A quick look at the weather in August

As we have now entered the month of August, we have started on the downhill portion of summer. Temperatures have already started their seasonal trend downward alongside decreasing solar heating this month. We review the climatology of August and highlight a few aspects of the weather to watch this month.

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Things to watch during the month of August

FLASH FLOODING

The monsoon is usually in full-force at the beginning of August, but slowly tappers off as the month progresses. This month also has the weakest steering winds on average across Colorado out of any month of the year. Because of this, developing thunderstorms tend to drift very slowly or remain stationary for extended periods of time, bringing the potential for tremendous amounts of rain to fall. The last week of July and the first week of August historically are the peak in flash flooding for our region.

EASTERN PACIFIC TROPICAL CYCLONES

Hurricane season across the eastern Pacific Ocean ramps-up significantly through the month of August. Much more-so than the Atlantic, Pacific hurricanes can and do influence the weather in Colorado through deep tropical moisture injection when they curve northeastward into Baja California. The current large-scale pattern, a high pressure center across Arizona, does not favor tracks for tropical cyclones towards Colorado. However, we are seeing indication in the models of a more favorable pattern arriving between August 10th and 15th.

DEVELOPING EL NIÑO

The latest guidance from both dynamical and statistical climate models suggests that there is about a 75% chance of an El Niño developing through the autumn months. If it happens, it will be the first El Nino winter since the strongest one on record three years ago.

RELAXING HEAT?

We’ve already had 28 days with temperatures hitting at least 90 degrees in Boulder. While not record-setting, this is well above normal. The Climate Prediction Center has the Front Range in the “Equal Chance” category for temperature this month, meaning “it could go any way”. We think August 2018 will not turn out as hot as the rest of summer has been, though we still believe it will conclude warmer than average.