Sunday, May 17, 2015

Summer Recreational Weather Outlook

We have had an unusual winter, with warmth and drought over the western U.S. and record-breaking cold and snow over the Northeast.  For over a year, the weather pattern was locked up with high pressure over the West Coast and low pressure over the eastern U.S.   We are now close enough to the summer to get a clearer view of what might be in store;  let me tell you about it.

The most powerful tool for forecasting months or seasons ahead available to U.S. meteorologists is called the Climate Forecast System (CFS), which is run by the National Weather Service.   Its prediction for surface air temperature for June through August (see below) indicates warmer that normal temperatures over the western U.S.  Such warmth will increase the danger of wildfires over the Sierra Nevada, the Cascades, and  the mountains of British Columbia.  The opposite is true of the High Plains and the Colorado, with below-normal temperature are predicted from Texas to the Dakotas.

Surface air temperatures forecast by the National Weather Service Climate Forecast System for June through August.  The colors show the difference of temperature from normal (°C), with red being above normal and blue below normal.

What about precipitation?   Generally near normal along the West Coast, but substantially wetter than normal over the Rockies and High Plains.  Most of this precipitation will be associated with convection:  thunderstorms, which also bring lightning.

Precipitation predicted by the same modeling system, with the colors showing differences from normal (green and blue are wetter than normal, orange and red drier than normal, units are in mm)

Lightning is a major initiator of wildfires, and with warmer than normal conditions drying the land and surface vegetation, the potential for wildfires will be substantially increased this summer.   Lightning is also a danger when ascending the high terrain, so it is always a good idea to get an early start, so that one is off peaks and crests by early afternoon, when thunderstorms tend to be most frequent.   If cumulus clouds are developing rapidly around you when ascending a ridge, you should descend as quickly as possible to minimize your risk.

So if plan on hiking along the West Coast be ready for sun and heat.  Be careful with fire.   In contrast, an excursion in the Rockies might require some rain gear and a watchful eye for thunderstorms.  Enjoy.