Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 15 2025 00:57:38 FOUS30 KWBC 150057 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 857 PM EDT Sat Jun 14 2025 Day 1 Valid 01Z Sun Jun 15 2025 - 12Z Sun Jun 15 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF OKLAHOMA AND THE MID ATLANTIC... ....Mid-Atlantic... Convection moving southeast along a stationary front will result=20 in isolated to scattered flash flooding this evening across=20 portions of northern and eastern VA. Given the location of the=20 front and instability gradient it appears that the heaviest=20 rainfall rates will remain in VA, and thus we were able to take DC and MD out of the Slight risk. High PWs and slow cell=20 motions/mergers near the front will allow for high rainfall rates=20 and isolated amounts exceeding 3" across portions of northern and=20 eastern VA. ....Oklahoma... At least some flash flooding appears likely overnight into early=20 Sunday across portions of OK. In the mid levels we have a well=20 defined shortwave across KS, which will slowly drift southward into OK tonight. To the south of this feature increasing low level=20 moisture transport/convergence will interact with a highly unstable airmass. Convection will expand in coverage by later this evening, and activity should initially be slow moving and exhibit=20 backbuilding characteristics. This will allow for areas of=20 excessive rainfall, with recent HRRR and RRFS runs depicting a=20 swath of 3-5" of rainfall, and both the 18z HREF and REFS showing=20 over a 40% chance of locally exceeding 5". By later tonight=20 convection will grow upscale and likely develop a stronger cold=20 pool resulting in a southward acceleration of convection. High=20 rainfall rates could still result in a localized flash flood threat after this faster southward propagation occurs...but the coverage=20 and magnitude of the threat should be lower by then. Thus the=20 greater risk is this evening into tonight when convection should=20 be slower moving and backbuilding...and do consider this a higher=20 end Slight risk centered over central OK. Scattered flash flooding=20 is probable, some of which could be locally significant. ....Upper Midwest... A Marginal risk was maintained across portions of far southeast SD into IA. Seeing a recent expansion of slow moving convection near=20 a stationary front which could result in localized flash flooding=20 through the evening hours. ....Central Montana... Convection over portions of central and eastern MT will continue to pose an isolated flash flood risk into the overnight hours.=20 Recent HRRR runs are likely under doing rainfall amounts over this area. Recent RRFS runs may be overdone, but likely do have a=20 better handle on the repeat nature of convection that should=20 continue into tonight. Impressive CAPE/Shear profiles will=20 continue to support convective clusters and supercells, and with=20 PWs over 1", heavy rainfall rates will be likely. Localized=20 rainfall upwards of 2-3" is possible through the overnight hours. Chenard Day 2 Valid 12Z Sun Jun 15 2025 - 12Z Mon Jun 16 2025 ....A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE MID ATLANTIC, SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY... ....Mid-Atlantic and Central Appalachians... 20Z Update: The previous SLGT risk remains favorable as the threat for flash flooding, some locally significant are forecast across portions of the Mid Atlantic and Central Appalachians Sunday. The area of focus will reside around the stationary front that will bisect the southern half of VA up through eastern WV, arcing back into Western PA as southwesterly flow remains steadfast west of the terrain in WV/PA through at least 18z. A corridor of elevated theta_E will remain situated over Western PA as far north as Butler county with a deep pool of moisture located along and south of the front. Shortwave trough that has slowly trudged eastward through the Central part of the CONUS will finally pick up forward speed and shift eastward through the Central Apps and Mid Atlantic by the afternoon hrs leading to increased large scale forcing over the aforementioned area. General instability coupled with the ascent pattern will lead to favorable conditions for scattered to widespread convective activity with mean cell motions moving slowly east and southeast through the course of the afternoon and evening. A very robust signal within the 12z HREF neighborhood prob fields indicate a likelihood of >3" (60-90%) of rainfall in the strongest convective cores with a modest signal for >5" located over the Appalachian front in WV (20-40%) and across the VA Tidewater into the Richmond metro (40-60%). These signals are aligned with a locally significant threat for excessive rainfall, especially in these particular zones due to sensitivity concerns from either complex terrain (Appalachians) or urbanization factors (Southern VA and the Tidewater). Hourly rainfall rates between 2-3"/hr are likely in the heaviest rainfall with instantaneous rates upwards of 5"/hr plausible across Southeast VA considering the available instability >1500 J/kg and PWATs approaching +2 deviations within a well-positioned front that should enhance local convergence pattern. The SLGT risk inherited was maintained in the previous location, but was expanded to the northwest to include more of Northern WV, Western MD, and Western PA given the signals within the latest HREF and the anomalous environment in place with the front nearby. There is a potential for an upgrade across parts of Eastern WV into the Tidewater where the highest probability of >3" is located, overlapping with what will likely be already saturated grounds after the activity yesterday and later this evening. We will be monitoring the setup closely over the next 12-24 hrs. Kleebauer ....Northern Plains into the Midwest and Mid-South... 