Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Mar 13 2024 00:17:54 FOUS30 KWBC 130017 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 817 PM EDT Tue Mar 12 2024 Day 1 Valid 16Z Tue Mar 12 2024 - 12Z Wed Mar 13 2024 ....01Z Outlook Update... A few thunderstorms have developed near/just east of the Kansas City, MO area. Both models and observations suggest that the orientation of the convection could favor localized spots of backbuilding within the moist/instability axis across western/northern Missouri for a few hours tonight, boosting local rain rates into the 1 inch/hr range on a localized/spotty basis.=20 Flash flood potential should remain low (less than 5% coverage), and no areal delineations are added to the outlook. Cook Day 2 Valid 12Z Wed Mar 13 2024 - 12Z Thu Mar 14 2024 ....A MARGINAL RISK OF EXCESSIVE RAINFALL IS IN EFFECT ACROSS PORTIONS OF THE CENTRAL PLAINS AND MID-MISSISSIPPI VALLEY... Sharpening trough out west will aid in the development of a lee surface low within the front range of the Rockies on Wednesday, strengthening through the period with accompanying 85H and 7H low pressures ejecting eastward into the plains. A warm front will develop ahead of the surface reflection across the central plains and Mid-Mississippi Valley, lifting north through the afternoon time frame. A surge of elevated theta-E's will occur south of the warm front with Gulf moisture advecting north thanks to prominent southerly flow ahead of the surface low to the west. Instability fields across guidance have become more robust over the past 24 hrs, along with the addition of the latest CAMs guidance at range in agreement with the global deterministic. Mid-level shortwave ejecting from the southwest within the difluent pattern aloft will help trigger a round of convection across portions of the plains within the confines of the warm front generally positioned over eastern KS into western MO, advancing northward towards the NE/IA border as the boundary continues its northward propagation. Locally heavy rainfall in excess of 1"/hr is becoming more likely with the latest 12z HREF probability fields signaling a stripe of up to 30% probability for exceeding the above interval during the Wednesday evening time frame, along with a 20-30% signal for at least 2"/3-hrs positioned over southeastern NE into northwest MO. This is generally along the warm front where hi-res deterministic has been most bullish in the general placement of the boundary and areal thunderstorm coverage during the initial development tomorrow evening. As we head through the overnight into Thursday AM, there's some discrepancies on the handling of the maturing 85H low as it ejects eastward through KS. The trend has been for a strengthening of the subsequent 85H low in-of central and northern KS which would provide ample support for a band of heavy rainfall to the north of the closed circulation within the developing CCB axis. Convective risks will be much lower due to the lack of sufficient buoyancy more co-located downstream along and south of the warm front. However, the ample moisture available within a broad expanse of 2+ deviations above normal PWATs signifies another local QPF maximum somewhere within the northern periphery of the low-level circulation. As of now, the prime candidate is likely within eastern NE where some deterministic shows north of 1" QPF within a 6-12 hr window after 00z Thursday, even some deterministic eclipsing 2" over the time frame of note. Latest ECMWF ML model output is also fairly consistent in showing a secondary QPF bullseye within the aforementioned zone, capable of localized flood potential within any small towns or urban corridors near Omaha/Lincoln. As of now, have added a MRGL risk encompassing the Quad state area across northeast KS, northern MO, central and southern IA, as well as eastern NE. Recent drought will likely limit some significant impacts within the above corridor, but hard soils from the lack of precip this winter and the threat of training within generated cold pools in the convective area of interest may lead to isolated flash flood returns, especially in any storms that exceed 1.5"/hr or greater.=20 Kleebauer=20=20 Day 3 Valid 12Z Thu Mar 14 2024 - 12Z Fri Mar 15 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE LOWER ARKANSAS VALLEY INTO THE LOWER MISSISSIPPI VALLEY... ....20z Update... The primary changes to the D3 ERO were for an expansion of the MRGL risk into the central Midwest and Mid-Mississippi Valley where trends in guidance and ML algorithms have increased the convective coverage and potential heavy rain threat into the above areas. There will be a long west to east QPF signature stretching from the north-central plains through the Midwest, including the northern half of IL through WI/MI as the surface low ejects eastward and the primary ascent pattern shifts in tandem. A broad zone of 0.75-1.5" of precip will be possible within the northern axis of QPF with locally higher totals over IL thanks to lingering instability brought by a tongue of higher theta-E's located south of the prevailing warm front bisecting the region. There was enough consensus to include the mid-Mississippi Valley up through IL for a MRGL risk with the convective pattern anticipated downstream within the warm sector.=20 The primary zone of impact still remains over the Lower Mississippi Valley into east TX where a sagging cold front will act as a focal point for convective development and subsequent training thanks to flow aloft running parallel to the boundary, along with a strong convergence pattern within a zone of appreciable instability. Rainfall totals on the order of 1-2" will be common within much of AR down into northern LA and east TX with local totals exceeding 3" plausible given the latest deterministic and NBM probabilistic output within the upper quartile range of outcomes. There is still some discrepancy within the deterministic suite on where exactly the front will be located which will play a significant role in where the heaviest corridor of rain will occur. Based on the latest ECMWF ML guidance and CIPS analogs, there's some merit to the threat being a bit further south than where some guidance (GFS/CMC) is focused with a stronger bias for a cold front in the expected pattern evolution to press further south. The highest threat for impacts is likely within central and southern AR into northern LA which includes a significant portion of the urbanized corridors within the states above. For that, have adjusted the SLGT risk a bit further south, along with the MRGL to account for the historical trends and latest bias-corrected QPF footprint. Kleebauer ....Previous Discussion... The low level southerly flow is expected to 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, PW values expected to rise to 2 to 2.5+ standard deviations above the mean in this increasing PW axis. Overall favorable large scale conditions, strong frontal convergence, well defined upper difluence, in this anomalous PW axis will support increasing convection late Thursday into the early hours of Friday along and ahead of the strong front pushing southeast through the Southern Plains into the Lower Arkansas Valley. There continues to be north-south model spread with respect to where the max convective qpf axis will set up. The NAM is the farthest north, EC, EC mean and CMC, the farthest south and the GFS, GEFS mean and UKMET in between. The slight risk was 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. Given this and the continued spread in the max qpf axis, the risk was kept at slight for the time being. The biggest change to the previous outlook was to trim the north end of the marginal risk to the south from northern Illinois to southern Missouri/far southern Illinois.=20 Model consensus is for mostly moderate precip amount here, across a region where soils are not saturated. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_IKNDXRyF-oHpgNyTQhxEZlLnMvfO8Mw1RNz0lmDpdeK= ylLMlqeMQzg3lyqeCDJyTPGuLhpwnRWFxLPVVVbgL9LmEqs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_IKNDXRyF-oHpgNyTQhxEZlLnMvfO8Mw1RNz0lmDpdeK= ylLMlqeMQzg3lyqeCDJyTPGuLhpwnRWFxLPVVVbgimQkLTg$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_IKNDXRyF-oHpgNyTQhxEZlLnMvfO8Mw1RNz0lmDpdeK= ylLMlqeMQzg3lyqeCDJyTPGuLhpwnRWFxLPVVVbgfKXX3FQ$=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) .