January 27-29 Northeast Coastal Clipper Storm

It looks like there will be a clipper system that will hit the Northeast around January 27-29, and it could bring another foot of snow to regions that will receive a foot of snow today (January 21).

Before we get into the system itself, we'll begin with how the pattern will set up prior to the storm.

This image shows the observed jet stream, as of 12z (6 AM Central Time) this morning. We can see the powerful Pacific jet stream roaring along at roughly 200 knots, which is considered a strong jet stream any way you slice it. The jet stream will be playing a crucial role when this clipper system comes along out of Canada, and it may work in favor of strengthening the clipper system as it traverses the Central US and when it jumps offshore. With strong Pacific jet streams like this, you have to be wary of any jet streaks that might carry a storm system onshore and dramatically strengthen it later on in the storm's life.

GFS Ensemble 500mb anomaly (left) and spaghetti (right) forecast for 6 days out.

When the clipper begins to move down towards the United States from Canada, the pattern will be a predominantly northwest flow regime, meaning the movement of the atmosphere is from the northwest to the southeast. This is portrayed well by the 500 millibar height anomalies on the left panel of the GFS Ensemble image above, as we can see the flow dropping southeast after hiking up the intense ridge of high pressure stationed over the western coast of North America. These northwest flow regimes are conducive to clippers as a whole, but this set-up really looks to favor the Northeast for snowfall, whereas we had been seeing the snow stay over the Midwest, Plains and Great Lakes earlier in December and January.

0z GFS 500mb vorticity (left) and 250mb wind (right) forecast for January 27

For the storm itself, the GFS model indicates we will see the clipper ride down from Canada via the northwest flow, and model guidance does have a jet streak riding southeastward with the clipper system. The panel on the right, showing the projected jet stream winds, indicates the jet streak will contain winds between 110 and 130 knots, in contrast to the 80-110 knot winds in the jet stream around the storm. The clipper is expected to drop some accumulating snow across the northern Plains and the Midwest, mostly on the order of 2-5 inches. In a similar scenario as the storm the Northeast is currently experiencing, the clipper will then be ushered offshore.

0z GFS 250mb wind forecast for January 28.

The jet stream will then shoot northward again as the clipper moves east over the Atlantic, which will make the storm ACT like a Nor'easter solely in terms of track. I want to emphasize that this storm will not be a Nor'easter- it will be a clipper system that will take a Nor'easter-like track, running along the East Coast. As the storm pushes offshore in time for January 30, the snow should stop falling across the Northeast, leaving 6-12" in its wake, as the forecast image below shows.

0z GFS total January 27-29 Clipper snowfall.

I believe we will eventually see forecasts bumped up just a bit more as we move closer to this event, mainly because the GFS wants to bring in some of the same convective elements that will be present in today's Northeast snow event to enhance snow totals. While high-resolution models should catch those mesoscale features the best, the GFS model forecast above shows a pretty reasonable forecast in my opinion, with widespread 6-12" along the coastal regions. The weather pattern is ripe for these coastal clipper snow events, and the Northeast should keep an eye out for another foot or two of snow as a result of these systems.

Andrew

Early February 2014 Forecast

This post will address the predicted weather pattern for the first half of February.

January 23-24 500mb height anomaly forecast

As we enter February, expect the pattern to be on the warm-up, as ridging over Japan on January 23rd and 24th means ridging over the US from a January 29th to February 3rd period. Because the ridge in Japan is rather progressive, I wouldn't doubt we see the same result here in the United States when the ridge comes along for early February. By the time we reach February 5-7, it appears we will see another shot of Arctic air.

This image shows an analysis (not a forecast) of the 500mb height anomalies over the Pacific, as of 6 PM Central Time last night. We can see the deep negative height anomalies over the Bering Sea, and the identifier of the Bering Sea Rule, Joe Renken, sees this as a signal that the February 7-12 period will see significant cold weather. I agree with this idea, and it does look like the first 10 or so days of February will be characterized by an up-and-down weather pattern.

