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Archive for June, 2008

Tornado Watch for New York, Vermont, and Western Mass?

June 10th, 2008 No comments
Tornado watches are usually rare in the Northeast. Nonetheless the SPC issued one this morning. As a strong squall line has already formed and is moving through central New York.

Their reasoning is shown below on the 12 Z sounding for Albany New York (Source: PSU Vortex). This squall line is entering an area of clear skies and very warm temperatures. This is generating some good cape (1300 J/Kg according to the sounding). If the cap can break, which it should, these storms can strengthen throughout the day. That, along with some moderate low level shear, could help to spawn some tornadoes.

While I personally believe the threat for tornadoes is near minimal, expect these storms to have some good hail and vivid lightning.

Mini Case Study: June 5th Tornado Outbreak

June 6th, 2008 No comments
Yesterday a system swept through the central United States and a reported 35 tornadoes broke out in the northern plains. Along with that there were many wind and hail reports ranging from northern Texas to Wisconsin and Michigan. (SOURCE: SPC)

This system was induced by an unseasonably large positively tilted upper level trough(Right: SOURCE: SPC) over the rocky mountains. Downstream of this trough, one can detect warm air advection. This is outstanding at the 500mb level. This indicates that warm, moist air is being surged into the area and is creating unstable conditions.

The sounding at Topeka Kansas below (SOURCE: PSU Vortex) shows something interesting. The conditions looke ripe for a severe weather outbreak, with cape values near 1500J/kg, lifted indices below -6 deg. C, and a low level jet. However there is a very strong cap at the 800mb level. If that cap doesn’t break, parcels (near the surface) won’t be able to rise and cool. However if the cap can be broken, the CAPE values would be outstanding. I believe that cap did break during the day, because for one, the sounding was taken around 7am, so daytime heating has not occured. Also the strong WAA that can be seen on the upper air maps hint that the temperature is indeed going to rise, and hence the cap would have broken.