Where is winter?

I will admit, I have been enjoying the mild conditions this Fall, but now that the holidays are within view, I could take some snow. Is there any in the near future? Possibly.

The pattern for much of this Fall is being dictated by a weak La Nina and a dominant, strong Pacific North America (PNA) pattern. This leads to a strong ridge of high pressure aloft over the Gulf of Alaska and a downstream trough over the intermountain west. I’m sure many people heard about the strong wind experienced most notably in CA and UT. That was caused by what is called an “inside-slider”, or strong vorticity maxima (upper-level low) that slipped down the West Coast, enhancing downslope winds off the Sierra Nevada and central Rockies. I did see some wind gusts that approached 120 mph. Amazing!

This troughing over the Rockies allows warmer air to ride north-northeast towards the Midwest and Mid-Atlantic. November was about 4 degrees above normal in Baltimore with areas of NJ between 4.5 and 5 degrees above normal. I haven’t done a full assessment, but I think mild was the rule for most areas east of the Rockies. There are some subtle hints at a change with time.

North Atlantic Oscillation (NAO) forecast for the next two weeks.
Pacific North America (PNA) forecast for the next two weeks.

For this post, I’ll just focus on the NAO and PNA. As you can see in the above images, the forecast for the PNA is for neutral conditions to develop which would indicate a relaxation in the very strong ridge in the Gulf of Alaska. Meanwhile, the NAO is forecast to drop towards neutral, which would allow some of the arctic air bottled up in Canada and the northern Plains to move east. This would provide an opportunity for some snow in the East, but it’s too early for details right now.

00z GFS sea level pressure and precipitation accumulation forecast for Thursday, 12/08.

After St. Louis sees its first bout with some snow and/or ice in the next 36 hours, the system will slowly move east. The front will have trouble at first since the Southeast ridge (upper-level high) is providing too much resistance. The above image is the Thursday afternoon forecast for precipitation and notice the area of moisture along the Mid-Atlantic. This is an eerie sign as the model has been moving this last wave along the front farther east with each run. Based on the GFS forecast errors, I would hedge my bets on the wave being more northwest of this position by Thursday. That would put most of the snow in the mountains, but I can’t rule out possible snowflakes mixed in from northern VA through NYC.

I’ll keep monitoring this situation as it looks to become more interesting as we head towards the official start of winter.

NOTE: The Atlantic Hurricane Season ended on 11/30 with a total of 19 storms for the season, 7 hurricanes, and 3 major hurricanes. This fit the NOAA forecast which called for 14-19 storms. I will be analyzing the season once all of the best track data is made available.

In the meantime, click here for a 4 minute satellite loop of the entire hurricane season.

Also, if you are interested, I have finished analyzing the 2010 and 2009 global tropics which you can find here.

Thanks for reading!

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