Nov 13, 2011: Above Average Temperatures Return

With a low pressure near south central Canada along with a strong high pressure off the eastern US driving out the cold from the Northeast US, a strong ridge began building into the region today, bringing warmer temperatures along with partly to mostly cloudy skies, reaching the mid to upper 50s inland and the upper 50s to lower 60s across the rest of the area.

The ridge will continue to build into the region, but unlike the last ridge, when widespread well above average temperatures were observed up to the Ohio Valley, a stalled cold front will keep the area near the edge of the warmer temperatures as several waves of low pressure move up along the front, with the final and stronger wave bringing widespread moderate rain on Wednesday. Although colder temperatures will return on Thursday and Friday with parts of the area dropping below freezing for the overnight lows, the pattern will prevent this cold spell from becoming sustained, and there are strong indications pointing that an even stronger warm spell than the current one may set up by next weekend.


Tomorrow's Outlook:

With a cold front approaching the region, mostly cloudy skies are expected across the area tomorrow, and although a risk of scattered showers is in place, potentially bringing a brief period of moderate rain especially to the west of NYC, widespread rain is not expected to fall across the area throughout the day. Along with a SW wind and 850 mb temperatures remaining near 10 degrees celsius, temperatures tomorrow will be slightly warmer than those of today, peaking in the upper 50s to lower 60s inland and the lower to mid 60s across the rest of the area.


Tuesday - Wednesday: Slightly Cooler, Widespread Rain Returns

The outlook for Tuesday and Wednesday became increasingly uncertain over the last few days as the model guidance had issues with handling the cold front and the waves of low pressure, but today a stronger consensus has emerged, with the model guidance showing the front near the area on Tuesday. With the front over the area, temperatures will end up similar to those of today, peaking in the upper 50s inland, and the lower 60s across the rest of the area, along with mostly cloudy skies and scattered showers. If the front is slightly to the west of the current expectation or if there is more sunshine, temperatures may get close to 65 degrees in parts of the immediate NYC area, although this is starting to appear not as likely as it did yesterday.

The front will finally move through the area late on Wednesday as a wave of low pressure brings the first significant precipitation event to the area in over half a month, since the late October snowstorm. This feature was the most variable on the models over the last few days, with some showing the cold front to our east on Wednesday, others keeping the storm to the west of the area with more warmth, and some did not show the secondary wave at all. There is still some uncertainty with the location and timing of the wave on Wednesday, but it appears that widespread rain should fall across the area. If the scenario currently expected verifies, occasional light to moderate rain would fall across the area throughout the day and into the evening/early overnight hours, with high temperatures peaking in the lower to mid 50s inland and the mid 50s across the rest of the area, potentially in the upper 50s in parts of the immediate NYC area. Temperatures could end up slightly warmer than expected if the rain is weaker or further west, with highs reaching the mid 50s to lower 60s across the area in that scenario. The rain is expected to continue throughout the day before ending by the early overnight hours, with a total of 1/2 to 1 inch of rain possible across the area. Stay tuned for more information on Wednesday's storm.


Thursday - Early Next Week: Cold, Then Warming Up

During the time that the wave of rain will affect the area on Wednesday, a strong trough will drop into the north central US, with 850 mb temperatures dropping slightly below -10 degrees celsius. Under this pattern, occasional cold spells, sometimes strong, will affect the region, but due to the pattern in the Pacific consisting of a -PNA and a +EPO, these troughs are only transient and quickly move out, replaced by more ridging in the East Coast. This will be the case once again, as a cold ending to the week is expected followed by a warmer weekend.

The trough will move into the area on Thursday, bringing clearing skies, breezy winds, and high temperatures in the mid 40s inland and the upper 40s across the rest of the area, possibly near the lower 50s in parts of the immediate NYC area. With mostly clear skies, colder temperatures are expected on Thursday night, dropping into the mid 20s to lower 30s across most of the area with mid 30s expected in NYC. Mostly sunny skies and chilly temperatures are expected for Friday, with highs likely in the mid to upper 40s across the area, potentially getting near 50 degrees in parts of the immediate NYC area.

As we have seen several times this month, in this time frame, and again beyond this time frame, the trough will move out of the region by Friday night, with yet another ridge building by Saturday and Sunday. With a very negative PNA expected, a rising EPO and the NAO/AO trending towards positive, there are strong indications that a significant warm spell is expected between Sunday and Monday, potentially including Tuesday. Temperatures as a result will gradually warm up throughout the weekend, reaching the lower to mid 50s across the area on Saturday, and likely getting into the upper 50s to lower 60s across the area on Sunday. Partly sunny skies are expected during the weekend. The warmest temperatures are likely to take place on Monday; should the cold front stay to the west of the area as currently expected, widespread temperatures in the lower to mid 60s are expected, potentially getting into the upper 60s in parts of the immediate NYC area in the warmer case scenario where there is more sunshine and the ridge remains solidly in place over the region.


Longer Range: Pattern To Stick Around Through Early December

The teleconnections supportive of a mild pattern will peak early next week, with a strongly negative PNA, +EPO, +AO and +NAO, all of which strongly support warmth in the East Coast. After early next week and towards Thanksgiving weekend, however, the PNA will become less negative, and there are some indications that the NAO may trend back towards neutral or slightly negative. The positive EPO, however, will send more warmth while pushing out the strong cold air starting to build over western Canada. Although slightly more frequent cool spells may be possible towards the end of the month and into early December, the -PNA/+EPO pattern will remain in place, delaying any pattern change and likely keeping mainly above average temperatures through early December. This does not mean that December will fail to produce cold and snow, however, as it appears that the pattern change is simply delayed but not canceled. When the pattern changes is still uncertain, but at this time, it is unlikely that a mild pattern without snow persists through all of December. My final winter outlook, which will be posted next Sunday, will discuss the pattern outlook for December in more details.