597 FOUS30 KWBC 190745 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 345 AM EDT Sun Apr 19 2026 Day 1 Valid 12Z Sun Apr 19 2026 - 12Z Mon Apr 20 2026 The probability of rainfall exceeding flash flood guidance is less than 5 percent. In coordination with CRP/Corpus Christi, TX and EWX/San Antonio, TX forecast offices, the inherited Marginal Risk across Deep South Texas was removed with this update. While there will be high moisture content (PWATs around 1.75 inches) and slow moving cells due to light steering winds across Deep South Texas, the lack of instability and very high FFGs will effectively squelch any flash flooding threat. MUCAPE values will struggle to exceed 300 J/kg through the day, which is simply not enough instability to generate the rain rates necessary to exceed the high FFGs. Wegman Day 2 Valid 12Z Mon Apr 20 2026 - 12Z Tue Apr 21 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTHERN CALIFORNIA... ...Northern California... A large upper level cutoff low located off the coast will drift eastward into northern California on Monday. The cutoff low will not have a connection to the tropics, which will limit both amount of moisture and any instability that can be transported into northern California. Despite that, as is typical of cutoff lows, the movement will be slow, which could allow for an extended duration of light to moderate rainfall. That rain will impact an area that has burn scars, urban areas (Bay Area), and steep terrain which favors localized flash flooding. Thus, the Marginal Risk is left unchanged with this update. ...South Texas... The inherited Marginal Risk over a portion of this area was removed with this update, in coordination with CRP/Corpus Christi, TX, EWX/San Antonio, TX, and HGX/Houston, TX forecast offices. As on Day 1/Sunday, the limiting factor once again will be a true lack of instability, with MUCAPE values again struggling to exceed a couple hundred J/kg anywhere in Texas. Thus, despite above normal atmospheric moisture, and below normal forward motions for any cellular convection that does form, the high FFGs and limited rainfall rates should continue to prevent any flash flood development. Wegman Day 3 Valid 12Z Tue Apr 21 2026 - 12Z Wed Apr 22 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF CALIFORNIA AND SOUTHEAST TEXAS... ...California... A cutoff large upper level low over the coast Tuesday morning will progress east/inland through Tuesday night. This will direct the southwesterly onshore flow further south and east across central California. A pocket of instability with MUCAPE values as high as 500 J/kg may move into central California during the day Tuesday as well. The primary forcing however will remain the steep slopes of the Sierras, where the greatest rainfall rates and amounts are expected. Due to the instability however, the more populous valley locations may also see periods of heavier rains, including across the Bay area and Sacramento. Burn scars and heavier rains into some of the coastal ranges and western Transverse Ranges could also result in localized flash flooding. Thus, the inherited Marginal risk was expanded south down the coast to Santa Barbara, while the Marginal in central California was left unchanged with this update. ...Southeast Texas... The Marginal Risk across southeast Texas was adjusted a bit to the northeast from inherited in keeping with the latest trends in the guidance, suggesting increased potential for heavier rains into the Houston area, and decreased potential around Corpus Christi. Unlike both Sunday and Monday, by Tuesday there's better agreement that the primary limiting factor, instability, will be less of a limiting factor. MUCAPE values are expected to rise above 1,000 J/kg across much of the MRGL risk area. Somewhat more saturated soils in the Houston area as a result of yesterday's rains could also have some lingering effects into Tuesday. Thus, the inherited Marginal was left largely unchanged with this update. Wegman 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