832 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://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt