Saturday, February 28, 2015
This complicated storm is largely evolving as forecast, though the kicker-wave currently rounding a ridge in the Gulf of Alaska is now forecast to split, adding additional complexity to an already complex forecast. This split should turn out to be good news for our area by later Monday and Tuesday.
First, the cutoff low currently over the western Great Basin is forecast to eject a piece of energy that moves near our area overnight. There will be some upward motion, but because I am not optimistic about snow amounts in the warming southwest flow, I expect only 1-4” to be reported by Sunday morning and possibly another inch or two during the day and another inch or two overnight.
The cutoff low will first be forced to move southward by the upstream kicker-wave tomorrow. As this happens, the kicker-wave itself splits, with the southern portion replacing the current cutoff low and ejecting it over our area by Monday night, while the northern portion mixes with some bitterly cold arctic air associated with the ever-present Hudson Bay vortex.
As the remnants of original cutoff low approach our area Monday, upward motion will increase through the day as temperatures and winds increase. Even though we will be in the negative influence of warming southwest flow, I expect snowfall rates to eventually increase on the hill as the strong upward motions dominate the atmospheric warming, especially later in the afternoon. The valleys, however, may be warm enough for rain or a rain/snow mix in the afternoon.
Snowfall will become heavy to intense around Monday night as the cutoff low phases with northern branch of the kicker-wave, veering the winds to our favored northwest direction by around midnight. Additionally, the very cold air now present in the northern branch of the storm will lower snow densities and enhance snowfall rates as the atmosphere continues to destabilize through Tuesday. I would expect 6-12” of snow to be reported Tuesday morning, with an additional 6-12” falling during the day and overnight to be reported Wednesday morning.
Temperatures will be unseasonably cold on Wednesday and will stay cold into Thursday. Valley inversion will form making as well, making the first few days of March feel like mid-winter. Temperatures will moderate under a building ridge for Thursday and Friday before we are clipped by a fast moving wave traveling through the ridge that may produce snow snow showers on Saturday.