2013-03-06 FCST: CA

[R R Smith]

Another post frontal tornado setup is possible for the Sacramento Valley tomorrow afternoon. An upper level low pressure system will affect the northern California this evening through late tomorrow. With the passage of the cold front tomorrow afternoon, conditions could be right for rotating storms and possibly a weak tornado. The NAM is showing 50 knot SW 500 flow and orographically backed 20 knot SE winds at the surface along the east side of the Sacramento Valley in the late afternoon, especially from Yuba City north past Chico. Some afternoon sunbreaks could get the CAPE cranking up towards 500 J/kg. This combined with steep lapse rates should be more than adequate for a low topped rotating thunderstorm. Dew points will be modest - in the low 40's. Whether or not the sun decides to shine will probably be the difference.

If I were able to chase (unfortunately I have to work), I would head south from Shasta Valley in central Siskiyou County through the Mt. Shasta area which will be under a winter storm warning. Quite a contrast to chasing in the Plains - which will have to wait for me until mid May when I have my driver/guide stint with Tempest Tours.

 

[David Biggar]

Numbers looked great this AM, but for the most part cirrus clouds took away much of the needed energy. RAP and RUC #s started trending back on CAPE and increased the LIs in the 18Z run which suggested the prime environment was most likely passing. Shear environment looked good backed by a healthy lee side trough setting up to deflect winds to an almost SE flow in a few spots with winds really ripping aloft...probably provided some really good venting up there. Shear values for SFC-1km and SFC-6km were moving into the correct region for "any tornado." (see chart at bottom)

We did get several smaller cells that produced small hail. What did pop had some characteristics of weak rotation. Another issue was a power outage at the NWS, knocking out the primary radars for the Sacramento Valley (Beale BBX and Davis DAX), so we were flying blind for ~1.5hrs...who knows what happened during that time.

Timing of the initial front was perfect, giving us time to clear out and warm up, but nothing...darn. I hope for better luck on the next system (whenever that is )


Shear Chart from NWS Sacramento: