textproduct: Reno

KEY MESSAGES

* Significant heat will impact outdoor activities each afternoon through the weekend, then cooler weather arrives next week.

* Isolated showers and thunderstorms return this afternoon through the weekend in parts of the eastern Sierra and far western NV, with increased storm potential later next week.

* Light haze from regional wildfires lingers with increasing smoke returning to northeast CA and northwest NV this weekend.

DISCUSSION

Strong high pressure ridge from the Great Basin to the southwest US will continue our hot August days, with triple digit highs in lower elevations and near or above 90 degrees for most Sierra locations through Sunday. Overnight lows will also trend a few degrees warmer for the next couple of nights, partially due to lingering cloud cover after afternoon showers and t-storms diminish. Continue to take heat safety precautions if your plans involve outdoor activities during the day. High pressure finally weakens early next week, providing a much needed cooling trend that lowers temperatures closer to seasonal averages by mid-late week.

Light haze from regional wildfires will continue to linger, although a change in wind pattern across Oregon is set to bring increased amounts of smoke/haze to northeast CA-northwest NV mainly from Susanville-Gerlach northward, especially overnight through each morning this weekend.

Moisture advecting northward into the region around the high pressure ridge combined with our continued heat, will support a low chance (10-20%) of showers and isolated thunderstorms this afternoon. The initial storms are expected to form near the eastern Sierra of Mono-Alpine counties around 1-2 PM, then develop northward across far western NV including the Reno-Carson City area and Lyon-western Mineral counties mainly between 3-7 PM. While coverage isn't expected to be widespread, dry low levels below the cloud bases could support strong outflow wind gusts of 40-50+ mph. Lightning strikes also bring a risk of new fire ignitions due to the prevailing hot and dry conditions.

For Saturday, a similar setup for thunderstorms is anticipated, although onset is trending a little sooner with first cells building up around midday. Coverage again looks to be isolated as overall forcing is limited, although instability and moisture extends northward to include a few showers or storms into eastern Lassen/N Washoe County.

From Sunday-Monday, the best storm chances retreat to south of US-50 Sunday afternoon and eventually to just the southern edges of Mono-Mineral counties by Monday, as the high pressure ridge becomes displaced by a low pressure trough reaching the Pacific NW coast. This trough could bring increased afternoon breezes and periods of elevated to locally critical fire weather concerns mainly from I-80 northward Monday and Tuesday. Later next week, blended guidance is favoring a more active shower and t-storm pattern spreading northward again across eastern CA- western NV. Advancing moisture may be combined with stronger forcing from an area of low pressure off the CA coast to provide increased storm coverage and impacts, especially Thursday-Friday. MJD

AVIATION

The primary weather concerns today and Saturday are a low chance (10-20%) of showers and isolated thunderstorms affecting the western NV terminals southward to KMMH mainly between 21-03Z, with less than 10% chance at KTRK/KTVL. Main hazards from these storms include strong outflow gusts up to 45 kts, occasional lightning, and mountain obscuration to accompany thunderstorms. Outside storm activity, lighter afternoon SW-W breezes are expected through Saturday with occasional gusts to 20 kt. Afternoon winds then trend upward Sunday through Monday with increased potential for gusts at least 25 kt. MJD Otherwise, widespread VFR conditions prevail with minor slantwise visibility reductions in light haze, and density altitude concerns each afternoon through the weekend due to the prolonged heat. MJD

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.