MONDAY, DECEMBER 26, 2005 9:35 AM
Ever since winter officially began last week, the weather in the Northeast (and across much of the country) has gone the other way. It's not that we're having a heat wave in the Northeast, but we are certainly in a different regime that we were earlier in the month.
One thing is similar: there is a trough anchored over the Aleutians. A new development has been a separate stream of storms that roll east across the Pacific and then move inland through California. San Francisco had more than 3 inches of rain on the 17th and 18th, more than an inch on the 21st and 22nd, more rain yesterday, then rain with thunderstorms and gale force wind gusts earlier this morning.
Now, if there was mound of cold air in Eastern Canada that unleashed cold shots behind oneach storm, the Northeast could experience quite a few snowfalls with this pattern, along with the ice that is common closer to the edge of the cold airmass. But now there is no real cold air around. Even on top of Mt. Washington, NH, it was 34 degrees this morning! Their average high at this time of year is 16; the low is minus 2. And, thunderstorms broke out in Connecticut this morning and were heading north-northeast!
The reason for the big warmup in the Northeast can be traced to the breakdown of high-latitude blocking. Earllier in the month, there was a high pressure area over extreme northeastern Canada and Greenland. When that happens, the cold vortex is forced to move south, and cold air pours across the Great Lakes and Northeast. Now the high is gone, and the vortex is way up where the high pressure had been. This setup can lead to mild winter weather for the Midwest and Northeast. However, that is not always the case. If the high pressure area between the Aleutian low and the Davis Staits low can amplify, a lot of cold air can drift southward through central and southern Canada. And, sometimes, there is a split in the flow farther east. Troughs can amplify in Southeast Canada to draw cold air into the Northeast.
On the other hand, if the split in the flow is farther south, a series of storms will simply move east from California across the Rockies and Central Plains, and then wind up on the Middle Atlantic Coast..all without tapping into the cold air. That's what's happening now. So far, we see this situation lasting through the end of the year, and the GFS shows it persisting next week as well. This suggests that today's California rainstorm will move east to cause rain the the Middle and North Atlantic states (snow is still a viable possibility in the mountains of Northern New England and there could be ice at the start farther south (though probably not in the cities from Boston to Washington)). Another one could visit during New Years weekend. Does that mean the traditional New Years Eve will be re-worded to "Cold acquaintance be forgot, and never brought to mind?" Or will things change to make that prospect into an auld lying syne?
Even if there is no fundamental shift in the pattern to extreme cold in the Northeast any time soon, that does not mean it cannot snow. It does appear that low level cold air will advance southward through Canada this week, and at least some of it could be tapped by storms passing to its south. In fact, some of the snowiest patterns the region has ever experienced (January 1978, for example) started out in ways somewhat similar to the situation in effect this week. So, for snow there is hope, but for most areas this week it is nope!
Elliot
Ever since winter officially began last week, the weather in the Northeast (and across much of the country) has gone the other way. It's not that we're having a heat wave in the Northeast, but we are certainly in a different regime that we were earlier in the month.
One thing is similar: there is a trough anchored over the Aleutians. A new development has been a separate stream of storms that roll east across the Pacific and then move inland through California. San Francisco had more than 3 inches of rain on the 17th and 18th, more than an inch on the 21st and 22nd, more rain yesterday, then rain with thunderstorms and gale force wind gusts earlier this morning.
Now, if there was mound of cold air in Eastern Canada that unleashed cold shots behind oneach storm, the Northeast could experience quite a few snowfalls with this pattern, along with the ice that is common closer to the edge of the cold airmass. But now there is no real cold air around. Even on top of Mt. Washington, NH, it was 34 degrees this morning! Their average high at this time of year is 16; the low is minus 2. And, thunderstorms broke out in Connecticut this morning and were heading north-northeast!
The reason for the big warmup in the Northeast can be traced to the breakdown of high-latitude blocking. Earllier in the month, there was a high pressure area over extreme northeastern Canada and Greenland. When that happens, the cold vortex is forced to move south, and cold air pours across the Great Lakes and Northeast. Now the high is gone, and the vortex is way up where the high pressure had been. This setup can lead to mild winter weather for the Midwest and Northeast. However, that is not always the case. If the high pressure area between the Aleutian low and the Davis Staits low can amplify, a lot of cold air can drift southward through central and southern Canada. And, sometimes, there is a split in the flow farther east. Troughs can amplify in Southeast Canada to draw cold air into the Northeast.
On the other hand, if the split in the flow is farther south, a series of storms will simply move east from California across the Rockies and Central Plains, and then wind up on the Middle Atlantic Coast..all without tapping into the cold air. That's what's happening now. So far, we see this situation lasting through the end of the year, and the GFS shows it persisting next week as well. This suggests that today's California rainstorm will move east to cause rain the the Middle and North Atlantic states (snow is still a viable possibility in the mountains of Northern New England and there could be ice at the start farther south (though probably not in the cities from Boston to Washington)). Another one could visit during New Years weekend. Does that mean the traditional New Years Eve will be re-worded to "Cold acquaintance be forgot, and never brought to mind?" Or will things change to make that prospect into an auld lying syne?
Even if there is no fundamental shift in the pattern to extreme cold in the Northeast any time soon, that does not mean it cannot snow. It does appear that low level cold air will advance southward through Canada this week, and at least some of it could be tapped by storms passing to its south. In fact, some of the snowiest patterns the region has ever experienced (January 1978, for example) started out in ways somewhat similar to the situation in effect this week. So, for snow there is hope, but for most areas this week it is nope!
Elliot
