Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 15 2025 07:10:18 FOUS30 KWBC 150709 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 309 AM EDT Sun Jun 15 2025 Day 1 Valid 12Z Sun Jun 15 2025 - 12Z Mon Jun 16 2025 ....A MODERATE RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF=20 SOUTHEAST VIRGINIA AND NORTHEAST NORTH CAROLINA... ....Mid-Atlantic and Central Appalachians... 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. ....Mid-South to the ArkLaTex... There remains a strong signal for one or more MCSs to develop in the latest deterministic guidance across Southeast KS and extending southward through much of Arkansas, owing to MCS propagation into=20 the area Sunday morning before the official start of the period at 12Z. The remnant MCV will enhance a redevelopment phase of the=20 regional convective threat over much of Arkansas and into the ArkLaTex region with some of the CAM guidance showing another 2 to 4 inches for this region, perhaps even higher in some cases where persistent convective training develops, and thus raise the potential for flash flood concerns. In this case, there was enough of a signal to warrant an expansion of the inherited Slight Risk southward to the ArkLaTex region. ....Upper Midwest... 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=20 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 MARGINAL RISK OF EXCESSIVE RAINFALL IS VALID FOR PORTIONS OF THE UPPER MIDWEST, MID-SOUTH, AND THE MID-ATLANTIC... ....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. There is a greater signal in the 00Z guidance for heavier QPF across central and southern North Carolina, but it does not appear to overlap much with the Day 1 QPF, so this will tend to mitigate the flooding potential. Although the magnitude of rainfall=20 expected on Monday is not impressive, the very saturated ground by=20 this time across West Virginia and western Virginia will be an=20 aggravating factor in terms of flooding potential, and therefore a=20 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... Consensus for locally heavy rainfall across portions of the=20 Northern tier of the CONUS remains favorable across a broad area=20 extending through the Dakotas, Nebraska, and the Upper Midwest on=20 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=20 time, and therefore a Marginal Risk remains valid there.=20 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 STATES=E2=80=A6 ....Midwest states... A well organized mid-upper level shortwave trough will eject=20 eastward from the Rockies to the central Plains Tuesday afternoon=20 into the early hours of Wednesday morning, and this will sustain=20 the development of a surface low that will develop along a frontal=20 boundary. Upper level dynamics will be favorable as the region will be place under the right entrance region of the main upper level=20 jet, and incoming mid-level positive vorticity advection will=20 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=20 range and an increasing southwesterly low level jet that will=20 advect copious moisture into the system.=20 Model guidance has trended a little to the south over the past few model cycles, with the greatest consensus for the heaviest QPF=20 across the southern half of Iowa and over the northern third of=20 Missouri, and extending to northeast Kansas and west- central=20 Illinois. Most model solutions have a broad corridor of 1-2 inches=20 with embedded 3-4 inch maxima within this region, with the majority of this happening within the 18Z Tuesday to 6Z Wednesday time=20 period. The heavy rain that fell across portions of the Upper=20 Midwest is generally north of where this expected rainfall will be, so grounds will not be saturated in most cases leading up to this=20 event. The inherited Slight Risk from the previous Day 4 outlook=20 will be maintained with a southward expansion to it, and a broader=20 Marginal Risk extending across South Dakota and eastward to include the greater Chicago metro area.=20 ....Appalachians... The stationary front that will be lingering across the Mid-Atlantic will start to slowly move back north as a warm front on Tuesday=20 with anomalous PW values remaining in place. Scattered to numerous=20 showers and storms, some of which will likely be slow moving, are=20 forecast to develop during the afternoon and evening hours, mainly=20 in the 18Z-00Z time period. Parts of the central Appalachians have=20 been hammered with multiple heavy rainfall events and this has=20 served to lower flash flood guidance values, and additional heavy=20 rainfall in the Day 1 and Day 1 periods will only make the ground=20 more saturated. Therefore, a Marginal Risk is valid from western=20 North Carolina to western Pennsylvania. Hamrick Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9E6h6JlmOAY1k0rFyLi4ZjVaMP0AeAI08kHcQomCd7kR= U4OvpQBiDGsQP8X1CTlwMbaAzLTioFT8wO98SaPWDsSkMqE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9E6h6JlmOAY1k0rFyLi4ZjVaMP0AeAI08kHcQomCd7kR= U4OvpQBiDGsQP8X1CTlwMbaAzLTioFT8wO98SaPWjtB9PMM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9E6h6JlmOAY1k0rFyLi4ZjVaMP0AeAI08kHcQomCd7kR= U4OvpQBiDGsQP8X1CTlwMbaAzLTioFT8wO98SaPWRUVs_yk$=20 --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .