February 8-9 Potential Winter Storm

A snowfall event looks to be setting up for the Northeast.

The above model shows the snowfall forecast for February 9th. Keep in mind this is total accumulated snow. The GFS model is printing out several inches for inland New York, southern Maine and other states in New England. Heavier totals, possibly close to a foot of snow, may hit eastern New York, Massachusetts, and even into Vermont.

I should mention that the shorter-range NAM model is much less enthusiastic with these totals, and other models are not supportive of such a big snowfall like the one shown above. Regardless, accumulating snow is likely to fall in this region. Totals will become more apparent with time.

Andrew

Valentine's Day Potential Coastal Snowstorm

There is potential for a coastal snowstorm near Valentine's Day on the 14th.

Above, the mean sea level pressure forecast is shown for February 12th. The synoptic overview is very stagnant, with strong high pressure in place across the nation. A large swath of modest low pressure is present north of the Yucatan Peninsula in the western Gulf of Mexico. This is the storm system we are watching for this event. To be perfectly honest, the prized Nor'easter track is quite nearly the only option this storm has. You have two strong high pressure masses that are essentially rolling out the red carpet between them. With strong high pressure over land and equally strong high pressure out to sea, any storm systems are easily persuaded into going up the East Coast.

Moving ahead to February 13th, the storm system has taken that red carpet path up the coast and is in the Mid-Atlantic. Although it shows two low pressure systems, I have a pretty good feeling that they would have a fair shot at merging, if this forecast were to verify. Regardless, both high pressure areas previously mentioned have now moved out of their domains, with the US high pressure pushing south and the Atlantic high pressure system also pushing south. This then raises the question, can the storm still continue on a path that would favor a lot of snow for the Northeast? Well, if we look again at the storm system, we see a tendency for lower pressure to apparently be trying to spread east towards the Atlantic. That tells me that it wants to go out to sea rather than going up the coast. In the Nor'easter track's defense, the storm is well enough inland that, even if it were to try and go out to sea, it would be moving northeast and would still make a clean hit on the Northeast for accumulating snow.

I want to dabble in that February 13th timeframe some more, but now we are looking at 500 millibar height anomalies, with warm colors indicating high pressure and cold colors showing low pressure. I'm taking a look at the atmospheric set-up for this storm, and i'm not really getting good vibes about it. In order for the storm to go up the coast, high latitude blocking in Greenland is almost a necessity. And while we do have some high pressure anomalies over Greenland, the majority is too far south for my liking. Also, high pressure in the Pacific Northwest and low pressure trying to rebuild in the Southwest makes me think a Rex Block is trying to form. The Rex Block consists of high pressure stacked on top of low pressure. Downstream of this blocking pattern is more zonally-oriented (west-to-east jet stream, little cold) wind flow, something that would try to force this storm to go more out to sea rather than up the East Coast.

Finally, we arrive on Valentine's Day. The storm has 'bombed out' to a central minimum pressure of 980 millibars in typical Nor'easter fashion. It is certainly giving quite a bit of love to the New England area, as very heavy snow is accumulating in much of the region as this event happens. As the projected snowfall graphic shows below, the accumulations would be extreme if this event happened:

I need to see multiple runs of the ECMWF in coming days to see if this event is still a go in the model's eyes, because right now, there is little support in other models and ensembles for an event of this magnitude to happen. I'm very on-edge about the lack of blocking high pressure over Greenland; I really want to see more enthusiastic high pressure over that land mass before I can look more positively at this storm's prospects. I would also like to see less of that Rex Block set-up; that puts me at an uneasiness I need to settle before I go ahead with more confidence on this event's potential.

Andrew

Winter Not Over Yet

I do not believe that winter is over just yet, although we begin to approach the final weeks of the winter season.

Pictured above is the GFS Ensemble 500 millibar forecast for the very end of the forecast period, February 20th. High pressure has built in over the North Pole, and strong low pressure is present over south central Canada, extending into the Great Lakes. This is all in response to the sudden stratospheric warming we saw earlier on last month. The warming is now dying off, but its effects will continue for at least another week or two. During this time, previous warming will continue to propagate down to the surface, leading to increased chances for cold weather. One thing I am fairly certain of is the high latitude blocking finally making it into the North Pole. This blocking high pressure is already in northern Asia in the medium range, so only a slight shove north would result in the high pressure system reaching the North Pole. This could also be another effect of the previous sudden stratospheric warmings, or SSW's. SSW's are known to provoke blocking high pressure in the higher latitudes, so such a solution is certainly plausible. I do have some concerns about that small low pressure area in the Southwest US and high pressure area in the Pacific Northwest. That is a common set-up for a Rex Block pattern, which can induce warm and dry conditions over the East US- something snow lovers are certainly fearing.

