Weekend storm heralds long-awaited pattern change
Wednesday, February 18, 2015
The current sunny weather will last through tomorrow, with warming temperatures noted. A storm currently rounding the west coast ridge near the coast of British Columbia will mix with some cold air from the Hudson Bay vortex and turn potent, first bringing clouds to the area early Friday followed by showers later in the day.
Temperatures should drop quickly Friday night accompanied by periods of moderate to heavy snows as the storm enters the Great Basin. Pieces of energy ejected from the storm along the frontal boundary will keep strong upward motion over the area through the day Saturday, continuing the moderate to heavy snows in seasonably cold temperatures.
The snowfall forecast will likely change as the event nears and models gain a better handle the storm’s evolution, but I expect significant snowfall to be reported through the weekend. If snow starts by Friday afternoon, I would expect 4-8” to be reported Saturday morning with probably another 3-6” during the day Saturday.
By Saturday night, the storm system becomes sheared as a piece of the storm moves westward over northern California, creating a broad area of lift extending across the Great Basin and into the Colorado Rockies. It looks like snows will continue Saturday night and through Sunday as some of the wave that initially contributed to the cold air on Saturday moves towards our area from the north and interacts with the weakening storm over northern California. Adding the 3-6” during the day Saturday with a forecast of 3-6” of snow overnight yields a 6-12” by report Sunday morning. And another 3-6” during the day Sunday which will be reported Monday morning yielding storm totals of 1 to 2 feet.
Snows should end by Sunday night or early Monday as we are caught between the California storm and the jet stream to our north and east. Though Monday will start cold, seasonable temperatures should return as the workweek progresses before another somewhat similar storm threatens our region by the end of the workweek.
The good news for the medium to long term is that these storms look to end the dominance of the west coast ridge for a while, allowing periods of stormy weather to cross over the area. It appears March might be coming in like a lion!
Once promising storm for Monday fizzling
Friday, February 13, 2015
After another couple of spectacular days today and Saturday, the once promising storm traveling through the dominant west coast ridge is expected to be considerably weakened as it approaches our area. There was hope in the last forecast that some phasing would occur between a loitering cutoff low near Baja, Pacific energy impacting the west coast and waves of cold air circulating around the Hudson Bay vortex. However, the west coast ridge will not only weaken the storm entering the west coast on Saturday, but will keep the Baja low to our south and the coldest air to our north and east.
By Sunday, likely early in the day, the weakened Pacific storm will bring some light showers to our area with only and inch or two of accumulations expected on the hill. Quickly following this wave will be a surge of moderately cold air from the north, bringing more persistent snows for Monday along with significantly colder temperatures. There is uncertainty with regards to the western extent of this cold air, but currently I expect 3-6” of snow during the day Monday.
Even though the threat of snow looks to end later Monday, we will be seasonably cool but mostly dry next week as waves of cold air rotating around the Hudson bay vortex graze our area.
There is another storm forecast for around next weekend or the end of the workweek, but this also might be weakened by the west coast ridge, so the forecast for then is uncertain.
Warm and sunny weather briefly interrupted on Tuesday
Monday, February 9, 2015
After another sunny and unseasonably warm day today, a storm currently over northwest coast will strongly split as it interacts with what has been a very dominant west coast ridge. There will be snow showers above the valley floor later tonight and Tuesday as the northern part of the splitting wave travels north of the area, with an inch or two likely falling overnight and again during the day. Unfortunately, the southern split looks to stay west of our area as it is forecast to eventually loiter over Baja by Thursday.
A dry wave from the north will graze our area on Wednesday and keep temperatures cooler than they’ve been recently, though they will still be warmer than average.
The west coast ridge quickly rebounds for Thursday and Friday bringing more record or near-record warmth to the area. Another grazing wave from the north will likely knock temperatures back on Saturday before they rebound by Sunday.
There is much forecast uncertainty by early to mid next week as models struggle with the evolution of the west coast ridge as it is attacked by Pacific energy. Additionally, this Pacific energy may or may not interact with the loitering Baja cutoff low and additional waves of energy rotating around the Hudson Bay vortex from the north. This leads to some hope that we may be returning to a snowier pattern sometime next week as the west coast ridge breaks down.
Surprise 5 inches this morning with more on the way
Monday, February 2, 2015
I had about 4” of now on my deck at 6:30 am this morning and an additional inch fell by 9 am. I have to admit I was a bit surprised this morning as I expected only several inches today as a wave moved over our area in moist northwest flow, but I discounted the model forecasts as they have not been verifying well for us this January. Furthermore, the European ECMWF model insisted on a much drier forecast, and again the American GFS provided a superior forecast for today. As a result, I will base my forecast on that model for the following week.
Two additional waves with similar trajectories to this morning’s wave will pass over our area Tuesday morning and Wednesday, with the Wednesday wave looking the most impressive of the three.
Snow should taper off today but begin again tonight, and I expect 2-5” on the hill by tomorrow morning. As today, snowfall rates should taper off during the day Tuesday before increasing again Tuesday night. This third wave looks to have more cold air and more dynamics associated with it, leading to a more prolonged event lasting through the day Wednesday and into the evening. I would expect 4-8” of snow for the Wednesday morning report, with an additional 3-6” during the day and overnight which will be reported Thursday morning.
A ridge moves over our area on Thursday, ending the snowfall but leading to a spectacular couple of sunny winter days for Thursday and Friday. Pacific energy is then forecast to flatten the ridge and lead to increasing cloudiness on Saturday and the possibility of some showers late in the day and overnight.
The ridge is forecast to rebound for later Sunday and Monday before another wave of Pacific energy threatens our area with showers around Tuesday or midweek. There is considerable model disagreement on the evolution of that storm.
Record dry January likely followed by chance of snow next week
Thursday, January 29, 2015
A portion of the cutoff low currently off the northern Baja coast will move inland over the next few days, spreading precipitation first into Arizona and New Mexico by Friday and then southern Colorado by Friday night. After a sunny day today, clouds will overspread the area tomorrow. There is uncertainty with regards to the northern extent of the precipitation, with our best chance of showers from Friday afternoon through Saturday afternoon before a dry wave rotating around the persistent Hudson bay vortex in northwest flow brings clearing to the area by Saturday night.
Due to the warm nature of the storm and lack of much wind, I expect modest accumulations at best, with optimistically around 1-4” falling by Saturday morning, Anything under about 6” would mark this as the driest January since the Steamboat Ski Area started record keeping in 1979!
The Hudson Bay vortex is forecast to further expand westward over the Canadian plains this weekend and into next week, and this increases the chances of snow for our area as cool air moves southward. Again, this will be a battle between the arctic airmass to our north and the persistent west coast ridge; periods of light to moderate snow can be expected Monday and Tuesday as a significant push of cool and modestly moist air moves over our area in northwest flow.
Additional weaker waves of energy are forecast for most of the rest of the workweek, leading to the possibility of additional light snow, though it is not clear if these will be productive as they battle with the flattened west coast ridge.
The west coat ridge appears to win by the end of the workweek leading to some warming and drying headed into next weekend. There is large model uncertainty after that as Pacific energy is expected to either weaken or ride over the ridge, hopefully leading to a snowier pattern change heading into mid-February.