Most fires are human caused, so when a Red Flag Warning is issued it is very important that we take it seriously. Strong winds carry a fire rapidly and the last thing we need in Northern Nevada after the Hawk and Bug Fires this summer is another fire. With that being said, there is a Red Flag Warning posted for much of Northern Nevada on Friday. The warning includes Southern Washoe, Lyon, Carson City, Douglas, Pershing, Churchill, and Mineral Counties from noon through 10 pm Friday. Wind gusts will be slightly lower east of Reno, but in general wind gusts will range between 40 and 45 mph.
Most of the time wind speeds pick up in the afternoon, after a quiet morning, but it will be a touch breezy even Thursday night with gusts in the teens to 20 mph. The Red Flag Warning begins at noon, and wind gusts will already be in the 20’s before that. Wind prone areas could see wind gusts over 40 mph, which is strong enough to spread a fire. Relative humidity values will be as low as 17%, adding to the fire danger.
The main concern will be the wind. This won’t be the biggest wind event we have ever seen, but certainly windy enough to increase fire danger to critical levels for an extended amount of time.
What’s causing the fire danger is a large trough moving through the Pacific Northwest, combined with a surface front moving through Northern Nevada on Friday. The trough is already bringing high level clouds to Northern California and rain to Seattle but will be overland on Friday. The Truckee Meadows is not going to get any rain out of this, as relative humidity values will be low and the center of the trough will stay well up to our north. Instead, temperatures will cool and winds will be strong.
As the trough moves over the Pacific Northwest the pressure gradient will tighten, increasing wind speeds. The pressure gradient is determined by the change in pressure and can be seen on a weather map with isobars, which are lines of equal pressure. Wind speeds increase when there is a big change in pressure. The trough will be close to a ridge, indicating a big change in pressure within a short distance. Pressure is also related to temperature, and a drop of 5-10 degrees is enough to increase wind speeds. Make sure to stay fire aware. This weekend will be breezy but not as bad as Friday.