Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Oct 18 2025 19:52:22 FOUS30 KWBC 181952 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 352 PM EDT Sat Oct 18 2025 Day 1 Valid 16Z Sat Oct 18 2025 - 12Z Sun Oct 19 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM FAR NORTHEASTERN OKLAHOMA AND NORTHWEST ARKANSAS UP THROUGH THE MID- MISSISSIPPI VALLEY... The current convective organization from the Red River of TX/OK up through MO lends credence to a continued scattered flash flood threat over the course of the afternoon and evening from eastern OK up into south-central IL and points in-between. Thunderstorm genesis over a zone of modestly unstable air and anomalous moisture running between +2 to +3 deviations this morning will continue its progression to the east-northeast with a cold front progression trailing back into the Missouri Valley and the adjacent plains. A shield of moderate to locally heavy rains will allow for spots of 2-3" of rainfall in its wake with maxima closer to 4-5" most likely near the mid-Mississippi Valley around the St.Louis metro and surrounds. This has been a strengthening consensus within the CAMs this morning, aligning very well with the ML output via the AIFS and AIFS ensemble, as well as the First Guess Fields from the past series of runs. This is likely in part to the overlap of multiple waves of heavy precip in this area of the CONUS as a trailing wave will migrate northeast out of TX and impact areas of southern MO down through the Lower Mississippi Valley later in the period. The flow across MO has a bit more deep layer uniformity with a speed shear axis between 45-60kts analyzed across MO extending into IL. This will lead to a greater alignment of thunderstorms with embedded stronger cores due to the enhancement of the shear present. The limiting factor into a greater risk is forward propagation speeds will be modest in nature with lower likelihood of back- building within the setup. The antecedent soil moisture also favoring parched grounds will lead to less of a threat of run off initially, unless approached by significant rates >2"/hr. This is why the urbanization factor will play a greater role in the threat as impervious surfaces already account for the full run off capabilities. 12z HREF neighborhood probs for >3" continue to run between 60-90% over a large area extending from south-central MO into south-central IL with the bullseye situated near and just south of St Louis. Lower, yet modest probabilities between 30-45% exist near the intersection of MO/AR/OK as well allowing for a minor expansion southwest of the SLGT risk inherited. Across OK, a stronger than forecast 2nd wave is making headway through the state currently with trends indicating some 2-3" totals expected over eastern and southeast portions of the state. To account for a low-end threat of flash flooding, there was enough of a signal to expand the MRGL risk into these locations as well. The rest of the forecast into the Great Lakes was relatively unchanged outside some minor adjustments on the northeast flank of the MRGL into MI. Kleebauer Day 2 Valid 12Z Sun Oct 19 2025 - 12Z Mon Oct 20 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL APPALACHIANS DOWN THROUGH WEST VIRGINIA AND SOUTHEAST OHIO... 20Z Update: Deepening mid and upper trough will move progressively to the northeast with a strengthening surface low and trailing=20 cold front migrating through the Great Lakes and Ohio Valley by=20 Sunday morning, entering into the Northeast and Mid-Atlantic areas=20 by the second half of the forecast period. Current forecast is for=20 modest instability pre-front and strengthening mid and upper=20 forcing will initiate a period of locally heavy rainfall across the eastern Ohio Valley into the Central Appalachian area during the=20 forecast cycle leading to isolated flash flood prospects in its=20 wake. Dry antecedent grounds and faster storm motions should=20 preclude any widespread flash flood prospects, however terrain=20 funneling and drainage concerns in-of the Southern Laurels into the Central Appalachian areas of WV are still cause for concern on a=20 local scale. 12z HREF EAS probs for >1" are incredibly high=20 (60-90%) across both regions with modest 30-50% probs also situated just west of the mountainous terrain. These areas are a bit more=20 suitable in this scenario for flash flooding in the grand scheme,=20 but previously mentioned antecedent conditions and forward speed=20 should curb the threat towards the lower end of the MRGL risk=20 threshold. The MRGL risk from previous forecast was trimmed=20 considering latest trends in guidance, but maintained over those=20 aforementioned terrain areas across southwest PA, southeast OH, and much of WV.=20 Kleebauer Day 3 Valid 12Z Mon Oct 20 2025 - 12Z Tue Oct 21 2025 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS NORTHERN NEW YORK STATE INTO WESTERN NEW ENGLAND... 20Z Update: General continuity was maintained for the D3 forecast as guidance remains steadfast on the heaviest rainfall focused over Northern NY state into interior New England. Run off concerns within the terrain are the greatest threat as the areas remains very dry overall. Rainfall rates between 1-1.5"/hr at peak are anticipated considering the environment. Rainfall threat will decay southwest to northeast as the cold front presses quickly through the region.=20 Kleebauer ...Previous Forecast.. The negatively tilted upper trof moving into the Lower Lakes/Central Appalachians/Mid- Atlantic region late day 2 will continue to be very progressive as it swings northeastward into Southern New England day 3. While there will be an axis of above average PW values, 2+ standard deviations above the mean and anomalous 850-700 mb moisture flux anomalies, 2 to 4+ standard deviations above the mean accompanying this upper trof day 3, the expected overall progressive nature of the precipitation area should preclude any widespread runoff issues. There is model consensus for max precip areas of 1.5-2"+ across northern NY State, Vermont, western MA, central NH and western ME. The previous marginal risk area was decreased in size and oriented to fit the above mentioned areas where isolated runoff issues in the higher terrain may occur. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8PG_S_L2eRkCqruPd8ZwJjrllSpvu-4apqBpnTa1G84l= mnp6NUBUQNprnAmCTFuBgSsxDcVWhkjlY0yZWrpnm-i3oTs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8PG_S_L2eRkCqruPd8ZwJjrllSpvu-4apqBpnTa1G84l= mnp6NUBUQNprnAmCTFuBgSsxDcVWhkjlY0yZWrpnB2utWzY$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8PG_S_L2eRkCqruPd8ZwJjrllSpvu-4apqBpnTa1G84l= mnp6NUBUQNprnAmCTFuBgSsxDcVWhkjlY0yZWrpnVmuNlrs$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .