Jan 9, 2012: Rain Thursday; Interior Mix?

With a slightly cooler air mass over the region, today brought partly sunny skies with temperatures still slightly warmer than average, peaking in the lower 40s across the area. A weak wave of low pressure brought moderate snow to the central Mid Atlantic with widespread accumulations of 1-2 inches from Washington DC and northern Virginia into Delaware, making today the second time recently that the central Mid Atlantic saw snow while the NYC area stayed dry. With the storm already moving out, the area will stay dry through tonight.

Temperatures will slightly warm up tomorrow, but will remain in the 40s for highs through Thursday as a storm moves through the region, bringing rain to NYC along with the potential for a wintry mix further north/west. Once the storm ends, a colder air mass will move into the region, bringing colder temperatures for the weekend before slightly moderating towards early next week.


Tomorrow's Outlook:


Mostly sunny skies are expected to return for tomorrow. As the cold air mass moves out, temperatures will warm up, reaching the mid to upper 40s across most of the area, nearly 10 degrees warmer than average. West/WNW winds are expected for tomorrow.


Wednesday - Thursday: Rain In NYC, Wintry Mix Inland?


As my afternoon update mentioned, there have been significant changes with the expectation for the Wednesday-Thursday storm. Originally, the storm was expected to phase while moving through the region into Maine and Canada. Since then, however, the storm is staying more separate from the low pressure to its northwest, and takes a track about just south of the area and then close to the coast of New England. With a strong high pressure to the northeast, this allows for a CAD, or a cold air damming scenario to take place, where cold air sticks around a bit longer at the start of the storm. CAD type storms tend to bring frozen precipitation to interior areas away from the coast, with NW NJ and SE NY the most likely to see frozen precipitation across the area.

There is still some slight uncertainty with the location of any wintry mix potential, but for now, I went with a scenario close to the general model agreement, with the storm starting around 11 PM-12 AM across most of the area. Most places will start out with rain, although parts of NW NJ and Orange County, NY are likely to start out with a wintry mix of rain, snow, sleet and freezing rain, although the highest risk of significant sleet/freezing rain amounts is to the north of the area. As the storm moves towards the area, warmer air aloft will move in and change the interior wintry mix to rain towards the morning hours, with the rain likely to end somewhere around noon along with high temperatures staying chilly, in the upper 30s to lower 40s inland, lower to mid 40s in the immediate NYC area and the mid to potentially upper 40s in Long Island and southern CT. By the time that the storm ends, at least 1/2 to 1 inch of rain is expected with locally higher amounts. Frozen precipitation accumulations, if any, are uncertain for the interior parts of the area, although the potential exists for up to 1/2 or 1 inch of sleet/snow along with light freezing rain. Stay tuned for more information on this potential interior wintry mix.


Friday - Longer Range: Colder, But No Pattern Flip


The cold front will move through the area around Thursday night, bringing another round of scattered showers for Thursday night into Friday morning. Some models are showing the potential for snow showers to mix with the rain, although until a better consensus emerges on this potential, for now I am keeping a slight chance of isolated showers in the forecast. Friday will bring slightly cooler temperatures, in the upper 30s to lower 40s across most of the area, with colder overnight lows dropping into the upper 10s to mid 20s across most of the area. Colder high temperatures will return for Saturday, reaching the mid 30s across most of the area.

Uncertainty noticeably increases on the models for the Sunday to Tuesday time frame, and for the first time this winter, the majority of the models are showing some sort of frozen precipitation affecting the area. The afternoon run of the GFS had two consecutive moderate snow events, with the 18z GFS showing a suppressed coastal storm with light snow for the area. In addition to the GFS, the 12z ECM showed a snow event for next Wednesday, with the 0z CMC run also showing a rain/snow mix around Sunday and Monday. The other model runs either did not show a storm or kept it offshore. Towards this time frame, some changes are evolving in the pattern, including the development of ridging near western Alaska, with a larger supply of cold air dropping further south closer to the US. The result appears to come in the form of a "gradient" type pattern where the Northeast and Great Lakes are the most favored for snow events, although the northern Mid Atlantic can see some frozen precipitation.

As a result of the factors above, although strong sustained cold is not expected, colder temperatures compared to the persistently above average temperatures the area has seen so far are expected for next week, along with the Sunday-Tuesday storm potential. It is still uncertain whether a storm actually does take place in this time frame, given that this is still nearly a week away, although given the minor changes in the pattern, whether it's this storm potential or not, the possibility is there that the first snow of the meteorological winter for most of the NYC area falls sometime between January 17 and 28. These changes in the pattern, however, do NOT mean that the pattern has officially flipped to a cold and snowy one, since the stratospheric warming is still ongoing and changes in the pattern are unable to completely settle in, with signs of a polar vortex attempting to return to Alaska in the longer range once again along with difficulty to establish a negative NAO and blocking near Greenland. Although some changes in the pattern will bring some more cold and slightly more frequent snow potentials for the Northeast, potentially including the NYC area in some cases, for the second half of the month, this is not expected to be a completely different pattern which favors much more frequent snow chances for the NYC area. Stay tuned for more information on the longer range.