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.
Continued cold with light snow
Friday, December 26, 2014
The Steamboat ski area reported 4” at mid and 3” up top this morning, and intermittent light snow is currently continuing with peeks of sun. The storm is currently directly overhead, and as it moves east, we should see snow showers increase later this afternoon and early evening as the flow eventually turns northwest. I still expect to see between 2” and 5” of snow reported Saturday morning.
Non-accumulating snow showers might be around early tomorrow morning as a weak trailing wave passes over the area and drags down another dose of arctic air. Showers will be ending by noon, if not before, with some sun in the afternoon, especially in the valley, though temperatures will be stay seasonably cold.
This brief break in snow will end when a storm currently in the Gulf of Alaska digs south along the west coast and brings more light snow into our area around Sunday morning. This storm is forecast to become cutoff from the main flow later in the weekend and meander in the Great Basin early in the workweek. Showers should become steadier by Sunday afternoon and continue through Tuesday. Snow amounts should be inflated due to the cold temperatures and resultant low densities, but amounts are expected to be generally modest. I would expect 4-8” by Monday morning and 2-5” for each of the Tuesday and Wednesday morning reports.
A dry trailing wave brings another push of reinforcing arctic air on New Years Eve day, and if skies clear overnight as currently forecast by some models, bitterly cold temperatures will follow for New Years Day. Again, the longer range models are struggling with the southern and western extent of the arctic air heading into the following weekend, so the forecast is uncertain for then.
Christmas Day storm brings snow and cold temperatures
Tuesday, December 23, 2014
This last storm was disappointing for us, as most surrounding areas received snow in the 18-36” range. I mentioned in the last forecast that any warming aloft is cause for concern. Indeed, freezing rain started on the hill about 2pm Sunday afternoon after a morning of heavy snowfall, which was eerily similar to the Opening Day Ice Storm. Luckily, there was minimal damage to the snowpack this time around, though the lack of accumulating snowfall surely hurt.
Unfortunately, I don’t have a good explanation of why we are getting these very unusual freezing rain events. I’ve sent emails to the National Weather Service and Colorado Avalanche Information Center asking for their opinions, but they are so concerned with future operations that the resources to investigate past events are scarce. I mentioned in the last storm forecast that warming aloft causes my forecasts to lean pessimistic, and apparently I need to increase that negative bias in the future.
After unsettled weather for today and tomorrow, attention turns to the impending Christmas Day storm, currently located in the Gulf of Alaska. This storm splits as it enters the west coast late Wednesday, but a considerable amount of energy is forecast to be in the southern branch as this portion of the storm traverses the Great Basin. Light snow should start around midday on Christmas and we should have a burst of heavy snow when the front moves through later that afternoon or evening. Most of the energy will remain south of our area, but we should continue to receive lighter snow behind the front, leading to 4-8” by the Friday morning report.
It does appear the flow will eventually turn to the northwest sometime on Friday, and that may allow for snowfall to keep accumulating through the day under much colder temperatures. Coincidentally, after the just-passed storm earlier in the week inundates the East Coast, it will help form the Hudson Bay vortex, which is one lobe of the Polar Vortex which received much media attention last year. The counter-clockwise rotation around this vortex allows the bitterly cold arctic air in the Canadian Plains to move southward, enhanced by energy entering the west coast from the Pacific.
Some of this Pacific energy will trail the Christmas storm and move west of us later Friday night, keeping snow showers going through early Saturday morning and leaving another 2-5” for the morning report before a break later in the day. Additional minor waves keep the unsettled and cold weather present from Sunday through midweek, leading to a general forecast of 1-4” for the Monday through Wednesday morning reports.
Current forecasts have a more significant wave bringing a threat of heavier snows around New Years Eve day, but the models are struggling with the westward and southern extent of the cold air, lending uncertainty to that forecast.
Unsettled weather turns stormy by Sunday
Friday, December 19, 2014
The current unsettled weather pattern continues with periods of light snow ending by this afternoon. A transient ridge will move over the area Saturday, but will be quickly followed by storminess starting Sunday and lasting through Tuesday.
Currently, what meteorologists are now calling an atmospheric river is inundating the Pacific Northwest, as shown in the infra-red satellite animation to the right. This is simply a relatively narrow and long fetch of concentrated moisture in the atmosphere. The Pineapple Express, for example, is the well-known moniker given to an atmospheric river originating around Hawaii.
The current atmospheric river with roots in the northern Pacific will move towards our area and begin producing precipitation around Saturday night. Even though we will be in strong and moist northwest flow, current model trends have the atmosphere warming during the day Sunday with very windy conditions, which throws a wrench into the previously very bullish forecast. My experience is that our forecast becomes far more uncertain, and generally leans pessimistic under a warming atmosphere. Our most recent experience with a similar scenario lead to our freezing rain event; we started out with moderate to heavy snowfall as temperatures rose in the morning, transitioning to freezing rain as the warming and upward motion associated with that warming ceased. I am not suggesting that we will see another freezing rain event as I’m STILL not sure what happened there, but wanted to highlight the uncertaintly present.
So, I am now very uncertain about snow amounts during the day. However, cooling does begin by later Sunday, and that increases confidence that heavy snows increase. Winds will stay very strong through the day Monday, continuing the moderate to heavy snowfall until the intensity drops off near the end of the day. Lighter snowfall, however, will continue overnight.
Snowfall from Sunday through Monday will likely be heavy, with what happens during the day Sunday being a bit of a wildcard. Travel will also be very difficult during this time period. At this point, I would guess maybe an inch or two by the Sunday morning report, with 5-10” reported Monday morning. Cooling increases later Monday, decreasing the density of the snow and increasing accumulations, possibly leading to another 4-8” by Tuesday morning.
Wednesday will be chilly with the 1-4” reported in the morning occurring during the day Tuesday. Models have trended significantly stronger with the ridging behind this storm, leading to warming conditions and weakening the storm earlier advertised for Christmas Day. The storm still looks to be significant though with snow increasing during the day Thursday and lasting through Friday morning, leaving another 6-12” by the morning report.
