textproduct: Reno

KEY MESSAGES

* Hot and dry with 10-15% chance of isolated showers along the Sierra crest in Mono County this afternoon.

* Near 100 degree highs for W.Nevada valleys Tue-Wed. Moderate to localized Major HeatRisk concerns.

* A pattern change Thurday-Friday may increase fire weather concerns due to increased T-Storm chances along with gusty winds and low humidity. Cooling expected by next weekend.

DISCUSSION

Hot, dry weather continues this week with temperatures 10-20 degrees above mid-June averages. Highs today will reach the mid to upper 90s in W.Nevada and the mid to upper 80s in Sierra communities. The hottest days of the year thus far are expected Tuesday through Thursday, when W.Nevada valleys heat up to around 100 degrees. Forecast highs are generally 1-3 degrees below records, but warm overnight lows in the low to mid 60s may break warm low records. Moderate HeatRisk will be widespread, with isolated major HeatRisk in hotter rural valleys. Stay hydrated and limit outdoor activity during peak afternoon heat.

Afternoon heating will still lead to increased instability and afternoon cumulus build-ups across the Sierra this afternoon; however, shower and thunderstorm potential will decrease through mid-week with generally less than 10-15% chances each afternoon along the E.Sierra.

Westerly Zephyr winds return Tuesday afternoon, with gusts of 20 to 25 mph. Considering the very dry air mass in place with single digit afternoon RH values across W.Nevada, afternoon gusts could yield localized and brief elevated fire weather conditions.

An approaching shortwave will break down the upper-level ridge on Thursday afternoon, bringing a 10% chance of showers and thunderstorms to the Eastern Sierra in Mono County and as far north as the Tahoe Basin. This system may also trigger overnight showers and isolated storms into Friday morning. The main threat arrives Friday afternoon north of US-50 across the Eastern Sierra and western Nevada, with a 25% to 50% chance of showers and a 15% to 25% chance of thunderstorms. These fast-moving, high-based storms will increase fire weather concerns due to potential lightning ignitions and gusty outflow winds. Fuentes

AVIATION

VFR conditions for all terminals through the majority of the forecast period. The exception may be KMMH today where isolated showers and thunderstorms have a 10% chance of developing this afternoon. Impacts from these storms include gusty and erratic outflow winds, brief downpours, and lightning. Additionally, mountain obscurations may develop along the highest peaks of the Sierra.

Above average temperatures through mid-week will result in density altitude concerns. Nevada terminals will be the most vulnerable to these concerns as temperatures approach the triple digits. Giralte/Fuentes

FIRE WEATHER

Late July-like heat will continue through Thursday, peaking on Tuesday and Wednesday with high temperatures heating to 10-20 degrees above normal. Alongside the heat, a very dry air mass will continue to drive afternoon humidity levels into the single digits and cause poor overnight recoveries in the teens and low 20% vicinity across the W.Nevada Basin and Range.

Winds will remain light this afternoon before typical afternoon zephyr breezes return on Tuesday, bringing gusts of 20 to 25 mph. These hot, dry, and breezy conditions will combine to create brief, localized areas of elevated fire weather where vegetation is already dry.

The weather pattern turns critical late in the week as a high- pressure ridge breaks down, opening the door for fast-moving, high-based dry thunderstorms. A few storms could develop as early as Thursday afternoon in Mono County before drifting north into the Tahoe Basin overnight and Friday morning. Friday afternoon will bring the highest threat, with scattered thunderstorms stretching across much of the E.Sierra and W.Nevada, mainly northward of US-50.

Due to the low chance of wetting rains (<10%), new lightning ignitions will elevate fire weather concerns. In addition, the dry low-level airmass will favor stronger thunderstorm outflows with wind gusts that could exceed 50 mph. Strong outflows could rapidly spread any new ignitions. After several days of hot, dry conditions, vegetation will be more susceptible to burning, raising the overall fire threat. Fuentes

REV Watches/Warnings/Advisories

NV...Heat Advisory from 11 AM Tuesday to 5 AM PDT Wednesday NVZ004.

CA...None.