20Z Update: The multi-MCS threat remains firm within the latest deterministic with agreement among the ensembles for a dual QPF maxima situated across both the Northern Plains/Upper Midwest, as well as portions of the Southern Plains into the Lower Mississippi Valley. The more robust signal for heavy rainfall is situated across Southeast KS down through Eastern OK into AR thanks to MCS propagation into the area on the back-end of D1 into the D2 period. HREF blended mean QPF indicated an areal average between 1-2" with the CAMs individual outputs putting down as much as 2-4" with the morning complex across the areas above. Remnant MCV concerns will enhance a redevelopment phase of the regional convective threat over the Lower Mississippi Valley with some of the hi-res windows indicating another 2-4" local maxima occurring the second half of the forecast cycle. In this case, there would be sufficient totals stemming from likely back to back to back occurrences of heavy rainfall from D1 through D2 leading to likely flash flood concerns. In this case, there was enough of a signal to warrant an expansion of the SLGT to cover for the threat across OK and AR with the greatest threat likely over the western Ozarks down into Central AR. Convective complex over the Northern Plains will likely be more on the progressive side compared to its southern counter-part leading to a capped higher end potential. Still, some of the heavier rain forecast would overlap with areas that have been affected, or will be affected by previous convective episodes leading to saturated soils and a higher chance of localized impacts. The threat remains within the MRGL risk threshold considering the signals and relevant probs within the latest CAMs. A targeted upgrade is plausible if the signal becomes stronger in later updates. Kleebauer ...Previous Discussion.. A building upper ridge situated over the southern Rockies will tend to result in northwest flow aloft across the northern Plains to the ArkLaTex region. Multiple convective complexes are likely to develop on the eastern periphery of this upper ridge, and convective development will depend on whether a low-mid level cap can be eroded, and this is more likely to happen across eastern portions of Kansas/Oklahoma/Texas. The latest model guidance is converging more on a concentrated area of enhanced rainfall across portions of southwestern Missouri and northwestern Arkansas and adjacent portions of Kansas and Oklahoma, where an organized MCS is more likely to develop. Therefore, a Slight Risk area has been introduced for this region. Hamrick Day 3 Valid 12Z Mon Jun 16 2025 - 12Z Tue Jun 17 2025 ....A MARGINAL RISK OF EXCESSIVE RAINFALL IS VALID FOR PORTIONS OF THE UPPER MIDWEST, MID-SOUTH, AND THE MID-ATLANTIC... 20z Update: Consensus for locally heavy rainfall across portions of the Northern tier of the CONUS remains favorable across a broad area extending through the Dakotas, Nebraska, and the Upper Midwest on Monday. The good news in the setup is the current evolution would favor the heaviest rain across the Nebraska Sandhills, an area much less prone to flash flooding due to the soil composition which would necessitate extreme rainfall rates (>4"/hr) and has a history of limited flash flooding due to the very low runoff capabilities. So long as this consensus remains, it is unlikely an upgrade would be necessary for the region so will be monitoring closely as a northern or southern shift in the maxima would offer a chance for a targeted upgrade. Heavy rain threat over the Northern tier of ND and MN remains fairly isolated at this juncture and will take a more robust signal to induce an upgrade. These areas are typically harder to flood and already exhibit relatively high FFG's for the 1/3/6 hr indices, so the threat will likely be of the isolated variety, but will monitor the trends closely as we move into CAMs range. Across the Mid-Mississippi Valley, flash flood threat will likely be tied to yet another MCS moving across the area comprised of the Ozarks, Southeast MO into the western Ohio Valley. Some of these areas will have fairly compromised soils given the daily occurrence of heavy rain the periods prior, so will have to assess the expected forward propagation of any complex closely to see if an upgrade is warranted. Considering the trickiness of narrowing down specifics for these convectively driven complexes, decided to maintain general continuity for the MRGL risk, but expanded based on ensemble QPF depiction with a slightly more robust output compared to previous iterations. The front across the Mid Atlantic will sink further south and pivot away from the areas that will have received significant rainfall the periods prior. The area with greatest overall potential is along the Appalachian front in WV where the signal for another round of at least isolated thunderstorm activity could very well offer another flash flood concern. The threat is highest over NC where the frontal positioning would be aligned as such that some of the activity that develops on Monday could provide elements of training within a well favored environment for heavy rain prospects. Some of the deterministic is already pushing areal averages of 2-3" across Central and Eastern NC, a signal that is favorable to at least a MRGL threat of flash flooding over the urban corridor. Pending trends within CAMs and the positioning of the front, an upgrade is certainly plausible for both eastern WV down through the NC Piedmont and points east. Kleebauer ...Previous Discussion(s).. ....Mid-Atlantic region... Overall, an improvement compared to what is expected over the weekend, but there should still be enough moisture in the general vicinity of a stalled stationary boundary over southern Virginia and North Carolina to produce scattered storms with heavy rainfall. Although the magnitude of rainfall expected on Monday is not impressive, the very saturated ground by this time will be an aggravating factor in terms of flooding potential, and therefore a Marginal Risk area is valid from central West Virginia to the Outer Banks of North Carolina. ....Mid-South... The latest model guidance is honing in on a potential MCS that could develop across portions of eastern Arkansas into western Tennessee on Monday, and perhaps extending into portions of southern Missouri and western Kentucky where the potential exists for 1 to locally 2 inches of rainfall. A Marginal Risk area is valid here since much of this rain would likely happen over a two hour time period. ....Dakotas to the western Great Lakes... A surface low over South Dakota with broad warm air advection ahead of it will fuel the development of additional scattered showers and storms on Monday. The model guidance remains varied in regards to placement of QPF maxima, so a broad Marginal Risk is valid. Hamrick Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4O9-09360acz4xiRDLkyWmgBBN1lSh1kXH6zmB1tkR8G= DGRu-olvh-5wLakSflTBTqT6agP_pYrxkFpnrn8FTwsqGsE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4O9-09360acz4xiRDLkyWmgBBN1lSh1kXH6zmB1tkR8G= DGRu-olvh-5wLakSflTBTqT6agP_pYrxkFpnrn8FFOqbv8o$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4O9-09360acz4xiRDLkyWmgBBN1lSh1kXH6zmB1tkR8G= DGRu-olvh-5wLakSflTBTqT6agP_pYrxkFpnrn8F3-1_2fo$=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) .