Dec 10, 2011: Cold Sunday, Warmer Week

As a weak coastal low pressure developed well offshore, today brought mostly to partly sunny skies across the area. Although temperatures inland peaked in the upper 30s, temperatures across the area peaked early in the day in the mid to upper 40s, steadily dropping throughout the day into the upper 30s to lower 40s by the afternoon. A stronger trough is currently moving towards the region, and while it will quickly move out after tonight, much colder temperatures are expected tonight into tomorrow. These temperatures do not signal that a cold pattern has established itself, however, as a ridge in the southeastern US will return once again, bringing temperatures into the upper 40s again this week and into the 50s by the late week.


Saturday's Outlook: Coldest Day So Far

With the trough moving into the region, much colder temperatures are expected for tonight. With clear skies, temperatures will drop into the mid 10s inland, lower to mid 20s in the north/west suburbs of NYC and southern Connecticut, lower to upper 20s in Long Island, and the upper 20s to lower 30s in NYC. New York City is expected to see its first sub-freezing temperature of the winter tonight.

Sunny skies will continue tomorrow with a high pressure in place, keeping the colder temperatures in place. High temperatures will reach the mid to upper 30s inland and the upper 30s to lower 40s across the area, making tomorrow the first solidly colder than average day across the area since November, although temperatures this cold will not be experienced again until after this week. In comparison, last year's December frequent featured high temperatures in the 20s to mid 30s across the area, as a result of strong blocking and a strong -NAO/-AO, a factor that is missing this year and is one of the reasons why a cold and snowy pattern is not taking place for December.


Monday - Wednesday: Slowly Warming Up

A high pressure will stay over the region through Tuesday, providing mostly sunny skies across the area in this time frame. Temperatures will warm up as well due to the trough quickly moving out of the region, and after cold temperatures again on Sunday night, with lows in the upper 10s to low 20s inland and the mid 20s to lower 30s across the rest of the area except for NYC, which would end up warmer, Monday will bring warmer high temperatures, reaching the lower to mid 40s inland and the mid to upper 40s across the rest of the area. Tuesday will warm up even more, with widespread mid to upper 40s across the area, once again warmer than average. Slightly colder temperatures will return for Wednesday, with lower to mid 40s inland and mid 40s across the rest of the area.


Thursday - Weekend: Rain And Warmer, Then Slightly Colder

By the late week, a cutoff low will be located over the southwestern US, a frequent feature this fall and early winter that is yet another reason why a colder than average pattern has failed to set up over the East. Along with a ridge in the southeastern US and nothing in Canada to keep this storm suppressed, the SW US cutoff low will move northeast, wit a low pressure developing near the central US and moving towards the Great Lakes region on Thursday. The exact timing is still uncertain, although scattered showers are likely on Wednesday night into Thursday as the majority of the precipitation stays to the north and west of the area. Temperatures are likely to warm up at least into the upper 40s to mid 50s across the area on Thursday, and depending on the timing of the storm, if it ends up as north as the latest model guidance suggests, temperatures on Thursday or Thursday night may get close to the upper 50s. The cold front will likely move through sometime around Friday, and while the timing is more uncertain, for now I am siding closer to the slower ECM than the faster GFS, which would support high temperatures reaching the lower to mid 50s across the area on Friday. A faster storm would mean highs in the 40s with colder and drier conditions for Friday, while a slower storm would mean highs returning into the upper 50s with scattered showers. Stay tuned for more information on the late week storm.

Behind this storm, colder temperatures will return, with high temperatures likely returning into the 40s, but at this time it does not appear that any strong trough would move into the region, especially with yet another southwestern US cutoff low developing. Although this is in the long range, the cutoff low indicates that there may be a storm potential for the region around early-mid next week. If there is a storm in this time frame, although snow in the northern Mid Atlantic is not impossible if the location of the storm is supportive, the pattern suggets that the Northeast would be favored over the Mid Atlantic once again for any snowstorm potential.


Longer Range: There have been recent suggestions by the models that the pattern may be changing towards a colder one by the end of December into early January. The current pattern remains locked in place, with a generally neutral EPO, slightly negative PNA, and a consistently positive NAO and AO. The stratosphere remains very cold, with the colder 500 mb departures failing to drop south of Canada into the US as blocking fails to take place. The MJO is currently located near phases 4-6, supportive of eastern warmth, but has been blocked from moving into phases 1+8, supportive of Eastern cold, showing that the pattern is not yet ready to flip into a colder and snowier one. There are signs of warming in the stratosphere starting to show up, but the response will not be automatic, as it will take time for the current pattern to break. Overall, my thoughts have not yet changed from my winter outlook; although slightly colder and snowier conditions may take place towards the very end of December, I still expect any large scale pattern change potential to wait until at least early to mid January, with the second half of the winter more likely to bring more frequent periods of cold and frozen precipitation to the NYC area.