Jet Stream Changes Bring In the Chills.

Last week I wrote about the “haves and have nots” in terms of favorable early season winter weather.  The East was very cold with occasional snow while the West was warm and dry.  For the most part, that is still the case, as the eastern Great Lakes and Northeast are in line for a reinforcing shot of arctic air this weekend.  Temperatures will be suitable for significant snowmaking Saturday and Sunday. About a half dozen resorts are open in the Northeast, and several more are planning on turning lifts for the first time on Saturday. 

The Great Lakes region has had the most consistently cold weather the past couple of weeks. At least a couple of Michigan resorts, Crystal Mountain and Boyne Highlands, will be in operation. 

The push of arctic air will be the last for a while, due to some changes in the jet stream configuration over the continent later next week, over the western U.S. in particular.  It’s not necessarily bad news in the East, but it certainly is good news for the West.  Here is a jet stream forecast map for next Tuesday that helps illustrates the change.

While a deep trough covers the eastern half of the country. I will get to that feature shortly. Notice a shorter wavelength trough along the Washington/Oregon coast.   That system will bring snow to the mountains of Alberta and British Columbia, but it looks as though snow levels will be very high in the Cascades of Oregon and Washington.  Remember, the waters of the northeast Pacific are quite a bit warmer than normal. That will help the eastern half of the country as we work through winter, but that warm water will tend to elevate snow levels in the Northwest.  Now, the other trough along the west coast—west of Baja—will play a role in snow production later next week as the northern and southern branch jet stream features consolidate into a larger trough by next Thursday. Take a look.

The more organized trough will have both the strength and the moisture to bring a meaningful snowfall to the mountains of the Southwest and the southern and perhaps central Rockies late next week into next weekend. 

This map also shows us the subtle changes that will cause the extreme November cold that we have seen in the Lakes and Northeast to back down somewhat as we head toward Thanksgiving.  If you recall, last week’s discussion made note of the direct discharge of arctic air from the high latitudes, the product of the combined circulation around a Gulf of Alaska ridge and an eastern trough.  That couplet combined for a straight shot from the arctic to the mid latitudes.  Look at that flow now on the second map.  Start in New York and head west along one of the lines.  You will see several changes in direction and eventually you will end up over those temperate waters of the northeast Pacific.  Yes, there is still some very cold air involved in the pattern, but Pacific air is blended in, cutting back on the intensity of the cold.

Fear not. The pattern is not going to turn noticeably warmer over the eastern half of the country, but it will turn “less cold”.  Temps will still be favorable for nighttime snowmaking, and a storm that works its way up the coast on Tuesday/Wednesday will likely produce some snow in the mountains of New York and northern New England.  Meanwhile, after a mild start to November, parts of the West will see some bonafide winter weather in the next week.