457 FOUS30 KWBC 160021 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 821 PM EDT Mon Jun 15 2026 Day 1 Valid 01Z Tue Jun 16 2026 - 12Z Tue Jun 16 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE TEXAS GULF COAST AND SOUTHEAST TEXAS AS WELL AS FOR A PORTION OF CENTRAL-SOUTHWEST LOUISIANA AND INTO WEST-CENTRAL MISSISSIPPI... 01Z Update: Significant rainfall remains the forecast this evening into early Tuesday morning across southern and eastern TX into the Central Gulf coast region with an alignment of heavy rainfall positioned near a quasi-stationary boundary analyzed along I-20 in LA/MS. Surface low situated south of the lower RGV is aiding in regional low-level convergence and surge of PWATs between 2.2-2.7 up through all of southern and eastern TX with some indications of PWATs approaching 2.8-3.0" based on the latest RAP analysis. 18z HREF and recent HRRR/RRFS runs continue to benefit the current MDT risk initiated across the aforementioned areas with probs in the ensembles really pinning a region of 2-5" of rainfall as an areal average from the lower RGV up through the TX coastal plain, extending north into LA/MS. Environmental conditions will be ripe for rainfall rates to breach 2"/hr with 3-4"/hr rates not out of the question as warm rain processes will be prevalent across the affected area as WBZ heights are forecast between 14-16k ft, a textbook example of tropical airmass presence and sufficient deep layer moisture. Highest probabilities for flash flooding will be situated across Deep South TX within the proximity of a surface trough extending north of the low level center positioned south of the lower RGV. After 06z is when we'll see a slow push of the convergence zone and increasing rainfall threat for areas further north along the TX coast, eventually making headway into the Central Gulf coastal areas of LA. Quasi-stationary front to the north will act as an inflection point for available low-level ascent as the flow will eventually make its way north with a strengthening BL convergence signature popping up between 07-12z Tuesday morning. Hi-res has been insistent on a regeneration of cells across the I-10/20 corridors and areas in-between putting areas within the upper TX coast to southwestern LA at play for significant rainfall the end of the period into the current D2. Rainfall will still be occurring over the Central Gulf prior, so the grounds will remain saturated with no reprieve in sight. Expect isolated flash flood prospects initially between 00-07z this evening with a potential for more scattered flash flood chances prior to sunrise. Considering all the above, the MDT was maintained with a greater than normal prospect for significant flash flooding over much of south TX and along the TX coastal plain into the I-10/20 corridors in LA into southwest MS. Lingering heavy rainfall across eastern FL will maintain a low-end flash flood prospect into the urban corridor before dwindling after 02z. Maintained a MRGL risk to account for the continued activity over the area. Kleebauer Day 2 Valid 12Z Tue Jun 16 2026 - 12Z Wed Jun 17 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE ENTIRE TEXAS GULF COAST INTO SOUTHWEST/CENTRAL LOUISIANA AND CENTRAL MISSISSIPPI... ...Texas Gulf Coast... 20Z Update... Today's update to the day 2 outlook included an expansion of the MDT risk through central LA into central MS, which matches the continuous plume of moisture and convergence axis extending northeast from the strengthening mid-level cyclone over South Texas early Tuesday. Expectations are for ongoing activity Tuesday morning across coastal TX to gradually shift offshore during the day, with lingering impacts crossing over from day 1. Some uncertainty remains regarding a more consolidated area of low pressure over the far northwest Gulf by Tuesday night and a developing feeder band to the east-northeast of this low. Most guidance keeps this highly efficient rain producing rain band offshore, but if it makes it any distance inland extreme rainfall and significant impacts for the TX Coast are possible. Snell Previous Discussion... 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. Wegman ...Lower Mississippi Valley to Southeast... 20Z Update... Much of the Lower Mississippi Valley and Southeast will remain in the favorable right-entrance region of a stout upper-level jet centered over the southern Appalachians. This will allow for ample moisture to flow northeastward out of the western Gulf and thunderstorms to focus along a lingering stationary front. Thunderstorms and widespread shower activity should start out well inland during the daytime and then shift to focus along the coast after sunset and overnight into Wednesday morning. The 12Z HREF and REFS highlight coastal MS, AL, and the FL Panhandle as having 30-60% chances for 3" in 6 hours. Snell Previous Discussion... 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 ...Southeast Florida... Added a MRGL risk for the urban corridor of southeast FL for Tuesday. PWs remain around 1.7-2.0" and the overall pattern remains similar to previous days as an upper ridge axis remains near and to the south of the region. This likely leads to a diurnal cycle of thunderstorms developing along a weak axis of convergence along the coast, with these storms slow to move and eventually weaken before sunset. Given the overlap of these storms, the potential for 2"/hr rates, and the highly sensitive urban corridor of southeast FL a MRGL risk was introduced for this time period. Snell 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 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 towards the central/western Louisiana coastline by Thursday morning. Immediately in advance of the center of this low, heavy rains will continue into the upper Texas Gulf coast 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. Uncertainty remains with the speed and therefore eventual eastward progression of this are of low pressure, which impacts where confidence exists in flash flood impacts by Wednesday. Guidance today has trended faster and east, which prompted the expansion of the MDT and SLGT risk areas across LA. More changes are likely as guidance comes into better agreement on the location and speed of this system. 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. If guidance continues to hedge eastward the risk level could be lowered for southeast TX on Day 3. Wegman/Snell ...Midwest... 20Z Update... Only change to this outlook area with to shrink the MRGL and SLGT on the northern section of the area where instability will be limited across central WI and the northern L.P. of MI. Otherwise, the forecast for scattered flash flooding appears to remain consistent with latest model guidance. Snell Previous Discussion... 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... 20Z Update: The main changes for the D4 period were the expansion of the risk areas, including the MDT risk, further eastward to account for the trends in being slightly faster with the PWAT surge and mid-level vorticity ejection. This was noted within the global ensemble means and correlated with a slight uptick in the pQPF probs for the 1/2/3 inch thresholds. Maxima within the probs was noted across south-central MS, expanding east to right around western AL. Highest confidence given probability consensus was across southern MS, so decided to align the MDT over the region encompassing much of the Jackson, MS CWA bounds. The SLGT risk was also expanded further east and north to account for the anomalous PWAT advection regime anticipated by mid-week and beyond. The expansion was to target the southern Appalachian front with emphasis on northern GA into the escarpment of SC and western NC. We'll be monitoring the trends closely as a further east push would indicate a further expansion of the risks to the east, including more of the I-20 corridor where Birmingham, AL and even potentially Atlanta, GA becoming in play for a higher risk. In any case, it's certainly the period to watch in the medium range for enhanced impacts. D5 is when we hit the back end of the more appreciable rainfall prospects, however lingering deep layer moisture of tropical origin will still allow for efficient warm rain processes and the ability for continued heavy rainfall through a good portion of the Southeastern U.S. up into the Southern Appalachians. The main change was an expansion of the SLGT risk further north through the southern Appalachians with a northern advancement into southwestern VA. There's some discrepancy on the eastward extent of the heaviest precipitation, however there was enough consensus to bring the SLGT north in the terrain and maintain the high-end SLGT posture across the Central Gulf coast into interior AL/MS. Kleebauer ..Previous Discussion.. 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 Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt $$