A squall line moved across the northern San Joaquin Valley early Saturday (14th) afternoon. Its effects weren't all that impressive in Turlock when it hit at 1320, just some lgt-mdt rain and a gradual wind shift from SE to WNW that took 15 minutes to complete. Fifteen miles to my northwest in Modesto, it was a different story - several trees were uprooted as the squall line passed. On Sunday afternoon, I drove up to Modesto to determine whether it was a microburst or a tornado which caused this damage.
By the time I arrived at the damage scene at 4 pm Sunday, all of the uprooted trees had been removed. However, there was still a lot of damage evident. Several roofs were dented in on the north side of the 1500 and 1600 blocks of Sheldon Avenue - obviously where the trees made impact on the houses. On the south side of Sheldon, the only significant damage I saw was a fence that was blown out on the 1500 block. There was also a roof which was missing about 1/4 of its shingles on the SE corner of Sheldon and Otis Avenues (Otis separates the 1500 and 1600 blocks of Sheldon). All of the damage seemed to be limited to this 1 1/2 block area - the rest of the neighborhood appeared to have been untouched.
Except for the deshingled roof, the only structural damage I saw was due to trees falling on objects. Although there was a lack of direct structural damage to determine this, it appeared that the damage path - although very small - was not erratic. All of the trees and the fence were downed in a SW-NE fashion. My guess is that a microburst hit Sheldon Avenue on Saturday afternoon - a southwesterly burst of wind perhaps in the 50-60 mph range.
This was the same squall line that produced 43 mph winds at San Francisco (SFO), 44 mph winds at Livermore (LVK), and 40 mph winds at Stockton (SCK) - as well as funnel clouds and waterspouts over San Francisco Bay. After that, t'storm after t'storm began to move onshore. Additional thunderstorms later that afternoon brought 44 mph winds to SFO, 46 mph winds at LVK, and 52 mph at Travis AFB (SUU). SFO ended up with a grand total FOUR thunderstorms that afternoon - all with winds over 37 mph!!!! We even had some gusty downdrafts here in Turlock from weak rain showers at 1700 and 1900 - 25 mph and 29 mph respectively.
Fast forwarding to today (18th), it looks like today will end up just our second completely dry day of the month. We're at 7.58 inches for the month - and should easily surpass our one-month rainfall record of 7.74 inches set in Jan 1995.*
* Follow-up.....We broke our one-month rainfall record on the 19th at 1316 PST. We finished Feb 1998 with 9.48 inches of rain.