GEFS 500mb height anomaly forecast for January 31

I expect we see tentative settling-down of the pattern by the middle of the month, as persistent high pressure just south of the Bering Sea at the end of January indicates we could see a zonal flow situation not unlike we saw earlier this winter, where high pressure dominated the Southeast and stormy weather affected the West Coast. Because of this Southeast ridge returning, I expect we see the late January East Coast snow zone retreating back into the Midwest and Plains. Unfortunately for those in the East, this winter does look to be confined more to the Central US as opposed to coastal regions.

To sum up:

•February 1-7: Warming up in the Central/East US before a cool-down at the end of the period.
•February 8-14: Potentially intense cold in the beginning and middle of the period before a relaxation into more moderate temperatures, especially in the South and East.

Andrew

Forecast for January 9, 2014

Forecast for Sunday, January 19

Sunday won't be too exciting of a day in the weather department, with the Great Lakes encountering only slightly wintry conditions. Snow and a variety of wintry precipitation will visit the Great Lakes and Northeast as a disturbance moves through the area. Some liquid precipitation can be expected around the Virginias tomorrow, but other than that, the Southeast looks to remain dry. Some showers will hamper outdoor activities along the Gulf Coast, but there's nothing except quiet, dry weather in the Plains and West. Those in the Dakotas and Montana may want to watch for some snow showers later in the evening on Sunday.

Andrew

Life-Threatening Cold Weather To End January, Begin February

It's looking more likely that we will see life-threatening cold weather end the month of January and kick off the month of February.

The whole cold weather sequence will begin with a wave breaking event over the far northeast Pacific and into the Gulf of Alaska. We can identify the placement of this event by the oranges and reds pushing north in that body of water. This wave breaking event translates to high pressure over those areas, and it is the resulting high pressure that will lead to the life-threatening cold weather outbreak in the last days of January and first days of February, possibly worse than the early January brush with the polar vortex.

Medium range ensemble forecasts (MREF) for the late January period confirm the big high pressure system forming thanks to the wave breaking, and as you can see, the polar vortex is nudged south into Canada and even the far northern Great Lakes to bring astonishingly cold temperatures back to the United States.

The image above shows minimum temperatures for the entire 12z GFS model run. That means the lowest temperatures forecasted for each area throughout the 384 hours that the model forecasts for are put on this image. We can see much of the nation is projected to dip below 0 degrees Fahrenheit at some point during the next 16 days, with the northern Plains trying to dip below -40 degrees. To be quite honest, I do feel that a solution like this is possible. The cold may not end up as extreme as this (hard to tell, because the GFS has a cold bias in its forecast, but it could also be this cold, as the weather pattern is extremely favorable for intense cold), but the gist of this all is that it will get pretty darn cold to end January and start February.

One thing I want to discuss is something I'm seeing on the GFS Ensembles two images above this sentence. If you look at the Pacific, you see that monster ridge of high pressure making the jet stream shoot way north. Then, in Canada, the polar vortex causes the jet stream to plummet back south. But then if we look at the United States, we see just regular west-to-east flow. No big spikes or drops in the jet stream. That raises a red flag to me. I'm not sold on the idea that an extremely meridional (wavy) flow just upstream will result in zonal (west-to-east, flat) flow here in the US. I believe that the polar vortex and cold would push further south and with greater intensity, similar to what the 12z GFS shows. I'm not endorsing that 12z GFS run, but I am saying that the GFS Ensembles look suspicious to me right now.

Andrew

Stratospheric Trifecta Signals Brutally Cold February Ahead

It now appears that the stratosphere will kick off a number of indices that deem February to be the coldest prolonged period of winter thus far. In today's post, I will address multiple indices that favor a significantly colder than normal February.

Part I: The Stratosphere

•First Warming

In the opening days of January, we saw a stratospheric warming event occur. This event was minor, as the chart above (depicting temperature anomalies in the upper latitudes) shows. Nevertheless, this first warming event, coupled with the ongoing warming event is helping to destabilize the polar vortex in the stratosphere. So far this winter, the stratospheric polar vortex has been resistant to any and all attempts to be put down. We can attribute this to the positive phase of the Quasi-Biennial Oscillation (QBO), which is unfavorable for a weak polar vortex. These two first warmings are just tastes of what is to come. While the first warming was minor, it seems to have shaken up the vortex at least a bit, and this ongoing warming event right now is most likely helping with some slight (at the very least) destabilization of the polar vortex.

