Stop your snow dances and start the sacrifices
Friday, January 23, 2015
Your snow dances have not been working. Please escalate the rituals to sacrifices immediately!
A wave in the western Great Basin will drop southward and form a cutoff low around the Baja peninsula this weekend. Additionally, a wave traveling over the top of the west coast ridge will pass to our northeast mid-weekend, dragging some cool air and the possibility of showers over our area for Sunday. There is uncertainty as to how far west the wave will travel so the there may be no snow or optimistically an inch or two during the day.
Temperatures will warm dramatically early in the workweek at all elevations, making the weather for those days feel almost springlike. The cutoff low loitering near Baja will have entrained substantial subtropical moisture and is forecast to move northward back into the Great Basin around Wednesday as some Pacific energy approaches from the west. Models are struggling with the track of this storm as it moves underneath the dominant west coast ridge, and our precipitation will be dependent upon how far east the cutoff low is from us.
Unfortunately, this will be an unseasonably warm storm, meaning any precipitation we do receive on Tuesday night or Wednesday will be rain below 9000 feet or so. But there may be some cooler air on the backside of the storm if the track is in our proximity, so that storm is a bit of a wildcard.
The weather looks to clear after the midweek storm as another Baja cutoff low is forecast to be established, leaving us in the quiet weather between that storm to our southwest and the arctic air to our north and east. Some longer term models show Pacific energy eventually moving over us after that weekend, but there is too much uncertainty in the medium term to have much confidence in those solutions.
Some snow this weekend and early next week
Thursday, January 15, 2015
A ridge currently over the Great Basin will keep sunny skies over our area today and deflect most incoming Pacific energy to our north and east. Some of this energy will graze the area, with clouds increasing ahead of the first wave during the day Friday and light snow developing by Friday night. Light snow will continue into Saturday morning with minimal accumulations before a quick moving ridge behind the departing wave brings the sun back in the afternoon.
After a clear and cool Saturday night, clouds will move back into the area Sunday morning or early afternoon ahead of a series of grazing waves in northwest flow that will keep light snow in the forecast for Sunday afternoon through Tuesday. Snow amounts for Monday and Tuesday are expected to be light and in the 1-4” range.
Model uncertainty is large by Wednesday as the Great Basin ridge rebuilds westward near the west coast. All models predict some some mixing between the relatively warm and wet Pacific airmass as it travels over or through this ridge and the very cold and dry arctic airmass currently entrenched in the northern Canadian plains and resupplied by the Hudson Bay vortex.
Our weather next week and likely beyond will very much depend on the outcome of this battle between the west coast ridge and the Hudson bay vortex. Furthermore, the battle line is forecast to oscillate around our area, meaning a small change in the location of this battle will mean large changes in our forecast weather.
Unsettled weather for Sunday - Tuesday
Friday, January 9, 2015
Four weak and disorganized waves will conspire to end the current stretch of warm and sunny weather by this weekend and produce unsettled conditions lasting through the early part of next workweek.
The first wave currently along the California coast will bring in clouds during the day tomorrow and may produce light snow by later in the day or overnight, with showers possibly increasing during the day Sunday as the wave moves overhead. Quickly following this first wave are three additional waves originating in the central Pacific, the northern Pacific and the Canadian plains which currently are forecast to combine into a moderate storm located in the southwestern Great Basin.
Unfortunately, this storm is forecast to stay first southwest of northern Colorado and then south of us as the storm turns east early in the workweek. While southern parts of Colorado and northern New Mexico might do well, I am not optimistic that we will see significant snow amounts during this period, with showers Sunday through Tuesday producing snowfall amounts in the 1-4” range.
Models then forecast another warm and dry ridge for midweek that will last into next weekend and possibly early the following week. Both the American GFS and European ECMWF are predicting some sort of storm moving into the west coast behind this ridging, but the large discrepancies in the predicted storm track make the forecast very uncertain for then.
Snow showers today lead to warm and dry midweek
Monday, January 5, 2015
A ridge over the west coast combined with a reinvigorated Hudson Bay vortex has allowed Pacific energy riding over the ridge to mix with some cold Canadian air and produce the current snow showers. This also occurred over this past weekend when I predicted 5-10” of snow, but there was not enough mixing to bring the very cold air and the main part of the storm over us, thus the disappointing forecast.
Due to similar conditions today, I would only expect 2-4” of snow by tomorrow morning, and snow showers may continue for at least the morning on the hill, with sun likely in the valley by the afternoon. By Wednesday, mountain temperatures warm significantly under mostly sunny skies, though the valley will stay cool as a temperature inversion reforms due to the cold nights.
Warm weather and mostly sunny skies will last another day or two before all models are predicting a major pattern shift around this weekend as Pacific energy is forecast to break through the west coast ridge. There is a large amount of uncertainty with regards to exactly how that will happen, and those details will affect the weather over our region.
The American GFS forecast has some Pacific energy undercutting the ridge and combining with some moderately cold air from Canada to produce snow showers by Saturday, with unsettled weather continuing though at least the early part of the workweek. The European ECMWF keeps this ridge stronger and the undercutting Pacific energy weaker, producing benign unsettled weather for the weekend. I expect the forecast will change as models get a better handle on how the west coast ridge breaks down.
Snowy weekend on tap
Thursday, January 1, 2015
A very cold low pressure system that brought our frigid temperatures is now cut off from the main jet stream and is spinning in the southern Great Basin. This storm’s weather will likely stay to our south as it moves eastward over the next day, keeping the current temperature inversion and cold valley temperatures around through tomorrow.
This eastward movement of the Great Basin cutoff low is due to a separate Pacific storm currently in the gulf of Alaska that entrains some cold Canadian air and moves towards our area from the northwest tomorrow. The amount of cold air that mixes with this storm system is currently not well forecasted and leads to uncertainty in the snow amounts from this system on Saturday.
There is also uncertainty as to whether a piece of energy from the southern cutoff storm breaks off from the main circulation and begins light snow over our area as soon as Friday night. Nonetheless, snowfall should be either starting or continuing early Saturday in advance of the cold front that should move through the area around Saturday afternoon. Moderate to sometimes heavy snowfall will accompany this storm, though its quick movement will limit accumulations. Ironically, the cold front and its associated winds will physically mix the stagnant valley air, breaking the inversion and warming low-elevation temperatures. I currently expect between 5-10” of low density powder to be on the Sunday morning report, with most of that falling during the day Saturday as snowfall should end by midnight Saturday.
Another weak storm in northwest flow looks to graze our area on Sunday, starting snow in the morning and peaking in the afternoon before ending around midnight. This storm looks to be weaker and warmer than the Saturday storm, producing 2-5” by Monday morning.
Models are currently forecasting a ridge of high pressure to build over our area around midweek, bringing dry weather and warmer temperatures that should persist through the workweek. More Pacific energy is forecast to cross the west coast around then and may bring some storminess into our area for next weekend.
