SPC AC 290530

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1130 PM CST Wed Nov 28 2018

   Valid 291200Z - 301200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   The risk for severe storms appears negligible across the U.S. today
   through tonight.

   ...Synopsis...
   In the wake of mid/upper troughing now progressing away from the
   Atlantic Seaboard, the westerlies have trended more zonal across
   much of the nation.  Generally dry and/or stable conditions prevail,
   with appreciable modification unlikely across most areas through at
   least this period.

   A developing southerly return flow across parts of the lower Rio
   Grande Valley and northwestern Gulf of Mexico may allow for modest
   moisture return in a plume inland of the Gulf coast, through parts
   of the southern Plains and northeastward toward the lower Ohio
   Valley, as the boundary layer over the western Gulf continues a
   gradual modification.

   At the same time, models continue to indicate that a significant
   short wave trough will progress inland of the California coast
   through southern portions of the Great Basin and Southwest today
   through tonight.  It appears that this will include the remnants of
   a lower/mid tropospheric cyclone, which are generally forecast to
   dig through the southwestern periphery of the larger-scale
   troughing, across much of central and southern California by 12Z
   Friday.  An influx of low/mid-level moisture from the subtropical
   Pacific preceding this feature, coupled with mid-level cooling
   associated with it, may contribute to sufficient destabilization to
   support at least low probabilities for thunderstorm activity.

   ...California...
   Given the somewhat modest mid-level cold core (around -24C at 500
   mb), and forecast weakening of the low/mid-level cyclone as it
   progresses inland,  severe weather potential associated with it
   still appears negligible.  The coldest air aloft is forecast to
   spread southeastward across the San Joaquin Valley during the
   afternoon hours, but it remains unclear from the output of the
   various models whether breaks in overcast will allow for substantive
   boundary layer warming and destabilization beneath it. 

   Strongest low-level wind fields may be confined to the weakly
   unstable post-frontal regime near coastal areas, south of San
   Francisco Bay through Santa Barbara County, where mean
   west/northwesterly flow in the lowest 5-6 km AGL may be on the order
   of 30-40+ kt during the afternoon hours.  Downward mixing of this
   momentum in the more vigorous convective cells may contribute to
   strong surface gusts, but any such activity seems likely to
   generally remain below severe limits.

   ..Kerr/Leitman.. 11/29/2018

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