Marin County Supercell Storm

This strong storm (may have been severe) moved onshore at around 5PM PST. The storm produced 1/2 inch hail in many locations. There are unverified reports of 1 " hail in Marin County. Large hail reports spanned the region from Stinson Beach, Muir Woods to Corte Madera.
Given the buoyancy/shear parameters and ratios discussed on the previous page, it is likely that this storm was supercellular. Like most California cool season supercellular events, without augmentation due to the shear-induced vertical pressure forces, the buoyancy would NOT have been sufficient alone to account for severe weather (if the 1" hail reports were true).

Visible Satellite, GOES 9, 2315 UTC

The large cumulonimbus southwest of Marin County moved onshore by about 0030 UTC (4:30 PM PST). The satellite image shows a flanking line of cumulus congestus southwest of the main anvil. The radar image for this storm is shown below.

Comparison of Visible Satellite, GOES 9, 2315 UTC to Model of Supercell

The expanded visible image of the cumulonimbus cloud southwest of Marin County shows the storm at a time approximately 3/4 hour before landfall. The schematic at the right shows some features associated with a typical supercell (after Doswell (1985)). Note the correspondence of the flanking line and anvil edge of the Marin storm to the schematic view.

Given the buoyancy and wind shear parameters, supercellular convection on this day is to be expected!

KMUX Reflectivity, 1/2 Degree Tilt, 0102 GMT 5 March 1996

Radar displays from San Francisco State University's Weather Graphics and Simulation Lab

This echo is intersected by the middle of the radar transect at 1/2 degree tilt at the 8000 foot level. The echo top was at approximately 27000 feet. At the 1/2 degree tilt, the core of the echo is returning 58 dBZ (VIP 6), indicating heavy precipitation and possible large hail. Given the distance of the radar from the storm (50 nautical miles) and the base elevation of the radar (approximately 3000 feet), it is unlikely that any of the algorithms designed to "alarm" or indicate large hail or mesocyclone would have been triggered for this low-topped (sometimes referred to as "mini" supercell). Forecasters must apply their own meteorological reasoning and intuition to these situations.

Shallow Supercell Page

Monitoring and Forecasting Shallow Supercells in California

Buoyancy and Shear

Marin County Storm

Merced County Storm

Oakland Storm

San Francisco County Storm

• Back to John Monteverdi's Storm Page
  
• Back to California Regional Weather Server
  
• Return to top of Geosciences Home Page