Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 08 2025 19:49:20 FOUS30 KWBC 081949 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 349 PM EDT Sun Jun 8 2025 Day 1 Valid 16Z Sun Jun 08 2025 - 12Z Mon Jun 09 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN PLAINS...GULF COAST...AND MID-ATLANTIC... ....Mid-Atlantic and Central Appalachians... Very few changes were made to the existing Day 1 outlook over this region, with observational trends generally matching earlier forecasts fairly well. The initial round of rain has moved through much of the Slight Risk area as of 15 UTC, and has produced a fairly widespread 0.5 to 1.0 inches of rain in much of the area. As cloud cover partially clears in the wake of the area of stratiform rain, rapid destabilization is occurring, and this is already beginning to support convective initiation. Although the PWs may be slightly lower in this area of clearing, they are still relatively high (around 1.4 to 1.5 inches) around the 90th percentile for early June. The combination of the increasingly strong instability and relatively deep moisture should support hourly rain rates of 1 to 2 inches per hour in the most vigorous and organized convection. This may lead to flash flooding, particularly in situations where the rain rates can be sustained for more than an hour, and either in the mountainous areas of N WV, W MD, SW PA that have been very wet lately, or in urbanized areas in the coastal plain. ....Gulf Coast... Training and backbuilding thunderstorm activity has been far more persistent this morning in portions of E MS and C AL than models have been indicating. However, 12 UTC hi-res guidance appears to generally have a better handle on the current mesoscale environment and state of the convection. There is good agreement that the convective line itself and/or the associated gust front will make steady progress toward the coast today, and then begin to stall later this afternoon or early tonight. This may focus additional convective clusters and lines later today and tonight, with a favorable configuration for backbuilding (southwesterly inflow with an upstream reservoir of strong instability). The combination of the very high CAPE values, and anomalously high PWs around 2 inches, will support very heavy hourly rain rates approaching or exceeding 2 inches in the most organized convective clusters. If the gust front interacts with the coastal convergence zone and anchors convection somewhere near the coastline, heavy rain rates could persist for several hours and lead to a locally extreme rainfall event with potential for significant flash flooding. ....Southern Plains... The heavy rainfall and associated flash flooding threat in this region is more conditional, given excellent hi-res model agreement in a very organized, rapidly forward propagating bowing line late this afternoon and this evening. Although the instantaneous rain rates in the line itself would be likely to be high, the fast forward speed would likely mitigate that factor a bit. Corridors of heavy rainfall in these cases tend to occur either: 1. Near the poleward bookend vortex, which can tend to move slower and still have relatively high rain rates. In this case, that would be most likely over portions of SC OK, although the fast forward motion of the line makes it uncertain how impactful this would be from a rainfall perspective. 2. Or along the upshear flank of the cold pool. That seems plausible in this case, and would be most likely either in far SW OK or in western N TX. In particular, a corridor of locally heavy rainfall and flash flooding would seem more likely if convective development occurs near a lingering front in advance of the main forward propagating MCS, thereby increasing the duration of the heavy rainfall. However, it's unclear whether this antecedent development and the eventual gust front location will be co-located. Therefore, the Slight Risk was maintained given these uncertainties, and was only nudged slightly to the southwest to account for latest observational data trends and hi-res guidance. Lamers Day 2 Valid 12Z Mon Jun 09 2025 - 12Z Tue Jun 10 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN PORTIONS OF PENNSYLVANIA AND NEW YORK...AS WELL AS THE GULF COAST... ....Northeast and Ohio Valley... Convective lines are expected to develop Monday just ahead of a strong, steadily advancing cold front over the eastern Great Lakes and Ohio Valley, and eventually advancing into the interior Northeast (PA and NY in particular). A narrow plume of PWs around 1.5 inches and