Wednesday was a great day for t'storms in the northern San Joaquin Valley...
Skies cleared rapidly throughout the northern San Joaquin Valley after sunrise Wed following an early morning frontal passage. Surface temps rapidly climbed into the mid to upper 60s by early afternoon. Combined with the cold air in the mid-levels of the atmosphere - it was clear this area would be the target for t'storms Wed afternoon. The center of the upper level low and strongest upper level winds seemed too far south for any severe storms, but the instability looked great enough for small hail and cold-air funnels.
The activity took its time getting going over the valley - it had been confined to the Bay Area and Diablo Range up until the early afternoon. At 1400, radar indicated some cells going up over the valley in southern San Joaquin County - as well as some intense cells over the crest of the Diablo Range in western Stanislaus County. I decided these were worth a look - so I got in my car and left Turlock at 1430.
As I was heading westbound on Hwy 132 out of Modesto, the cells over southern San Joaquin County appeared to be weakening. The cell over the Diablo Range looked very ominous near the surface, producing heavy precipitation - but its tops were getting soft. Meanwhile, three cumulus towers began going up over the valley in west-central Stanislaus County - with an even larger cumulus tower far to the SE over Merced County. I decided to pursue the developing storm in Merced County. To get to this storm, I continued on Hwy 132 west to I-5, then took I-5 south to the Sperry Ave exit, then went east on Sperry to Hwy 33, and headed south on Hwy 33 to the town of Gustine.
Once I got to Gustine, some interesting things began to happen with this storm - which was about 10 mi to my E. It tops began to get soft, and appeared to become dominated by downdrafts. But just as it appeared to be weakening, new updraft towers began to shoot skyward. I watched this new development as I turned left on Hwy 140 and headed east out of Gustine. As I crossed the San Joaquin River (at 1557), I saw a small cone-shaped point dip from the cloud base. I watched it closely for about 10-15 sec before realizing that this was a funnel cloud! At the intersection of Hwy 140 and Edminster Road, I pulled off the side of the road to get some video of the funnel. The funnel cloud was very small - extending no more than 10% from the cloud base. It lasted for about 5 min before becoming needle-thin and vanishing. After that, I got back in my car and continued east on Hwy 140.
I didn't see any more funnel clouds out of this cell - and decided to head back home once I was east of it. And that's when I saw the developing storms over west-central Stanislaus County had followed me home!!!!
Light rain began falling and thunder began booming almost right as I arrived home in Turlock at 1700. However, the heart of the storm was to my W and heading SSE - missing my neighborhood. But at 1723, another cell passed over my house - dropping 1/4 inch hail for two minutes. At this time I called the NWS in Sacramento with the hail report. Yet another cell moved overhead at 1730, and this was the heaviest of them all. Extremely heavy rain and 1/4 inch (pea-sized) hail fell for 10 minutes. Rain totaled .26 of an inch between 1730 and 1740, and resulted in street flooding. Hail covered the ground, and accumulated 1/2 inch deep - even on sidewalks and roads! The hail was very slow to melt on grassy surfaces - there were still hailstones in my front yard at 1900!!!
A few wrap-up notes.....
Cells I was pursuing in southern San Joaquin County produced funnel clouds at 1430, about 15-20 min before they came into my view.
The funnel cloud I witnessed was located about 2 mi SE of Stevinson in central Merced County. Funnel lasted from about 1557 to about 1602. Since the funnel was over an uninhabited area, I was concerned I might have been the only one who saw it. Turns out the observer at Merced Airport (MCE) saw it too, as evidenced in this special observation taken at 1605...
SPECI KMCE 260005Z 00000KT 30SM FEW015 BKN035 17/06 A2975 RMK FUNNEL CLOUD E0005
Suspect there may have been weak rotation in last cell that passed through Turlock. Wind shifted from NW, to W, to SW, to S, to SE as cell moved SSE over my house. Hail was most intense as winds became southerly.
Things calmed down quickly once the sun went down Wed evening, and skies cleared overnight. Today looks like a mostly calm wx day - but then the wx fun starts all over again Fri!!!!