Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 15 2025 22:10:56 FOUS30 KWBC 152210 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 610 PM EDT Sun Jun 15 2025 Day 1 Valid 224Z Mon Jun 16 2025 - 12Z Mon Jun 16 2025 ....A MODERATE RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF SOUTHEAST VIRGINIA AND NORTHEAST NORTH CAROLINA... 22z Update: Main change was to add a Marginal risk to portions of southeast NM and southwest TX. High res guidance is under doing=20 the extent and magnitude of convection over this area. Wind=20 profiles support slow cell motions, which combined with the high=20 instability and moisture in place, supports a continued isolated=20 flash flood risk. See MPD #449 for more details. Chenard ....Previous Discussion...=20 ....Mid-Atlantic and Central Appalachians... 16Z Update: The previous MDT risk was maintained with some expansion to the northwest to reflect the latest prob fields highlighting a greater threat north of Richmond as convection fires and slides down the instability gradient aligned with the front. Biggest shift was the expansion of the SLGT a bit further north and northwest into Southeast OH and more of Western PA as area 1/3/6 hr FFG indices are incredibly low given the saturate grounds lingering from yesterdays convective impacts. Environment in place is conducive for locally enhanced rainfall rates with the stronger cores more apt to produce intra-hour rates closer to 3"/hr with an average 1-2"/hr intensity in any thunderstorm development. The area over Northern and Eastern WV is also under a greater threat for flash flooding today due to similar characteristics noted to the north. Complexity of the terrain adds more opportunity for locally significant flash flood concerns, something that has historical precedence in these areas encompassing the Central Appalachian's. In all, the setup remains on the higher end of the SLGT spectrum for much of VA into WV and Southwest PA with a targeted MDT down over Southern VA and the Tidewater due to the more robust PWAT and instability signatures within the confines of quasi-stationary front creating a greater threat for training convection. Kleebauer ...Previous Discussion.. A back door cold front will continue to slow down its forward progress and idle across the Mid-Atlantic region through Father's Day. Moist southwesterly flow will intersect this boundary and result in enhanced moisture convergence and lift. A combination of ample instability on the order of 1000-2000 J/kg of mixed layer CAPE, PWs nearing 2 inches, and a strong frontal boundary will set the stage for additional heavy rain over grounds that are becoming much more saturated leading up to this. There are two main areas of increased concern, with the first being over eastern West Virginia where HREF probabilities of flash flood guidance exceedance are elevated due to antecedent conditions and the prospects of 1-2 inches of additional rain on Sunday. Although this area still remains in a Slight Risk, there is the potential that an upgrade to Moderate Risk may be needed once the event starts to materialize midday Sunday, so this will continue to be closely monitored. The other area of concern is across the Tidewater region of southeast Virginia into adjacent portions of northeast North Carolina. The 00Z CAM guidance strongly supports swaths of enhanced QPF from just south of Richmond to the northern Outer Banks, and rainfall totals on the order of 2-3 inches, and locally higher, are expected. This would be falling on top of grounds that already had 1-3 inches on Saturday near the U.S. Highway 460 corridor into Southside Hampton Roads, so that is an aggravating factor. All of this combined with higher HREF flash flood guidance probs resulted in areas south of the James River and north of the Albemarle Sound to now be in a Moderate Risk for this time period. Hamrick ....Mid-South to the ArkLaTex... 16Z Update: MCS currently migrating south across the Red River will continue propagating towards Southeast TX before fizzling out on approach once south of I-45. Current indications are a combination of differential heating causing destabilization over Southeast TX will initiate another round of pulse convection with the remnant cold pool of the MCS eventually interacting with storms already in the area. Some minor convergence signatures are popping up within CAMs, but the threat seems to be relatively minor compared to previous setups as the stable component behind the complex provides a cap on the activity pretty quickly once the interaction occurs. HREF probs are generally modest for >3" potential, but fall off a cliff to near 0% for >5", so the realistic maximum is somewhere between 3-5" with an areal average closer to 1-2" where convection does occur. The greater convergence signature is up closer to the Northwest Ozarks where satellite combos and even regional radar composite depict a broad MCV slowly drifting eastward with the mean flow leading to a small band of light/moderate rainfall in the northern quadrant of the circulation. The area to the southeast is the most prone to convective initiation and relatively impacts due to the proxy and persistent advection of moisture within the southeast and eastern flank of the meso-low. Visible satellite indicates a broad area of clearing which will likely enhance regional instability prospects given the "green light" for diurnal destabilization pattern. CAMs are in agreement on another round of heavy convection over the areas outlined within the zone of clearing leading to elevated neighborhood probs for >3" (50-70%) across Central and Northern AR into Southeast MO. The former area has been hit multiple times over the past 24-48 hrs leading to some priming of the soils so the threat for flash flooding is a bit higher compared to Southeast MO. Will need to monitor that region closely overnight to see how the convective pattern evolves, but the previous SLGT risk inherited was sufficient to warrant continuity as the setup has maintained similar posture within the 12z CAMs suite and ensemble. The threat over TX is still well within the MRGL threshold and given the cap on potential, the risk was not upgraded as the threat remains more localized with greatest potential in urbanized zones. Will monitor the MCS evolution closely as any changes in the near term could allow for a targeted upgrade, namely in the area along I-35. Kleebauer ....Upper Midwest... 