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   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   800 PM EST Wed Nov 19 2025   
      
   Day 1   
   Valid 01Z Thu Nov 20 2025 - 12Z Thu Nov 20 2025   
      
   ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF   
   SOUTH-CENTRAL TEXAS, INCLUDING PORTIONS OF THE HILL COUNTRY...   
      
   ...Texas...   
   A targeted Moderate risk was maintained across portions of south   
   central TX, including portions of the Hill Country. The 18z HREF=20   
   and REFS show increasing probabilities of 1"/hr rainfall by=20   
   04z-05z, increasing further after 06z. The pattern is favorable=20   
   for localized areas of heavy rainfall by late tonight into the day   
   Thursday. PWs will be above the 90th percentile, with abundant low   
   level moisture advecting in from the Gulf, and mid and upper level   
   moisture out of the Pacific ahead of the approaching upper low.=20   
   Instability will be sufficient deep convection and high=20   
   rates...thus the extent of the flash flood risk will come down to=20   
   the longevity of these higher rates. Cells should initially be=20   
   rather quick moving of to the Northeast, however as low level flow   
   increases we should tend to see an increasing=20   
   backbuilding/training component to the convection. This should be=20   
   enough to result in an uptick in the flash flood risk.   
      
   Both the 18z HREF and REFS have high neighborhood probabilities of   
   exceeding 3" by 12z Thursday over the Moderate risk area. The most   
   recent 23z run of the HRRR as rainfall of 3-5" over this same=20   
   period. The rainfall continues into Thursday, with another uptick=20   
   in rainfall intensity and potential backbuilding convection by mid=20   
   morning into the early afternoon as large scale low level=20   
   convergence increases. Thus it still appears like the highest=20   
   chances for significant flash flooding is after 12z Thursday, when   
   this 2nd round convection potentially trains over areas that have=20   
   already received heavy rainfall and are thus saturated. In fact,=20   
   the REFS probabilities of exceeding the 24hr 100yr ARI are as high   
   as 25%, with the HREF around 10%. This is indicative of the higher   
   end impact potential Thursday should both rounds of convection=20   
   materialize over the same portion of the Hill Country.   
      
   Even though the higher probability threat is likely tomorrow, the=20   
   flash flood risk tonight should not be understated. While the model   
   consensus of upwards of 3-5" through 12z would result in some flash   
   flooding, there is certainly a possibility that enhanced=20   
   backbuilding results in more localized totals over 5" in just a=20   
   couple hours...which would likely be enough to produce significant=20   
   flash flooding over these more flood prone areas. Thus a Moderate=20   
   risk remains for both tonight and tomorrow across this corridor.=20   
   The Moderate risk areas are quite small, but in reality the axis of   
   most extreme rainfall and higher end impacts will likely be even=20   
   narrower than these risk areas. However predicting exactly where=20   
   this occurs is not feasible, warranting the slightly larger risk=20   
   areas to account for location uncertainty.   
      
   ...Southwest...   
   A Marginal risk was maintained for portions of AZ and NM. The   
   approaching upper low will result in continued showers and embedded   
   thunderstorms into the overnight period. The highest rainfall rate   
   potential is likely this evening over central AZ, but this should=20   
   be isolated and generally on a downward trend into the overnight.=20   
   The highest areal averaged rainfall (~1") will be across portions   
   of southwest NM, but lower instability should keep these rates=20   
   mostly at 0.5"/hr or less. Thus overall the flash flood threat=20   
   should stay isolated in nature.   
      
   Chenard   
      
      
   Day 2   
   Valid 12Z Thu Nov 20 2025 - 12Z Fri Nov 21 2025   
      
   ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF   
   SOUTH-CENTRAL TEXAS, INCLUDING PORTIONS OF THE HILL COUNTRY...   
      
   ...20z Update...   
      
   A couple of significant changes to the outlook areas for this   
   update.   
      
   This first is to introduce a targeted Moderate Risk upgrade for   
   the same areas as detailed for Day 1. This is due to increasing   
   likelihood for localized 5"+ storm totals beyond the 12z Thursday   
   Day 1/2 cut- off, which may result in numerous instances of flash   
   flooding in a relatively small area (with higher confidence overall   
   in locally significant flash flooding as opposed to the total   
   areal coverage). While 6-hr FFG exceedance probs from the HREF are   
   below 20% through the end of Day 1, they increase meaningfully to   
   near 60% going into Day 2 (through 18z Thu).   
      
   The second significant change was to split up the larger Slight   
   Risk area into two distinct areas, 1) South-Central TX and 2)   
   eastern OK into northern AR and southern MO. This reflects the   
   consensus of the latest CAM guidance which suggests a large gap in   
   convection across North TX during the period (with questions still   
   lingering regarding the eastward extent of both the South-Central   
   TX and Ozarks clusters of convection into the later half of Day 2).   
      
