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   FOUS30 KWBC 211858   
   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   158 PM EST Fri Nov 21 2025   
      
   Day 1   
   Valid 16Z Fri Nov 21 2025 - 12Z Sat Nov 22 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF   
   SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA...   
      
   16z update:   
      
   ...Southern California/Lower Colorado River Valley...   
      
   GOES-W shows solid Atmospheric River has turned westward into the   
   TROWAL north of the initial closed low/occluded surface low across   
   southern California. This has directed enhanced (95th-99th   
   percentile) moisture and moisture flux across the Imperial Valley,   
   Mojave Desert and Lower Colorado River Valley to maintain enhanced   
   rainfall potential. Some filtered insolation may allow for   
   increased instability later this afternoon especially within the   
   Lower Colorado, for some scattered thunderstorm development capable   
   of .5-1"/hr rates and localized 1-1.5" totals.   
      
   The strong upstream digging shortwave on the western side of the   
   upper-level closed low will elongate the pattern from NNE to SSW   
   over the California Bight which will stall the frontal zone and   
   moisture plume. While most of the flux will be directed toward NW   
   Baja California, this will also maintain the placement of the AR   
   across the areas that longer duration light to moderate showers   
   could result in longer duration FFG exceedance (6+hr) as well. As   
   such, the the current Slight Risk in place remains solid. Have   
   expanded the Marginal Risk a bit further northwest into the   
   southern San Joaquin Valley to account for the longer term trends   
   of persistent TROWAL moisture flux across the area.   
      
      
   ...Lower Missouri, Ohio and Tennessee River Valleys...   
      
   12z CAMs along with 06z/12z HREF probabilities continue a show a   
   downward trend with only a few locations of 1"/hr or 1"/3hrs   
   reaching above 25% across Middle TN and S KY. Additionally,   
   observational trends depict the deeper moisture and more   
   unstable/warmer air has been trending south and eastward with a   
   broadening of the drier EML extending through the Delta Region   
   of the Lower MS Valley, further severing needed moisture   
   connection to the the Gulf. In coordination with local forecast   
   offices and river forecast centers, it was determined to remove the   
   Marginal Risk area from the eastern third of the U.S. Please note,   
   this does not remove the potential for an isolated incident or two   
   of flash flooding/FFG exceedance across the area, but the coverage   
   potential is considered less than 5%.   
      
   Gallina   
      
      
      
   ~~~~Prior Discussion~~~~   
   Showers and thunderstorms are expected across southern California,   
   southern Nevada and southwest Arizona as lobes of vorticity rotate   
   to the east of the low offshore. Instability appears to be on the   
   weak side which will likely be a limiting factor, however some   
   brief heavier rates are still possible from short training segments   
   within the deep layer southerly flow. A Slight Risk for excessive   
   rainfall remains in effect for southern California and southwest   
   Arizona and a Marginal Risk spans from the California coast to   
   south-central Arizona.   
      
   For the Missouri/Ohio/Tennessee Valleys there will be an elevated   
   threat for locally excessive rainfall. During this period a steady   
   stream of above average moisture will be transported northward and   
   encounter an east-west boundary. Isolated areas of moderate to   
   heavy rainfall that leads to spotty problems from run-off can be   
   expected. However...the flow aloft becomes increasingly flat and   
   confluent during the day which will reduce the risk of any   
   excessive rainfall. A Marginal Risk area was maintained from   
   eastern Kansas to West Virginia/western Virginia/western North   
   Carolina.   
      
   Campbell   
      
      
   Day 2   
   Valid 12Z Sat Nov 22 2025 - 12Z Sun Nov 23 2025   
      
   The probability of rainfall exceeding flash flood guidance is less   
   than 5 percent.   
      
   Churchill/Campbell   
      
      
   Day 3   
   Valid 12Z Sun Nov 23 2025 - 12Z Mon Nov 24 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF   
   THE SOUTHERN PLAINS...   
      
   ...20z Update...   
      
   Maintained the inherited Slight Risk with only minor adjustments   
   made, primarily to shift the axis slightly south to southwest and=20   
   tighten the gradient along the north and south. This reflects the=20   
   latest trends in QPF, which are fairly tightly clustered for this=20   
   time range (relatively high spatial confidence). This is somewhat   
   concerning, as this brings the forecast axis of QPF even more into   
   alignment with areas that realized heavy rainfall in prior days.=20   
   However, the categorical outlook is still held at a Slight Risk=20   
   due to a combination of meaningful time between the prior event   
   and the upcoming event (three full days inbetween should allow for   
   soil moisture and streamflow recovery) and uncertainty with regard   
   to the amount of training and resultant QPF (with most of the new=20   
   guidance suggesting localized 2-3" totals, while some solutions,   
   including the downscaled 12z ECMWF, depict localized totals of up=20   
   to 4-5").   
      
   Churchill   
      
      
   ...Previous Discussion...   
      
   The low pressure system that brought heavy rainfall for the West   
   Coast during the Day 1 period will be exiting into the Southern   
   Plains and the warm, moist air will support scattered to widespread   
   heavy rainfall. There is an increasing signal that this setup could   
   be a significant event, especially for north-central portions of   
   Texas and into southern Oklahoma where a couple of solutions are   
   suggesting a narrow swath of 4 to 6 inches possible. A Slight Risk   
   for excessive rainfall is in effect for for much of north-   
   central/northeast Texas and south/east Oklahoma. A broader Marginal   
   Risk spans from the Big Bend vicinity to southwest Missouri and   
   western Arkansas. This part of the country will continue to be   
   monitored for a possible upgrade to a Moderate with future updates.   
      
   Campbell   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!4_ZzqUAF4sMff32qvYRAQ-G3VBOxR_fbSkn64pNv0Jvw=   
   RWBg1QlPeokKvGcX2e5d1_ITwfBxTGrulV5T7YbdQVaGgS0$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!4_ZzqUAF4sMff32qvYRAQ-G3VBOxR_fbSkn64pNv0Jvw=   
   RWBg1QlPeokKvGcX2e5d1_ITwfBxTGrulV5T7YbdLiPPQ5A$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!4_ZzqUAF4sMff32qvYRAQ-G3VBOxR_fbSkn64pNv0Jvw=   
   RWBg1QlPeokKvGcX2e5d1_ITwfBxTGrulV5T7Ybd9IWYM8U$=20   
      
   =3D =3D =3D   
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