Sunday, December 8, 2013
Most of the remaining part of the storm is currently moving through the area as temperatures up top have dropped from 0F at 5am to -7F at 8:30am as light snow continues. Temperatures will likely continue to fall or remain this cold until tomorrow morning when a trailing wave finally pushes the coldest part of the storm east of the area. Snow showers on the hill will likely continue until tomorrow afternoon, though additional accumulations after noon today will be minimal due to the very cold temperatures and drying airmass.
Another grazing wave in northwest flow will keep temperatures cold and start light snow showers on the hill again during Tuesday afternoon and evening. There should be some warming on the mountain slopes by Wednesday, but it will be most noticeable on Thursday as the trough that had been sitting over the western part of the US moves east. Mountain valleys, on the other hand, are likely to remain cold as strong inversions develop and persist.
Models currently forecast a weak storm for the following weekend. A flat ridge looks to build in the Gulf of Alaska which may shunt Pacific energy to our north and create mostly dry conditions after that.
Friday, December 6, 2013
The very cold temperatures these last few days will moderate a bit later today and into the weekend as another surge of colder air drops into the western part of the large trough over the western US. This forces more southwesterly flow over our area by late tonight which should bring some noticeable warming to the mountain slopes. Valleys will remain cold.
That energy to our west will begin to move over our area by Saturday afternoon and will produce light to moderate snowfall through Sunday. While the absolute moisture in the air is low due to the cold temperatures, we may see some significant accumulations if the temperatures warm enough for the snow crystals called dendrites to form. Dendrites are the easily recognizable pointy star-shaped crystal that leads to very low density fluffy snow. If temperatures are too cold, as they are today, the snow crystals that form are more needle-like and pack together much more efficiently, leading to higher snow densities and denser snow.
Due to the snow continuing Saturday night and most of Sunday, I may expect a fluffly 6-12” on the hill by Sunday afternoon. The flow does finally turn to the northwest during the day Sunday which is constructive for snowfall, but moisture should be decreasing then partly offsetting the favorable wind direction.
A final dry trailing wave looks to cross the area early on Monday bringing another surge of arctic air into the area, but no snow. If skies clear Monday night, Tuesday morning could see the coldest temperatures of this event in the valleys as the fresh snow very efficiently cools the low-lying surfaces. However, mountain slope temperatures will begin to moderate as the week progresses, becoming noticeably warmer by Wednesday.
Another storm approaches the west coast near the end of the work week, though current model trends have this storm splitting and weakening as it enters the US.
Wednesday, December 4, 2013
I had another 6” on my deck this morning, and it is snowing lightly. The tail end of the first part of the storm cycle is moving through our area, and snowfall will decrease by this evening after an additional 3-6” during the day. I was optimistic we would be getting near the upper range of my 14-28” forecast, but it appears we will be at the lower end. The mountain-top wind direction never really turned to the northwest for an extended period during the storm and snowfall rates were lighter than I originally anticipated.
A longwave trough extending through the western US and Canada will keep the bitterly cold temperatures in place for the next week. Periods of snow and reinforcing cold air surges will occur this entire period as energy moves down from the polar regions into this longwave trough.
One of these surges is currently timed for Friday but only very light snowfall is expected. Another series of waves moves over us this weekend continuing the cold and forcing higher snowfall rates. Even though there will not be a lot of moisture in this very cold air, snow densities of around 2-4% will create extremely light and fluffy snow leading to not insignficant accumulations.
A final trailing wave on Monday will likely bring the coldest temperatures of this arctic outbreak. Mountain slopes should begin warming by mid-week, though the valleys will remain locked in bone-chilling cold as inversions develop, strengthen and persist.
Tuesday, December 3, 2013
Models are struggling with the exact timing of the moderate snowfall, but it still is forecast to arrive sometime this afternoon. The cold front just to our north gets pushed northward or held stationary by the southwesterly winds aloft until it regains forward progress, certainly by sunset today. Snow will become moderate to heavy then, and continue through Wednesday afternoon. I still expect accumulations likely exceeding 2 feet by sunset Wednesday on the hill, with significant accumulations in the valley as well.
Very cold air will accompany the decrease in snowfall late Wednesday as the main upper low moves overs us. Frigid Thursday temperatures will be reinforced by another wave of extremely cold air entering the area Friday. Another storm dropping south from the arctic will bring yet another wave of cold and significant snow by mid-weekend.
The cold and snow pattern looks to persist into early next week as the currently forecast last very cold wave moves overs us on Monday. This one is not as far west, and it appears that the storm cycle will end then as westerlies begin to infiltrate our area. However, the significant valley snowfall combined with low sun angle this time of year promises vigorous and long-lasting valley inversions, even as the mountain slopes begin to moderate by Wednesday or Thursday. Winter is here to stay!
Monday, December 2, 2013
A storm currently situated to our northwest will affect our area perhaps as early as Monday night with light showers and very windy conditions. The cold front that will bring the very cold winter-like temperatures southward is now projected to move across the area a bit faster than earlier forecasted, perhaps as early as Tuesday morning. Good snows Tuesday should produce 8-16” on the hill by Wednesday morning. Our snow on Wednesday will be dependent upon how far south the frontal boundary moves, and current forecasts have this a but further north and more stationary. For this reason, I’m increasing the forecast a bit and I might expect an additional 6-12” after the morning report that will appear on the Thursday morning report.
There may be a break in snowfall Thursday and Friday before a Pacific wave rounds a building ridge in the Gulf of Alaska kicks the main part of the storm over us late Friday. More snow and likely the coldest temperatures of this arctic outbreak are expected then. Snow and cold will continue through the weekend as additional waves of energy form the north move over the area in the very cold and unstable air mass.
It appears that early in the next work week the ridge in the Gulf of Alaska that has shunted this very cold over our area will not break down as earlier forecast. A small wave is forecast early in the next work week and then a much larger storm is forecast mid week as another surge of arctic air moves over the west.