Now, you may have seen some Madden-Julian Oscillation (MJO) forecasts that were moving into Phases 1-3 during this timeframe, which decreases cold and snow chances with each increasing phase. However, it looks like those models may be on the wrong track. As several global models have also been hinting at, this forecast shown above depicts Outgoing Longwave Radiation (OLR) anomalies for the next few weeks. The images are centered over the Equatorial Pacific, where the MJO occurs. For those unfamiliar with the concept, the MJO changes phases by tropical convection moving from one part of the Equatorial Pacific to another. Cold and snow is most favored when this enhanced convection (negative OLR) is shown in the Atlantic or the Indian Ocean. The above forecast from the Roundy Waves Albany indicates that very powerful negative OLR anomalies may evolve going into the last week of February. It is plausible that the last week of February may then be very active. I would like to wait a little longer until we get closer to this timeframe, but right now, it appears that a cycling MJO in phases 8-2 may occur throughout February. Those three phases are notorious for bringing cold and snow to parts of the US in the cold season.

Andrew

Valentine's Day Possible Winter Storm

It looks like the atmosphere is preparing itself for a winter storm that would hit around Valentine's Day.

Above is the GFS Ensemble 500 millibar height anomaly forecast for February 10th. We can see low pressure in the Southwest US, as well as high pressure stacked on top of it in the Pacific Northwest and Southwest Canadian regions. This stacking formation is an atmospheric blocking pattern called the Rex Block. When the Rex Block sets up, you have two centers of low pressure and high pressure that are essentially not moving unless the other does. As a result of Rex Blocks that form on the West Coast, one tends to find high pressure and zonally-oriented (plain west-to-east wind flow, no cold shots pushing south) wind flow. This is exhibited well in the forecast image above, where you can see strong high pressure in the East US as a byproduct of not only the solid Rex Block, but also due to the deep trough in the Bering Sea. This trough of low pressure means an index called the West Pacific Oscillation is positive. The positive WPO brings about low pressure in the Bering Sea and high pressure (and warm temperatures) in the East US.

Moving ahead to February 12th, we see that it is the low pressure system in the Southwest that has budged first. As a result, the high pressure system in the Pacific Northwest and Southwest Canada has backed off and begun to shift a tad west back towards the Pacific Ocean and Gulf of Alaska. Due to the concurrent weakening of the trough in the Bering Sea, the positive WPO regime weakens, and the high pressure system in the East US begins to move out to sea and weaken in the process. But back to the storm, that low pressure system that essentially blinked first in the Rex Block has to go somewhere. And the only option is for it to go east into the Plains. This is displayed well in the ensemble forecasts for this depression in 500 millibar heights to shift towards New Mexico and Texas. If we look at the rest of the Northern Hemisphere, we can get a feel for the factors that will play into the eventual track for this system. For one, low pressure is centered over southern Greenland, so this storm is unlikely to go up the coast....for now. Low pressure in the Bering Sea and high pressure in the East pretty much rules out a coastal track or even a track that brings the best snow to the Ohio Valley and central Great Lakes. It is very possible that the track would be up through the central and Northern Plains, a track that has fooled the Central and East US out of far too many storm systems this winter.

This is certainly bound to change, and I will update when it does. This is a look at what could happen come Valentine's Day.

Andrew

February 3-4 Strong Alberta Clipper

GFS Snowfall forecast

NAM Snowfall forecast

A strong clipper system looks to put down as much as half a foot of snow in parts of the Midwest and Ohio Valley, as many models are now catching onto.

Alberta clippers are small low pressure systems that originate from the Canadian province of Alberta, hence the name Alberta Clipper. The systems are fairly strong, but are coming from the dry climate of Canada. As a result of this dry environment, the clippers are so moisture-starved they usually can only put down a few inches of snow at a time. However, when the environment is primed, some moisture from the Gulf of Mexico can be forced north, and may be able to get caught in these Alberta Clippers. This scenario looks to unfold tonight into tomorrow. Some of this Gulf moisture will be far enough north that the Aberta Clipper can make something happen. As is typical of an Alberta Clipper, the snow band will be narrow, and the gradient will be tight. Wherever this narrow band hits, one can expect a solid 4-5 inches, possibly more if you're lucky.

Andrew