16Z Update: The signal for the SLGT is favorable on the threat as most CAMs remain aggressive for the evening complex anticipated to slide down the eastern flank of the theta_E ridge positioned over the Plains. HREF EAS and neighborhood prob fields still highlight that area of far Southeast SD, Northwest IA, and Southwest MN this evening with the greatest chance for locally 2-4" of rainfall. Considering the antecedent soil moisture being elevated after this mornings convective impacts, the foundation was laid for a targeted opportunity to see some localized flash flood prospects. This allowed for little to no change in the previous forecast as the threat is still on track. Kleebauer ...Previous Discussion.. The expected convective complex over the Dakotas and moving into Iowa will likely be more on the progressive side compared to the MCS farther south across Arkansas. However, some of the heavier rain that is expected will likely happen over more saturated soils and therefore a higher chance of localized impacts. The 00Z CAM guidance suite has trended wetter, especially the 3km NAM, and the global guidance to include the GFS and the CMC also have a more concentrated QPF signal. Therefore, northwestern Iowa and portions of adjacent states are now in a Slight Risk area for this time period. Hamrick Day 2 Valid 12Z Mon Jun 16 2025 - 12Z Tue Jun 17 2025 ....A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE MID-ATLANTIC, CENTRAL APPALACHIANS, AND OHIO VALLEY... ....Mid-Atlantic to Central Appalachians... 20Z Update: Convective focus along a stalled quasi-stationary front will lead to another period of locally heavy rainfall with training potential existing over portions of North Carolina. The setup is just a continuation of a broad convective regime with a general alignment of stronger convection within the confines of a front that will lie from Western PA down through Northern and Eastern WV, Southwest VA, arcing back towards Eastern NC. Relatively buoyant environment and elevated PWATs running +1.5 to +2 deviations will be sufficient in producing local rainfall rates between 1-2"/hr across much of the above zones with the Eastern NC area more likely to see closer to 2-3"/hr in heavier cores as projected within the latest hourly rate probs via the 12z HREF. HREF blended mean QPF output is a general 0.5-1" in areal average across Southwest PA down through Northern and Eastern WV, but scattered deterministic signals of 2-3" are pretty common within the latest suite. A more robust 1.5-2" areal average is positioned from the NC Triangle across through Eastern NC with a general maxima between RAH to Hatteras. The eastern fringes of the heavier precip will be positioned over sandier soils leading to a naturally lower probability for flash flooding compared to inland areas of NC. Points north are a combination of low FFG's and complex terrain that will likely cause some problems with almost any heavier QPF core that materializes. Given the signatures above, and a forecast SLGT from the recent First Guess Fields in the interior Mid Atlantic, a SLGT risk upgrade was generated for the D2 forecast with a footprint extending from just east of RAH along I-40 and points northwest up through Southwest VA, Northern and Eastern WV, and Western PA. Kleebauer ....Ohio Valley... 20Z Update: A persistent MCV will create an environment favorable for locally heavy rainfall across portions of the Mid-Mississippi Valley into the Ohio Valley. Area convergence under the general circulation from the remnant complex will create a zone of enhanced precip potential with most of the CAMs indicating the area from far Western KY through the Ohio River Basin encompassing IL/IN/KY/OH with the magnitude of heavier totals between 2-4". 12z HREF neighborhood probs for >3" is pretty high (40-70%) along that corridor of the Ohio River with the maximum depiction between that intersection of IL/IN/KY. This is the general location of the circulation when you assess the 500mb vorticity panels, so it makes sense synoptically that the threat would converge over the strongest mid-level ascent focus. FFG's are relatively modest overall, but with 1-2"/hr rate potential in any cell development, this would be sufficient to exceed the hourly FFG's currently, but the biggest signal comes from the 3hr FFG exceedance probability with the latest ensemble output showing 30-50% chances for several 3hr increments between 12-00z tomorrow. A targeted upgrade to a SLGT risk is now in place over the aforementioned region for the threat of flash flooding under the guide of a remnant MCV/low- amplitude shortwave moving from the Mid-Mississippi Valley into the Western Ohio Valley. Kleebauer ....Dakotas to the western Great Lakes... 20Z Update: Little to no adjustment was necessary for the broad MRGL risk as the previous forecast remains steadfast in its presentation for locally heavy rainfall across the Upper Midwest into parts of the Northern Plains. The heaviest rain is still forecast to occur in the heart of the Sandhills of NE, an area that will likely be void of many flash flood concerns due to the soil composition and very high FFG's in place. Kleebauer ...Previous Discussion.. 