Jan 11, 2011: Rain, Wind, Then Cold

This winter’s theme repeated itself once again over the last two days, as a transient cool air mass was pushed out and yet another surge of warmth is returning, with temperatures over the last two days ending up above average once again, just as the majority of the days since December 1 have. Increasing clouds were observed today with temperatures peaking in the upper 40s from NYC and further west and the lower to mid 40s in Long Island and southern Connecticut.

A complex storm moving into the region will bring a wide variety of weather events, ranging from heavy rain and wind tonight to very mild temperatures tomorrow, followed by a cold front moving through on Friday morning, bringing a short round of showers followed by a significant drop in temperatures along with strong winds across the area, gusting above 50-55 mph in some places. The winds will calm down throughout the weekend with temperatures staying chilly, but this pattern is known for transient cold spells, and this will be no exception, with the cold already moving out by early next week with rain returning into the forecast by the middle of next week.

Tonight through Friday: Rain, Wind, Warm to Windy, Cold

Storm Set Up: The latest radar, posted to the left, shows that rain is moving up the coast and into the area. This is a part of a large low pressure system currently near the Ohio Valley. With some cold air trapped over the region, the storm is starting out with a wintry mix in parts of New England, but with temperatures too warm, the area is starting out with rain, with the exception of possible freezing rain this evening towards northwestern NJ and SE NY before also changing over to rain. A part of the storm’s energy is staying separate from the Ohio Valley low, and as a result, the rain currently affecting the area will split from the main system later tonight before moving towards Maine while weakening. At the same time, the main low pressure will move into Michigan, where it will stall through Thursday night. At the same time, the main energy will dive into Kentucky before moving through the Northeast, with the result being another low pressure forming near Pennsylvania on Friday morning. This low pressure will merge with the Michigan low, moving through the Northeast states on Friday afternoon and evening while intensifying.

Impact on NYC Area: With the initial low pressure moving through the area, a tight pressure gradient will develop, with gusty winds expected across the area tonight. Moderate to heavy rain will fall along with rising temperatures, reaching the upper 40s to lower 50s across most of the area by Thursday morning, with wind gusts between 30-40 mph possible, especially in Long Island where gusts may exceed 40 mph in some places later tonight. The first round of rain will end by 8-10 AM across most of the area, with a total of 3/4 to 1.5 inch of rain expected. Mainly cloudy skies will continue through the day on Thursday with highs reaching the upper 40s inland and the lower to potentially mid 50s across the rest of the area.

With the second low pressure developing near Pennsylvania, a cold front will move towards the area on Thursday night. As a result, temperatures will stay steady in the lower to mid 40s inland and the mid to upper 40s across the rest of the area throughout the overnight hours. A line of rain showers will enter the area between 12 and 2 AM, bringing widespread showers until about 5-7 AM, when the line will clear most of the area. A few snow showers may be possible especially towards NW NJ and SE NY on Friday morning.

Friday’s Outlook – Colder, Very Windy: A much colder air mass will quickly move into the area on Friday afternoon behind the cold front. In addition, the intensifying low pressure to the north of the area on Friday afternoon will result in a tight pressure gradient across the region. These factors will result in very windy conditions on Friday and Friday night, with widespread wind gusts near or above 40 mph likely across the area. Wind gusts are also likely to reach and/or exceed 50 mph in parts of Long Island, southern Connecticut, and potentially NYC, with gusts at most reaching the 60 mph range in the windier case scenario in parts of Long Island. Along with the winds, a noticeable drop in temperatures is expected on Friday morning, with temperatures by the afternoon in the 30s across the area, meaning that the high temperatures will take place on Friday morning. Stay tuned for more information on the wind outlook for the area.

Saturday – Monday: Colder, Dry

The cold air mass moving in behind the cold front will stick around through Monday, resulting in colder than average temperatures for the weekend. Partly sunny skies are expected for Saturday with highs in the mid 30s across most of the area. Sunday will bring colder temperatures, with mostly sunny skies and highs in the mid to upper 20s across most of the area. There is some uncertainty for Sunday night, with the GFS showing very cold temperatures, in the single digits further north/west of NYC, while the ECM model is nearly 10 degrees warmer. Considering the clear skies, cold temperatures are expected, although for now, I went slightly warmer than the GFS, expecting widespread low temperatures in the upper single digits to mid 10s north and west of NYC, although it is possible that if the GFS continues to show its current solution, temperatures may be adjusted slightly colder. Sunny skies are expected for Monday with high temperatures in the upper 20s across most of the area.

Tuesday – Beyond: Mild Again, More Rain

As with the pattern so far this winter, the cold air mass for the weekend will be transient, moving out by Tuesday with temperatures warming back up well into the 30s. A low pressure will approach the region on Wednesday, and is likely to bring scattered showers to the area; although the exact location of the storm is uncertain, it is very likely that it tracks to the north of the area.

There has been some talk of a change in the pattern that would bring in a lot of cold and snow into the region after this time frame. After reviewing the latest model guidance and other factors involved, however, not only do I not expect the pattern to flip, but the medium to long range appears to return to the above average temperatures spell. In the medium range, transient ridging builds near western Alaska, which is typically considered a positive, while much stronger cold air begins to build in Canada. This pattern, however, does not support ridging near Alaska, and as can be expected, the ridging is only transient, already moving out towards the middle of next week with yet another polar vortex returning into Alaska. As a result, one of the most zonal flows we have seen so far this winter develops, with a nearly due west to east flow modeled from the Pacific to the Atlantic. By this time, strong cold covers almost all of Canada, but there is very little to no amplification anywhere to be found in the western Atlantic and near Alaska. Without the amplification to “squeeze” the cold air into the United States, the zonal and very progressive pattern will keep storms moving mostly from west to east, while the core of the cold air stays trapped in Canada, occasionally dropping slightly southwards but only to retreat north as a strong, mild Pacific air mass moves through most of the United States. Eventually, the cold air is also likely to weaken in Canada.

This set up is a recipe for above to potentially well above average temperatures across parts of the United States, especially further south. The coldest departures will be focused near the northern US near the border with Canada, where the cold air will be able to have some impact. Further south, however, from about NYC’s latitude and further south, above average temperatures are likely to continue through at least January 22-24, with the occasional cold spells quickly moving in and out, although the potential for significant warm spells is just as possible in this time frame in the southern/central US up to NYC. The latest NCEP teleconnections show the NAO and AO trending negative; these forecasts, however, have busted way too far on the low side by constantly trying to flip the NAO back to negative over the last month while failing. The more reasonable ESRL/PSD teleconnection outlook as well as the models have frequently supported the NAO staying positive, correctly doing so, and their latest outlooks still show the NAO mostly positive, which combined with the MJO still struggling to move into phases 8+1, supportive of East cold, are indications that the current pattern isn’t going anywhere anytime soon. Although February is likely to bring somewhat more cold and snow potentials than what we have seen now, chances of a big pattern flip to much more cold and snow through the end of the month are low at this time. Stay tuned for more occasional updates on the longer range pattern.

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