Chicago, Detroit, New York City Targeted for Biggest February Snows

It looks like the end of winter will go out like a lion for a good chunk of the north-central and northeast US, with cities like Chicago, Detroit and New York City in the mix for the biggest snow events.

We're going to start with the Lezak Recurring Cycle. The Lezak Recurring Cycle, or LRC, is a tool developed by meteorologist Gary Lezak that, in essence, can enable forecasters to predict the overall weather pattern months in advance. The gist of the LRC involves a cycling weather pattern that develops in October and November of each year; no pattern is the same from year to year. Around mid November, the LRC begins to repeat, meaning we start to see a similar weather pattern in mid November that we saw in early October. This means that the cycling pattern has begun, and it will continue to cycle on a regular (non-changing) 40-60 day interval for the next ~10 months before it dissipates over the following summer.

This season's LRC cycle is on a 57 day cycle length, meaning the weather we saw in December can be expected to "come back" as we enter February. The image above shows the surface condition map on the left and 500mb map on the right from December 14, 2013. If w extrapolate that date out 57 days, we come to the February 7th mark. To make up for natural shifts that occur in the weather pattern, we can reasonably stretch the timeframe out to February 6-8 if we want to. As the 500mb map above shows, we have high pressure over the West Coast, with only slight ridging in the Southeast and the storm system easily working its way across the Plains. Based on the pattern I'm seeing to start February, I'm thinking a storm track similar to the one this system took in mid-December could very well be in the cards, or possibly suppressed a bit to the south (not by much). Regardless of where this storm ends up tracking, we should be watching out for a wintry system to impact the Plains, Midwest and eventually the Northeast in the February 5-10 period (I put February 5-10 instead of 6-8 to cover the timeframe the storm will affect all regions of the US, not just for the image shown here).

The second snow potential to watch would fall around the February 11-15 period, as this December 20th disturbance brought precipitation to the central Great Lakes and northern Ohio Valley, with additional precipitation extended into Kansas and Nebraska. The pattern here had a nearly-closed low in the Southwest, with high pressure in the Southeast. I'm a little cautious of saying that this storm track may repeat exactly as shown- I'm thinking we'll see a slightly different track this time around. If it is to deviate from the December 20th track, I expect it would be more to the south as of right now. Again, we would want to watch February 11-15 for this potential storm.

The ECMWF model then has an intense storm moving north in the far western Bering Sea, and by using the Bering Sea Rule (which states a storm in the Bering Sea results in a storm in the United States 17-21 days later), we can find that this January 27th storm would equate to roughly a February 13-17 period for a storm in the US. By seeing how the storm is in the far western Bering Sea, we can guess that the February 13-17 storm potential would then be based in the Central US. Time will tell, as always, but the evidence is mounting for a storm system in this mid-February timeframe. The storm could also be significant if the projections of a rather strong storm in the western Bering Sea are correct.

Just two days later, on December 22nd, surface and 500mb observation charts show precipitation associated with a disturbance stretching from the Plains to the Northeast. I wouldn't be too surprised to see a similar storm track play out on the expected February 14-16 period based on the LRC's 57 day timeframe, mainly because the pattern I think we'll see in mid-February will continue to resemble the pattern showing up in early February.

The ECMWF model zoomed on the Bering Sea then sees a storm system enter the far western waters of its domain on January 30th, meaning we would then be eyeing the February 16-20 period after extrapolating out 17-21 days using the Bering Sea Rule. Again, since the storm is in the western Bering Sea, we might anticipate a storm in the Central or near-Eastern US in roughly this timeframe.

These LRC and Bering Sea images do seem to favor the Plains, Midwest, Great Lakes and Northeast regions for snow events, especially if the storms are able to transfer offshore (which I believe we may see in February). I'm cautiously optimistic that those in the north-central and northeast may see a full three month winter of not only cold, but snowy weather.

