textproduct: Reno

KEY MESSAGES

* Significant heat persists today across western Nevada and lower Sierra valleys, with a gradual cooling trend expected next week.

* Isolated to scattered showers and thunderstorms this afternoon and Monday, with increasing coverage and chances by mid-week.

* Increased breezes elevate fire and recreation concerns today and Monday afternoon.

DISCUSSION

The prolonged period of significant heat will continue through Monday morning across the region, particularly for western Nevada and lower Sierra valleys. Temperatures cool slightly on Monday, though a more noticeable cooling trend begins Tuesday, with temperatures dipping below seasonal averages by Wednesday. A broad upper-level ridge centered over the Four Corners region continues to dominate the weather pattern today, maintaining above-normal temperatures. Daytime highs today and Monday will generally be in the upper 90s to 104F for lower valleys, with Sierra communities seeing upper 80s to low 90s. Overnight lows will continue to offer little relief due to lingering cloud cover, remaining in the mid 60s to low 70s across western Nevada valleys through Monday morning.

Increased afternoon breezes are expected today and Monday afternoon, with W/SW gusts of 25-30 mph (locally 35+ mph), particularly along the Sierra Front and across far NE California/NW Nevada. This will elevate fire weather concerns today and Monday for those areas, especially due to active, ongoing wildfires across western NV. Haze and areas of smoke from regional wildfires will also persist across western NV and into NE CA today and Monday.

Hi-res model soundings in the pre-convective environment show residual mid-level moisture atop a deep, well-mixed subcloud layer, supporting isolated to scattered showers and thunderstorms this afternoon. The greatest chances (10-30%) will be confined to areas south of I-80, including Mono, S.Lyon, Mineral, and Churchill counties. DCAPE values of 1400-1800 J/kg and LCL heights 3000-4000m support the potential for strong outflow winds, which remain the primary hazard with today's activity. Gusts of 45-55 mph and isolated severe gusts of 60+ mph possible, especially in S.Lyon, Mineral, and S. Churchill counties. A very low (5%) chance of localized flash flooding exists, mainly in higher/steeper terrain that received previous rainfall.

Shower and thunderstorm activity is expected to continue early this week over Mono/Mineral counties, then increase each day from mid-week through the weekend. With chances for multiple days of repeated showers and thunderstorms, flash flooding concerns will increase across portions of the eastern Sierra and Mineral County, especially over urban areas and steep terrain. While t-storms late in the week are favored to be on the wetter side with PWATs 0.6-0.9", new lightning ignitions and gusty outflow winds cannot be ruled out. Model guidance generally agrees on this overall trend of increasing moisture and convective activity, with the main uncertainties revolving around the exact timing and spatial distribution of the heaviest rainfall.

-Justin

AVIATION

Showers and thunderstorms return to the forecast this afternoon for KMMH and KHTH with chances increasing to 10-30%. Strong, erratic outflow gusts of 40-50 kts, brief heavy rain, and occasional lightning are the main hazards with any thunderstorms. Chances decrease to 15% or less Monday afternoon and favor a similar area as today.

Smoke filtering down into far NW NV and NE CA from wildfires in Oregon may reduce slantwise visibilities across those areas. Conditions are expected to improve in the afternoon hours due to afternoon breezes diffusing it, then smoke will settle again in the overnight hours. This will likely continue into Monday, possibly Tuesday as well. KRNO may have a higher likelihood of smoke impacts to slantwise visibility due to the Bug Fire and other fires north of Reno.

Otherwise, widespread VFR conditions and typical afternoon breezes prevail this weekend with continued heat posing density altitude concerns.

-Jyler

FIRE WEATHER

Breezy W/SW winds with gusts of 25-35 mph and RH reductions to 5-15% will support 2-5 hours of elevated to marginally critical fire weather conditions this afternoon and Monday afternoon across far NE California and NW Nevada -- including the Bug, Ironwood, Fred, and Ruby fires in the Sierra Front. Nighttime recoveries remain poor each night through Tuesday AM as RH struggles to exceed 30-40%, extending burn periods into the overnight hours.

There is a low 10-30% probability of thunderstorms south of I-80 today and Monday afternoon, posing a risk of new lightning ignitions and strong and erratic outflow gusts of 50+ mph. Moreover, an unstable airmass will allow for deeper vertical plume growth each afternoon, increasing the likelihood of locally stronger inflow winds near the fire, and sudden/erratic downdraft winds from collapsing plumes.

A pattern change brings cooler temperatures and higher humidity from Tuesday onward, but also increasing chances of thunderstorms. Thunderstorms are favored to be wet with heavy rain/flooding impacts to operations, but new lightning starts and gusty outflow winds cannot be ruled out.

-Salas

REV Watches/Warnings/Advisories

NV...Heat Advisory until 8 AM PDT Monday NVZ001-003-005.

Extreme Heat Warning until 8 AM PDT Monday NVZ004.

CA...Heat Advisory until 8 AM PDT Monday CAZ070-071.