Friday, December 26, 2014

January to Commence With Wintry Central US, Balmy East

The pattern to kick off January 2015 is looking cold for the central section of the country, while the East looks to bask in warmth.

Tropical Tidbits
The above image shows 500mb geopotential height anomalies, valid for December 28th, when we expect this pattern to start establishing itself. The atmosphere is quickly turning very La Nina-like, as we see atmospheric angular momentum values begin to circulate in anomalously low regions. This La Nina-like set-up will kick off with a strong ridge forming in the Gulf of Alaska, the primary indicator of a negative East Pacific Oscillation (EPO) pattern, which favors cold weather in the United States. Energy coming down the pipe from the Pacific will ride the jet stream and crash into the West US, setting up a nightmare scenario for the East US' cold weather fans.

Shown above is the typical jet stream alignment for a La Nina pattern. Notice the aforementioned ridging in the Gulf of Alaska, as well as the polar jet stream arcing over that ridge and then pushing southward into the West. Due to all the energy crashing into the West, we will see a ridge form over the East US, shown by the push north in the polar jet stream over the eastern CONUS in the above image. What ends up happening is a dream scenario for snowstorm fans in the Central US, and a nightmare scenario for all winter weather fans in the East US.

Energy that does crash into the West US will have the potential to become a substantial winter storm in the Plains and Midwest. This is due to what looks like phasing of the jet streams over the Central US. Notice how the polar jet stream shifts south from Canada and then mixes in with that other jet stream coming in from Mexico. This phenomenon supports potential strengthening of any storm systems that form and maintain their structure as they eject into the Plains, eventually progressing east-northeast into the Ohio Valley.

To summarize:

- A pattern change is currently in the works, and is expected to take hold in just a couple of days.
- This new pattern resembles a La Nina pattern.
- This pattern will favor cold and possibly snow in the Plains and Great Lakes, as well as very wet conditions in the West.
- Warmth and relative quiet will prevail to end 2014 and start the month of January in the East US.



Anonymous said...

Andrew, if I remember correctly, the pattern in October was very progressive as well and our flow was cut off from the arctic similar to this December. But as we ended October and came into November.. arctic air began to spill in the lower 48. Early November in the east was still fairly mild, but mid-late November was very cold.

Are these similarities a sign that the November pattern is beginning to set up again? Or am I just making up stuff?

Anonymous said...

Finally we in the Rockies and central US catch a break from that unusually dry, freakishly warm weather we had most of November and especially most of December.
Before this last week and a half, we had all but completely lost our snowpack...which is definitely not normal for Steamboat, but boy, what a difference 1.5 weeks makes, we now have around 3 feet on the ground again, more snow coming, and temps back to what is typical for this time of year, cold and lots of it lol

Anonymous said...

Dang it! I was really looking forward to a cold and snowy winter in the Tennessee valley. Do you think that this arctic air will push eastward, increasing our chances for more snow and ice? Please answer this question if you have the chance. Thanks for all your hard work Andrew!

Andrew said...

Anonymous on Dec. 26: I'm skeptical of such an assumption, as El Nino winters tend to start out warm and end rather cold & stormy. That could be what we're seeing now on model guidance.

Anonymous at 12:57: For the foreseeable future, this cold should be confined to the Plains, as a sharp ridge stays in place along the Southeast.

Anonymous said...

For Ohio, could this pattern still shoot in periodic cold, like what is happening this Tuesday/Wednesday?

I'm hoping it's not this entire winter being lost to a La Nina pattern. When you say 'foreseeable future' for the cold air staying in the Plains, how long of a time are you talking - likely the rest of the winter, or more like a couple of weeks before it could change?