If you look back at the discussions from yesterday, you will see a water vapor image I posted showing the position of the storm system out in the Pacific that promises to be a trouble maker for us along about Tuesday. Comparing that one to the image on the right, you can see that this system is now moving into northern California pretty much on schedule. Also, a time lapse shows it moving to the SE which is also what has been expected.
Now that it is over our land based observational network, we will have better sampling and therefore better data to work with. The guidance has been remarkably consistent to this point and the guidance we receive later this afternoon should provide us with a much better idea of just what to expect.
Between now and then, we have some other issues to deal with. Obviously, a cold front moved through during the overnight hours and the brisk northerly winds and cloudy skies will result in a very short thermometer today. There is some concern about some light rain or drizzle possibly forming overnight tonight and since temperatures will be near freezing Monday morning, that could create some travel issues; particularly the bridges and overpasses.
Monday will not see much of a warm-up and temperatures will likely be falling all day Tuesday. With temperatures only in the teens or low 20s and strong northerly winds, that will create a very dangerous wind chill with values likely in the single digits or below zero for Tuesday and quite likely much of the day Wednesday as well.
Notice I have not said much about accumulations as yet. There are several reasons for that, not the least of which is the high degree of uncertainty that we are still dealing with until we get better sampling of the storm system and a better idea of its track. All indications up to this point strongly suggest it will rival the Christmas Eve blizzard of 2009, but as we have also mentioned, the devil will be in the details. Those details involve the exact track the surface and upper level features take and the horizontal and vertical profiles of temperature and moisture. For example, some of the guidance we have received suggests there will be a significant accumulation of ice before the changeover to snow and some of the other guidance suggests more snow and less ice.
Anyway you look at, this promises to be a significant winter weather event which will be followed by the coldest weather we have had in at least 10-15 years. By later this afternoon, we should start getting more reliable guidance so stay tuned and check back for updates.