Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 356 PM EDT Sun Jun 14 2026 Day 1 Valid 16Z Sun Jun 14 2026 - 12Z Mon Jun 15 2026 Day 2 Valid 12Z Mon Jun 15 2026 - 12Z Tue Jun 16 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER SOUTH TEXAS... ...Southeastern Texas to the Lower Mississippi Valley... In coordination with the Brownsville and Corpus Cristi offices, we have introduced a Moderate Risk area to South Texas for this Excessive Rainfall Outlook. Though there remains uncertainty in the path/strength of the mid-level system over northeastern Mexico, most of the guidance does bring it to the US/Mexican border by 12Z Tue, acting as a trigger to the moisture-laden atmosphere with PWATs of over 2 inches up to near 2.5 inches (>99th percentile or +4 sigma). As this feature pushes northeastward out of the mountains of Mexico towards south Texas, it will not only increase the low level inflow of tropical moisture, but will provide ample forcing to organize the storms into slow-moving lines of training cells that track northward/northwestward with time up the Rio Grande. Any and all storms will have impressive amounts of moisture to work with to produce heavy rain given the fully saturated lower atmosphere all the way up to the tropopause per some forecast soundings. Instability due to extensive cloud cover commensurate with such amounts of moisture will likely be the only limiting factor for coverage of heavy rain. Focused the Moderate Risk on the highest HREF/REFS probs for heavier rain and some very robust CAM QPF (>5-8"), but with room to maneuver in subsequent issuances based on the rainfall that falls tonight.