Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 14 2025 19:48:37 FOUS30 KWBC 141948 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 348 PM EDT Sat Jun 14 2025 Day 1 Valid 16Z Sat Jun 14 2025 - 12Z Sun Jun 15 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID ATLANTIC, SOUTHERN PLAINS, AND LOWER MISSISSIPPI VALLEY... ....Mid-Atlantic... 16Z Update: The setup remains conducive for locally heavy rainfall across a good chunk of the Central Mid Atlantic today. Environment is sufficiently buoyant with the 12z KIAD profile indicating significant saturation from the surface to the tropopause. Sounding revealed a PWAT output of 2.01", putting it above the 90th percentile for the day and even above the climatological 30-day moving max (99th percentile) for the period. Quasi-stationary front will waver this morning and early afternoon before a slow advancement south through the Piedmont down into VA by later this afternoon and evening. Local MUCAPE forecasts between 1500-3000 J/kg will be plentiful for maintaining a strong instability regime capable of enhancing any convective flare ups leading to heavy rain prospects within any cell that initiates. Biggest trend in the setup is a more robust convective depiction over the Laurels down through the Potomac area, including the WV Panhandle, Northern Neck of VA, DC metro, and NoVA. This aligns within the confines of the surface frontal progression, outlined decently in the theta_E field when looking at the latest CAMs. A quick 2-4" of rain with locally up to 4" are plausible in the above zone with a maxima of closer to 6" possible over Southeast VA where a stronger convergence pattern and potential training is forecast with an alignment of the mean wind along the front once it reaches a latitude south of the line from Harrisonburg/Fredericksburg/St. Mary's. Greatest threat for significant flooding will reside just south of that line putting more prone areas in Southern/Southeast VA under a threat for enhanced flash flood concerns. The main change was the adjustment of the SLGT risk further northwest to encompass the expected zone of greatest convective coverage with a high-end SLGT worded for the areas referenced above with greater inclusion of portions of NoVA. Kleebauer ...Previous Discussion.. An unsettled weather pattern continues across much of Virginia and extending into adjacent portions of eastern West Virginia and northeast North Carolina going into Saturday and Saturday night. Multiple rounds of slow moving showers and thunderstorms will develop generally along and ahead of a cold front that is gradually settling to the south across Virginia. This boundary is intercepting an anomalously moist airmass with PWs on the order of 1.75 to 2 inches and mixed layer CAPE on the order of 1000 J/kg on average. The band of highest QPF is expected to be from the northern Shenandoah Valley to the Hampton Roads area of Virginia, with 2 to locally 4-6" inches of rainfall possible. Slow cell motions and efficient rainfall could result in some hourly rainfall rates approaching 2 inches per hour, especially where cell mergers occur. This could result in some instances of flooding, especially across urban locations and also areas that had heavy rainfall through the early morning hours Saturday. Hamrick ....Southern Plains, Southeast, and Tennessee/Ohio Valleys... 16Z Update: Our broad MCV over KS/OK is maintaining a signature of persistent rainfall with embedded convective clusters capable of a quick 1-2" of rain with some locally high amounts possible. This threat will continue for a few more hours before the remnant cold pools end up thwarting the maintenance of the convective regime and fizzling out to mere lingering showers as we move through the afternoon. The persistent circulation with the MCV will meander across the Plains with an redevelopment of convective activity after 00z as the nocturnal LLJ kicks back in and we see general destabilization aid in the process of reigniting the pattern over basically the same area. A one-two punch from this mornings activity and this evening will be enough to enhance some flash flood prospects within the overlapped zone across Southern KS into Northern and Northeast OK where 12z HREF blended mean QPF is signaling a broad area of 2-3" of rainfall with HREF neighborhood probs for >5" running between 20-35% across portions of Eastern OK. Considering the FFG's in place, this would prompt a better risk for flash flooding given the priming and then secondary development later this evening. The previous forecast for the SLGT was relatively maintained with some expansion to account for QPF trends within the latest CAMs and associated prob fields. SLGT risk was expanded through AR into Northern MS and the far southwest corner of TN to account for another zone of elevated impact later this afternoon and evening as convection fires along a lingering surface trough/quasi-stationary boundary on the southwestern flank of the departing trough situated to the north- northeast. Shortwave progression over the Plains will allow for enhanced diffluent flow across Northwest AR later in the period with convective development likely forming along the flanking surface trough/quasi-stationary boundary that bisects the state. Any storm within that region will exhibit slower storm motions with increasing likelihood of training overhead leading to local totals