Today's Weather Discussion: Brrrr!


Meteorologist Trent Okerson

Saturday, Dec. 4:

Today's discussion is brought to you by the Snuggie......okay, not really, but a Snuggie/blanket/coat/ etc. is going to be a hot item for the next few days as our most significant batch of cold air this fall will make for some frigid days ahead.  With the passage of a cold front to our south today, winds picked up out of the NW this afternoon, ushering in that cold air mass.  The leading edge of the cold air is just starting to penetrate the area tonight, and as cold Canadian high pressure builds in over the next few days, temperatures will continue dropping, taking us all the way into the teens at night before a gradual late-week warmup.

Wind has been a bit of an issue today, gusting up to 30 mph, and those cold winds will continue to blow for a couple more days.  We'll be looking at average NW winds at 10-15 mph tonight through Monday, with gusts up to 25 mph, especially during the daytime. 

So why so cold all of a sudden?  Most of the blame can actually be placed on an area of high pressure way up over the country of Greenland....something we call a blocking high.  Huh?  How does Greenland have anything to do with the weather here in the Local 6 area?  Well, this area of high pressure over Greenland, known as a "Greenland Block", diverts the jet stream way south, allowing arctic air to spill south as well.  Here's what this looks like graphically:

If you have read the blog very much, you know that I have explained a time or two that the jet stream has a huge effect in temperature trends.  Think of the jet stream as a sort of permanent cold front at about 30,000 feet high.  On the north side of the jet is cold air, and milder air lies south of the jet.  The jet stream is basically a river of air....constantly flowing from west to east in the northern hemisphere, with lots of north and south twists and turns (ridges and troughs).  This blocking high acts sort of like a giant rock that blocks the flow of a stream.  If you throw a big rock in a stream, the stream bends around the rock an keeps flowing.  In this case, since this high blocks the flow of the jet stream, it bends way south, and all of the cold air follows suit.  All of this happens in the upper levels of the atmosphere.

A little closer to the surface of the earth, it's actually low pressure that is the result of this pattern, resulting in something called a "polar vortex".  Here's another colorful map to look at:

In the top, right corner of the map is the center of a deep area of low pressure....located at the center of all of the white circles.....that's our vortex.  As you can gather by looking at the arrows around this vortex, which represent wind directions and speeds, the flow around this vortex is counterclockwise, which in turn helps drive all of the cold air farther southward.  Blocking patterns usually tend to persist for several days, so while a modest warmup is in store for the end of the week, we'll have to cope with this cold air for at least the first half of the coming week.  Aside from the chilly weather, things look pretty calm over the next week or so, with no noteable chances for precip through next weekend.