moderate instability should support heavy rain rates on the order of 1-2 inches per hour in the most intense activity. The Slight Risk was maintained but retracted a bit to be focused primarily in Pennsylvania and southern New York. The model QPF signal was reduced a bit in eastern Ohio and West Virginia. Greater confidence in the possibility of training thunderstorms or convective rain bands exists over PA and NY where the deep layer mean wind will be more parallel to the cold front orientation. Further southwest into portions of SE OH, WV, KY, TN, the HREF and experimental RRFS ensemble both show a scattering of low chances of rainfall exceeding flash flood guidance on a 1-hr or 3-hr basis, but overall ensemble mean QPF is lower and the mean wind is more crosswise to the cold front. This suggests convective lines should be more progressive and any flash flooding impacts may be more isolated. ....Gulf Coast and Southeast... A Slight Risk was introduced from SE MS into S AL, SW and C GA, and the FL Panhandle. Multi-model ensemble QPFs show the greatest chances of 2+ inches of rainfall now increasingly concentrated in this area. Scattered clusters of thunderstorms are expected to develop by Monday afternoon across the Gulf Coast region in an environment characterized by strong instability and PWs around 2 inches. The availability of deep moisture and favorable instability would support very heavy rain rates. While hi-res models differ a bit on the details, they all generally show clusters and lines of thunderstorms developing in west-east oriented bands along mesoscale boundaries. Some of these boundaries may be related to convection from the day and night prior, or increasingly the arrival of a synoptic cold front from the northwest. Any lines that are oriented in this fashion would be more parallel to the deep layer mean wind and could create corridors of training convection and swaths of localized heavy rainfall.=20 ....West Texas and New Mexico... For now, a broad Marginal Risk was maintained in these areas as any concentrated areas of heavy rainfall would likely be highly dependent on the convective evolution from Sunday afternoon into Monday morning across the region. A forward propagating MCS across S OK and N TX should push an outflow boundary somewhere into C TX, and that could become a feature that focuses renewed convective development on Monday. Broad low-level east to southeast flow from the coastal plain all the way into W TX and E NM should cause PWs to gradually increase, and support scattered convection well into C/E NM during the afternoon hours. Some hi-res models show this activity in NM coalescing into a MCS and pushing southeastward into W TX during the evening and overnight, and existing boundaries would be important to that process as well. It's possible a Slight Risk may be needed in future outlook updates. Lamers Day 3 Valid 12Z Tue Jun 10 2025 - 12Z Wed Jun 11 2025 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WEST TEXAS AND SOUTHEASTERN NEW MEXICO... ....West Texas, Texas Hill Country, and Southwest New Mexico... Greater confidence exists in a heavy rainfall event on Tuesday (compared to Monday) in SE NM and W/C TX. A shortwave ejecting out of the Desert Southwest will push through NM early Tuesday and approach the Slight Risk area over the aforementioned region. The combination of abundant deep moisture, with PWs generally above the 90th percentile for early June, strong instability, the approaching shortwave, and upper level divergence will favor widespread thunderstorm activity. Deep layer mean winds will not be particularly strong, around 10-15 knots, which should favor slow eastward propagation with time. It seems most likely that convective initiation will occur closer to the Sacramento, Guadalupe, and Davis Mountains from SE NM into far W TX, near the nose of a low-level moisture transport maximum. Slow propagation of convective clusters could then lead to flash flooding issues from near those areas, to eventually as far east as the Edwards Plateau and Texas Hill Country. Lamers Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!8XGL2i_OSwnHEoKk6CXtAhKP3cGc4Jnsr3YWD9b9_ilr= qJM4eXveBf0z9KlBxC7j4C2wjcystZFhd_fFXsciaISq-Mw$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!8XGL2i_OSwnHEoKk6CXtAhKP3cGc4Jnsr3YWD9b9_ilr= qJM4eXveBf0z9KlBxC7j4C2wjcystZFhd_fFXsci7AE7eBM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!8XGL2i_OSwnHEoKk6CXtAhKP3cGc4Jnsr3YWD9b9_ilr= qJM4eXveBf0z9KlBxC7j4C2wjcystZFhd_fFXsci5CRmA68$=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) .