•Second Warming

There looks to be a second stratospheric warming event in the making about 5 days away from today. The GFS model indicates we will see a spike in stratospheric temperature values on January 17th, centered in northern Russia. If we take a look at how this warming is angling itself at the polar vortex, so to say, it is clear that this is going to be a Wave 1 event. There are two major types of wave activity- Wave 1 and Wave 2. In Wave 1 activity scenarios, the stratosphere undergoes distress as a major ridge attempts to displace the polar vortex from the Arctic, while keeping it fully intact. With Wave 2 activity, the polar vortex is experiencing ridging across the upper latitudes, making the vortex want to split into two vortices. These vortices can then shift to lower latitudes and bring extreme cold weather to the regions affected. The Wave-1 activity is usually seen as the strongest stratospheric intrusion out of the two, as a significant push of ridging/warm air is made to displace the vortex. With a Wave 2 pattern, you have two areas of high pressure, making it relatively easier to break up the vortex. Considering we see the polar vortex (depicted here as the very cold air mass) being pushed off to one side, with a swath of warm temperatures to the west, it does appear that this would be a Wave-1 stratospheric intrusion. Interestingly enough, this warming is one of the trifecta of warmings that could ultimately significantly damage the polar vortex...

The ECMWF model system is in agreement on this Wave 1 activity, and we can see how it projects temperature and geopotential height values to spike in Wave 1 denotations, as seen in the dark blue lines on the first two panels from the top, and the dark red lines on the third and fourth panels from the top. The top image shows Wave 1 and Wave 2 forecasts for temperatures at the 10 millibar level, and the spike in the dark blue line there confirms what the GFS is already telling us about the chances of a Wave 1 intrusion. The same is true for the second panel, where we see geopotential height forecasts for Wave 1 and Wave 2 activity at the 10 millibar level. Again, the anomalously high Wave 1 values confirm the idea that this second stratospheric warming event would come as a result of strong Wave 1 activity. The same ideas are portrayed in 30 millibar projections of temperatures (third panel from top) and geopotential height values (fourth panel from top)- the consensus is that this would be a Wave 1 intrusion.

•Third Warming

On January 23rd, the GFS starts another stratospheric warming event in roughly the same location as the warming event we just analyzed above. The difference from the second warming event and this third event is that the polar vortex is now well displaced from its usual domain in the Arctic Circle. The polar vortex is now elongated and is being pushed down towards Eurasia as the stratospheric warming events are now having significant impacts on the vortex. The ECMWF does not forecast past 240 hours, and since this forecast is valid at hour 276, we'll have to rely on the GFS. The effects these significant Wave 1 events can have are quickly shown by these two projected stratospheric warming events, and if they're true, we could be dealing with a pretty weakened polar vortex by the time we get around to February.

•Fourth Warming?

The long range GFS indicates that we will see a fourth, even stronger warming event in the closing days of January. We see the polar vortex has now reconsolidated itself from an elongated vortex to a more compact version. Despite this effort to regather itself, the polar vortex remains significantly displaced from its usual spot in the Arctic Circle. Based on temperature anomalies, it looks like this stratospheric warming event would be the strongest one so far in this series of warmings, though because this is just before the end of the GFS forecast time (forecast valid for roughly 16 days away), we can't really guarantee that this event will happen. However, if it did, there is a strong likelihood that it would be another crushing blow to an already-distressed stratospheric polar vortex.

Part II: The Bering Sea

This is the GFS Ensemble 500mb height anomaly forecast for January 18th over the Northern Hemisphere. We can see the highly meridional (wavy) jet stream, as is shown by the significant ridging and troughing over North America. The big story we will focus on here is the Bering Sea. If we look over towards the Bering Sea, we see a plethora of deep negative height anomalies, with the spaghetti charts on the right highlighting that body of water as being the epicenter of at least a decent-sized portion of the polar vortex. According to this forecast image, the Bering Sea would be encountering the polar vortex on January 18th. The reason I'm showing this is because of the Bering Sea Rule.The Bering Sea Rule states that by watching storm systems make their way across the Bering Sea, one can identify where and when a storm system will show up in the United States. The general timeframe is 17-21 days after a storm appears in the Bering Sea, a storm will appear in the United States. In this case, it looks like instead of watching for a storm, we might just have to watch for the polar vortex to enter the United States. If we extrapolate January 18th out 17-21 days, we arrive at a February 4-8 time frame. But that isn't all. The Bering Sea looks to be stormy from January 14th and onwards, meaning we could kick off February with some very cold weather- and stay that way. Time will tell, but this Bering Sea Rule signal is looking mighty cold for the US.

