textproduct: Reno

KEY MESSAGES

* Dangerous heat persists through the weekend across western Nevada and lower Sierra valleys, with a gradual cooling trend expected next week.

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

* Breezy conditions will increase Sunday and Monday afternoons, elevating fire weather concerns and creating choppy lake waters.

DISCUSSION

The synoptic pattern for the short term remains dominated by a broad upper-level ridge centered over the Great Basin, maintaining a hot and dry airmass across the region. Monsoonal moisture continues to advect into the area from the south on the periphery of the high pressure, providing fuel for afternoon convection the next several days.

Dangerous heat will persist through the weekend. High temperatures today and Sunday will reach the upper 90s to low 100s across western Nevada valleys, with some areas potentially exceeding 105F, especially in lower desert sinks. Lower Sierra valleys and foothills will see highs in the 90s, while Lake Tahoe and higher elevations of the eastern Sierra will be in the upper 80s to low 90s. Overnight lows will offer little relief, generally remaining in the upper 60s to low 70s in the valleys, contributing to widespread Moderate to Major HeatRisk across the region. Heat Advisories and an Extreme Heat Warning remain in effect through Monday morning. A gradual cooling trend will begin on Monday, with highs dropping by 10 degrees by Wednesday.

Isolated to scattered afternoon showers and thunderstorms are expected today and Sunday. Convection will primarily be focused on the eastern Sierra, S Lyon, and Mineral counties (20-30%). Lower chances for showers and thunderstorms will be possible farther north along the Sierra Front this afternoon around 10-20%. High DCAPE (1600-1800 J/kg) support the potential for strong outflow winds (45-55 mph gusts) as the primary hazard with any storms that develop. PWATs around 0.60-0.90" are sufficient for brief heavy rainfall, especially in areas with antecedent moisture. Coverage is expected to decrease slightly on Monday as drier air begins to filter in from the west, though isolated activity will likely continue for the eastern Sierra and Mineral County.

Afternoon breezes will increase through the weekend. Westerly to southwesterly winds of 10-15 mph with gusts up to 30 mph are expected Sunday afternoon and evening, particularly along the Sierra Front and in northern Washoe County. These increased winds, combined with hot and dry conditions, will elevate fire weather concerns. Smoke from Pacific Northwest wildfires may also be directed into Lassen and N Washoe counties during overnight hours Sunday into Monday.

Looking ahead to next week, the upper-level ridge is forecast to gradually shift eastward, allowing for a more zonal flow pattern to develop across the region by mid-week. Monsoonal moisture is expected to increase significantly mid-week, leading to higher chances and coverage of showers and thunderstorms, especially Wednesday through Friday. While the primary threat will likely remain strong outflow winds, the increased moisture and slower storm motions could lead to localized flash flood concerns, especially in Mono County.

-Justin

AVIATION

Showers and thunderstorms return to the forecast this afternoon for KMMH, KHTH, and the Sierra Front. Chances from KRNO to KMEV are 15%, and increase to 30% over KMMH. Probabilities for showers and thunderstorms become confined to Mono/Mineral counties Sunday afternoon, with similar chances.

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 through this weekend into Monday.

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

-Justin

FIRE WEATHER

Typical afternoon zephyr breezes out of the west this afternoon and Sunday with gusts up to 30 mph across the Sierra Front, N Washoe, and Lassen counties. This will combine with significant triple-digit heat to create elevated fire weather concerns this weekend. Warm overnight temperatures of more than 70 degrees in lower NV valleys will yield poor RH recoveries through Sunday morning.

In addition, isolated dry thunderstorms are possible today and Sunday along the Sierra Front and eastern Sierra over Mono/Mineral counties due to fast storm motions of 15-20kt. Chances for dry t-storms next week will be limited to Mono/S Lyon/Mineral counties for the most part, though location and storm motion uncertainty increases as we head into mid-week.

-Justin

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.