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Posted at 2:15 PM ET, 11/22/2010

Cold blast over interior West to fizzle East

By Jason Samenow

* Very mild start to week: Full Forecast | Climategate: one year later *

Forecast temperatures Wednesday midday in northern Rockies, western Plains, and southwest Canada. Pinks are below zero. Graphic courtesy StormVista Weather Models.

The early season cold snap diving into the Rockies and western Great Plains is stunning. By Wednesday, large portions of that region will experience lows below zero and highs in the single digits or colder.

The National Weather Service Office in Salt Lake City is cautioning (h/t WeatherBug): "An exceptional high impact event still on tap for Tuesday evening. Utah has not seen an Arctic front like this in many years."

But while the East will turn colder Thursday into Friday as an Arctic front presses east, the cold air will lose much of its bite. Let's take a look at why.

Snow cover over southern Canada and the United States today, expressed in snow water equivalent. Source: NOAA.

The fact the East Coast will turn "a little bit" cold as opposed to "bitter" cold is related to the evolution of the Arctic high pressure center, the source of the cold air. The High, now plunging from the western provinces of Canada into the intermountain West, is on a course almost due south.

Forecast position of Arctic high pressure center Tuesday (top), Thursday (middle) and Saturday (bottom) at 7 a.m.

As the High drives southward, two things happen:

1) It loses its source of refrigeration, i.e. snow cover. Look at the evolution of the high pressure center in the image to the right compared to the locations with snow cover above. South and east of Northern Rockies and Northern Plains, there's no snow cover to help sustain the cold air.

2) It encounters more daylight. In its source region over the northwest provinces of Canada, there is little daylight this time of year. So as the Arctic high sinks south, it encounters more sunshine and, thus, the cold air erodes.

In addition, the High won't start to head east until it reaches the southern Plains around Thanksgiving Day. By the time it reaches the East Coast this weekend, it will be a shell of its former self.

To be sure, the High's arrival will usher in colder air -- but highs will be in the 30s to near 50 from the New England to the mid-Atlantic Saturday as opposed to the single digits and teens that impacted the Northern Plains just two days prior on Thanksgiving. In short, the East Coast will be served the West's stale cold air leftovers.

The evolution of this High is pretty characteristic of a La Nina winter as the primary jet stream trough (or dip) sets up from the interior West into the Great Plains pushing the heart of the cold air away from the East Coast. So expect to hear a lot more about "stale" cold air this winter.

By Jason Samenow  | November 22, 2010; 2:15 PM ET
Categories:  Extreme Cold  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: A year after climategate, applying lessons learned
Next: PM Update: Staying mild through tomorrow


I expect this pattern of moderating cold fronts 4 the E 2 cont. most of this winter. Still thinking temps will b 1.5-3.5 degrees above av. this winter.

Posted by: VaTechBob | November 22, 2010 3:35 PM | Report abuse

VaTechBob - Do you have high confidence in your call? Let me know what you are basing it on. I am surprised you would think the entire winter would end up being that warm--but I do admire your 2 degree-wide range ;)

Posted by: Camden-CapitalWeatherGang | November 22, 2010 3:38 PM | Report abuse

VTB -- I love your comments, always insightful. However, I, for one, would be grateful if you'd use english instead of txt for them. Way more brain power can then focus on your arguments rather than translation.


Posted by: Registration1982 | November 22, 2010 3:47 PM | Report abuse

Bummer re: the cold air moderating. We need something, anything to stop the stink bugs dead in their tracks. I'm still wasting 1-2 of them every day.

Call this the fall of the stinkbugs. Except they haven't fallen, at least in DC!

Posted by: JerryFloyd1 | November 22, 2010 5:27 PM | Report abuse

Thankfully, we've had a couple of stink-bug-terminating freezes out west. It's bliss to be finally debugged! Except for the occasional one that crawls out of a coat that's been hanging in the closet for months... Yuck.

Posted by: tinkerbelle | November 22, 2010 6:04 PM | Report abuse

It's my feeling, based on living in this area since 1954 & following the weather for 50+ yrs, that strong La Nina yrs are generally milder. It looks to me that this yr is going to follow the same pattern. I also think the NAO will trend more to the positve phase most of this winter.

9 out the 1st 10 mons. this yr have been + & Nov is probably going to end up on the plus side. I just don't see anything to indicate a pattern change anytime soon. That's my temp prediction for this winter & I'm sticking with it. Would love to crow if wrong.
Will give my offical winter prediction next week.

Posted by: VaTechBob | November 22, 2010 10:29 PM | Report abuse

As I posted earlier today, I tend to support VaTechBob.

These highs are tending to pass just over or to the south of us, causing a return SW flow of boringly mild to warm air, rather than holding us in a NE flow of cold air in place. We might see some near-record high barometer readings this winter, but not much snow-producing cold air. This particular high might pass right over us Sunday or Monday.

Hopefully we might get some cold air damming events later in the season or a few flurries behind strong cold fronts as in 2008/09.

Posted by: Bombo47jea | November 22, 2010 11:56 PM | Report abuse

folks if you look at the POST from last I said this was going to happen way back on NOV 12 and NOV 14...

dont wanna say I told ya so.... but if you go back and read WES thread and Thanksgiving and beyond....

well it is there to see

Posted by: wxrisk | November 23, 2010 12:29 AM | Report abuse

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