Thursday, March 20, 2014

March 25-27 Potentially Significant Blizzard

I'm watching the potential for a potentially significant snowstorm that model guidance believes will become a blizzard.

The image above shows 500mb geopotential height anomalies from the latest run of the GFS model over the Western Pacific, valid for March 20th. As this image shows, we see strong negative height anomalies present over Japan on March 20th, indicative of a rather strong storm over the area. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. So, if we take this March 20th storm and move it ahead 6-10 days, we find a potential storm system around the March 26th through 30th period.

Let's take a look over current model guidance. Shown above is the latest forecast from the Canadian GGEM model, valid on March 26th. We see an extremely strong storm system positioned just offshore of the Northeast, dumping heavy precipitation on the order of over 12" on inland areas, with multiple FEET of snow falling on coastal locations. The GGEM model has already been shown to be suffering from convective feedback issues on this run, meaning precipitation amounts are grossly exaggerated and incorrectly altered due to this specific bias. Thus, this forecast run is overdoing precipitation amounts and is not correct in its forecast at this time. What I do agree with, however, is placement of the storm. We look to be in a northwest flow regime, a pattern notorious for providing a very favorable environment for East Coast snow events, and we'll discuss this a bit later.

We now move on to the ECMWF model, which also shows a very strong storm system displaced just east of the Northeast coastline. This is of similar strength to the GGEM model and would likely be putting down some pretty darn heavy snow amounts, but because we lost access to the main provider of our weather maps, we can't give an indication as to just how severe this storm looks to be on the ECMWF. However, once again, we're seeing this strong storm in the midst of a northwest flow pattern, as we see the dashed lines dropping down to the southeast from Canada. This is crucial to the forecasts of a strong East Coast storm.

The American GFS model is far less enthusiastic about this storm, only putting down modest precipitation along the coastline and sparing inland regions from any accumulating precipitation, snow or otherwise. This is considered the outlier forecast when taking into account how the GGEM, ECMWF and ECMWF Ensembles believe we'll see a strong East Coast-hugging storm, but in the grand scheme of things, there is high model agreement on a storm at least threatening the East Coast in this timeframe, and that's what we're looking at here.

Take a look at this graphic above. This image shows a few things important. The main item we see first are the negative 500mb and positive 500mb anomalies, marked by contour lines in blue and red, respectively. Just glancing over the image, we find a sustained northwest flow scenario unfolding, with deep negative height anomalies pressing into the East US, with high pressure surging northward in the West US. The second item we need to discuss are the dates on the bottom right hand corner. They are analog dates, listed from top to bottom, and the date at the top means its pattern is most similar to the pattern forecasted in the graphic itself, which is valid around the March 26-30 period, right on top of the timeframe outlined for this potentially significant storm. Look closely at the dates- are you picking up on one particular date in that list? If not, check out the second date from the top. That pattern was deemed to be the second most similar to the pattern expected to unfold as this storm system impacts the East US. And that date - March 16, 1993 - spawned the 'Storm of the Century'.

Now, there are some who are anticipating another Storm of the Century because its date has shown up on these analog images, and they might tell you to prepare for feet of snow. All that we know now is that model guidance is hinting rather consistently at the potential for an all-out blizzard in the East US, specifically the Northeast. As of right now, there is disagreement on who could get hit by the storm, and there's even disagreement on if there'll be a storm at all. As of now, the potential for a significant storm is rather high due to the East Asian correlation, but it remains to be seen if this could be a blizzard for the East Coast, hence all the caveats throughout the post.