Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Apr 05 2025 01:28:25 FOUS30 KWBC 050128 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 928 PM EDT Fri Apr 4 2025 Day 1 Valid 01Z Sat Apr 05 2025 - 12Z Sat Apr 05 2025 ....THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE=20 OZARKS AND MID- SOUTH... ....LIFE-THREATENING FLASH FLOODING EXPECTED FRIDAY AFTERNOON THROUGH EARLY SATURDAY... A few areas of ongoing concern for significant flash flooding tonight. The first is over portions of far northeast TX into southwest AR and far northwest LA. This is along the tail of the front where frontal motion is slower with ample upstream instability and moisture advecting into the front. This is allowing for slow moving convective clusters capable of producing as much as 2-3" of rain per hour. This cluster of convection will only slowly propagate off to the east and will likely stall completely at some point tonight. The consensus of recent HRRR runs is for an additional 3-5" of rain over this area, with isolated swaths as high as 5-8" where the line stalls longest. This will be enough rain to produce widespread flash flooding, some of which will likely be significant in nature through the overnight hours. The other area is from northeast AR into southeast MO, and adjacent areas of far western TN and KY. A weak wave of low pressure along the front is helping enhance moisture convergence across this corridor this evening. Convection is making some slow eastward progress, however seeing enough training to result in widespread flash flooding. Much of this area has already seen heavy rainfall over the past couple days resulting in higher streamflows and saturated soil conditions. Recent HRRR runs support 3-5" of additional rainfall trough 12z across this area, with isolated higher amounts. The northern portion of this axis of convection is more likely to continue making gradual eastward progress over IL and IN. However the southern end...in the vicinity of northeast AR into southwest MO and far western KY/TN...may slow further tonight. If and where this occurs localized totals more in the 5-8" range through 12z are possible, along with significant and potentially life-threatening flash flooding. By later tonight the region will begin experiencing the effect of approaching larger scale forcing from the west. Organized convection is expected to develop over TX later tonight and begin moving off to the northeast at a relatively fast clip. The approach of this forcing will result in an uptick in southerly moisture transport and a stalling of the front over portions of AR and TN. In fact, expect that the front will orient itself more west to east across AR and into TN by Saturday morning. This should eventually set the stage for west to east training convection as moisture convergence increases into the stalled front. It remains a bit unclear exactly where and how organized this late night convection will be over AR, far northern LA and TN...but there is certainly a risk for widespread and life threatening flash flooding where it does set up. Even a weaker scenario would result in flood concerns given the wet antecedent conditions over the area. Overall, a broad swath of flash flood impacts are expected tonight all the way from northeast TX into portions of IN and KY. Some of this flash flooding will be significant and potentially life-threatening, especially from far northeast TX into AR, southeast MO and far western KY/TN. Unfortunately the situation will likely get worse on Saturday morning. In fact the highest impact flash flooding is shaping up to be Saturday morning and afternoon, likely across AR into western TN/KY. A robust MCS is forecast to track east across this area, merging with the stalled front (and likely training convection associated with it), and overrunning areas that will likely be saturated and already in flood by this point. Thus while significant impacts are likely tonight, the coverage and severity will most likely increase further on Saturday. Chenard Day 2 Valid 12Z Sun Apr 06 2025 - 12Z Mon Apr 07 2025 ....THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20 ARKANSAS, THE MID-SOUTH, AND THE LOWER OHIO VALLEY... ....LIFE-THREATENING FLASH FLOODING IS EXPECTED ON SATURDAY AFTERNOON THROUGH SUNDAY MORNING... Saturday is forecast to be the final day in the multi-day high- impact flood event that is unfolding across the Mid-South, Lower and Mid-Mississippi Valleys, and Lower Ohio Valley. Deep slow- moving convection is anticipated to be ongoing across the Mid-South at the beginning of the Day 2 period, and another wave of widespread convection should develop by late morning/early afternoon. Saturday night, veering flow aloft and increasing eastward momentum of the frontal boundary draped from Texas to the Ohio Valley will result in faster forward storm motion as convection pushes into the South. The ingredients will be in place and the synoptic setup will support widespread, deep convection with efficient/high rain rates across the Lower and Mid-Mississippi Valleys. Deep southerly flow across the region will continue to push warm, moist, unstable air into the region. Anomalous precipitable water values 2-3 standard deviations above normal, and high MUCAPE values of 2000+ J/Kg will support rainfall rates in excess of 1-2 inches per hour. Additionally, areas from Arkansas to the Lower Ohio Valley will be in the favorable right entrance region of the upper level jet with a slow-moving frontal boundary across the region. The combination of slow storm motion and efficient/high rainfall rates is expected to result in widespread significant additional rainfall totals of 3-6 inches, with locally higher amounts. The High Risk of excessive rainfall encapsulates areas from Arkansas through southeastern Missouri to western Tennessee and Kentucky. All major deterministic models depict an expansive footprint of 3-6 inches of rainfall, with locally up to 7-9 inches. These areas have already received significant rainfall since Wednesday, and any additional rainfall could result in a very dangerous flash flooding scenario with considerable to potentially catastrophic impacts. For the afternoon forecast, the High Risk area remained in place with small adjustments based on latest high-res model guidance and WPC QPF. A broad Moderate Risk extends around the High, stretching from the Ark-La-Tex to southern Ohio, which encapsulates areas that could also be prone to significant flash flooding. This remains a life-threatening situation for areas of the Lower and Mid- Mississippi Valley regions. Dolan/Bann Day 3 Valid 12Z Sun Apr 06 2025 - 12Z Mon Apr 07 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHEAST ON SUNDAY... On Sunday, upper level southern stream energy that had been supporting the heavy rainfall event over the past 4 days will begin to interact with a northern stream trough and accelerate northeastward. This will push the surface cold front across the southeast, with an axis of high moisture ahead of and along the front. There should be enough instability and shear to support thunderstorms with locally heavy rainfall from the Central Gulf Coast through Central Alabama and Northern Georgia. Rainfall totals are expected to reach 2-3+ inches in these areas, and rainfall rates could challenge FFGs of 2-2.5 inches per hour (although the 3+ inches per 3 hour FFG may be be less likely to be met/exceeded). Dolan/Bann Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!76iP79qngcs1LzVOit9HtEUiHbYvw-GKq3f_s8GY2XhX= gn8yRaSJv-a8uTXskuqnafnS7XriRFkNQiTVWZJzcvrv2vY$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!76iP79qngcs1LzVOit9HtEUiHbYvw-GKq3f_s8GY2XhX= gn8yRaSJv-a8uTXskuqnafnS7XriRFkNQiTVWZJzPJ6AGjk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!76iP79qngcs1LzVOit9HtEUiHbYvw-GKq3f_s8GY2XhX= gn8yRaSJv-a8uTXskuqnafnS7XriRFkNQiTVWZJzSzQ4-Fw$=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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