Wednesday, November 20, 2013

Thanksgiving Potential Arctic Outbreak

It is looking increasingly likely that Thanksgiving will contain a significant cold weather outbreak for much of the nation.

850mb temperature anomalies for the evening of November 27
The ECMWF ensembles and GFS ensembles have been telling of the entrance of a very cold air mass into the US, to the tune of nearly 20 degrees below normal, in Celsius (that's 36 degrees below normal in Fahrenheit). This would most likely bring about the coldest air seen in many parts of the nation thus far, with many in the Plains, Midwest, Great Lakes and Ohio Valley in line for temperatures that may flirt with single digits, like Chicago, or smash right through the single digit mark, like many areas closer to the border with Canada.

ECMWF temperature forecast for the morning of November 27
It remains to be seen if the models are correct in their estimation of a brutally cold Thanksgiving, but right now, it looks like such an outcome is within the realm of possibility.

There is also the potential for a Nor'easter in the day or two before Thanksgiving...


Thanksgiving Potential Major Nor'easter

There is potential (keyword here is potential) for a Nor'easter to form along the East Coast in time for Thanksgiving, and if true, may drop copious amounts of snow on the inland Northeast.

The overnight 0z ECMWF model projects a rather strong piece of energy to slide along the Gulf Coast in the few days leading up to Thanksgiving, drifting almost due east as the jet stream allocates the energy in that direction. At the same time, another piece of energy will be dropping south and east from Canada, and if you know what phasing is, you know what happens next. The model then has the Canadian and Gulf Coast energies combine into a single system that forms just off the East Coast to form a strong coastal storm, as the forecast below (valid November 27) shows.

The ECMWF model has this Nor'easter bring massive amounts of snow and liquid precipitation to the Northeast, and spreads the wealth north and east to cover most of the interior Northeast. The minimum pressure is projected to be at 991 millibars, which pretty much qualifies the statement that this would be a substantial coastal storm. 

Now, the new runs of the ECMWF and GFS do not show this happening. The ECMWF takes the southern energy and pushes it out to sea as the two pieces of energy do not merge in time to form this possible Nor'easter. So why bring it up? Well, there is most likely going to be a storm system somewhere in the US in the days just before Thanksgiving. As I've told on this blog, there has been a storm forecast to hit East Asia just two days ago. It ended up verifying, and the text from a post on that discussion a handful of days ago is below.

This is a forecast from the GFS Ensembles out to the Hour 60 timeframe. While all of the colors and lines may seem a little overwhelming, we're only going to focus our attention on East Asia, which is under the deep blue swath in the top left part of the left panel. Another correlation that has been proved effective is how weather in East Asia can be reciprocated in North America 6-10 days after the weather anomaly in East Asia. This includes the presence of storm systems or high pressure in East Asia. The November 18 forecast from both the GFS Ensembles and ECMWF model indicates that a deep negative height anomaly swath will slide down over Japan. If we extrapolate November 18th six to ten days out, we come up with a potential cold weather and storm system time frame of November 24 to 28. This narrows down the timeframe previously set out by the Bering Sea correlation, and if we match up the two timeframes (November 24-28 for the East Asian connection and November 25-29 for the Bering Sea connection), we come up with a November 24-29 potential timeframe for a storm, which can be isolated into the November 25-28 period, which is shown by both connections. Based on these two connections coming up with a common timeframe for a potential US storm system, confidence is quickly rising that this event will happen. 

The evidence doesn't stop there- here's text from a post on this storm potential I made back on November 13:

Take a look at the Bering sea in this two-panel reanalysis of the weather on November 8th. If you look closely, you can see that the Bering Sea was in the midst of a decent storm system on this date, just three days ago from today. This storm system passed along those waters in the midst of a mammoth ridge of high pressure just to the south. The 500mb height anomaly chart on the left best reflects this storm system, but its presence is confirmed on the right panel, which displays mean sea level pressure contour lines and denotations, as well as cloud cover. This Bering Sea storm has a connection to this potential Thanksgiving winter storm. Based on research done by Joe Renken, weather in the Bering Sea correlates to weather here in the US approximately 2.5 to 3 weeks after the Bering Sea weather anomaly occurs. This storm system in the Bering Sea happened on November 8th, and extrapolating that out 2.5 to 3 weeks ( 17-21 days) leads us to a potential storm system impacting the US around November 25 to 29. Considering November 28th is Thanksgiving, there does appear to be at least decent potential for a winter storm around the Turkey Day timeframe.

There is something else that must be noted with the ECMWF model I discussed at the top of this post. There has been discussion that the model has a bias, in which it holds energy in the Southwest US for longer than it ends up being there. I have a feeling that if this bias ends up working out in this situation, we would see the merge occur in the Northeast, resulting in that coastal storm. That is, if the energy in the South is able to latch on to the Canadian energy- in the most recent ECMWF model run, the southern energy was unable to phase with the Canadian energy until it was too late and the potential coastal storm was already off to the Canadian Maritimes. To give you an idea of what the snow forecast might look like if this Nor'easter occurred, take a look at the overnight ECMWF forecast below (warning, don't take this as a legitimate forecast just yet):

What I'm saying is, there really is potential here that needs to be monitored.