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

Our prolonged stretch of significant heat is entering it's final couple of days before noticeably cooler temperatures arrive Tuesday onward. Until then, daytime highs remain in the upper 80s to 90s for Sierra communities and upper 90s to 105F across lower NE CA/W NV valleys. While many Sierra and NE California locales cool off nicely each night, temperatures will only fall to mid 60s and 70s through Monday morning across W Nevada valleys -- offering little to no relief from the daytime heat. As mentioned, a cooling trend will lower temperatures to seasonal averages and mitigate heat impacts by the middle of the week.

Dampening of the western ridging pattern will allow for more pronounced troughing to develop in the eastern Pacific basin today and Monday. This achieves two notable results for today and Monday: 1) Increased afternoon breezes from the OR border south along the Sierra Front, and 2) Greatest shower and thunderstorm chances confined to areas south of US-50. While winds won't be unusually strong, W/SW gusts of 25-30 mph (35+ mph locally) will heighten fire concerns (more details in the fire weather discussion) and make for rougher lake waters in far NE California and NW Nevada each afternoon through Monday.

Meanwhile, residual mid-level moisture atop a deep, well-mixed subcloud layer will support a low probability (10-30% chances) of showers and isolated storms this afternoon from Mono County eastward into the broader S.Lyon-Mineral-S.Churchill Co region. Strong outflow winds of 45-55 mph remain the primary hazard with today's shower and storm activity, especially in S.Lyon, Mineral, S. Churchill counties where DCAPE values of 1700+ J/kg could support isolated severe gusts of 60+ mph. There is also a very low 5% chance of localized flash flooding this afternoon due to abundant moisture and slower storm motions, especially in higher/steeper terrain that received antecedent rainfall Friday and Saturday. A brief drying trend will decrease shower and storm chances to 15% or less Monday afternoon, still favoring areas south of US-50.

Low pressure continues to deepen in the eastern Pacific as the week progresses, drawing deeper moisture into the region Tuesday onward. As a result, shower and thunderstorm activity should increase each day from mid to late week, and perhaps continue through the weekend depending on how long moisture hangs around. Given the moisture quality, flash flooding is favored as the main threat, new lightning fires and strong outflows will also be possible with this week's thunderstorm activity.

-Salas

AVIATION

Showers and thunderstorms return to the forecast this afternoon for KMMH, KBAN, and KHTH with chances increasing to 10-30%. Strong outflow gusts of 45 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 wind mixing it out, then smoke will settle in the overnight hours. This will likely continue into Monday. KRNO may have a higher likelihood of smoke impacts to slantwise visibility due to the Bug Fire.

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, Hunter, Double Springs, 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 US-50 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.