Current Weather for Southern California Communities
Monday, July 6, 2020 3:59 AM PDT

Dry start to 2020

By Reginald Stanley. Posted February 16, 2020, 3:38 AM.



The new year is off to a relatively dry start in Southern California, with little precipitation having fallen through mid-February, and forecasts have not been promising.

For most of the region, the last significant rains fell back on December 26th, 2019. Since then, only sporadic, weak storms have affected the region in between extended periods of high pressure ridging and cold offshore flow events. January and February, which are two of the wettest months of the year in the region on average, have both brought very little rain or mountain snow this year. While extended winter dry periods are not particularly uncommon for the region, they tend to foster drought conditions and increase fire danger later in the year.

A persistent ridge of high pressure, centered over the eastern portion of the Gulf of Alaska, has propped the polar jet stream in a somewhat unusual position since January - placing Southern California sometimes directly in the path of the jet stream, but storms that do develop instead travel over land rather than water, and therefore lack moisture. This also allows for frequent, cold episodes of offshore flow. Northern California has been even worse-affected by this high pressure ridge, keeping rain out of the region almost entirely since January. This persistent ridge of high pressure is similar to, although still quite different from another ridge of high pressure over the Gulf of Alaska that was largely responsible for California's string of dry years between 2012 and 2016. That ridge was larger, stronger and centered several hundred miles west of the current ridge, which allowed for much above-average temperatures - this was most potent in 2014 and 2015.

Long-range forecasts have not indicated any major pattern change occurring any time soon. The Climate Prediction Center predicts a 50 percent chance of drier-than-normal conditions prevailing over California through at least February 29th, as well as a 40 percent chance of a dry February-April-May period. There is, however, a chance of a split jet stream occurring over North America in early March, according to computer forecast models. This would allow for greater chances of deep troughing and large-scale precipitation events over the region during that period, although this is far out enough to remain very uncertain for the time being. In the meantime, low pressure is forecast to allow for a Pacific storm system to affect the region next weekend, although timing and intensity are not yet clear.

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