textproduct: Reno

KEY MESSAGES

* Heavy, wet Sierra snow and strong winds peak this afternoon and evening, so avoid Sierra travel until the storm clears Saturday, when a travel window opens through Sunday.

* A colder, weaker storm will likely bring snow to Sierra passes late Sunday night into Monday, with rain in the valleys.

* A stronger and colder storm Wednesday into Thursday could bring heavy Sierra snow and snow down to western Nevada valley floors.

DISCUSSION

Busy week ahead with three storms lined up off the Pacific. Today's storm is the big one for wind and Sierra snow, Monday's is colder but weaker, and the midweek storm is the one to watch for snow down to the valley floors.

Primary Changes:

* We tightened up the timing of the heaviest Sierra snow this evening and nudged snow levels higher early in Monday's storm. We're also starting to get a better feel for how confident we can be with the midweek storm.

Today into Saturday morning:

* This is the storm with the most bite. A 500 hPa shortwave swings through this evening with strong QG ascent ahead of it, while a 165-170 kt 300 hPa jet sits just offshore. Down lower, 55-65 kt of 700 hPa flow is pushing into the Sierra, and that's why ridges could gust 70-90 mph around Tahoe while the Reno- Carson City-Minden area sees gusts to 55 mph (65 mph in wind- prone spots along US-395 and I-580). Expect a rough ride for high-profile vehicles and 2-5 ft waves on Tahoe and Pyramid Lake. The HRRR and RRFS both pack the heaviest snow into a narrow band right along the cold front, roughly 3-7 PM at Tahoe and 4-9 PM in Mono County. Rates of 2-3"/hr with brief bursts near 4"/hr will make Sierra travel very difficult this evening, so if you can wait until Saturday, do. Totals of around a foot above 7000 ft at Tahoe (up to 20" on the crest) and 1-2 ft above 7000 ft in Mono County still look on track. Western NV won't see nearly as much since the SW flow keeps the valleys shadowed most of the day, so expect just 0.2-0.4" of rain, mostly as the front comes through. It won't be a smooth day for flying either, with wind shear and mountain waves.

Saturday afternoon-Sunday:

* A nice break between storms. It'll be cold Saturday morning with lows in the teens and 20s, then milder Sunday with valley highs in the mid 50s. If you need to get over the Sierra, this is your window, but snow left over from today's storm could still cause travel issues, so check road conditions before heading out.

Sunday night-Monday:

* The ECMWF, GEFS, and Canadian ensembles are in good agreement on a quick-moving 500 hPa shortwave with the 300 hPa jet overhead Monday morning. The tricky part is the snow levels. They start near 7000-8000 ft Sunday evening, right around pass level, settle near 6000-6500 ft Monday, then fall to around 4000 ft Monday night as the storm winds down. That's why Carson Pass, which sits higher, has a 75-95% chance of more than 6", while Echo Summit (30-80%) and Donner Summit (20-60%) are lower. Some of the early precip there falls as rain or wet snow. Lake level has a 50-90% chance of more than an inch of snow. In Mono County, snow arrives later, Monday afternoon into Monday night. Mammoth Lakes and June Lake have a 50-90% chance of more than 2", and Mammoth Mountain has a 50-85% chance of more than 4". Ridges gust 50-65 mph Sunday night, but the valleys stay much calmer than today. Rain chances in western NV are higher than they looked earlier, with a 70-85% chance of more than a tenth of an inch in Reno, Carson City, and Minden and a 30-50% chance of more than half an inch. Plan on winter travel over the passes Monday morning.

Tuesday:

* Colder start with lows in the teens in the Sierra and mid 20s in western NV, and a few leftover snow showers near Tahoe. Tuesday afternoon into evening looks like another short travel window, but it closes fast. Shower chances in the Sierra climb to around 30% Tuesday night, and winds and snow pick up Wednesday afternoon ahead of the next storm.

Wednesday-Thursday:

* We're confident a colder storm shows up, but the details are still fuzzy. The GEFS and Canadian ensembles dig a deeper 500 hPa low farther south and park it over Nevada into Friday. That would mean a longer, colder storm and a better shot at valley snow. The ECMWF ensemble moves it through faster and farther north, so it'd be a shorter hit with less valley snow. The 12Z GFS leans toward the slower idea. Either way, another round of strong 700 hPa flow ahead of the front brings gusty winds Wednesday, and ridges could top 70 mph. Snow levels fall toward valley floors Thursday, so if you have midweek travel plans or commute around Reno and Carson City, keep an eye on updates. We'll hold off on snow totals until the models come together.

Next Friday:

* The coldest air of the week looks to settle in Thursday night into next Friday. If the slower GEFS and Canadian solution wins out, snow showers could hang on into Friday. If the faster ECMWF solution is right, Friday turns drier as high pressure builds in. Either way, the ensembles favor a drier stretch heading into next weekend.

-Johnston

AVIATION

KRNO Outlook:

* It will be a bumpy afternoon. Strong south winds gust to 30-40 kt until the cold front comes through around 00Z, and pilots have reported light to moderate turbulence and LLWS on approach early this afternoon. The front brings a quick round of rain and lower clouds from about 00Z-03Z, then winds turn west and ease. Even after the surface winds calm down tonight, strong winds just above the ground mean wind shear on approach and departure is likely, especially 05Z-10Z. Saturday looks quiet, with VFR and light winds.

Regional Outlook:

* The Sierra airports take the brunt of this storm. Rain turns to heavy snow at KTRK and KTVL in the late afternoon, and visibility could drop to 1/2 mile or less from about 23Z-03Z, with snow piling up on runways. Lighter snow showers hang on overnight before skies clear early Saturday, with around a 10% chance of fog or low clouds at KTRK Saturday morning. KMMH gets its heaviest snow from about 02Z-08Z. Wind shear near the surface is likely at all terminals at times through 14Z Saturday. It's most widespread at KTRK and KTVL this evening, at KMMH overnight, and at KCXP and KMEV after midnight. Ridgetop winds of 55-65 kt will make for rough rides over and east of the Sierra into this evening, with strong mountain waves. Expect icing in clouds and mountain obscuration until the storm clears. As of this writing, AIRMETs are out for turbulence, wind shear, strong surface winds, icing, low clouds, and mountain obscuration. A SIGMET is also out for turbulence over the eastern Sierra through 23z Friday.

36-72 Hour Outlook:

* Saturday afternoon and Sunday are the best flying days, with VFR and lighter winds between storms. There is a small chance (5% or less) of fog or very low clouds at KTRK over the fresh snow late Saturday night, with increasing high clouds ahead of the next storm limiting it. The next storm brings snow and low clouds back to the Sierra terminals late Sunday night into Monday, with IFR likely at times. The western Nevada airports should mostly stay VFR, with a few light rain showers Monday morning potentially reducing visibility to MVFR.

-Johnston

REV Watches/Warnings/Advisories

NV...Wind Advisory until 7 PM PST this evening NVZ005.

Wind Advisory until 10 PM PST this evening NVZ001-003-004.

Winter Storm Warning until 10 AM PST Saturday NVZ002.

CA...Wind Advisory until 7 PM PST this evening CAZ070.

Wind Advisory until 10 PM PST this evening CAZ071.

Winter Storm Warning until 10 AM PST Saturday CAZ072-073.