Subj : HVYRAIN: Excess Rain D3-5 To : All From : Mike Powell Date : Mon Jun 15 2026 07:30:06 FOUS30 KWBC 150903 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 503 AM EDT Mon Jun 15 2026 Day 3 Valid 12Z Wed Jun 17 2026 - 12Z Thu Jun 18 2026 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE UPPER TEXAS GULF COAST INTO SOUTHWEST LOUISIANA... ....Upper Texas Gulf Coast into Southwest Louisiana... A potent upper level disturbance which includes some of the upper level remnants of former East Pacific tropical storm Cristina will interact with an incredibly deep moisture plume over the western Gulf to continue a multiple day heavy rainfall event over a small portion of the upper Texas Gulf Coast on Wednesday. The disturbance itself will make better forward progress during the period, moving from off South Padre Island at the start of the period into western Louisiana by Thursday morning. Immediately in advance of the center of this low, heavy rains will continue into the upper Texas Gulf coast and the Houston metro from the D2/Tuesday period. The axis of heaviest rainfall through the day is likely to be directed east of Houston, along the Texas/Louisiana border near Beaumont. Thus, this area is likely to see the worst impacts from flash flooding overall through the day. The strongest storms will become increasingly tied to the movement of the surface low and attendant upper level shortwave, as the front that plagued much of Texas will follow behind the low, clearing much of the rest of the state from heavy rains for a brief time. Across the South, the front that was stalled from central Mississippi through Georgia the past few days will dissipate entirely in advance of the next strong cold front. tracking across the Midwest. There remains considerable uncertainty as to how fast the low will track up the Texas Gulf Coast towards the lower Mississippi Valley. A faster progression may require a northeastward expansion of the Slight to cover more of central Louisiana, and if even a bit faster still, would re-impact western Mississippi late Wednesday night, requiring a significant upgrade from the current blank ERO for that area. Thus, significant changes are probable with future updates. Since the upper Texas Coast area will have been hard hit on 2 consecutive days prior to Wednesday, the Moderate Risk continuation into Wednesday was needed due to likely ongoing heavy rains through the period. While there's better certainty into southwest Louisiana for Moderate Risk level heavy rains, the Houston Metro was included in coordination with HGX/Houston, TX forecast office due to uncertainty largely on Wednesday morning as to how far west the heavy rain shield will extend at that time. ....Midwest... A potent area of low pressure over the Plains at the start of the period will progress east across the Midwest at a rather fast clip through the day on Wednesday. As the low moves into the mid- Mississippi Valley, it will increasingly tap into the large moisture plume present across much of the Southeast. The low will create its own moisture feed allowing the moisture to rapidly advect into the Midwest ahead of the low. The area from northern Illinois into Indiana has also been hard hit by periodic rounds of heavy rain in recent days, allowing for moist soils and high river levels to remain. Light rains at times are expected in the area Tuesday afternoon and evening, but due to lack of moisture, no significant flash flooding concerns are expected then. By Day 3/Wednesday however, the tap into the Gulf moisture will change all that. Numerous showers and thunderstorms will develop along the cold front ahead of the low as PWATs rise well above 1.5 inches, reaching as high as 2 inches at times. This will support storms capable of 1-3 inch per hour rainfall rates Wednesday afternoon through the overnight. The storms will be very fast moving, which will reduce the flooding threat, but the aforementioned moist soils, urban concerns, and increasing availability of deep moisture will all support the potential for widely scattered instances of flash flooding. Expect a warm front to move across the area around midday to early afternoon, then a strong cold front to move through late afternoon through the evening, which may consist of one or 2 lines of storms. These lines of storms in rapid succession could support training- like effects as far as flash flooding potential. Given the very favorable hydrology for flash flooding, it's possible targeted Moderate Risk upgrades may be needed for portions of the area, particularly northern Illinois into northern Indiana, where a higher-end Slight is in effect. Wegman Day 4 and Day 5 Valid 12Z Thu Jun 18 2026 - 12Z Sat Jun 20 2026 ....THERE IS A MODERATE SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE LOWER MISSISSIPPI VALLEY & CENTRAL GULF COAST ON DAY 4... Attention is on the multi-day Excessive Rainfall threat in the Deep South where an abundance of tropical moisture will engulf areas from southeast TX to as far east as GA. There are notable timing differences across guidance on the placement of the heaviest rainfall, and this will come down in large part to the development of the low-level disturbance in the western Gulf. Both its development and track will likely be troublesome for guidance to key in on for another 24-36 hours until the circulation is formed over South TX. That said, the region in total will have witnessed multiple rounds of Excessive Rainfall, particularly east TX, central and northern LA, and into western MS in lead up to Day 4. The 12Z ECMWF EFI showed a notable overlap of >0.7 signals from southwest LA on east into central MS, including at least a 2 contour on the Shift of Tails. In collaboration with several WFOs along the central Gulf Coast and the Lower MS Valley, a Moderate Risk was issued to account for the concerns of additional Excessive Rainfall over areas that will likely be dealing with ongoing flash flooding in the days leading up to Thursday. It is worth noting that the same axis of anomalous moisture in the South will stream north into the TN/OH Valleys. These areas will have the benefit of strong synoptic-scale forcing to produce widespread thunderstorms. A Slight Risk stretches as far north as southwest PA to account for flash flooding in these more flash flood prone areas. Day 5 will see a weak 500mb trough axis over central TX tap into lingering tropical moisture along the Gulf Coast. Lower pressures over the Rio grande and persistent high pressure east of the Bahamas will maintain the seemingly endless moisture tap emanating out of the Bay of Campeche. Moisture out ahead of the upper trough will also collide with a frontal boundary that will extend across much of the South. The future of the upper-level feature that originated over South TX early in the week may also still play a key role in Excessive Rainfall, especially from southern LA on east into northern GA. Accounting for various ensemble guidance tonight, there is a sufficient signal for Excessive Rainfall in areas across the South that received copious amounts of rainfall the first four days of the work-week to be concerned for more scattered instance of flash flooding that could be locally significant. A Slight Risk was issued from the Lower Rio Grande Valley to as far east as the Appalachians of northern GA. Mullinax $$ --- SBBSecho 3.28-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/107) .