   Churchill   
      
   ..Previous Discussions..   
      
   ...Southern Plains...   
      
   The environment continues to becomes more supportive of storms   
   capable of producing heavy to potentially excessive rainfall as the   
   flow aloft backs over portions of Texas and Oklahoma and becomes   
   increasingly diffluent as an upper trough approaches the region. At   
   lower levels...an airmass with precipitable water values gets   
   drawn northward an converges along a surface front over parts of   
   Texas and Oklahoma. Excessive rainfall is possible by means of   
   intense rainfall rates by individual storms in regions with the   
   highest amount of instability (presumably ahead of the approaching   
   cold front) and by training of cells/multiple rounds of convection   
   (more of a factor where synoptic scale forcing and mesoscale   
   forcing act in tandem farther north). The axis of highest   
   precipitable water values... 1.5-1.75"... sets up over the eastern   
   half of Texas into southeastern-most Oklahoma and into Arkansas.   
   Those values are well above average for mid-November. Localized   
   rainfall amounts up to 2.5" in an hour with additional local totals   
   of 5" possible within this set up which would result in scattered   
   instances of flash flooding.   
      
   ...California...   
      
   Maintained a Marginal Risk area from continuity for portions of   
   coastal Southern California as the next area of low pressure over   
   the eastern North Pacific drops southward off the California coast   
   and brings another round of rainfall Thursday into early Friday.   
   Rainfall amounts at this point look to be pretty modest but the   
   rain will be falling on areas where antecedent conditions have   
   been wet for the better part of 5 or 6 days. That may result in   
   additional localized flooding on Thursday or Thursday night.   
      
   Bann   
      
      
   Day 3   
   Valid 12Z Fri Nov 21 2025 - 12Z Sat Nov 22 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF   
   THE OHIO VALLEY AND PORTIONS OF THE SOUTHWEST US...   
      
   20Z Update: Limited changes necessary from the previous forecast due   
   to general run-to-run continuity. Heaviest rainfall still trending   
   closer to the southern Peninsular Range with an extension of   
   convection back over the southeast CA deserts and southwest AZ for   
   the MRGL over the west. Moderate to locally heavy rain possible for   
   the Ohio Valley. Steady forward propagation of broad QPF shield   
   should limit the necessity for more than the current MRGL risk. Will   
   assess the southern portion of the risk area closely in the coming   
   days as this region, extending into the Southeast CONUS will be most   
   coincident with a purely convective regime as instability is   
   prevalent within a broad, but modest theta_E depiction. This area   
   would promote higher rate potential, but could be a case where   
   forcing is not enough to activate the better thermodynamic   
   environment. For now, maintain relatively continuity of the MRGL   
   with some minor adjustments overall.   
      
   Kleebauer   
      
   ..Previous Discussions..   
      
   ...Ohio Valley...   
      
   Rain will be spreading northward and eastward from the Plains on   
   Day 2 into the Ohio Valley on Friday and Friday night in   
   association with the surface low coming out of the mid-Mississippi   
   Valley. Between above normal levels of moisture being transported   
   into the region from the south and flow aloft becoming confluent...   
   there is still the possibility for isolated downpours that lead to   
   spotty problems from run-off despite the set up becoming less   
   favorable with time.   
      
   ...Southwest US...   
      
   A mid- and upper-level trough with an embedded closed low will   
   continue to drop southward on Friday...with an embedded closed low   
   expected near the US border with Mexico by 00Z on Saturday. Showers   
   and embedded thunderstorms should be developing in the highly   
   diffluent flow to the east of the trough where precipitable water   
   values approaching an inch rotate into southern California and   
   western Arizona. Opted to remain at a Marginal threshold given the   
   timing of the best upper support but a Slight may still be needed.   
      
   Bann   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!6K4lPdv3xrSBM669JtbPghpQXJhUJINEortaCvhDnA3X=   
   7Gj6Wj5xZueYfIAhRljOtTwATYgHdNznWlXPin6lVxqRXXI$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!6K4lPdv3xrSBM669JtbPghpQXJhUJINEortaCvhDnA3X=   
   7Gj6Wj5xZueYfIAhRljOtTwATYgHdNznWlXPin6l5kAnZOM$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!6K4lPdv3xrSBM669JtbPghpQXJhUJINEortaCvhDnA3X=   
   7Gj6Wj5xZueYfIAhRljOtTwATYgHdNznWlXPin6lkdRFka4$=20   
      
   =3D =3D =3D   
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