Quick Update: Thunderstorms Possible This Afternoon

Quick Update: Thunderstorms Possible This Afternoon

MARCH 30, 2014

It’s been one heck of a week thunderstorm wise, and even today (Sunday), we may not be out of the woods completely.

Cold air aloft combined with mostly sunny conditions across the region will promote moderate to very steep low-level lapse rates, with mid-level lapse rates in the 7 – 7.5c range, which is moderately steep. A bit of lower-level moisture combined with the decent lapse rates will also support surface-based CAPE values to climb into the 100 – 300 j/kg range, locally a bit higher, from around Sacramento north. Shear today isn’t too strong, however winds do veer decently with height, and terrain-enhanced winds in the lower levels may be sufficient for some robust updrafts today, even with limited general upper support.

Mesoscale analysis most-unstable CAPE (fill) and visible satellite in the background, from 10:30am.

Convection allowing high resolution models including the 4km NAM, NSSL WRF, and HRRR indicate showers and possible thunderstorms developing along the west side of the Sacramento valley this afternoon, moving east to northeast through the early evening. HRRR indicates slight potential for some rotating thunderstorms given terrain enhanced shear in the central and northern Sacramento valley.

Modest instability and shear could be sufficient enough to support thunderstorms capable of hail and gusty winds, however if the HRRR is near-correct, cannot rule out a rotating storm or two in the Sacramento valley this afternoon/early evening, generally north of Sacramento with the hotspot highlighted by the HRRR being between Yuba City and Redding.

15z HRRR’s forecast radar reflectivity for around 5pm.

Things decay after around 7 – 8pm ahead of our next, stronger system. I’ll have an update out this evening regarding this system, I just didn’t want to let today’s threat go unposted.