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   QPFERD   
      
   Excessive Rainfall Discussion   
   NWS Weather Prediction Center College Park MD   
   328 AM EST Mon Nov 17 2025   
      
   Day 1   
   Valid 12Z Mon Nov 17 2025 - 12Z Tue Nov 18 2025   
      
   ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF   
   SOUTHERN CALIFORNIA...   
      
   A vigorous mid-level wave (initially centered near 39.9N, 125.5W=20   
   at the start of the forecast period) will migrate south-   
   southeastward along the California coast today while cutting off=20   
   from westerlies farther north. As this occurs, strong ascent=20   
   (associated with areas of 0.3-0.6 inch/hr rain rates in northern=20   
   California this morning) will spread southeastward along a cold=20   
   front and also within a robust upslope regime on the western sides=20   
   of the Sierra. 1-1.2 inch PW values near the coast and aforementioned   
   synoptic factors will foster several areas of 1-2 inch rainfall=20   
   totals, with locally higher amounts possible across the Transverse=20   
   Ranges of southern California.   
      
   The aforementioned front will result in a focused axis of heavy   
   rain that will translate from north to south along the southern   
   California coast. Across the Slight Risk area, this heavy rainfall   
   will occur over both sensitive locales (from recent burn scars and   
   debris flows) and urban/hydrophobic surfaces. The greatest   
   concentration of flash flood risk will likely occur across the=20   
   Transverse Ranges and adjacent areas of Los Angeles Metropolitan=20   
   area through tonight.   
      
   Outside of this area, models indicate very isolated, but slow-   
   moving convective activity beneath the upper low center across   
   northern and central California, with heavy rainfall potentially   
   falling over soaked ground conditions and burn scars. Isolated   
   flash flood potential cannot be ruled out here.   
      
   Lastly, the cutting off upper low will spread strong mid/upper   
   difluence across the Lower Colorado River Valley especially in the   
   03-12Z timeframe. Models are consistent in developing at least one   
   or two bands of convective structures that drift northward across   
   the area fairly quickly, but also result in localized training. One   
   or two instances of flash flooding cannot be ruled out in this   
   regime.   
      
   Cook   
      
   Day 2   
   Valid 12Z Tue Nov 18 2025 - 12Z Wed Nov 19 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20   
   THE SOUTHWEST AND LOWER GREAT BASIN...   
      
   Maintained the previous;y issued Marginal risk area over portions=20   
   of Arizona with little need for more than cosmetic changes in=20   
   deference to the model guidance. A closed low within a broader=20   
   trough digs southward along the the west coast of the US and then=20   
   starts to move inland late. The overall synoptic pattern seems to=20   
   be handled comparably by the ECMWF/GFS and UK models for much of=20   
   Day 2 but some of the subtle differences in the details result in=20   
   non-negligible differences in QPF and the attendant risk of=20   
   excessive rainfall.=20   
      
   Precipitable water values get near 2 standard deviations above normal   
   for this time of year in southern-western AZ and most-unstable=20   
   CAPE values climb above 500 J/Kg south of the Mogollon Rim and into   
   the deserts and Phoenix Metro. This will maintain the risk of=20   
   elevated (0.50"+) hourly rainfall rates Tue-Tue night as noted from   
   the RRFS exceedance probabilities (through 00Z Wed), while also=20   
   implied from the 16/12Z RRFS 3-hourly QPFs. Much like the models=20   
   from Sunday afternoon...the 24hr QPF guidance from the 17/00Z model   
   cycle has come up. At this point there is still not enough=20   
   confidence from a duration perspective to upgrade to a Slight Risk=20   
   over the lower terrain south of the Mogollon Rim, which would=20   
   conceivably include the Phoenix area, but the potential to do so=20   
   will exist over the next day or so. The machine-learning first=20   
   guess fields also highlight part of the Marginal risk area with=20   
   some spotty 5 to 10 percent of exceeding flash flood guidance. At=20   
   this point...the machine-learning covers only the first half of Day   
   2...so the upcoming day shift will have a complete look at the   
   objective guidance for the Day 2 period.=20   
      
   Bann   
      
      
   Day 3   
   Valid 12Z Wed Nov 19 2025 - 12Z Thu Nov 20 2025   
      
   ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF=20   
   SOUTH CENTRAL TEXAS TO A PORTION OF THE ARKANSAS RIVER VALLEY...   
      
   a mid- and upper-level trough will be making its way eastward   
   across portions of the southern Great Basin on Wednesday and into=20   
   early Thursday. East of that system...low level moisture will start   
   to be drawn northward with dewpoints in the 60s by Wednesday afternoon   
   which should help feed showers and thunderstorms from the afternoon   
   into Wednesday night/early Thursday morning. Most unstable CAPE=20   
   pushes 1000 J per kg and precipitable water values in excess of=20   
   1.5 inches becomes established from parts of south-centrsl Texas=20   
   into eastern Oklahoma and western Arkansas. Based on the=20   
   GEFS...the precipitable water axis is roughly between 2 and 2.5=20   
   standardized anomalies above climatology for this time of year.=20   
   Based on that combination...suspect locally heavy rainfall rates=20   
   are possible. There has been a tendency for the upper trough to=20   
   slow its forward speed with a similar delay in convection=20   
   initiation. With the event spanning into Thursday with broader=20   
   areal coverage and an increasing risk of excessive rainfall (see=20   
   WPC Medium Range graphics and discussions for further=20   
   details)...opted to maintain the Marginal risk on the uncertainty=20   
   of timing.   
      
   Bann   
      
      
   Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/94epoints.txt__;!!DZ3fjg!6RWdsHX1zuvkXXWz4tPxvapEvFB8U_OyI9yetb6ynN3w=   
   OQNNW-Z81E_Zj9WG6O6hHKPPdgnOtRQK999WJMJMfRokc-o$=20   
   Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/98epoints.txt__;!!DZ3fjg!6RWdsHX1zuvkXXWz4tPxvapEvFB8U_OyI9yetb6ynN3w=   
   OQNNW-Z81E_Zj9WG6O6hHKPPdgnOtRQK999WJMJMQ8CVD-Q$=20   
   Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=   
   v/qpf/99epoints.txt__;!!DZ3fjg!6RWdsHX1zuvkXXWz4tPxvapEvFB8U_OyI9yetb6ynN3w=   
   OQNNW-Z81E_Zj9WG6O6hHKPPdgnOtRQK999WJMJMuveNg0M$=20   
      
   =3D =3D =3D   
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