WeatherWhys Blog

Thunderstorm threat on the horizon

Thunderstorm threat on the horizon

Following a wet weekend in which many areas picked up substantial amounts of rainfall, Monday will be a short break in the action. But Tuesday should snap back to our wet weather ways.

Bakersfield officially picked up .53” for the period Friday through Saturday. There was flooding of highway 58 near the base of the ascent to Tehachapi on Saturday afternoon and lots of rain in mountain/desert areas. That system is now east of Kern County and will bring another threat for paralyzing snow in parts of the eastern U.S. A huge blizzard hit the Washington DC area with up to 40” of snow in some spots, and they are still digging out. That storm came through here just days earlier. It is all part of the current El Nino pattern that has affected much of the southern United States this winter. The El Nino may have peaked last month as the Oceanic Nino Index (ONI) is now down just a bit from last month, going from +1.5 to +1.2. Nevertheless, a significant event will continue through the rest of this winter and spring as equatorial Pacific temperatures slowly begin to cool.

Meanwhile, we are entering our severe storms season which runs from February 1st through May 15th. At the same time, Tule fog season is coming to an end. It runs from November 15th through February 14th. And as our focus turns from fog to potential severe thunderstorms, the first such threat is coming down the pike for Tuesday. A small and compact low pressure system is already spinning off the Washington coast and will be moving straight south into California en route to Baja. As the storm moves overhead it will bring extremely cold air in the upper atmosphere into California. It is this frigid air at 20,000 and 30,000 feet that causes the relatively warmer air below to bubble up into it. The atmosphere normally gets colder with elevation, but when it either is much warmer (and more humid) in the lower altitudes OR it is much colder in the upper reaches- then the air become unstable. This calculation of temperature change with height is known as the “lapse rate”. When it becomes very high thunderstorms may develop. This will happen during the afternoon on Tuesday. While the California severe storm season is not like the Kansas season with powerful thunderstorms that spawn deadly tornadoes, we do see lightning, heavy rainfall and hail. Occasionally a funnel cloud or tornado occurs but they are rarely as damaging as back east.

When the tightly wound low pressure system drifts overhead on Tuesday, watch for clouds with extensive vertical development and lots of showers forming by mid and late afternoon. Lightning with small hail is also likely in some of the storms. One thing I look for is 500 Mb (18,000’) temperatures to get colder than about -25C. In tomorrow’s case, the forecast is for -30C air to move overhead for the afternoon. So it could be a busy day. Things improve for Wednesday. And now computer models are showing a ridge of high pressure to overspread the region by late in the week. This coming weekend, so full of meaning from Valentine’s Day to President’s Day weekend to the end of fog season- and Chinese New Year (Year of the Tiger), looks to be nice with sunshine and a warming trend. No rain this weekend, but El Nino is not finished with us yet. Some have pointed to an analogy of this El Nino to the 1957-58 El Nino event. That water year Bakersfield received just over 10 inches of rain (normal is 6.49”), with March and April getting 2.05 and 2.23 inches, respectively. Above normal precipitation continued right through May. Perhaps something like that will happen this year too.