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   FOUS30 KWBC 181824   
   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   124 PM EST Tue Nov 18 2025   
      
   Day 1   
   Valid 16Z Tue Nov 18 2025 - 12Z Wed Nov 19 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN   
   ARIZONA, FAR SOUTHEASTERN CALIFORNIA, AND FAR SOUTHEASTERN   
   NEVADA...   
      
   ...Southwest U.S...   
      
   16Z Update: Current radar and IR satellite composite continues to   
   indicate a broad area of diffluence within the eastern periphery of   
   a closed ULL situated just off the CA coast. Radar indications and   
   observational ground truth pinpoint some instances of locally   
   moderate to occasionally heavy rain this morning across western AZ,   
   alignment within the greatest MUCAPE and deepest moisture presence   
   in the proximity of 0.9-1.1" PWATs. Both 12z RAOB soundings out of   
   KVEF (Las Vegas, NV) and K1Y7 (Yuma, AZ) indicate relatively deep   
   saturation within the profile and PWATs well within the 90-99th   
   percentile overall for the time of year. These indicators are   
   textbook for more efficient rainfall prospects, especially with the   
   additional instability maxima expected later during prime   
   differential heating.   
      
   A more defined shortwave over Baja is currently progressing north-   
   northeastward with an indication of greater ascent being initiated   
   across southwest AZ at this hours as scattered convective pulses   
   begin materializing to the east of the Colorado River Basin. This   
   has been well-forecast within the CAMs on the hourly outputs, and   
   should maintain some persistence the next several hours with the   
   convective footprint shifting north within deep uni-directional   
   steering flow positioned along that eastern flank of the upper-   
   level circulation. This would put areas further north between   
   Prescott, AZ to Lake Havasu City, extending into the southern half   
   of Clark county in NV during the peak of the late-morning and   
   afternoon convective threat. Highest HREF neighborhood   
   probabilities for >2" of precip align within that general zone with   
   the highest probs >60% situated between Prescott and Lake Havasu   
   City. Considering the nature of the precip likely exhibiting more   
   convective schemes and the lower FFG presence in that area of the   
   Southwest CONUS, there is enough to warrant a continuation of the   
   SLGT risk from previous forecast with a broader MRGL encompassing   
   the lower deserts in AZ/NV/CA, including major metros of Phoenix   
   and Las Vegas proper.   
      
   Kleebauer   
      
   ..Previous Discussion..   
      
   Upper difluence will become quite pronounced over the Lower   
   Colorado River Valley today downstream of a strong mid-level trough   
   approaching from California. Meanwhile, pockets of surface heating,   
   near 50s F surface dewpoints, and cold air aloft will all combined   
   to support one or two focused bands of showers and thunderstorms   
   especially across western Arizona. These storms will migrate   
   quickly to the north given seasonably strong wind fields aloft for   
   steering. However, pronounced backbuilding should develop toward   
   the source region of nearly 1000 J/kg SBCAPE (across   
   southwestern/west-central Arizona) that should result in potential   
   for several hours of heavy rainfall. While local rates may not   
   exceed 0.5 inch/hr on a widespread basis, multiple hours of   
   convective training potential will support at least a few instance   
   of flash flooding as rainfall totals exceed 2 inches in several   
   areas from Mohave to Yavapai Counties. A Slight Risk has been   
   maintained for this outlook due to the aforementioned trends.   
      
   A few areas of heavier rainfall may also occur across southeastern   
   California during the afternoon and evening as the large/cold upper   
   trough moves into that area. Buoyancy should be a bit weaker   
   compared to farther east, although recent rainfall and relatively   
   wet soils suggests at least modest/isolated excessive runoff   
   potential. Marginal Risk remains in place for this scenario.   
      
   Cook   
      
   ...Ohio Valley...   
      
   16Z Update: Little change necessary in the previous forecast as the   
   prospects for flash flood remain within the lower threshold of a   
   MRGL risk, but still enough of a signal to warrant a general   
   continuation. CAMs are still in agreement on some convective   
   potential later today with the aid of some regional ascent stemming   
   from the passage of a relatively strong shortwave trough migrating   
   out of the Midwest through the northern Ohio Valley. Surface low   
   across the Mid-Mississippi Valley will shift eastward with a warm   
   front arcing over the Ohio River Valley with modest instability   
   focused along and south of the front. General convergence pattern   
   within proxy of the front will be the best area of interest for   
   some heavier convective cores which aligns well with the higher HREF   
   prob fields for >1" and >2" potential with modest signals for even   
   >3" located over northern KY into southern OH. The missing piece in   
   all this is a greater instability maxima, or any in that regard   
   with the signal leaning pretty mundane in that department for the   
   period. This should subdue the overall setup to warrant only   
   isolated flash flood instances with more of the rain leaning the   
   beneficial side of the proverbial impact coin. In any case, there's   
   just enough of a signal for a cell or two to potentially cause   
   problems over an area where 1 and 3-hr FFG's running between   
   1-1.5", matching the prospect rate in the forecast. This led to a   
   general continuity of the previous MRGL with some trimming on the   
   western edge to match trends in guidance.   
      
