Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Oct 12 2023 00:53:09 FOUS30 KWBC 120053 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 852 PM EDT Wed Oct 11 2023 Day 1 Valid 01Z Thu Oct 12 2023 - 12Z Thu Oct 12 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE FLORIDA PANHANDLE... ....Florida... We opted to upgrade a small portion of the FL Panhandle to a Slight risk with this update, from approximately Gulf to Taylor counties. Thus far the warm front and instability has stayed offshore, which is resulting in a mainly stratiform and lower rate rainfall over the Southeast. However the front is getting very close to the coast, and it may move just inland over the next several hours across the aforementioned corridor. Current convection offshore looks pretty good, and if the front can move inland this higher rate rainfall and potential backbuilding/training would also move inland. While not a guarantee, the threat of this heavy rain getting just onshore appears to be increasing. Recent HRRR runs support 6"+ rainfall amounts near the coast...now whether this falls over land or just offshore is still not clear...but given the increasing probabilities of it getting over land, think the introduction of a Slight risk is warranted. This is a conditional flash flood risk, but there is certainly some potential for localized higher end flash flooding with this setup. ....IA/IL... A Marginal risk was maintained across portions of eastern IA into northern IL. We are seeing some west to east moving convection across this corridor, and the general expectation is that this threat will continue into the overnight. Not expecting a continuous training convective threat, however periodic cell training will remain a possibility within the corridor of elevated convergence north of the warm front. Given activity has been a bit more robust this evening than advertised by most models...it seems plausible that amounts through 12z could overperform compared to the model consensus. Thus some localized totals over 3" seem possible, which could drive an isolated flood risk. Chenard Day 2 Valid 12Z Thu Oct 12 2023 - 12Z Fri Oct 13 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG PORTIONS OF THE MID MISSOURI VALLEY... ....2030Z Update... Previous outlook remains on track and only a couple of minor nudges were needed to get a better fit to the 11/12Z guidance.=20 The large scale picture was well handled. Bann ....0830Z Excessive Rainfall Outlook Discussion.. ....Northern Plains/Mid Missouri Valley/Upper Midwest... A deep cyclone developing over the central Rockies and High Plains early Thursday is forecast to drift east across the Plains and into the mid and upper Mississippi Valley by early Friday. Strong southerly winds ahead of the system will continue to transport moisture into a region of strong ascent afforded in part by favorable upper jet forcing. For most areas the combination of ample moisture and strong forcing, but little instability, will produce an extended period of moderate rains, resulting in locally heavy accumulations but limited impacts. The placement of the Slight Risk area remains largely the same and centered near where greater instability and deeper moisture along the axis of strongest inflow may help to increase rainfall rates and the threat for short-term heavy accumulations and rapid runoff.=20 Training storms may also raise the threat for heavy amounts and excessive runoff across this region. ....Southeast... Low pressure moving from the northern Gulf to the Southeast coast Thursday morning is forecast to move quickly offshore. However, rich moisture and mid level energy embedded within deep southwesterly flow in its wake may continue to produce periods of heavy rainfall across the same portions northern and central Florida impacted on Day 1. Pereira Day 3 Valid 12Z Fri Oct 13 2023 - 12Z Sat Oct 14 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY/GREAT LAKES REGION... ....2030Z Update... Few...if any...changes needed given run to run consistency of the models regarding QPF amounts and the potential for some overlap of rainfall on Day 3 and what is expected later tonight/early Thursday morning in parts of the Midwest.=20 Bann ....0830Z Excessive Rainfall Outlook Discussion... ....Upper Mississippi Valley to the western Great Lakes... The overall setup on Day 3 is largely similar to the one expected on Day 2, except farther east as a closed low tracks from the Plains into the Great Lakes. Similar to Day 2, ample moisture and strong forcing will support an extended period of moderate rains north of the low, but the lack of instability will limit the threat for heavy rainfall rates and flash flooding concerns. A relatively greater threat is expected to center near and ahead of the low, where deeper moisture and greater instability along the low level jet may help to elevate rainfall rates and short-term runoff concerns. Areas that may possibly be impacted with heavy rain on Day 1, including northern Illinois, may see additional heavy rains this period, increasing the risk for flash flooding for those areas. Pereira Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-kZ3YCzAY_Wnjuf2kqpS4ZuQCi6GiPzMv-9puqu1dF6B= MMxjUMO9NdpA0Q_rXcBpOtktxEqFo0OAvzGOPlIy-XMunzs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-kZ3YCzAY_Wnjuf2kqpS4ZuQCi6GiPzMv-9puqu1dF6B= MMxjUMO9NdpA0Q_rXcBpOtktxEqFo0OAvzGOPlIyFmpgV3s$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-kZ3YCzAY_Wnjuf2kqpS4ZuQCi6GiPzMv-9puqu1dF6B= MMxjUMO9NdpA0Q_rXcBpOtktxEqFo0OAvzGOPlIyj201ni8$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .