WeatherWhys Blog

Lammas Day- Rest of Summer Forecast

Lammas Day- Rest of Summer Forecast

Lammas Day is upon us- the halfway point of summer. Lammas Day, the warm season equivalent of Groundhog Day, is the symbolic start of harvest. Lammas means “Loaf Mass”, indicative of grain harvest that results in bread to eat. The first half of summer has been cooler than normal, with only 14 triple digit days (normal is 20). So what does the second half our of historically infamous summer season look like? Regardless of what Lammas the dog says, it doesn’t look excessively hot for central California.
 

The horrible ridge of high pressure that has brought an accelerating drought to the Southern Plains has been mimicking what occurred in that same area during the 1930s. This ridge has demonstrated the feedback effect of hot and dry weather- dry ground that is the result of dry weather in essence perpetuating more dry weather. That is a snowballing phenomenon (if only it was cold and snowy). As this upper level ridge from hell is locked in place by the overall northern hemispheric jet stream pattern, very hot and dry weather is observed. But dry ground conditions help permeate the very same conditions over that region and hence lock in the drought for even longer. Hot weather begets hot weather, in this case.
How does that affect us way out here in California? Well, the semi-permanent ridge over the Southern Plains does not want to move. It will not be dislodged in the short term. Everything is blocked and in a non-dynamic stationary state. The cooler than average conditions along the west coast refuse to change as well. July in Bakersfield ended about a degree below normal and even posted .02” of rain on July 19th  making for a slightly cooler and wetter than an average month. This was not due to a strong jet stream in the eastern Pacific. No, instead it was due to the massive ridge over Oklahoma which invoked upstream cooling over California. Even the remnants of former Hurricane Fabio that brought the light precipitation were channeled into our state by the effects of that Oklahoma ridge.
With all of that in mind, I am forecasting near normal to slightly below normal temperatures for August and September. Rainfall will probably be sparse, but by September we may see an increase in precipitation over southern California for the same reason Fabio’s remains were sent in our direction from the Mexican Riviera- namely upstream channeling around the huge ridge.
As we proceed into the autumn and winter there is some very good news to report. Computer models are becoming more bullish by the day that an El Nino episode is right around the corner. Warming of the equatorial Pacific waters (El Nino) would mean above normal precipitation for southern California and Kern County beginning in December and lasting through March or April. After a drier than average water year 2011-12, we could use more rain and mountain snow this winter. So the bottom line is looking generally favorable. A hot second half of summer, but not excessively hot with long heat waves as sometimes happens. And El Nino is coming to rescue us from our moderate drought situation this winter. That would also mean more activity for ski resorts in the Sierra and in Kern County at Alta Sierra. We will see what Lammas the dog has to say on Wednesday. If he picks the blue north cookie it ostensibly means 6 more weeks of summer. If he picks the red south cookie it means summer through the “Ides of October”. If he is smart.. Lammas will pick the blue cookie.