Monday, January 27, 2014
The current complex forecast has shown signs of stability the past few model runs, increasing confidence that a possible 20-40” long-lasting snowfall event will grace our area for the second half of the workweek and into the weekend.
The Steamboat ski area reported 3” mid at 1pm and 2” up top today, but light snow will continue until about midnight, producing a 4-8” report by Tuesday morning. Tuesday will be a beautiful in-between day before the weather fireworks begin by mid-day Wednesday.
Similar to today, another cold wave drops down the west side of the Hudson Bay vortex and phases with a Pacific wave in the undercutting polar jet stream that is forecast to contain copious quantities of subtropical moisture. Indeed the moisture feed extends all the way from the Hawaiian Islands earning this branch of the polar jet stream the moniker Pineapple Express. The end result is our flow backs from the north to the west, warming temperatures and increasing winds. Snow is currently forecast to begin on Wednesday with periods of heavy snowfall lasting through at least Thursday morning, creating 6-12” by the Thursday morning report.
Most models then slam another undercutting wave into the northern California coast early Thursday, and waves of energy should continue to travel over our area, still interacting with cold waves from the north rotating around the Hudson Bay vortex. There is some uncertainty here, but currently I’m thinking another 8-16” by the Friday morning report if things hold together as forecast.
If the Pacific wave does travel over our area relatively intact, heavy snows will continue through the day Friday followed by moderate to light snow, producing another 6-12” by the Saturday morning report.
During the weekend, the polar jet stream is forecast to buckle and drop a storm into southern California, backing our flow further to the southwest and eventually ending snows by late in the weekend. I would expect another 3-6” by Sunday morning as this storm cycle ends.
Sunday, January 26, 2014
The uncertainty displayed in the numerical model guidance this past week is resolving itself as Pacific energy is forecast to undercut the persistent west coast ridge. This is the first time this season the polar jet stream is finally forecast to carry seasonably warm and very moist air into the west coast, bringing snow to the drought-plagued ski resorts located there and bringing a Pacific storm track into the Great Basin and Rockies.
Before this new regime takes hold, a weak but cold storm currently to our north will bring clouds to the area later today and light snow beginning around midnight. The westward extent of this storm is still bouncing around in the models, but I would expect snow all day on the hill tomorrow with 1-2” by Monday morning and possibly 3-6” by Tuesday morning, with most of that occurring by midnight Monday.
A break on Tuesday before the undercutting jet stream slams into the northwestern coast by late Tuesday. Similar to tonight, another cold wave drops down the west side of the Hudson Bay vortex and phases with a wave in the undercutting polar jet stream that is forecast to contain a fair bit of subtropical moisture. The end result is the polar jet stream is pushed southward to California and our flow backs from the north to the west, warming temperatures and increasing winds.
Snow is currently forecast to begin on Wednesday, and the interaction of the polar jet stream with the cold waves rotating around the Hudson Bay vortex will keep our weather snowy through the week. Additionally, the polar jet stream is forecast to buckle by the weekend, dropping a storm into southern California by the weekend and backing our flow further to the southwest. Snows are likely to continue through the weekend as this very dynamic weather pattern evolves.
With so many interacting pieces, predicting snow amounts is difficult at this time, but an extended period of moderate to heavy snows with periods of high winds is likely starting Wednesday and lasting through the weekend.
Friday, January 24, 2014
The hemispheric circulation pattern is changing next week, but the details are still uncertain. One source of uncertainty is coming from the much hyped polar vortex as it currently has split into two pieces. One vortex resides over the Hudson Bay as it has for much of this winter and last summer, while another vortex has settled over Siberia. The cross-polar flow between these airmasses is decreasing, and they are forecast to become isolated from one another by next week. However, the cross-polar flow is expected to increase near the end of next weekend, and the strength and location of this flow determines how much cold air flows from Siberia into Canada and vice versa.
Additionally, the west coast ridge has also been a dominant and long-lasting feature this winter, and models forecast major changes as Pacific energy is predicted to undercut the ridge. Furthermore, phasing of the undercutting energy with the cross-polar flow around next weekend will keep the west coast ridge evolving and uncertainty high in the medium to long range.
In the shorter term, mountain slopes will warm and valley will stay cool as inversions persist through the weekend. There is a dry grazing wave Friday night, but that won’t have much, if any impact on our weather. A far more substantial lobe of cold air rotating around the Hudson Bay vortex may begin dropping temperatures late Sunday, with light snow possible for Monday and Tuesday.
Forecast uncertainty then increases as another cold wave is forecast to drop down from the north and phase with Pacific energy undercutting the west coast ridge midweek. I’d like to emphasize the timing of the Pacific energy undercutting the west coast ridge is uncertain since the feature has been so dominant this entire winter, but it seems likely to happen. Furthermore, there are additional waves of energy forecast to rotate down from the north through Thursday, and if the west coast ridge undercutting eventually happens as predicted, we should remain in cool and moist northwest flow with accumulating snows, likely significant, through much of the week.
A major wave is then forecast to move through this undercutting flow around next weekend and will likely keep snows going. But the forecast for then will evolve as there is so much uncertainty midweek.
Sunday, January 19, 2014
Beautiful sunny and dry weather will persist through Wednesday as a large and stable west coast ridge dominates our weather, though a grazing wave in northwest flow will knock temperatures back a bit on Monday. A small Pacific storm will interact with the ridge early in the workweek and the result of that interaction as well as the effects of another impulse dropping down the east side of the west coast ridge from the north will determine our weather for Thursday.
I don’t expect much precipitation from this scenario as the strong west coast ridge minimizes impacts from the Pacific storm. Cooler temperatures and perhaps only light snow with minimal accumulations are expected on Thursday before current forecasts cut off this storm from the mean flow and leave it over California to our south and west.
There has been and continues to be a large amount of uncertainty in the forecast for next weekend and beyond. It appears that all models want to change the hemispheric pattern and either undercut or break down the west coast ridge. Numerical models often struggle with pattern changes like this, and the uncertainty with next weeks forecast has persisted longer than normal. At this point, there is no use guessing what our weather may be until more stability emerges in the solutions not only between models but also within models.
Monday, January 13, 2014
The Steamboat ski area reported 8” mid and 10” up top at 5am this morning, with about 2” of that coming overnight. Additionally, another 2.5” has fallen between 5am and 9am and it is currently lightly snowing.
The storm yesterday disappointed as a stabilizing and warming airmass not only stopped the snowfall that I expected to continue, but allowed winds to rake the ski area. By 1pm yesterday, much of the upper mountain had wind affected snow and skiing was not that great.
Another subtle wave in moist northwest flow passes over the area tonight, increasing snowfall again. The atmosphere should gradually cool through tomorrow afternoon keeping light snow showers going on the hill even as the valleys see some sun. I would expect 4-8” to be reported in the Tuesday morning report and 1-4” on the Wednesday morning report, all of which will occur during the day Tuesday.
The snows then stop for an extended period as the atmosphere warms and dries as the west coast ridge builds over our area. A grazing cool and dry wave to our northeast on Thursday will knock temperatures down a bit, but it appears the ridge and its associated warm and dry weather will continue through most of next weekend. Mountain slopes will substantially warm, though valleys will be on the cool side as temperature inversions reform and persist.