Lingering Showers & Thunderstorms Today

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After a very active evening across interior northern California with a line of thunderstorms that produced hundreds of lightning strikes in a few hours, some areas aren’t quite done yet.

March 6th

Currently, the same low that send yesterday’s cold front through is just now pushing into southern British Columbia, and to the south of the low from northern California to Washington the cool air aloft combined with a moist westerly flow is making for a favorable environment for convective development. Here in northern California, unlike up north, we’ve seen some widespread clearing throughout the day, allowing for surface temperatures to rise into the mid to locally upper-60s, which is promoting some decent low-level instability, including SBCAPE values in the 200 – 500 j/kg range, and low-level lapse rates in the 7.5 – 8.5c range.

Mesoscale analysis of SBCAPE (fill), and background visible satellite imagery.

Mesoscale analysis of SBCAPE (fill), and background visible satellite imagery.

Lift is being provided by a weak shortwave, and upper level support is rather strong due to a 60 – 80kt 500mb jet blasting overhead associated with the larger-scale trough and low impacting the BC/northern WA coast. This setup has already spawned some thunderstorms in Shasta county, and deepening cumulus field can be noted over the coastal mountains west of the central valley. The line of storms in the north end of the valley will likely slowly track southeast, and support the development of additional storms in Tehama and Butte counties through the mid-afternoon… possibly working a bit further south.

500mb wind vectors and strength colors. Deeper the purple, the stronger the winds.

500mb wind vectors and strength colors. Lighter the purple, the stronger the winds.

The CU field in the coastal mountains will likely promote some convective development as well, and these showers and possible thunderstorms would track east into the central valley.

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Effective shear of 20 – 35kts from Sacramento north combined with the notable instability and low-level buoyancy caused by surface heating supports thunderstorms capable of hail, and given the strong mid/upper level jet perhaps gusty winds. Directional shear will increase a bit by mid-afternoon, with SR helicities of 25 – 75 M2/S2 in the Sacramento valley. That would support some storm rotation if storms were to develop and strengthen enough in zones of stronger veering, thus I can’t completely rule out a slight funnel cloud or weak tornado threat… just note it’s not a major/widespread threat.

Effective bulk wind difference via mesoscale analysis data, indicating 20 - 35kt values from Sacramento north.

Effective bulk wind difference via mesoscale analysis data, indicating 20 – 35kt values from Sacramento north.

Things wind down tonight, making for some warmer days Friday and Saturday. Another system moves through Sunday with some more precipitation, and I’ll have an update on this system out Friday or Saturday.

Next week looks fairly dry and warm, and not seeing much potential for storms in the next 1 – 2 weeks, though that can certainly change.

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