textproduct: Reno

KEY MESSAGES

* Summer-like heat will maintain widespread moderate to areas of major HeatRisk today. Widespread minor with isolated moderate HeatRisk tomorrow will reflect the cooler, more seasonal temperatures arriving for the weekend.

* Thunderstorm activity increasing today and peaking Friday. This will bring impacts to fire, recreation, travel and aviation on both days.

* A warming trend resumes for next week, with a return of typical afternoon breezes.

DISCUSSION

Clouds leftover from last night's showers and storms demonstrate the existing moisture in mid and upper levels of the atmosphere as the surge of subtropical influence and the upper trough move into the region. Various model guidance shows CAPE fields blossoming across the Sierra and gradually spilling over into the Sierra Front. CAPE fields will start over the terrain, with added orographic influence boasting values ranging 2000-3000 J/kg depending on the guidance and timing. Some solutions represent values spilling to the Sierra Front in the later portion of the afternoon, and remaining into the overnight hours. This suggests elevated instability support for overnight showers and storms to linger into Friday morning. Today's chances (15-35%) focus on the Sierra for storm initiation with the same potential for lightning. Upper level winds are expected to sweep storms to the north once they grow to an appropriate height to realize the upper jet steering winds. Hazards for today include possible brief heavy rain under storm cores, gusty and erratic outflow winds up to 50-60 mph, frequent lightning and potential for small hail accumulations with stronger storms capable of producing isolated instances of up to 1 inch hail. For outdoor recreation or work, have multiple sources for receiving weather warnings, pay attention to the skies and have plans in place for sheltering should a storm develop overhead or nearby.

The trough advances on Friday, bringing another round of similar parameters of CAPE with a slight increase in atmospheric moisture content. If the overnight convection holds into Friday morning, we could start the day with storms over far northwestern Nevada and northeastern California. Another solution keeps the clouds from the overnight convection, that may act as a capping mechanism for instability into Friday morning. Whichever solution, expect cloudy morning skies once again, with a ~5% chance for ongoing showers to linger. As the afternoon heating develops, guidance suggests the cloud field will lift to the northeast, as showers and storms once again initiate along the Sierra. Similar storm motions will steer the storms to the north-northeast, which will introduce the threat to the Basin and Range into the late afternoon. So, similar weather parameters will produce similar hazards on Friday, but these will have more widespread coverage than today's showers and storms. Shower chances also increase and move slightly northeastward, with a focus on Lassen, Modoc and northern Washoe counties where chances range 40-60%, and an area that includes Reno-Carson City-Minden to the Smith and Mason valleys and out to Fallon and Lovelock, where chances will range 30-80%. Additionally, the potential exists for blowing dust over dry lake beds and desert sinks, such as the Carson Sink or Black Rock Playa, will emerge as strong gusty outflows blow northeast across the Basin and Range.

Both days present critical fire weather danger, today more so for a lightning threat, Friday for the widespread lightning threat as well as areas of low relative humidity and gusty winds across Mineral County. See the Red Flag Warnings as well as the Fire Weather section of this discussion.

Behind the trough, we will take temperatures back toward seasonal readings, with upper 80s to near 90 across western Nevada valleys and Sierra valleys with upper 70s to low 80s. We also return to typical summer afternoon breezes. The ridging pattern resumes heating next week, sending temperatures back to the upper 90s to near 100 across western Nevada and upper 80s to near 90 for Sierra valleys. HRICH

AVIATION

* Density altitude concerns continue today at terminals in NE CA and W NV due to afternoon heating.

* Showers and storms developing within the region starting around 21-22Z today. The Sierra and Sierra Front have around a 15-35% chance for precipitation today. Storms may contain increased gusty outflow winds up to 55 kts, brief periods of heavy rain and frequent lightning. Terrain obscuration, LLWS and turbulence may also be present near storm cores. MVFR conditions are possible at most TAF sites should a storm develop or pass nearby. Another round of showers and storms is forecast for Friday with increased chances and coverage which expect to bring similar aviation concerns. 078/HRICH

FIRE WEATHER

Fire weather concerns today and Friday with thunderstorm potential across the region. Antecedent hot and dry conditions with poor overnight recoveries have helped in drying fuels further which also increases fire danger.

Storms will move quickly toward the north-northeast 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 50-60 mph are possible, increasing the threat of rapid wind direction shifts.

An area over Mineral County (US-95 and east) will have a lesser threat of storms, but will retain the Red Flag Warning due to RH around 10-15% and the potential for gusts from gusty outflow winds that could reach up to 60 mph.

A Red Flag Warning is in effect today across the Sierra Front from 1 pm to 10 pm.

A Red Flag Warning is issued for Friday, see details in the Red Flag Warning product. 078/HRICH

REV Watches/Warnings/Advisories

NV...Red Flag Warning from 8 AM to 11 PM PDT Friday NVZ458.

Red Flag Warning until 10 PM PDT this evening NVZ420-421.

Red Flag Warning from noon to 9 PM PDT Friday NVZ420-421.

Red Flag Warning from noon to 11 PM PDT Friday NVZ423-429.

Heat Advisory until 5 AM PDT Friday NVZ004.

CA...Red Flag Warning from 8 AM to 11 PM PDT Friday CAZ270-278.