Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Mar 13 2024 20:25:47 FOUS30 KWBC 132025 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 424 PM EDT Wed Mar 13 2024 Day 1 Valid 16Z Wed Mar 13 2024 - 12Z Thu Mar 14 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHEASTERN KANSAS AND NORTHWESTERN MISSOURIT... ....16Z Outlook Update... Morning model guidance (particularly CAMs) depict a scenario for developing (and initially slow-moving) convection to form along a warm front along and north of the I-70 corridor in northeastern Kansas/northwestern Missouri this afternoon. Models also generally grow the developing convection upscale, promoting cell mergers and eventual transition into one or two forward-propagating linear segments through the night. This evolution should prolong rain rates in certain spots - allowing for local 1-2 inch/hr rates and 2-3 inch rainfall totals to materialize where training is most pronounced. Given the scenario, a targeted Slight Risk area (15% or greater flash flood probabilities) was introduced where the most likely axis of heavier rainfall is expected to develop primarily between 22-06Z. A broader Marginal Risk area was maintained for this outlook, but was expanded northeastward into more of northern Illinois/Indiana where recent guidance depicts potential for localized training of deep convection to materialize tonight. See the previous discussion below for more information. Cook ....Previous Discussion... ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL PLAINS...LOWER MISSOURI VALLEY AND MID-MISSISSIPPI VALLEY... A stationary frontal boundary is expected to drape southwest to northeast from eastern portions of the Central Plains into the Lower Missouri Valley and Mid Mississippi Valley regions. The low level southerly flow is expected to re-strengthen into this front late Wednesday into Wednesday night/early Thursday, with 850-700mb mb moisture flux anomalies increasing to 1 to 2 standard deviations above the mean by early Thursday morning. This will support potential for an increasing area of organized overrunning convection along and to the north of this front, with potential for localized areas of training or more than one batch of convection moving over the same area. The marginal risk area fits well with where the HREF neighborhood probabilities are high for 1"+ totals day 1 from northeast Kansas/southeast Nebraska, across northern Missouri, southern Iowa and northwest Illinois.=20 While the HREF 1"+ probabilities are high over a large area, the EAS probabilities are showing a much smaller area of probabilities of over 40% along the Iowa/Missouri border area, suggesting poor hi res model overlap of 1"+ areas. 2"+ HREF neighborhood probabilities are showing a very small area of high probabilities over the Iowa/Missouri border area, and low EAS probabilities for 2"+ amounts. Hourly probabilities for 1"+ totals during the 0000 to 1200 UTC period are generally less than 20%. At the moment, the risk level is kept at marginal with hourly FFG values mostly 1.5" and greater. Changes to the previous outlook were to elongate it approximately 100-120 nm to the east and west and to narrow it on the north end by about 60 nm. Oravec Day 2 Valid 12Z Thu Mar 14 2024 - 12Z Fri Mar 15 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS AREAS FROM NORTHEAST TEXAS INTO THE MID-SOUTH AND MISSOURI OZARKS... ....21Z Outlook Update... Westward and northward expansions of the ongoing Slight Risk area were made for this update amid substantial model spread and uncertainty. Early in the D2/Thu period (around 12-15Z), models depict potential for training convection to focus along a warm frontal zone across northern Illinois/Indiana. That activity will be heavily modulated by the eventual eastward movement of convective complexes late in the D1 forecast period. That activity should maintain isolated flash flood potential through the morning, although a weakening trend in convection is expected after 15Z. Later in the D2 period, a southward-moving cold front is expected to provide a focus for scattered to numerous thunderstorm development from the Red River in southern Oklahoma into southwestern Missouri. Models vary substantially with respect to development and upscale growth of this activity, and rising geopotential heights throughout the forecast period over the front and warm sector raise concern that convective coverage may be sparse in some parts of the Slight Risk area. However, storms are expected to develop and foster local cell mergers/training to support flash flood potential. The highest potential for flash flooding should reside from southeastern Oklahoma into southern Missouri (including much of the Ozarks) where areas of 2 inch/hr rain rates are expected to materialize. Some uncertainly also exists with respect to upscale growth of convection and downstream rainfall potential across portions of the ArkLaTex, central Arkansas, and the Mid-South. The Slight risk area continues to depict potential for at least localized flash flood potential through the overnight hours depending on the eventual evolution of upstream convective complexes that form in the 19Z-00Z timeframe. Portions of Mississippi and northeastern Louisiana were trimmed from the inherited Slight as it appears less likely that deep convection will materialize in these areas during the 00Z-12Z period (per 12Z models). The Marginal risk area was expanded southwestward across central Texas with the expectation that scattered thunderstorms could focus along a cold front in that area late Thursday and train/repeat, boosting local rain rates. The Marginal risk area was also expanded northeastward across the Ohio Valley with the expectation that isolated to scattered, fast-moving storms could train and promote isolated areas of 1+ inch/hr rain rates from afternoon through the overnight hours. A low-end risk of similar activity extends as far northeast as southern New York State after 00Z Fri, although confidence in this scenario was too low to add Marginal probabilities at this time. See the previous discussion below for more information. Cook ....Previous discussion... The low level southerly flow is expected to once again strengthen significantly late Thursday into early Friday across the eastern portions of the Southern Plains into the Lower Arkansas and Lower Mississippi Valleys downstream of the strengthening closed low over the Southern Great Basin. 850-700 mb moisture flux anomalies and PW anomalies rise to 2 to 2.5+ standard deviations above the mean along and ahead of the associated cold front pushing southeast through the Southern Plains into the Lower Arkansas Valley. There is a strong model signal for heavy precipitation from northeast Texas, southeast Oklahoma, northern Louisiana, much of Arkansas, northwest Mississippi, far western Tennessee, far southeast Missouri, far southern Illinois and far western Kentucky in a region of favorable large scale conditions, strong frontal convergence, well defined upper difluence, late Thursday into the early hours of Friday. Similar to the past few model cycles,there continues to be north-south model spread with respect to where the max convective qpf axis will set up. The NAM continues to be the northern outlier, the EC and EC mean, the farthest south and the GFS, GEFS mean and UKMET in between. The slight risk continues to be drawn to encompass the current model spread, with only some minor changes from the previous outlook for this period. The slight risk is across areas that have had below average precip over the past few weeks and subsequently relative high FFG values. The heaviest precip totals over the past few weeks and the most saturated soils area well to the southeast of the slight risk area across portions of the South and Southeast.=20 Given this and the continued spread in the max qpf axis, the risk was kept at slight for the time being.=20 Oravec Day 3 The Day 3 outlook will be updated by 2030Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5QmKoM65A00n-audpMSpFpR8EHNwD0YcHOq0zQLCjQLm= 2OpN3m9wNhpb572Ly0L3Vy7vmu69EFc3vm6R0FXkflCa-gs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5QmKoM65A00n-audpMSpFpR8EHNwD0YcHOq0zQLCjQLm= 2OpN3m9wNhpb572Ly0L3Vy7vmu69EFc3vm6R0FXkdSF_MfE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5QmKoM65A00n-audpMSpFpR8EHNwD0YcHOq0zQLCjQLm= 2OpN3m9wNhpb572Ly0L3Vy7vmu69EFc3vm6R0FXkScdh5Us$=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. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .