Subj : HVYRAIN: Excess Rain D1-2 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 1 Valid 12Z Mon Jun 15 2026 - 12Z Tue Jun 16 2026 ....THERE ARE MODERATE RISKS OF EXCESSIVE RAINFALL FOR MUCH OF THE TEXAS GULF COAST AND SOUTH TEXAS AS WELL AS FOR A PORTION OF WEST- CENTRAL MISSISSIPPI... ....Texas Gulf Coast and South Texas... A very impressive setup for flash flooding will begin to unfold along the Gulf Coast of Texas today, and will continue into future days. The impressive ingredient is the sheer amount of moisture that will be advecting north into south Texas and the Gulf coast over the next few days in advance of a potent upper level low, some of the remnants of former east Pacific tropical storm Cristina. PWATs advecting into deep south Texas are likely to broach close to record territory today, as they climb to as high as 2.75 inches. This is a function of well above normal sea-surface temperatures in the Gulf adding low-level moisture, and preexisting upper level moisture from Cristina. The combination of these could fully saturate the atmosphere up to the tropopause, with melting layers as high as 17,000 ft. This will make any storms that develop in this environment having an almost unnatural ability to produce heavy rain. As the aforementioned upper level disturbance approaches and lee cyclogenesis begins east of the Mexico mountains tonight, expect multiple rounds of storms across Deep South Texas to impact the area. A westward moving band may start off around peak heating this afternoon, then as the disturbance approaches tonight, a nearly stationary or slowly eastward moving band is expected to develop overnight tonight which will persist for much of the night as competing forcings create an area of low level convergence over Deep South Texas. There is some uncertainty as to where this convergence sets up, but it appears it's most likely closer to the Rio Grande Valley on the western side of Deep South Texas. Given the incredible moisture available for the storms, localized cells could produce rainfall rates as high as 5 inches per hour, with 3 inch/hour rates common. Despite dry soils going in, these incredible rain rates will easily overwhelm the areas experiencing them, resulting in widespread and locally catastrophic flash flooding, especially in any towns or cities that experience an extended duration of rainfall rates of that magnitude. Further north, the north-south oriented bands over Deep South Texas will impact a strong but slow-moving cold front drifting southeastward towards the Texas Gulf Coast. This will funnel the prodigious moisture northeastward paralleling the coast. The storms will follow, resulting in training. As in Deep South Texas, despite slightly, and I mean only slightly lower PWATs, rainfall rates to 3 in/hr will be common with localized rates to 5 inches/hour here as well. FFGs are significantly lower from Corpus Christi northeast to Houston as compared with further south down the coast, thus, these prodigious rainfall rates will have no trouble exceeding FFGs. Frictional convergence of the onshore flow and the front will make for nearly stationary bands of storms along much of the middle Texas Coast. Thus, expect storm total rainfall amounts today easily exceeding 3 inches, but localized amounts will be much higher, perhaps approaching 8 inches, as noted by the HREF probabilities. With some uncertainty as to how prolific the storm total rainfall amounts will be, the Moderate Risk may need to continue to be upgraded in the hardest hit areas through the day, especially if those include urban areas from Brownsville through Houston. ....West-Central Mississippi... The same incredible moisture plume as over Texas is already in place across all of Louisiana and southern Mississippi this morning. The same front as in Texas will be even stronger to the east in Louisiana and Mississippi. Thus, with southwesterly LLJ flow into this front, expect numerous thunderstorms to develop across northern Louisiana and west-central Mississippi by midday today. The storms will run into a "wall" that is the cold front, forcing them to turn eastward, resulting in a well-defined line of storms along the frontal interface. It appears this is most likely to occur along the I-20 corridor. The heaviest rains will occur from midday through sunset, after which there may be a break before more scattered convection redevelops in the early morning hours of Tuesday. Multiple inch per hour rates are likely with these storms as well due to the deep moisture with PWATs at record territory between 2.25 and 2.5 inches. Portions of western Mississippi have been recently hard hit with heavy rains, resulting in wet soils, and the Jackson area due to urban concerns is also vulnerable to flash flooding due to heavy rainfall. In coordination with the JAN/Jackson, MS forecast office, a Moderate Risk upgrade has been introduced. While soils are less supportive of flooding further west into northern Louisiana, persistent multiple inch/hour rates along the I-20 corridor could result in an expansion of the Moderate Risk with future updates. Wegman Day 2 Valid 12Z Tue Jun 16 2026 - 12Z Wed Jun 17 2026 ....THERE ARE MODERATE RISKS OF EXCESSIVE RAINFALL FOR THE ENTIRE TEXAS GULF COAST AS WELL AS FOR WEST-CENTRAL MISSISSIPPI... ....Texas Gulf Coast... A plume of incredibly deep tropical moisture over the entire Texas Gulf Coast will be in place at the start of the period Tuesday morning. Ongoing lee cyclogenesis in advance of a strong upper level disturbance will support continuous numerous showers and thunderstorms in the onshore flow up the western coast of the Gulf and into the Texas Gulf Coast. This disturbance will further increase the amount of moisture available for the storms, as PWATs rise to record territory in some areas, possibly exceeding 2.75 inches. Any and all storms that continue to develop ahead of the low will be capable of multiple inch/hour rainfall rates, despite the reduced instability in the early morning. When added to Monday's rains, flash flooding is likely to continue all along the Texas Gulf Coast until the low itself, which will track northeastward roughly parallel to the coast passes a given longitude, switching the wind direction from onshore southward to offshore northwestward. Since the low will be barely moving, a steady onshore flow across the middle and upper Texas Gulf Coasts will continue to favor training storms impacting coastal areas, with the Houston Metro remaining particularly vulnerable. Meanwhile for the lower Texas coast, once the low moves offshore, the northwesterly flow will dramatically decrease storm coverage and intensity, though not completely shut it off due to the deep moisture still in place even behind the low, with the front lagging behind along the Rio Grande. There is considerable uncertainty as to the northern and western extent of the rainfall threat on Tuesday. The cold front bringing much drier air will continue its progress south and east across South Texas, so the threat will end from west to east during the day. Meanwhile extensive cloud cover should limit instability well away from the coast. Thus, the storms will have a progressively narrowing portion of the Texas Gulf Coast that they will be able to impact. Regardless, heavy rain will continue to impact the Lower Texas Coast from the D1 period into Tuesday morning, and the heavy rains will continue further up the coast throughout the period. This supports a continuation of the Moderate Risk into the southwest corner of Louisiana. ....West Central Mississippi... Heavy rains across western Mississippi are likely to redevelop in the same area along the I-20 corridor during peak heating Tuesday afternoon, and perhaps in some areas never completely stop Tuesday morning from any overnight rainfall. The front driving the heaviest rainfall with the strongest storms will be completely stationary over Mississippi, whereas in Louisiana and points west, it will continue painfully slow south and eastward progress. Thus, when storms refire Tuesday afternoon, they will be over many of the same hard hit areas of central Mississippi as on Monday. Further east, on Monday the storms will align east-southeastward from western Mississippi to northern Florida. By Tuesday however, northward progress of the front as a warm front will allow the heaviest rains to impact further north into Alabama and Georgia. Despite a lack of rain on Monday, the still wet soils across central Alabama towards Birmingham and Montgomery may require an eastward extension of the Moderate Risk area into central Alabama. Regardless it appears western Mississippi will still be the area that gets the most rain, especially over the combined 2 day period. Rains in west central Mississippi should diminish with loss of daytime heating Tuesday night with lingering storms pressing southeastward toward southern Alabama and the Florida Panhandle Tuesday night. Wegman $$ --- SBBSecho 3.28-Linux * Origin: ILink: CCO - capitolcityonline.net (454:3/107) .