Part III: The Teleconnections

Long range Madden-Julian Oscillation forecasts from the University of Albany's Kyle MacRitchie call for the MJO to enter Phase 7 to kick off February. A common bit of knowledge for those familiar with the MJO is that the latter and early phases of this phase space (particularly phases 7, 8, 1 and 2) tend to favor more wintry weather over the central and eastern United States, whereas the middle phases aren't as supportive of snow and cold in those areas. This CFS Ensemble forecast image takes the MJO into Phase 7 for the first week or two of February, before it starts to swivel down into Phase 8. If the MJO can enter Phase 8 and stay there for the remainder of February, I can easily see the chances of significant cold weather in the US rising.

Temperature composites centered on February for each phase of the Madden-Julian Oscillation show how the big cool-downs start in Phase 8, and continue through Phase 3. While Phase 7 may look warm, I'm not that confident in the idea that the MJO would be able to overpower the other indices (i.e. PNA, NAO, etc) and create a warm environment. Regardless of just how the MJO plays out, it is apparent that we will see a shift towards those latter, wintry phases of the MJO. That should be enough to continue the early February cold through the month. The intensity may vary, but the idea of a cold February will most likely remain intact, especially after accounting for the stratosphere and the Bering Sea.

The second teleconnection to discuss is the atmospheric angular momentum index, or the AAM.

This AAM forecast, from Nicholas Schiraldi, shows the GFS projection of AAM anomalies on a time/latitude graph on the top panel, as well as an overall AAM anomaly forecast on the bottom panel. In the short and medium range we see a relatively neutral AAM, but towards the longer range, the GFS has been consistent in its idea that the AAM will be tanking well into negative territory as we approach February. If you were to take a look at the AAM phase space, the AAM is projected to hit Phase 1 before beginning to cycle through the low AAM phases, as you can see below.

If the AAM does cycle through these early, low AAM phases, one could expect an anomalously cold February. The reason? I took the time to look up February mid-level geopotential height anomalies when accounting for the January AAM values. The result is below.

This map shows correlation values over the Northern Hemisphere. Basically, this chart was constructed by taking January AAM values and looking at the next month's (February) 500mb height anomalies. If the AAM in January was positive, one could expect high pressure in Canada and the Northern US because there are positive correlation values shown. In the same sense, if the AAM were positive in January, February 500mb anomalies would ne negative, due to the negative correlation shown in the Southern US. In our case, we look to average out in slightly negative AAM values for the month of January. If we look at the chart above, we could anticipate seeing unusually cold and stormy weather in the North US, because the positive correlation means a negative AAM produces negative height anomalies. It's even possible that the polar vortex would come down to Canada again, but it's way too far out to speculate about that. As far as the South, it's possible we see some high pressure due to the negative AAM showing a negative correlation there (that equals positive height anomalies: high pressure). I don't think we would see that significant of ridging in the South, mainly because the other parts of the pattern support much of the East being chilly, not just the Northeast. Regardless, this does bode well for cold weather prospects for February in the US.

Part IV: The Forecast

I believe we will see February start out with brutally cold temperatures, as the Bering Sea argues. I have relatively high confidence in this cold really hitting the US hard to open February. Beyond the opening week of February, I anticipate we will see a continued cold pattern, but it will likely fluctuate. As any stratospheric influences begin to affect the US, we may or may not see enhanced cold weather- it will depend on the synoptic pattern around North America that will dictate where the core of the cold will go. Beyond mid-February, we should see the MJO enter Phase 8, which, if the forecast is correct, will allow for continued cold weather, specifically focused on the East US. Naturally, as time goes on my forecast confidence lowers, but the point is, there is definitely potential there for a very cold February.

Andrew