavy rainfall axes looks to be within the Moderate Risk   
   which was expanded northeastward into western Alabama where 24 hour   
   rainfall of at least 3 to 6 inches looks likely.   
      
   Other adjustments for the 16Z update included a small southwestern   
   shift to the Marginal, Slight and 25% contour across eastern Texas   
   into Louisiana, in line with the latest 12Z HREF.   
      
   Otto   
      
   ...previous discussion follows...   
      
      
   The classic synoptic setup for a winter flash flooding event   
   continues to slowly adjust to the timing/orientation of the   
   upstream shortwave over the Southwest U.S. The very strong leading   
   cyclone across the Great Lakes will continue to zip along to the   
   east-northeast with well above normal (4 Standard Anomaly/99th   
   percentile) moisture and flux still streaming across the Ohio and   
   Tennessee Valley. Ongoing thunderstorms are expected across the   
   Lower MS Valley as morning surge of Gulf air streams northward   
   becoming increasingly confluent/convergent well ahead of the   
   upstream synoptic front in the Plains.   
      
   The strong upstream base of the positive tilt trof will be   
   advancing throughout the day into the Plains, though the upper-   
   level jet streak also be expanding and strengthening across the   
   Ozark Plateau into the Ohio River Valley from 110kts to over 150kts   
   by the end of the forecast period. The trough will also be shearing   
   into the confluent, increasingly unidirectional low to mid-level   
   flow allowing for a deep southwest to northeast atmospheric river   
   from the western Gulf up the Lower Mississippi and through the   
   Tennessee River Valley into the southern Appalachians/Cumberland   
   Plateau through the majority of the day. While the low level flow   
   will be weaker than Thursday, 850-700mb 40-45kts and 1.5-1.75"   
   total PWat values will allow for high moisture flux convergence and   
   support efficient rainfall production.   
      
   As the trends have slowed the upstream shortwave, this allows for   
   greater flux of unstable air northward and forcing to   
   overlap/intersect with 1000-1500 J/kg of MLCAPE across the Coastal   
   Plain reducing toward 500 J/kg near the southern TN border, pulsing   
   with northward surges as the shortwave lifts out. This will provide   
   enough ascent and low level shear for organized bands of   
   convection that will likely have training elements throughout the   
   day. Rain-rates of 1.5"/hr are probable though 00z Hi-Res CAMs   
   support occasional up-ticks to 2"+/hr locally. Combined with the   
   training profiles, 00z HREF shows solid 15-25% 3"/3hr probability   
   across Southern MS into far northeast LA, with nearly 50%   
   neighborhood probability of 5". As such, and in coordination with   
   local forecast offices, WPC is introducing a small Moderate Risk of   
   Excessive Rainfall for S MS and adjacent NE LA. It should be   
   noted, there is solid agreement within the guidance suite of 5-8"   
   total streaks but there is limited agreement in the placement   
   particularly west or east.   
      
   Thunderstorms will train, but as they move northeast into Middle to   
   eastern TN and northern and central AL, intensity and rainfall   
   totals are likely to diminish, given instability will be limited   
   to 200-300 J/kg. Yet, prolonged duration and sizable totals of 2-4"   
   are still possible and so the Slight Risk continues to be in place   
   downstream across much of AL, northern GA, and southeast TN.   
      
   Upstream, as the main forcing exits, a secondary axis of   
   convergence along instability/moisture gradient across eastern   
   Texas will produce additional, slightly more elevated   
   thunderstorms. Similar rates of 1.5" to 2"/hr are possible with   
   some repeating/training tracks across NW LA, though overall   
   duration and coverage should limit rainfall totals to 2-4" relative   
   to the Moderate Risk area further southeast. As such, the Slight   
   Risk was also expanded westward along the axis of best overall   
   model agreement.   
      
   Gallina   
      
   Day 2   
   Valid 12Z Sat Jan 10 2026 - 12Z Sun Jan 11 2026   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS   
   OF THE SOUTHERN APPALACHIANS...   
      
   20Z Update...   
   No significant changes were made to the Marginal Risk area.   
      
   Pereira   
      
   Previous Discussion...   
   Heavy rainfall early in the period is expected over what should be   
   at least partially saturated ground across portions of the   
   Southern Appalachians before heavy rainfall ejects into the   
   southern Mid-Atlantic States. Added a Marginal Risk as a   
   precaution for this reason; the threat not expected to persist past   
   18z Saturday.   
      
   Roth/Gallina   
      
      
   Day 3   
   Valid 12Z Sun Jan 11 2026 - 12Z Mon Jan 12 2026   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 (five) percent.   
      
   Pereira   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!5K9mWYMUttFtzsX6SvIglCO7-AZoukmcYzz4h9Nr2Exn=   
   _CTXoFQYXV9XT0C0EbnMlgUIJEqsHeFWFCfy6KkLwIUrGzs$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!5K9mWYMUttFtzsX6SvIglCO7-AZoukmcYzz4h9Nr2Exn=   
   _CTXoFQYXV9XT0C0EbnMlgUIJEqsHeFWFCfy6KkLHB25TKM$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!5K9mWYMUttFtzsX6SvIglCO7-AZoukmcYzz4h9Nr2Exn=   
   _CTXoFQYXV9XT0C0EbnMlgUIJEqsHeFWFCfy6KkLUauQozI$=20   
      
   =3D =3D =3D   
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