textproduct: Reno

KEY MESSAGES

* Better chances for valley rain and mountain snow expected today with isolated to scattered thunderstorms possible. Thunderstorms in Western Nevada this afternoon have potential to become severe. * Winter Storm Watches remain in effect for the Sierra and Northeast California for significant snowfall and strong winds with impacts starting as early as Friday evening for the Eastern Sierra.

* Precipitation chances will continue through the weekend as temperatures trend cooler and winds increase. Light snow showers may be possible down to the valley floor in the Sierra Front on Saturday night.

DISCUSSION

Current radar imagery reports showers continuing in the region this morning mostly in Pershing and Churchill Counties as well as the Sierra with a few stray showers in other areas. Forecast guidance shows an upper level low moving into N CA today which starts open into a shortwave and become absorbed within a stronger PacNW low right behind it tonight. This upper pattern will allow for precipitation chances to increase today to between 40-90% by this afternoon. Upon looking at model convective parameters, forecast CAPE values look to top off between 200-800 J/kg with midlevel lapse rates over 7C/km and 0-6km wind shear reaching around 35-55 kts. With this sort of unstable environment today, thunderstorm chances will be 15-35% with storms being of the isolated to scattered variety. Areas that see the higher-end values in convection potential look to be Pershing and Churchill Counties as well as adjacent portions of Washoe, Storey, Lyon, and Mineral Counties. Because of this, the SPC has placed these parts of the CWA in a Marginal Risk (Level 1 out of 5) for severe thunderstorms. This means that storms that occur in these areas have the potential to produce erratic outflow wind gusts up to 60 mph and large hail up to around 1 inch in diameter. Not going to rule out severe thunderstorms outside of the aforementioned areas, but they are leaning non-severe currently (outflow wind gusts up to 45 mph and small hail possible). Please have a way to receive weather updates and alerts today and stay safe! While shower chances are seen throughout today, the window for storms looks to open around 11AM-12PM with peak convection time in the late afternoon. Models do show thunderstorm chances continuing in the NV Basin and Range area going through the overnight hours though the severe threat should diminish before today ends. Winds still look to increase today as well with south to southwest winds gusting to 60-80 mph at the crest.

With the stronger low moving into N CA through the weekend, Saturday and Sunday see similar precipitation chances as today with a slightly lower thunderstorm chance (10-20%). As area temperatures are in a cooling trend (around seasonal normals today and below normal through the weekend), snow levels will drop to around 7500- 8000 ft by this evening allowing for snow to start accumulating especially for the higher portions of the Eastern Sierra. Going through the weekend, snow levels in NE CA and the Sierra look to continue to drop (with a brief rebound to around 7 kft on Saturday afternoon) before getting to below 6 kft on Sunday morning. As such, Winter Storm Watches remain in effect in NE CA and the Sierra for Saturday and Sunday (the Watch in Eastern Sierra starts on Friday evening as accumulating snow in the higher elevations may occur sooner). For more details including snowfall forecast amounts as well as the increased strong winds in these areas (up to 100 mph at the Sierra crest), consult the Winter Storm Watch product. The latest Winter Storm Severity Index (WSSI) shows minor to moderate impacts expected over the weekend with pockets of major to extreme impacts at the Sierra crest. For more information on what these impact levels mean, visit weather.gov/rev/winter especially if you plan to travel over the Sierra this weekend. There is a still good chance for a boom-bust scenario situation based on how unreliable the models have been with this system through this week. However, the latest NBM probabilities show around a 50-60% chance for 2+ ft of snowfall at the Sierra crest by Sunday night. Hopefully later today, confidence will improve on forecast snowfall amounts so continue to watch for forecast updates as they become available.

As for other areas of the CWA, snow levels are likely to come down to 4500 ft by Sunday morning which could result in light amounts of snow for valley floors over western NV, especially for the Sierra Front. Foothill areas above 5000 ft could get a few inches, generally less than 4 inches by Sunday morning. The Reno-Carson City-Minden areas may just see a rain-snow mix Saturday night, but there is 10-30% probability according to the NBM to see at least 0.1 inches of snowfall by Sunday morning which could cause some slick roads for those driving around at that time. In the valley areas, gusts of 30-40 mph are going to be likely this weekend with wind-prone areas potentially reaching 40-50 mph.

For Monday through around mid-week, drier conditions are expected with temperatures starting to rebound before models indicate the potential of another system pushing through the Great Basin. There still is plenty of uncertainty with that next storm system, so continue to monitor for updates as models come into better agreement next week. -078

AVIATION

Precipitation chances increase to around 40-90% and become more widespread across the region today. Isolated to scattered thunderstorms (15-35% chance) are also forecast today within the region with the W NV Basin and Range seeing a marginal risk for severe thunderstorms. Higher portions of NE CA and the Sierra transition to snow during the day which may affect visibilities. Area terminals expect to see increased wind gusts up to around 25-30 kts while Sierra ridge winds reach up to around 50 kts. KTRK and KTVL will have MVFR ceilings starting around 10/17-18Z while the other TAFs sites stay with VFR restrictions. Cannot rule out a shower or thunderstorm this afternoon around all terminals, which could produce sub-VFR conditions and erratic outflow gusts. Will monitor for this and amend TAFs as needed.

Similar precipitation chances are expected through the weekend. Snow impacts for Sierra terminals are looking more likely by Saturday with generally around 5-10 inches of accumulation possible for KTRK, KTVL, KMMH by Monday morning. Sierra Front terminals could also see -SHRASN on Saturday night. -078

REV Watches/Warnings/Advisories

NV...Winter Storm Watch from Saturday morning through Sunday evening NVZ002.

CA...Winter Storm Watch from Saturday morning through Sunday evening CAZ071-072.

Winter Storm Watch from this evening through Sunday evening CAZ073.