633 FOUS30 KWBC 082029 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 PM EDT Fri May 8 2026 Day 1 Valid 16Z Fri May 08 2026 - 12Z Sat May 09 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF SOUTHEASTERN LOUISIANA AND SOUTHERN MISSISSIPPI... ...16Z Update... The overnight Slight Risk area was maintained as an area of training showers and thunderstorms take shape across Louisiana and Mississippi. 12Z HREF and RRFS EAS neighborhood probabilities continue to depict a high probability of rainfall exceeding 2 inches in the highlighted area. This aligns with the location of an instability gradient/stationary front analyzed near the Gulf Coast which will focus convection today. Otherwise, the forecast in South Texas remains somewhat uncertain, with some 12Z CAM guidance trending more dry in the area. However, based off of the synoptic setup and moisture profiles outlined previously, thunderstorm clusters capable of producing isolated flash flooding certainly remain plausible. Thus, the Marginal Risk was kept in for this update. Asherman ...Previous Discussion... ...Lower Mississippi Valley/Central Gulf Coast... A robust moisture pool is expected to deepen along the central Gulf Coast today as southwesterly winds amplify ahead of energy moving out of eastern Texas and the northwestern Gulf. This flow will support PWs climbing to around 2 inches along a slow-moving front, or more than 2.5 std dev above normal. The majority of the CAMs are in good agreement indicating a corridor of training convection developing by the afternoon across southeastern Louisiana and southern Mississippi. Given the high moisture content and potential for training, localized totals of 2-3+ inches are possible. High hourly rates within these training storms will pose a risk for flash flooding, particularly in low-lying and urban areas, with the highest potential impact centered along the I-10 corridor. The introduced Slight Risk area reflects high neighborhood probabilities shown by both the HREF and RRFS for amounts exceeding 2 inches. ...South Texas... Farther west, a well-defined mid-to-upper level shortwave/low moving through northern Mexico into West Texas will provide increasing ascent. Moist southerly flow interacting with this feature and upslope into the Sierra Madre Oriental will support storms developing over northeastern Mexico. While much of this activity may remain south of the international border, there are some hi-res members that show some of these convective clusters moving into South Texas. Though model spread is higher in this region, both the HREF and RRFS indicate that localized totals exceeding 2 inches are possible. Therefore, a Marginal Risk was maintained to account for this potential. Pereira Day 2 Valid 12Z Sat May 09 2026 - 12Z Sun May 10 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHEAST LOUISIANA AND EXTREME SOUTHWEST MISSISSIPPI... After coordination with LIX, a Slight Risk was hoisted over Southeast Louisiana roughly along the I-10 corridor. By 12Z tomorrow morning, CAM guidance shows fairly good agreement in depicting a training signal within an overnight MCS forecast to track towards the Central Gulf Coast. Ahead of the complex, a moist and unstable airmass characterized PW values near 1.75-2" and MUCAPE of 1500-2000 J/kg should favor rainfall rates exceeding 2"/hr within the most intense cells -- locally even higher where cell mergers occur. As this activity overlaps with ongoing heavy rainfall in Southeast Louisiana, additional scattered flash flooding could result with 2-4" expected in the main training axis. Asherman Day 3 Valid 12Z Sun May 10 2026 - 12Z Mon May 11 2026 ...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF NORTHEASTERN TEXAS, SOUTHEASTERN OKLAHOMA, SOUTHERN ARKANSAS, AND NORTHERN LOUISIANA... Little change was made to the outlook as a shortwave dives into the base of broader scale trough and drives a cold front southward across the region. Southerly flow ahead of the boundary will boost PWs to over 1.5 inches. This moisture, combined with favorable right entrance region ascent, will support storms developing along and ahead of the front. Model spread remains too high to support a higher risk category within the broad Marginal Risk, while antecedent conditions in the region are quite dry. That said, there remains a signal in the global and AI guidance for some areas of training and repeating cells to develop in any MCS that forms on Day 3. Locally intense rates within some areas of repeating cells could result in isolated flash flooding. Asherman/Pereira 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