“Trough luck” for southern California?

As a person who grew up in the Midwest, and spent a lot of time living in the Great Plains, it took a while for me to get used to forecasting in southern California.

My first summer out here, a wise Lead Forecaster at the NWS in San Diego advised me, “troughs in the summer are a good thing”. And he was right.

The low pressure troughs aloft bring a stronger onshore flow of cooler air, which for us, is modified by the cool currents of the Pacific. They are also associated with a deeper marine layer, bringing higher humidities, and more nighttime and morning cloudiness.

But unlike troughs moving across the central and eastern parts of the US, the troughs over the vast cool waters of the north Pacific often are dry just a bit above the surface.

This helps to bring us that “Chamber of Commerce” weather combination to the area. Cloudy and cool with some moisture in the air in the late nights and mornings…sunny, mild, and a bit drier in the afternoon.

Sorry to say…it won’t last forever. Long range models are indicating around the 11th of June a warm high pressure ridge will build in the upper parts of the atmosphere over the southwestern US, and possibly bring more moisture after the 13th…although it is still a bit early for the monsoon season.

Jim Purpura
Certified Consulting Meteorologist
Director, Weather Forecasting


WXExtreme.TV Social Media Pages are Up!

wxextremeblog-1-680x380We are pleased to announce the creation of the new social media pages that will showcase the new online television show by WeatherExtreme, wxextreme.tv. Stay tuned for upcoming events, and status updates leading to the launch of the new online television show. For now, weatherextreme.com will remain the primary source for news but the new Facebook and Twitter pages will be updated with content from the website and will provide yet another avenue. So don’t forget to “like” and “follow” the new pages for the latest! A New Experience Coming Soon….Count On It!!


The beginning of Fire Season??…no… it’s getting to the end (at least in southern California)

Some politicians have implied recently last weeks fires show we are at the beginning of a long fire season. That may certainly be true in the Sierras and northern California, but southern California has a different fire season. Let me explain…

Across much of the west, summer means melting snows in the mountains give way to warmer and drier conditions. Meadows that were green in the spring are beginning to dry. Other fuels are drying for the summer season. And fire threat is increasing.

But for southern California (outside the mountains) it is normal to be without rain for the summer. Most summer fires are not fanned by hot, dry offshore (Santa Ana) winds. They are fanned by the sea breeze as it pushes into the valleys. Besides having higher humidities, these breezes are diurnal, meaning they tend to cease late in the day after the peak heating. Thus they generally can be more easily attacked by fire fighters. To be sure, there have been exceptions…but you will find the history of large fires in southern California shows a peak season from mid September to early or mid May.

In the early fall the peak threat for the Southland begins in September when cold outbreaks in the Plains and Great Basin push southwest and turn into our offshore, or Santa Ana winds. The threat ends when fuels are wet for the winter, usually after widespread rainfall of several inches.

The threat often returns briefly around May 1. I used to call this “mini-season” at the National Weather Service in San Diego. Cool season rain has pretty much ended, it’s warming up. The fuels are drying out again, and there are a few Santa Anas left. So we generally see a short-lived increase in large fires for a while in May. But this years “mini-season” was not so mini. Two very strong Santa Anas in May, combined with fuels dry from a winter with precipitation less than 50% of normal in many places, set the stage for some catastrophic fires, especially in San Diego County.

When the Santa Anas go away, and the deep marine layer returns (like today) the threat of large fires goes with it. That is…until September!!

Jim Purpura, CCM
Director of Weather Forecasting


Fires in San Diego County

While some fires have been extinguished, others are still burning in San Diego County.

This is a NASA Moderate Resolution Imaging Spectrometer (MODIS) which is aboard the Terra Satellite. The image is from yesterday, May 14, 2014, showing the fires burning in southern California and the offshore flow blowing the smoke out over the Pacific Ocean.

Today is the final day for extreme heat and offshore winds as this evening things should begin to change tomorrow as the heat begins to diminish and onshore flow starts to dominate once again.

Screen shot 2014-05-15 at 2.12.07 PM

Courtesy of San Diego County- California Chaparral Institute

Another Santa Ana heading our way

Wind gusts across San Diego County at 8:40 am PDT 5/12/14 (Image Courtesy San Diego Gas and Electric Mesonet)Sill Hill is at it again…

Just a bit more than a week ago I wrote about our fierce late-season Santa Ana, with wind gusts to 101 miles per hour at Sill Hill in the San Diego Mountains west of Cuyamaca Peak.

Now, almost into the middle of May, another Santa Ana wind event is upon us. The cold air still is coming down from Canada into the northern Plains, and Rockies, and has pushed back into the Great Basin. It’s heading our way. This cold air is compressed, dried, and warmed as it squeezes through mountain passes, or in the case of Sill Hill, strong east winds aloft in a wave cresting the mountains is driven down to the ground.

Already this morning, winds have gusted to 60 mph at Sill Hill (see graphic from San Diego Gas and Electric Mesonet).

Yet the main impact from this event will not be so much wind as last time, but unseasonably warm temperatures west of the mountains. Many inland valley locations could see highs well into the 90s, or approaching 100 degrees, especially Wednesday through Friday.

Saturday and Sunday will see a cooling trend, thankfully, as the upper ridge over the west coast begins to weaken.

Jim Purpura
Certified Consulting Meteorologist
Director, Weather Forecasting