textproduct: Reno

KEY MESSAGES

* Relatively fair weather continues through much of Sunday with localized freezing fog in the usual valleys in the mornings. It is a good time to prepare for the upcoming winter storms.

* This will be the most significant series of winter storms since the holiday season starting on Monday.

* Plan on large impacts to travel due to periods of heavy snow and wind, including the lower elevations, through most of the work week.

DISCUSSION

Satellite imagery this morning is showing mostly clear skies across the region, except for a few pockets of low clouds and fog or freezing fog. Areas of fog are expected to continue during the early morning hours at their usual locations, including the Martis Valley and other low valleys in western NV. A repeat of this is likely tonight as light winds, dry conditions, and mostly clear skies will lead to inversions allowing for moisture to be trapped in valleys. Mild temperatures are expected through Sunday, as the upper ridge aloft allows for warmer and drier conditions to prevail across western NV, the Sierra and NE CA.

Our winter storm system for this weekend into next week keeps shying away from us. This system was initially expected late tonight (several days ago), but now it has moved all the way to late Sunday into Monday with significant impacts starting by Monday. In other words, it has been a difficult system to forecast. Anyway, periods of valley rain, mountain snow and gusty winds should slowly start by Sunday afternoon. The winds start early over ridgetop areas on Saturday as the upper low slowly approaches the region.

Sunday is currently looking like a low impact day with gusty winds mainly over mountain areas as 700 mb winds are likely to go into the 35 to 45 kts range. This will definitely bring some aviation and recreation concerns. Rain and snow appear to be mostly restricted to portions of NE CA and the northern Sierra from the Tahoe Basin northwards. Any accumulations appear to be relatively light with liquid amounts generally below 0.15 inches, and only a 10-40% chance of exceeding said value (the higher probability is for areas near the Sierra crest). Similarly, snow amounts above 5.0-5.5 kft will be light below 0.5 inches, and 10-40% probability of exceeding 0.5 inches of snow.

Monday through Wednesday will be the main days for the winter storm with significant impacts, as a series of lows/shortwaves swing through the Sierra and into the Great Basin. There are high chances for significant accumulations of snow in the Sierra. The chances for exceeding 3 ft of snow at the Sierra crest from Monday through Wednesday night are 60-90%, while the Sierra valleys (Lake level/US-395) have a 50-90% chance of exceeding 18 inches. So, a lot of snow is likely and regardless of how much we actually get, it will cause significant impacts. There will be some breaks but at the moment they appear to be brief. Plus there is enough uncertainty with the timing and position of the systems to say for sure.

Meanwhile, western NV will start with rain Sunday into Monday. However, the transition to snow is expected late Monday evening into Tuesday, as the snow levels drop below valley floors and don't appear to come back up for the rest of the work week. The foothills, including Virginia City have a 40-70% chance of exceeding 6 inches, while the valleys, including Reno have a 20-50% of exceeding 4 inches. Take these numbers with caution as the end of this system is still far away. Thus these numbers will definitely change through the weekend as we get more data. The message here is to prepare for the potential of multiple days of winter weather, especially for those that commute to work as it doesn't take a lot of snow to have road travel delays.

Winds will be of concern through the week. Gusty winds are likely over the ridgetops starting on Saturday through much of next week. The strongest winds are expected on Tuesday, and the past several days have been highlighting that same day. So, we have moderate to high confidence for those winds on Tuesday as NBM guidance continues to show a 40-70% chance of gusts greater than 45 mph. Wind prone areas also have a 30-50% chance of Tuesday of observing damaging winds.

When is this going to end? Well, long-term deterministic and ensemble data suggests a transition to warmer and drier conditions towards the end of next week. However, some members are also hinting at some type of weak system possibly affecting the region again over the next weekend.

-HC

AVIATION

Mostly VFR conditions are expected across the region through tomorrow. The only exceptions will be for isolated areas in the Sierra, including KTRK, where low clouds and FZFG will lead to MVFR to LIFR conditions through 16-18Z. FZFG is likely to return to KTRK tonight between 07Z-17Z, give or take an hour or two. Localized mountain obscurations persist through 15-20Z today. A thick deck of high clouds moves in after 18Z too. Otherwise, expect dry conditions with winds generally light and VRB through tomorrow.

-HC

REV Watches/Warnings/Advisories

NV...None. CA...None.