Wednesday, November 26, 2014
Boy, forecasting is hard. And humbling. And what did I say about changing a forecast in the last post!?
Originally, I had thought the final wave in the storm cycle timed for Tuesday would struggle to produce snow in the warming atmosphere forecasted by the models. In fact, the temperature up top rose from about 3F first thing Tuesday morning to about 19F by the early evening. However, during the morning hours and until the early afternoon, snow was falling both up top and here in the valley at about 0.5”/hr as temperatures warmed, and that prompted me to revise my guarded forecast to be more optimistic.
I even joked how I don’t like to revise forecasts for the very reason that it tends to break BOTH the original forecast and the revision!
I heard reports from the hill today that by about 2pm or so yesterday, freezing rain had started on the upper mountain and quickly crusted over the high quality powder. The valley saw freezing rain by around 4:30pm, and then periods of mixed precipitation and freezing rain through the evening hours. Furthermore, the Tower SNOTEL site indicated about an inch of precipitation fell from late afternoon yesterday through early this morning without any increase in the snowpack depth, indicating rain or freezing rain was impacting the measurement there as well.
Freezing rain occurs when an elevated warm and moist layer above freezing sits above a cool layer of air below freezing. So, there must have been this layer somewhere above 10,000′, though I can’t find it in any of the upstream observations. Animations of satellite pictures do show the north-northwest to south-southeast jet stream moving eastward and allowing warmer air to enter the area as forecast, but I did not expect it to be above freezing above 10,000′. Furthermore, the average temperature profile of the atmosphere over our area was cold enough for snow, but in hindsight a thin warm layer would not significantly change the average temperature over a much deeper layer.
The end result was I missed forecasting freezing rain on the hill because of this thin warm layer, which meant the inch of liquid that should have produced a foot of snow stayed as rain. And produced a layer of ice 1/4” thick up top. In fact, the ice crust grew thicker with elevation as there was not enough time for any of the rain to turn to sleet before freezing on the snow surface near the top. At this point, I’m finding it hard to find the evidence I missed that would have created a better forecast.
While rain on the upper hill is not likely in the winter here, it does happen, albeit very infrequently. Freezing rain, on the other hand, is a much rarer occurrence.
Tuesday, November 25, 2014
Snow has started earlier than I anticipated, with a couple of inches of snow already accumulated on my deck. There was some slight warming aloft that I though would inhibit snowfall this morning, but this warmer layer ended up being above mountain top and thus has not adversely affected snowfall production.
So, not only will we have more snow than the 5-10” I forecast yesterday because it started earlier, but it is likely to be more productive than I originally thought. I usually don’t change a forecast this close to an event (since that has a habit of breaking BOTH the original forecast and the updated forecast), but it seems likely we will see 8-16” on the hill by tomorrow morning.
Monday, November 24, 2014
The forecast from last Tuesday was so good I did not need to update it! It appears that the Steamboat Ski Area started posting mid-mountain 24 hour snow totals on their website, though I am assuming (because Steamboat STILL insists on NOT including a datestamp on their observations - feel free to email them and let them know their numbers are near useless if we don’t know the time period they represent!) 8” was reported yesterday morning and 9” was reported this morning.
As you can tell from the Powdercam picture taken around 9 am this morning, there is over 2 feet of settled storm snow up top from Saturday afternoon when the current storm cycle started.
More snow will accumulate through the daylight hours today, with an enhancement increasing snowfall rates early this afternoon. Probably 5-10” of snow will be reported by tomorrow morning, though most of that has already fallen.
Snow will taper off after sunset tonight, though it may not completely stop. The last wave in this storm cycle will bring some slight warming and windy conditions starting tomorrow afternoon and lasting through midday Wednesday. Snow will increase during the day tomorrow and become moderate to heavy overnight before tapering off by Wednesday around noon, but I would expect another 5-10” for the Wednesday morning report, with another 1-4” of new snow falling by noon.
Conditions will rapidly improve later Wednesday with significant warming by Thanksgiving Day, as the forecast made by the American GFS last week verifies over the European ECMWF forecast from then. Beautiful and mostly sunny weather should persist into the weekend before a weak wave in northwest flow grazes our area on Saturday. At this point, some cooler air and clouds look to be the only impact.
Temperatures warm again heading into early next week before another strong storm is forecast to affect our area sometime around Tuesday.
Tuesday, November 18, 2014
Lots of weather to talk about for the upcoming week, with a couple of rounds of heavy snows likely starting later Saturday and extending into Thanksgiving week.
Currently, a weak wave to our northeast has brought cloudiness and some high elevation flurries to our area. This wave will reinforce the cold valley temperatures before they will moderate a bit by tomorrow afternoon. Concurrently, a west coast ridge will be weakened as two waves move through it; the first moves over our area on Thursday and may produce some minor accumulations Thursday night.
The second wave takes a southerly track through the desert southwest and looks to miss our area entirely. However, these waves destroy the west coast ridge and allow another and much stronger Pacific storm to cross the northwest coast late on Friday and move over our area late Saturday night or Sunday. This is forecast to begin a long-duration snowfall event that may last most of Thanksgiving week as additional waves of energy in moist and cold northwest flow move over our area.
Snow will begin ahead of the wave around Saturday afternoon and will become heavy overnight. Depending on when the snow starts Saturday, there may be as much as 5-10” of new snow on the hill by Sunday morning. Additional waves of energy will keep Sunday cold and snowy, with another 5-10” of snow by Monday morning. Snow may taper off on Monday before increasing again on Tuesday as yet another moist and cool wave in northwest flow moves over our area, likely leading to additional significant snow accumulations for Wednesday’s Scholarship Day.
By midweek, there is considerable disagreement between the models, though at this point I would side with the European ECMWF which shows another cold and snowy arctic outbreak around Thanksgiving Day.
Saturday, November 15, 2014
The storm forecast for today is winding down and is expected to end by midnight, with 8” of snow showing on the Steamboat Powder cam as of 5:30 pm this afternoon and possibly another inch or two added for the morning observation. Cold temperatures will follow in the wake of the storm, falling from the current 2 F up top and 15 F in the valley.
There may be some clouds the next 2 days as waves of energy skirt to our northeast around a very cold mid-west trough, but we should see increasingly sunny skies headed into midweek. Warmer temperatures will return by Tuesday afternoon ahead of a Pacific disturbance undercutting the west coast ridge. This is the storm originally forecast to bring significant weather to our area, but now the storm is forecast to be considerably warmer, weaker and slower. Furthermore, there is model uncertainty with respect to the strength and timing of this wave.
Models indicate some sort of storm for next weekend after a transient and shallow late-week ridge moves over the area, but the details of that forecast are in doubt considering the midweek uncertainty.