Cold blast over interior West to fizzle East
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.
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.
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.
| November 22, 2010; 2:15 PM ET
Categories: Extreme Cold
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