Andrew

Long Range Lookout: Model Confusion Signals Pattern Change Ahead

It's time we start up our weekly Long Range Lookout segment, though this particular post will focus more on the medium range. Nevertheless, this discussion will be as important as the rest of them.

8-10 day 500mb height anomaly forecasts from the ECMWF (left), GFS (middle) and CMC models.

Medium range model guidance above shows rather drastic model differences between each guidance system, with multiple areas of the Northern Hemisphere differing in what exactly is going to happen. We see the ECMWF model on the far left prefers to hold a negative Arctic Oscillation (AO) regime in place, as is shown by stagnant high pressure in the Arctic Circle. In this forecast, the polar vortex appears to be broken into two pieces, with one lobe located in northern Eurasia and the more significant piece of the vortex displaced over Greenland, producing a strong positive North Atlantic Oscillation (NAO). The positive phase of the NAO tends to induce zonal flow over the nation, meaning no huge cold or warm outbreaks anywhere in the nation. Despite this, we still see suppressed high pressure over the West Coast producing a positive Pacific-North American (PNA) index, and that leads directly to suppressed low pressure anomalies over the Central and East US. I'm not buying the positive PNA forecast, and the reason for that will be explained a bit later down in this post. I do agree with the negative AO projection, though I think we may see high pressure near the Gulf of Alaska expanded a bit in the future.

For the GFS forecast in the middle, we see a much stronger negative Arctic Oscillation signature, with high pressure forming a bridge across the North Pole. This splits the vortex fully into two pieces; one part ends up in northeast Asia, while the other part is weakened and stretched out between Greenland and the United States. The GFS also shows a positive NAO forecast, which is why I'm a little hesitant accepting that deep low pressure anomaly in the Eastern US. However, strong high pressure blocking in the upper latitudes over Alaska would support such an idea, though the lack of support from the Pacific North American index gives me the feel the GFS is a bit too ambitious by bringing the vortex down towards the United States. Other than that issue, I believe the remainder of the forecast is rather sound. 

The CMC model on the right has a very similar forecast as the ECMWF model, though in this case we see a closed low offshore Baja California, in what appears to be an attempt at a Rex Block (high pressure directly north of low pressure, see image below). In this particular case, though, adding to the issues I find with the ECMWF forecast, the subtropical jet stream would most likely be strengthened by this closed low. Due to the positive NAO forecast in both the ECMWF and CMC forecasts, and due to how we aren't finding an El Nino in east Pacific waters (as the image below shows), I'm not so sure the pattern is conducive for strengthening of the subtropical jet stream after this northwest flow pattern we are currently in dissipates.

Typical Rex Block pattern. Notice the zonal flow to the east of the blocking pattern.
(TheWeatherPrediction)

Observed SST anomalies over the El Nino-Southern Oscillation (ENSO) monitoring area. The lack of significant warm waters at the bottom of the image tells us there is no El Nino currently in place. (CPC)

Let's take a look over teleconnection forecasts now, and see what they can tell us about the medium range period.

We'll begin with the Arctic Oscillation teleconnection forecast. As I stated above, the Arctic Oscillation has a negative phase, which means stagnant high pressure over the Arctic, and there is also a positive AO phase, which indicates stagnant low pressure over the Arctic. The -AO argues for a colder weather pattern in the United States, while the +AO argues for a warmer weather pattern.
The first thing we notice when looking at the ensemble forecast for the Arctic Oscillation is the wide spread in ensemble members at the medium and end of the forecast period. This tells us that the weather pattern is about to flip after we get out of this northwest flow pattern, and the discrepancies among the medium range models above confirm this idea. So, how can we pull a forecast from here? We can look at the errors previous forecasts made. Looking at the bottom panel of this image, we see the observed Arctic Oscillation value superimposed on the spread of forecast members from previous days, weeks and months of forecasts. Looking at that image, it seems that the observed Arctic Oscillation usually ended up more positive than the forecasts thought it would be. This has been the trend through much of the winter, until recently. Looking at the observed Arctic Oscillation from December 14th onwards, the trend has been for the observed AO to be more negative than forecasts believed it would be. I do not believe the idea that the Arctic Oscillation will be positive in the medium and long range, so it may be best to ride the new trend of lower AO values than forecasted and predict a neutral or negative Arctic Oscillation in the medium and long range time period.

