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.

Unsettled weather on tap for next week

Friday, March 20, 2015

After a stellar start to the weekend today, beautiful sunny and warm weather will persist through Saturday. The ridge responsible for this weather will be flattened by Pacific energy to our north on Sunday, bringing some cooling and perhaps some high clouds. However, more Pacific energy attacking the ridge Sunday night and Monday conspires with some energy moving over Alaska and lobes of energy rotating around the ever-present Hudson Bay vortex to bring unsettled conditions from Monday through most of the rest of the workweek.

There may be some rain showers during the day Monday ahead of the leading shortwave which is forecast to cross our area Monday night, with snow initially only at the highest elevations. There is some cool air associated with this wave, and the northwest flow behind the front should lead to accumulating snow on the hill, perhaps in the 3-6” range by Tuesday morning.

Following this leading wave, further energy and cool air from the Pacific, Alaska and the Canadian plains will move over the area in several pieces, with snowfall enhanced early Wednesday and again Wednesday night into Thursday. As we will be between waves for most of Tuesday, I would expect only 1-4” of snow to be reported Wednesday morning. The last wave currently timed for Wednesday night will be the strongest and coldest, and though amounts are currently uncertain, we could do quite well from this with snowfall in the 4-8” range by Thursday morning.

A break in the weather look likely Friday into Saturday with dry weather and significant warming before the rapidly building transient ridge is flattened by incoming Pacific energy by mid-next weekend. There is model disagreement on the strength and southern extent of this Pacific energy, so the forecast for then is uncertain.

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.

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