In-depth discussion about Friday’s fire risk

Fire danger will be elevated to critical on Friday as the Washoe Zephyr kicks in Friday afternoon and evening. While it is usually breezy this time of year, afternoon breezes will be stronger than normal on Friday leading to pockets of critical fire danger along the Sierra Front. As a result, a Red Flag Warning is up for Washoe, Lyon, and Douglas counties from 2 pm Friday through 9 pm Friday. Wind gusts could reach 35 mph and relative humidity values will be low. Places like Washoe Valley could see wind gusts over 35 mph. This won’t be the biggest wind event we’ve ever seen, but enough to raise fire danger.

It won’t be windy all day, but fire conditions will reach critical levels for three or more hours north of I-80 and slightly less in the Reno area. Fuels are dry too. Friday and Saturday will be the hottest days of the week, with highs in the upper 90’s on Friday and around 100 degrees on Saturday. One can assume, fighting fires in hot temperatures is grueling.

Nevada will be located between a ridge centered to our east and a trough to our northwest. While, the ridge will be the main player, the low is close enough to tighten the pressure gradient and increase wind speeds. Especially where the trough and ridge meet along the jet stream, which goes through Tahoe and the Sierra Front.

A max of wind speeds develops late Friday along the jet, enhancing the Washoe Zephyr. The pressure gradient widens on Saturday, so wind speeds won’t be quite as strong. A southwest flow this time of year typically keeps us dry, with low relative humidity values. This usually happens when there is a trough nearby.

The wind flow becomes more southerly on Sunday bringing in some monsoon moisture from a ridge of high pressure over the Four Corners region. This will cool us down and give us a chance for rain. Lowering the fire threat due to wind as well. However, lightning can’t be ruled out either.