This image shows the Pacific North American index (PNA) forecast over the same timeframe as the AO forecast above. We also see those superimposed panels like we saw in the Arctic Oscillation image. The PNA has two phases: positive, which means high pressure dominates the West Coast and leads to wintry weather over the East US, while a negative PNA depicts low pressures over the West Coast and warmer weather in the Central and East US. The forecast members here appear in sync with the idea of the Pacific North American index trending more negative in the future, and I agree. Some model systems haven't really caught on yet, and are still projecting frigid forecasts for the long range. I anticipate we see a gradual warming of those forecasts, though the Pacific should still be conducive for at least some decently cold weather. If we use that trend idea in the bottom panel here like we did with the Arctic Oscillation image, we don't see a particular trend right now- the PNA has stuck relatively close to its forecasted values in the long range. Thus, I see no reason to back off the trends now. I expect an eventual -PNA to evolve.

Why are models so confused? Well, we can look to the shorter term for that answer. This image shows an ensemble projection from the Climate Prediction Center for 5 days out, unlike the week-plus forecasts we discussed above. On the left is the ensemble projection for one height level (5520m), while the right panel shows the forecast for another height level (5760m). These images are both valid at the same time, they're just forecasting for different parts of the atmosphere, if you will. The pattern is clearly defined in the left panel, with ensemble members agreeing on the northwest flow pattern continuing, but the picture is more muddled with the panel on the right. On the right, we see high model disagreement with the pattern in the waters west of Mexico, with some members wanting to develop a closed low, and other members wanting to retain high pressure over the West US. Still other ensemble members want to keep the pattern more zonal and not contaminated with high or low pressure. So, who do we believe? Well, considering the Pacific-North American (PNA) index looks to still be positive over the next few days, and other ensemble guidance agreeing on intense cold weather staying in the US 5 days away, I would buy more into the high pressure on the West Coast solution than the closed low idea.

Long range ensembles still aren't faring too well.

This four-panel image shows the 500 millibar height anomaly forecast over the Northern Hemisphere from the GFS model (top left), the GFS Ensemble Control (top right), and the GFS Ensemble mean (bottom left). The bottom-right image shows the ensemble spread across the Northern Hemisphere. All four forecasts are more or less similar to the GFS image we discussed at the beginning of this post, but take a look at the ensemble mean. We can observe the continued model confusion with deeper purples emerging over both the Bering Sea region and over Greenland, signaling higher model uncertainty. The model uncertainty in the Bering Sea is likely due to how strong developing high pressure in that area will be, with some forecasts suppressing the ridge of high pressure to the south of the Bering Sea, and other forecasts flooding the body of water with high pressure. Similarly, models don't know how to handle pressure anomalies over Greenland. If there's low pressure present there, as some models indicate, we would see the positive North American Oscillation (NAO), which would support that warmer and zonal weather, while a negative NAO would support a continued northwest flow and cold weather in the East US.

So what do I think will happen in the long range, since models aren't giving too much to work with at face value?

Well, we can probably expect a break from the intense cold we will see to round out February. In its place ought to be a warm Southeast as some ridging takes hold thanks to that negative PNA, but also some cold weather in the Northern US as the negative Arctic Oscillation persists. It is possible the ridge in the Southeast is suppressed if we can get high pressure over Greenland to get a negative North Atlantic Oscillation going, though model guidance everywhere is having trouble with that aspect of the forecast. The West can anticipate a well-deserved break from the persistent high pressure, with stormy weather making a comeback... to some degree. We'll need to see how model uncertainty in the Bering Sea resolves itself before we can be sure the West will get at least a bit of relief.

Andrew

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