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AN EYEWITNESS ACCOUNT OF THE FORMATION OF THE SUNNYVALE T'STORM & F2 TORNADO OF 5/4/98. The morning started with low stratus and light rain throughout the region - quite similar to late spring along the New England coast. During the late morning up to noon hour, intermittent bright sun and light winds raised temps in Silicon Valley to the high 60's and locally to the 70's. Concurrently, a major cell was forming directly upwind SE of the Mount Hamilton area, (the highest peak in the Bay Area - 4,2000 K'). A major contributor to the primary cell's intensity was the perfect combination (and timing) of a cutoff upper low(s) anchored about 200 miles of the coast spinning in bands of cold unstable air mixing with tropical (El Nino influenced?) surface air. By 1500, the storm became active with C-C and C-G lightning and small hail was noted in East San Jose as the storm continued it's march directly over the still warm Silicon Valley. Peak lightning activity with 6 bolts (in my vicinity alone) noted in just one minute occurred around 1600, with larger hail noted (to almost 1/2"). Heavy, well defined mammotus and billowing side walls of the Cb visible along sharply delineated clear air boundaries to the N and NW. Max tower height reported 34K'. Max straight line winds estimated (locally) to 35mph in gusts By 1630, activity had significantly lessened and the underside of the storm started to loose definition. Mammotus no longer visible. On a hunch, I had brought my video camera to work and caught some large hail, thunder and lightning from the central and trailing edge of the storm. on tape. Unknown to me however, around 1635, a Tornado touched down on the opposite (NW) side of the cell, and I was shielded by the rain! All my life I've wanted to see a Tornado, and living near San Francisco I thought I'd never see one...then suddenly there I am THREE MILES from maybe the most exciting storm of my life, camera in hand, and came up a hailstone short. Sunnyvale was worst hit and the first touchdown point, with extensive damage to a number of homes over a few blocks distance. The Tornado then continued to hopscotch to the WNW and briefly touched down again in Mountain View and Los Altos hills, where only minimal damage was reported. The twister was videoed by at least three amateurs, and each appeared to indicate a clockwise, or anti-cyclonic rotation. After initial ratings for the Tornado of F0-F1, it was later revised to F2, with peaks winds estimated to 120mph. Well better "Chasing" next time!