between 2-4" in any of the cells that develop. The area over Eastern AR into Northern MS will have the "benefit" of seeing two periods of rainfall with the morning MCS moving over the area with training already an issue in parts of the aforementioned area. This will deteriorate soil absorption capabilities, opening the door for potential flash flood concerns when the next round of convective materializes. The ongoing threat is also a concern and even extends further east into AL overnight with plenty of CAMs depicting heavy rainfall prospects over the region. The environment is more than capable of heavy rain across much of the Ohio Valley and Southeast, especially on the southwest and eastern flank of the slow-moving trough. Any cell will be capable of isolated flash flood concerns in those regions leading to a broad MRGL risk surrounding the SLGT risk located over the Plains into the Lower Mississippi Valley. Kleebauer ....Upper Midwest... 16Z Update: No changes were necessary to the previous MRGL risk forecast as 12z guidance remains on track for the overall setup. Heaviest rainfall will likely form across Eastern SD through Southern MN and Northern IA with the neighborhood probability for >2" of rainfall running between 30-60% within those bounds. Lower probs for >3" (<20%) are forecast meaning the projected maxima is likely to fall between 2-3" over the area, enough to warrant a maintenance of the MRGL risk previously forecast. Kleebauer ...Previous Discussion.. A warm advection pattern returns to the region, bringing a return to more widespread organized convection, mainly during the 00Z-12Z time period Sunday. Heavy rainfall over this same region in recent days has resulted in saturated soils in many cases, and this will increase the vulnerability to flooding, even though the expected rainfall is not expected to be overly impressive with mainly 1 to locally 2-3 inch totals expected, and therefore a Marginal Risk area remains valid for this time period. Hamrick ....Central Montana... 16Z Update: Only change was a minor expansion to the east and northeast for the MRGL risk across MT. The primary synoptic and mesoscale setup is still on target. Low FFG's over the region outlined will allow for the threat of isolated flash flood concerns within the stronger cores that develop late-afternoon and evening. A quick 1-2" is anticipated in any stronger cells. Kleebauer ...Previous Discussion.. A wave of low pressure developing along a frontal boundary should provide enough forcing to produce some scattered 1 inch rainfall totals across this region, mainly late Saturday afternoon into the evening as CAPE increases and dewpoints getting well into the 50s. Some of the storms that develop may produce high enough rainfall rates to result in a few instances of flooding. Hamrick Day 2 Valid 12Z Sun Jun 15 2025 - 12Z Mon Jun 16 2025 ....A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE=20 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=20 into Western PA as southwesterly flow remains steadfast west of the terrain in WV/PA through at least 18z. A corridor of elevated=20 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=20 the Central part of the CONUS will finally pick up forward speed=20 and shift eastward through the Central Apps and Mid Atlantic by the afternoon hrs leading to increased large scale forcing over the=20 aforementioned area. General instability coupled with the ascent=20 pattern will lead to favorable conditions for scattered to=20 widespread convective activity with mean cell motions moving slowly east and southeast through the course of the afternoon and=20 evening. A very robust signal within the 12z HREF neighborhood prob fields indicate a likelihood of >3" (60-90%) of rainfall in the=20 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.=20 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.=20 Kleebauer ....Northern Plains into the Midwest and Mid-South... 20Z Update: The multi-MCS threat remains firm within the latest=20 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=20 across Southeast KS down through Eastern OK into AR thanks to MCS=20 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.=20 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=20 the signal becomes stronger in later updates.=20 Kleebauer ...Previous Discussion..=20 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=20 history of limited flash flooding due to the very low runoff=20 capabilities. So long as this consensus remains, it is unlikely an=20 upgrade would be necessary for the region so will be monitoring=20 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=20 will take a more robust signal to induce an upgrade. These areas=20 are typically harder to flood and already exhibit relatively high=20 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=20 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.=20 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!71l6R-5l4T0eft7UrEgF_06mIU0HyzgDqSg4mOjZCxUK= FGa8SORwXzo5lqiDLBXW1sNChdDZavxSp69_2AUEm4GMD_w$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!71l6R-5l4T0eft7UrEgF_06mIU0HyzgDqSg4mOjZCxUK= FGa8SORwXzo5lqiDLBXW1sNChdDZavxSp69_2AUEN4Maga0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!71l6R-5l4T0eft7UrEgF_06mIU0HyzgDqSg4mOjZCxUK= FGa8SORwXzo5lqiDLBXW1sNChdDZavxSp69_2AUE-pzJ2b8$=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) .