textproduct: Reno

KEY MESSAGES

* Summer-like heat will maintain widespread moderate to areas of major HeatRisk through Thursday.

* Thunderstorm activity increases each day through Friday, peaking Friday. This will bring concerns for impacts to fire, recreation, and aviation.

* Cooler and drier weather is favored to return over the weekend.

DISCUSSION

The heat is on across western Nevada and northeastern California through Friday, with some areas seeing repeat attempts to reach 100 degrees. Even those escaping to the mountains for relief will find high temperatures spanning the upper 80s to near 90 again. Overnight lows will only be a degree or two cooler across the region, maintaining major HeatRisk today. Friday will be a touch cooler, but still within Moderate HeatRisk territory.

Along with this heat, the ridge that has built in this heat will have a shortwave breakdown moving in Thursday, and deepening for Friday. The heating coupled with a shortwave will see an increase in instability, supported by an upper jet streak that appears sourced from a subtropical flow, and also appears to receive a bit of moisture feed from a southerly flow off the Baja California. These two subtle features are aiming to combine near the southern Sierra, which is increasing the PWAT and instability fields across the Sierra and Sierra Front. PWAT values start to increase for Thursday, with values as high as 0.6-0.7 inches found through late Thursday. As for the SBCAPE, the range will be from 500-1500 J/kg stretched along the Sierra, with DCAPE values of up to 1800 J/kg in the Sierra Front for Thursday. This suggests that any storms that build over the Sierra will have the potential for strong gusty outflow winds up to 50 mph, along with lightning outside of storm cores and heavy rain under storm cores. If you have outdoor plans Thursday, make sure to check with us before you go outdoors, and have a plan for shelter for when storms develop, around the noon to 1 pm time frame. Our best chances for storms will be 25-35% along Sierra, with 15% chances along the Sierra Front along and south of US-50.

This pattern deepens for Friday, as the trough digs south and glides into northeastern California. A couple things to mention here, the PWAT will climb toward 0.7-0.8 inches, with a more favorable upper jet position for strong to severe storms. The heat will linger into Friday, offering similar SBCAPE and DCAPE values, but further north into the northern Sierra and northwestern Nevada. Some storms may have held on overnight, which could either signal early convection carrying over and developing Friday morning, or some form of cloud cover that could limit early day development, and favor the early afternoon for initiation. Similar hazards to include gusty erratic outflows to 50 mph, lightning outside of rain cores, fast moving storms, and heavy rain under storm cores. The main area of concern will be along the Pine Nut Mountains, the Sierra Front and north to the Oregon border. Chances will range 30-60%, with the best opportunities across Lassen, Modoc and northern Washoe counties. Friday is another day for having alternate sheltering plans if you are outdoors. Travel may be impacted by blowing dust near desert sinks, should a gusty outflow arrive. HRICH

AVIATION

* Density altitude concerns continue with heating across the region. VFR conditions through today, with afternoon gusts 15-20 kts.

* KTRK, KTVL, KMMH, KBAN may all contend with showers and storms tomorrow, with a 25-35% chance. Storms may contain gusty outflow winds up to 55 kts, brief periods of heavy rain and lightning. Terrain obscuration, LLWS and turbulence may be present near storm cores. HRICH

FIRE WEATHER

Continued hot and dry weather, with poor overnight recoveries as an approaching storm system brings showers and storms for Thursday and Friday. The current conditions will help fuels to dry further as we anticipate storms for Thursday and Friday.

Storms will move quickly once developed, with a mix of wet and dry storm modes. This increases potential for dry lightning strikes outside of wet storm cores as well as dry storms that produce more lightning than moisture. Gusty, erratic outflows of 50+ mph are possible, increasing the threat of rapid wind direction shifts.

A Red Flag Warning has been issued for Thursday across the Sierra Front from 1 pm to 10 pm. A Fire Weather Watch still stands for Friday, in effect from 8 am through 11 pm. HRICH

REV Watches/Warnings/Advisories

NV...Fire Weather Watch from Friday morning through Friday evening NVZ458.

Red Flag Warning from 1 PM to 10 PM PDT Thursday NVZ420-421.

Heat Advisory until 5 AM PDT Friday NVZ004.

Fire Weather Watch from Friday morning through Friday evening NVZ423.

CA...Fire Weather Watch from Friday morning through Friday evening CAZ270-278.