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. It remains the case that some of the heavier rainfall is expected over the Sandhills of Nebraska where flash flood guidance is high, and therefore not rising to the level needed for a Marginal Risk in that area. Elsewhere, there remains a scattered heavy rain threat over the northern portions of the Upper Midwest at this time, and therefore a Marginal Risk remains valid there. Hamrick Day 3 Valid 12Z Tue Jun 17 2025 - 12Z Wed Jun 18 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE MIDWEST, EASTERN OHIO VALLEY, AND CENTRAL APPALACHIANS=E2=80=A6 ....Midwest... 20Z Update: The previous forecast SLGT was general maintained with some expansion of the risk area to the southwest given the latest trends slowly shifting the threat more into Northwestern MO and far Northeast KS. The latest ML output is also leaning towards the southern end of the envelope when it comes to the heaviest QPF distribution, so it's plausible the shifts will continue to trend more into the I-70 corridor across KS/MO if this holds. For now, wherever the threat materializes, there will be heavy rain with totals likely between 3-5" in the hardest hit areas. Some training potential is plausible considering the upwind trajectory behind the vacating surface low as it cuts to the northeast. Will be monitoring closely for both the positioning of the risk, and a potential for a targeted upgrade if the magnitude of the precip forecast increases, or focuses over some of the larger urban corridors where flash flood potential is most likely. A higher end SLGT is certainly forecast at this juncture. Kleebauer ...Previous Discussion.. A well organized mid-upper level shortwave trough will eject eastward from the Rockies to the central Plains Tuesday afternoon into the early hours of Wednesday morning, and this will sustain the development of a surface low that will develop along a frontal boundary. Upper level dynamics will be favorable as the region will be place under the right entrance region of the main upper level jet, and incoming mid-level positive vorticity advection will further aid ascent. Precipitable water values in the warm sector of this surface low are expected to rise into the 1.75 to 2 inch range and an increasing southwesterly low level jet that will advect copious moisture into the system. Model guidance has trended a little to the south over the past few model cycles, with the greatest consensus for the heaviest QPF across the southern half of Iowa and over the northern third of Missouri, and extending to northeast Kansas and west- central Illinois. Most model solutions have a broad corridor of 1-2 inches with embedded 3-4 inch maxima within this region, with the majority of this happening within the 18Z Tuesday to 6Z Wednesday time period. The heavy rain that fell across portions of the Upper Midwest is generally north of where this expected rainfall will be, so grounds will not be saturated in most cases leading up to this event. The inherited Slight Risk from the previous Day 4 outlook will be maintained with a southward expansion to it, and a broader Marginal Risk extending across South Dakota and eastward to include the greater Chicago metro area. Hamrick ....Ohio Valley and Central Appalachians... 20Z Update: The threat for a broader impact flash flood threat is increasing as we move into Tuesday afternoon and evening before we finally end the incessant heavy rain pattern generated by scattered to widespread convection across parts of the Eastern Ohio Valley into Western PA and the adjacent Appalachians. The upper pattern will be a significant driver in the area precip coverage as we move into Tuesday with large scale forcing on the rise as we see an approach of a potent shortwave trough out of the Ohio Valley. Area moisture field will be running ~2 deviations above normal with forecast PWATs between 1.7-2" likely across much of Ohio, Eastern KY, WV, and the western half of PA. The combination of a stagnant elevated moisture regime and plentiful forcing will generate a period of scattered to widespread thunderstorm activity migrating across the above areas creating a heightened threat of flash flooding when you take into consideration the compromised soils from all the rainfall leading into the setup. The area of Northern WV, Western PA, and Eastern Ohio is by far the most sensitive in this pattern and the threat for heavy precip is as genuine as you can get, in a synoptic sense. Ensemble depictions of 1-1.5" areal average at a D3 lead is a testament to the threat and has a lot of support from the QPF distribution within the latest ML consensus. For now, a SLGT risk was introduced to encompass that corridor referenced above in the Ohio Valley up through Western PA. If this trend becomes more favorable in the QPF maxima exceeding 3" across some of those more compromised areas, a further targeted upgrade is plausible. This is a setup to monitor closely over the coming days. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-SRgWyYCJTpHGepzKAF_MhvmcTPS-CBtFXbSgifEugqo= QcAlEuqQUm3d8ZHaqNQQkkOw7iEdXF2lEcElZwSzov6inno$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-SRgWyYCJTpHGepzKAF_MhvmcTPS-CBtFXbSgifEugqo= QcAlEuqQUm3d8ZHaqNQQkkOw7iEdXF2lEcElZwSz_im52NU$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-SRgWyYCJTpHGepzKAF_MhvmcTPS-CBtFXbSgifEugqo= QcAlEuqQUm3d8ZHaqNQQkkOw7iEdXF2lEcElZwSz3RzYlNg$=20 --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .