Operational Aspects of Monitoring and Forecasting Shallow Supercells in California


The small size of shallow supercells can lead forecasters to minimize the risk with such storms because unless such storms are immediately adjacent to Doppler radar sites, lowest tilt scans will over shoot rotational signatures.

This figure schematically illustrates the portion of a shallow supercell over Marin County intersected by the lowest tilt (1/2 degree) of the KMUX 88D (~4000 feet) radar.

Since rotational features with shallow California storms are not liable to be monitored by distant Doppler radars, vertical and time continuity of rotational signatures will be impossible to judge from radar data alone.

Nevertheless, forecasters need to be aware that the same range of features observed with conventional supercells can occur with shallow storms, including damaging tornadoes, giant hail and destructive straightline winds.

Click on map or chart to obtain larger version.


Coping with the Supercell Radar Detection
Problem at the Operational Level

"...forecasters will have to rely on conceptual storm model knowledge to interpret WSR-88D reflectivity and velocity, storm spotter reports and satellite imagery when mesocyclone detection is impossible..."

"...coping with supercell events in operations will depend on forecasters having adequate knowledge of supercell conceptual models..."

"...forecasters should have a more agressive warning attitude than one of waiting for Doppler velocity-detected mesocyclone formation..."

Moller, A.R., C.A.Doswell, M.P. Foster and G.R. Woodall, 1994: The operational recognition of supercell thunderstorm environments and storm structures. Weather and Forecasting. Vol. 9, 327-347./TD>


Recognition of Buoyancy and Shear Environments Conducive to Shallow Supercell Formation

"...our results indicate that for moderate to high vertical shears and small parcel buoyoancy below 500 mb, the simulated mini supercells generate similar mesocyclones (compared to high buoyancy Great Plains' cases), even though the total CAPE was a factor of 2-3 times smaller for mini-supercell cases..."

Wicker, L.J. and L. Cantrell, 1996: The role of vertical buoyancy distributions in miniature supercells. 18th Conference on Severe Local Storms, San Francisco, CA.

"...although parcel buoyancy is often small...(with shallow supercells), its concentration in the strongly sheared lower troposphere promotes the development of vertical pressure forces comparable to those seen in simulated Great Plains' supercells..."

"...such storms (shallow supercells) are often forecast poorly because of the unusually low CAPE. Our results help to clarify how such environments may still produce shallow supercellular updrafts that could lead to tornadogenesis and other severe weather manifestations..."

McCaul, W.W. Jr. and M.L. Weisman, 1996: Simulations of shallow supercell storms in landfalling hurricane environments. Monthly Weather Review, Vol. 124, 408-429.

Shallow Supercell Page
Buoyancy and Shear
Marin County Storm
Merced County Storm
Oakland Storm
San Francisco County Storm