FOUS30 KWBC 060044 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 844 PM EDT Tue May 5 2026 Day 1 Valid 01Z Wed May 06 2026 - 12Z Wed May 06 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE MEMPHIS METRO AND SURROUNDING AREAS... ...01Z Update... The western flank of the Marginal Risk area was trimmed down given the waning instability in wake of the cold front. The Slight Risk area was moved a little farther south in southwest TN and northern MS to align with the moderate chances (40-60%) for >2" of rainfall between 01-12Z depicted by the 18Z HREF. There were also some low chance probabilities (20-305) for localized rainfall totals over 3" in northern MS. The Memphis metro area remains most at-risk for potential flash flooding due to its greater urbanization, but with SPC mesoanalysis showing over 500 J/kg of MLCAPE available and PWs over 1.6", rainfall rates of 2"/hr could occur and support localized flash flooding in poor drainage areas east and south of Memphis. Mullinax --Previous 16Z Discussion--- In collaboration with MEG/Memphis, TN forecast office, a Slight Risk upgrade has been introduced with this update for the Memphis metro and surrounding areas. Ongoing locally heavy rainfall on the southern bow end of otherwise light rain near and over Memphis has dropped up to 2 inches of rain over small areas of northeastern Arkansas this morning. This morning rainfall, while all beneficial, is working to saturate the very dry soils in the area, while simultaneously moistening the atmosphere. Behind the line of rain this morning, a much more moist and unstable air mass moves in from the south and west. PWATs across western Tennessee and surrounding areas rise well above 1.5 inches, while instability over southern Arkansas could rise above 2,000 J/kg of MUCAPE. This evening and tonight, as a cold front approaches from the north and the nocturnal LLJ to the south strengthens, a renewed round of showers and thunderstorms are expected to develop across Arkansas and southwest Tennessee before moving into Mississippi. As the storms are forming into a line, there will be increased potential for training. As this appears likely to occur over the same areas currently picking up up to 2 inches of rain, expect a small area of higher potential for flash flooding. For northeastern Arkansas, there was more rain there this morning, so the soils will be more primed by tonight. Meanwhile for southwest Tennessee, in addition to the ongoing rainfall, urban concerns around the Memphis metro could also support more widely scattered instances of flash flooding. Once the line moves into northern Mississippi late tonight, the storms are expected to organize into one progressive line, which should limit any flash flooding concerns to isolated instances. Across southern Arkansas, the storms, while strong and capable of heavy rainfall rates, are likely to be much more widely scattered. They will be unlikely to train in such a way as to cause more than isolated flash flooding, especially considering the very dry soils in place there. Wegman Day 2 Valid 12Z Wed May 06 2026 - 12Z Thu May 07 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE INTERIOR SOUTHEAST... ...19Z Update... A broad expansion to both the Slight and Marginal Risks was introduced with this update, in collaboration with BMX/Birmingham, AL and FFC/Peachtree City, GA forecast offices. The high-resolution guidance left a lot to be desired as to the expected evolution and convective footprint with all of the storms expected on Wednesday. Generally speaking, most of the guidance suggested there would be a bimodal distribution to the heavy rainfall. The northern peak in rainfall will occur first, on Wednesday morning, with the remnant convection associated with the diurnally-weakening LLJ aimed along Tennessee's southern border. Fast-moving, but training convection may continue from northern Alabama east into far western North Carolina through the day, though the guidance is far from unanimous as to how strong that convection will be. On the surface of it, it appears that the steady supply of moisture and instability should favor continued convective development through the midday, and any convection should be strong enough to produce 1-2 inch per hour rainfall rates. Further, the topography of the GA/NC/TN border region would also support that runoff converting to flash flooding. A higher end Slight, albeit an uncertain one, was introduced for this area, to highlight the possibility of multiple inches of rain in a few hours causing scattered instances of flash flooding. In keeping with past trends, the Slight and Marginal further south across Mississippi, Alabama, and Georgia continued to expand southward, as simulated convection in the guidance continues to favor the refiring of storms further south with the front on Wednesday evening. After the morning and early afternoon rains further north, the front should sink to the south during the afternoon, with scattered convection still around in some areas. By Wednesday evening, the restrengthening of the LLJ will allow for a blossoming of storms in a line along the front, leading to a renewed maximum of rainfall. Most of the guidance suggests this line sets up from just south of Birmingham to about midway between Birmingham and Montgomery, and just south of Tuscaloosa. Rainfall amounts suggest this should be the more significant of the two areas as far as totals are concerned, with more moisture and instability advecting into the front than areas further north earlier in the day. The area remains very dry soil-moisture-wise, so it will take a lot of rainfall to result in significant flash flooding. While this is likely to occur somewhere in this area, the unsurprising lack of agreement on where this will occur and the buffering a dry environment gives to the prospects of flash flooding did keep the area from upgrading to a Moderate Risk for now. However, further increases in expected rainfall and better agreement in the guidance would result in an upgrade with future updates. Wegman ...Previous Discussion... Maintained the slight southward shift of the previously issued Slight Risk area introduced a couple of days ago. The coverage and rainfall intensity should be increasing on Wednesday as a large scale trough over the northern Plains continues to amplify and result in a 140 kt to 160 kt upper level jet over the Tennessee Valley during the latter part of the period. The resulting upper divergence, steepening mid-level lapse rates and increasing moisture and instability should result in convection capable of producing heavy rainfall rates and embedded areas of rainfall amounts of 3 to 5 inches as suggested by the latest run of the RRFS. There is a fairly wide spread in the north/south placement of that heavier axis. As a result...the Slight area was expanded somewhat and tended to cover the greatest overlap of higher QPF and exceedance probabilities. Thinking is that there are some probabilities supportive of a higher-end slight risk embedded within the broader Slight. The continued amplification of the upper trough should keep the convection moving southward with time during the overnight hours. Bann Day 3 Valid 12Z Thu May 07 2026 - 12Z Fri May 08 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE GULF COAST REGION INTO THE SOUTHEAST... ...19Z Update... Abundant moisture along a stalled frontal boundary on Thursday will support additional thunderstorm formation along the front. Rapidly weakening forcing will greatly diminish convective coverage along the Gulf Coast and into central Georgia and South Carolina as compared with Day 2/Wednesday. The only significant change from the previous outlook was to extend the Marginal back through Houston, due to the potential for isolated convection that will still be capable of very heavy rainfall. Should an eventual Slight be needed, it would likely focus along the urban I-10 corridor from New Orleans east through Pensacola. Wegman ...Previous Discussion... Showers and thunderstorms along and ahead of a surface cold front will be lingering into Thursday from parts of the Gulf coast region northeastward into parts of Georgia and South Carolina. At this point...rainfall rates look to be decreasing as the better upper level dynamics pull off to the northeast and low level flow becomes directed along...rather than normal...to the front. Maintained a Marginal Risk area where there could be overlap with areas somewhat higher soil moisture content from recent rainfall. Overall the rainfall looks to be more beneficial than not. Bann 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