   Kleebauer   
      
   ..Previous Discussion..   
      
   Farther east across the Ohio Valley, models are all indicative of   
   scattered, west-to-east oriented convection that should gradually   
   propagate southeastward through much of the forecast period.   
   Substantial differences exists, however, with respect to peak   
   precip maxima - Nam solutions tend to favor higher precipitation   
   totals across southern Ohio/northern West Virginia on the nose of   
   confluent 850mb flow in that area. Other solutions and higher-res   
   guidance/CAMs point to more backbuilding and training across   
   Kentucky (and perhaps as far west as the MS/OH River Confluence).   
   The spread in solutions has necessitated broad expansions of the   
   inherited Marginal Risk across the region, although the likelihood   
   of widespread training and or greater-than-isolated flash flood   
   potential seems a bit on the low side. Modest PW values (around   
   1-1.25 inch) and instability (especially with eastward extent) also   
   support the notion of relatively isolated excessive runoff issues.   
      
   Cook   
      
      
   Day 2   
   Valid 12Z Wed Nov 19 2025 - 12Z Thu Nov 20 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF=20   
   SOUTH-CENTRAL TEXAS, THE CONCHO VALLEY, & THE TEXAS HILL COUNTRY...   
      
   The upper level trough moving across the Southwest US continues to   
   allow for sufficient coverage of scattered showers and embedded=20   
   thunderstorms into Wednesday across these areas for a Marginal Risk   
   threat level.  Localized flash flooding could continue to be a=20   
   concern.   
      
   Across the Southern Plains, low level-moisture will be drawn=20   
   northward with precipitable water values rising into the 1.5-1.75"   
   range, abnormally high for mid-November. When combined with   
   500-1500 J/kg of MUCAPE and 850 hPa inflow of ~25 kts, the   
   development of organized convection late Wednesday night into=20   
   early Thursday morning is becoming increasingly likely in and near   
   South-Central TX. Hourly rain amounts to 2.5" and local totals to   
   5" are anticipated early Thursday morning. This potential led to a   
   new Slight Risk which was coordinated with the EWX/New Braunfels   
   and SJT/San Angelo forecast offices. Its footprint was most in line   
   with the 06z REFS 30%+ chance of 3"+ amounts.   
      
   Roth   
      
      
   Day 3   
   Valid 12Z Thu Nov 20 2025 - 12Z Fri Nov 21 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF   
   THE SOUTHERN PLAINS INTO ARKANSAS/MISSOURI...   
      
   ...Southern Plains...=20   
   The flow aloft backs over portions of Texas and Oklahoma and=20   
   becomes increasingly diffluent Thursday morning as an upper trough=20   
   makes its way from the southern Great Basin into and across the=20   
   southern Rockies. This configuration aloft with increasingly moist=20   
   flow in the low levels ahead of a surface cold front will foster an   
   environment producing excessive rainfall by means of intense=20   
   rainfall rates by individual storms and by training of cells/repeat   
   convection. The axis of highest precipitable water values...=20   
   1.5-1.75"...sets up over the eastern half of Texas into   
   southeasternmost Oklahoma and Arkansas, which is well above=20   
   average for mid- November. Localized rainfall amounts up to 2.5" in   
   an hour with additional local totals of 5" possible within this=20   
   set up which would result in scattered instances of flash flooding.   
   Changes to the risk areas were mostly confined with some paring=20   
   back of the Slight across OK.   
      
      
   ...California...=20   
   Maintained a Marginal Risk area from continuity for portions of=20   
   coastal Southern California as the next area of low pressure=20   
   produces another round of on-shore flow of moisture and associated=20   
   rainfall Thursday into early Friday. Rainfall amounts at this point   
   look to be pretty modest but will be falling on areas where=20   
   antecedent conditions have been wet for the better part of 5 days.=20   
   That may result in additional localized flooding on Thursday or=20   
   Thursday night.   
      
   Roth   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!-AhuzLXlNp76CrJ1p3PQso2xJf8yXSr3T3miBVeg5yoD=   
   7r_WSw5v2BJUcQOyo2vTekWHJBJRwfydi-PMuzXIjQ0Gjlo$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!-AhuzLXlNp76CrJ1p3PQso2xJf8yXSr3T3miBVeg5yoD=   
   7r_WSw5v2BJUcQOyo2vTekWHJBJRwfydi-PMuzXIy7oLkfs$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!-AhuzLXlNp76CrJ1p3PQso2xJf8yXSr3T3miBVeg5yoD=   
   7r_WSw5v2BJUcQOyo2vTekWHJBJRwfydi-PMuzXIK2Cb6oM$=20   
      
   =3D =3D =3D   
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