The potential for a significant winter storm on Tuesday continues to take shape although the devil will be in the details. If you look at the water vapor image on the right, one thing that immediately stands out is the swirl out in the Pacific Ocean to the NW of California. That is the system that is projected to be the trouble maker for us.
As Nick pointed out in his excellent discussion on Friday, that system is out over the Pacific Ocean where it is not yet being sampled by our land-based observational network. We do get observations of opportunity if some aircraft happen to fly through that area and satellite imagery helps, but by and large systems of this type are coming from an area with very limited, at best, observational data. Once it moves inland, then we have better data to work with. Therein lies the problem for us as the observational data base is critical in our ability to forecast the impacts of a particular system. Thus, our guidance can and occasionally will flip from one scenario to a completely different one once the system has been adequately sampled.
Having said that, the guidance over the last 24 hours has been quite consistent so barring any surprises, we are in for a significant winter storm on Tuesday. Leading up to it we have a fantastic, Spring-like day today with lots of sun and temperatures once again warming into the 60s and 70s across the area.
The first surge of colder air will be arriving during the overnight hours and by Sunday morning we will have northerly winds, cloudy skies and temperatures in the 30s which will only reach the lower 40s by afternoon. There may be a few sprinkles or a brief shower for the more SE counties.
Monday morning could pose some problems as there is a slight chance of some light rain or drizzle and temperatures will be near freezing…thus the potential for some icy patches first thing in the morning, but at least we expect to be above freezing for much of the day.
Tuesday is when things start getting interesting as surface temperatures will be below freezing all day long, but the forecast vertical profile of temperature currently indicates a warm layer aloft which would suggest freezing rain and/or sleet eventually transitioning over to all snow as colder air aloft arrives during the day. Again, the devil is in the details regarding the total accumulation of each precipitation type, but the total liquid equivalent could be as much as an inch. We certainly need the moisture, but would rather not have to deal with the ice.
So, stay tuned and check back for updates.