The sounding shown here, modified for afternoon surface conditions, showed a buoyancy of only around 600 J/kg (preliminary, more detailed calculations of all buoyancy and shear paramenters are ongoing). However, shear profiles, as described below, were favorable for supercellular updrafts in some of the storms.
Note the directional (veering) and speed shear suggested by
the wind barbs on the right margin of the image.
For this sounding and hodograph, the following apply (these are
preliminary calculations and are subject to change): (a) CAPE=600
J/kg; (b) BRN=13; (c) 0-3 km Positive Shear=3.8 X 10 exp-3 s-1.
This 0000 UTC 5 March sounding was "polluted" by rain showers at the observation site. Thus, the low level wind information and the temperature sounding are not indicative of the environmental conditions. Note the stronger midlevel flow, compared to the morning wind information. The 0-3 km positive shear has increased from 3.8 X 10-3 s-1 to 4.7 X 10-3 s-1. Also of significance is the increase in 850 mb wind speed to 50 knots.
Combining the estimated buoyancy (based upon interpolated morning sounding) and shear yields a BRN of 9.3, within the range observed for modeled supercells.
The OAK hodograph showed favorable shear for development of supercells if buoyancy developed. Note the slight clockwise curvature in the lowest layers. The morning shear was nearly 4 X 10-3 s-1 for the 0-6km layer. The Bulk Richardson Number of approximately 13 (morning) [and 9 (afternoon)] (subject to change upon more detailed calculations) suggests that the buoyancy-shear combination was in the range for supercells.
Forecast hodographs for the Central Valley, in which strong
surface southeasterly flow prevailed AND a 1000 feet Above Ground
Level "barrier" jet in the eastern Valley developed,
had storm relative helicities in the range of 400 to 500 J/kg
(personal communcation, S. Weiss, Storms Prediction Center). As
a result, the SPC issued a Tornado Watch for the Sacramento Valley.
(Height levels are printed backwards on hodograph; this will be
corrected.)
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