Cold front later Wednesday should bring snow
Tuesday, March 31, 2015
A storm currently crossing the Pacific Northwest coast will bring a cold front through our area around Wednesday afternoon, temporarily ending the abnormally warm and dry conditions for a few days. The atmosphere will destabilize tomorrow and we will be prone to gusty winds with falling temperatures, with even the possibility of some thunder and lightening later in the afternoon or early evening. Some of these showers may produce an inch or two or snow on the hill which would be reported Thursday morning.
While most of the energy stays north of us for Wednesday, by Thursday a trailing wave brings a reinforcing surge of cold air into the area. There is a much better chance of snow as the storm is forecast to move more directly over the area by Thursday night. Winds do look like they will turn to the northwest for a period of time between Thursday night and Friday morning, and this will be the best time for snow. I expect 2-6” by the Friday morning report and another inch or two during the morning hours. While we are likely to see snowflakes even in the valley, the very warm temperatures of the past few weeks have warmed the ground surfaces and will preclude accumulating snow.
Skies should clear later Friday and temperatures should warm during the day after a chilly start. Another spectacular weekend is on tap as dry air in generally westerly flow invades the area.
Another Pacific Northwest wave approaches our area early next workweek and brings some cooler temperatures, but this storm will pass well north of our area and likely be responsible for some windy but dry conditions.
Temperatures will warm again behind this grazing wave, but there is a lot of model uncertainty heading into closing weekend. The American GFS has a strong trough crossing the West Coast around Friday and threatens significant snow during the latter half of the weekend. The European ECMWF has a similar trough slightly further west at the limit of its 10 day forecast, but the forecast beyond that has not been generated yet.
Storm on track for Tuesday and Wednesday
Monday, March 23, 2015
The storm advertised in last week’s blog is on track to deliver snow tonight and tomorrow night through Wednesday. There is a slight change in the forecast as the last wave timed for Wednesday night, though still cold, will be drier than originally predicted.
The atmosphere has destabilized ahead of the cold front currently moving through Utah, and any showers that form this afternoon will likely fall as liquid below 9500 feet or so. Upward forcing will increase just ahead of the front by late this afternoon, increasing showers and lowering snow levels until the front moves through around 6pm or so.
Rain will change to snow in the valley around sunset while moderate to sometimes heavy snow should fall on the hill. We should continue accumulating snow in the cool and moist northwest flow into the early morning hours before the snow decreases and becomes more showery during the day Tuesday. I would expect 3-6” on the Tuesday morning snow report.
Another wave bringing more snow is currently forecast to move across the area around sunset Tuesday, leaving another 3-6” on the hill by the Wednesday morning report. Conditions will remain unsettled and showery Wednesday before the last and coldest, but driest wave moves over the area Wednesday night. I expect accumulating snows to end by midnight, with 1-4” reported Thursday morning.
There may be some isolated snow showers in the cool and unstable airmass Thursday before a building ridge brings much warmer and dry weather for Friday into Saturday morning. Current forecasts have the northern portion of a splitting Pacific wave moving through the ridge by later Saturday, bringing some cooling, though showers are currently forecast to remain north of us.
The warmer southern portion of this split wave is then forecast to approach the area Sunday afternoon, increasing the chance of showers later in the day and into the evening and bringing another unsettled start to the next workweek.
Chance of precipitation Thu. / Fri. and again in about a week
Wednesday, March 11, 2015
High clouds in advance of a spitting West Coast storm have invaded our area today as temperatures stay warm. The northern portion of the split storm will move eastward tonight and graze the northern half of Colorado tomorrow and Friday, bringing some cooling and the chance of light high-elevation snows. I expect only 1-4” of snow above 9000 feet from this system between Thursday and Friday afternoons before dry and warm weather returns for the weekend and the beginning of next week.
Interestingly, the southern portion of this storm is forecast to move south into the Baja area by this weekend and loiter for a few days before being nudged inland by another possible Pacific storm timed for mid-next week. As might be expected for a forecast a week away, there is a lot of uncertainty with not only the Pacific storm itself, but how it will interact with the West Coast ridge and the Baja low.
There is hope that an active pattern will return around mid-next week, though there is a lot of model disagreement on whether that will happen.
Continued dry with warming for the next week
Friday, March 6, 2015
The arctic air mass brought by the last storm is still influencing our weather today with cold morning temperatures even as it is being rapidly moderated by the strengthening early March sun. Though we are in a warming trend for the next week, a couple of weak waves embedded in the fast northwest flow north and east of us will keep temperatures near normal Saturday and then again Sunday. The stronger and further west Sunday wave will bring more cooling than Saturday and also showers to southern Colorado.
Temperatures will warm to above average beginning Monday and last through much of the workweek as the West Coast ridge builds. A weak and disorganized Pacific wave interacts with the ridge by the end of the workweek increasing the chances of light showers for then and into the next weekend. Another significant push of Pacific energy is forecast to attack the ridge early in the next workweek, possibly beginning another storm cycle.
Heavy snows likely Monday and Tuesday
Saturday, February 28, 2015
This complicated storm is largely evolving as forecast, though the kicker-wave currently rounding a ridge in the Gulf of Alaska is now forecast to split, adding additional complexity to an already complex forecast. This split should turn out to be good news for our area by later Monday and Tuesday.
First, the cutoff low currently over the western Great Basin is forecast to eject a piece of energy that moves near our area overnight. There will be some upward motion, but because I am not optimistic about snow amounts in the warming southwest flow, I expect only 1-4” to be reported by Sunday morning and possibly another inch or two during the day and another inch or two overnight.
The cutoff low will first be forced to move southward by the upstream kicker-wave tomorrow. As this happens, the kicker-wave itself splits, with the southern portion replacing the current cutoff low and ejecting it over our area by Monday night, while the northern portion mixes with some bitterly cold arctic air associated with the ever-present Hudson Bay vortex.
As the remnants of original cutoff low approach our area Monday, upward motion will increase through the day as temperatures and winds increase. Even though we will be in the negative influence of warming southwest flow, I expect snowfall rates to eventually increase on the hill as the strong upward motions dominate the atmospheric warming, especially later in the afternoon. The valleys, however, may be warm enough for rain or a rain/snow mix in the afternoon.
Snowfall will become heavy to intense around Monday night as the cutoff low phases with northern branch of the kicker-wave, veering the winds to our favored northwest direction by around midnight. Additionally, the very cold air now present in the northern branch of the storm will lower snow densities and enhance snowfall rates as the atmosphere continues to destabilize through Tuesday. I would expect 6-12” of snow to be reported Tuesday morning, with an additional 6-12” falling during the day and overnight to be reported Wednesday morning.
Temperatures will be unseasonably cold on Wednesday and will stay cold into Thursday. Valley inversion will form making as well, making the first few days of March feel like mid-winter. Temperatures will moderate under a building ridge for Thursday and Friday before we are clipped by a fast moving wave traveling through the ridge that may produce snow snow showers on Saturday.
