Jan 30, 2011: Snow, Ice And Rain Coming Up

Today finally brought a return to dry conditions after the area has seen snow for 5 consecutive days. Temperatures tonight will drop into the single digits inland with highs in the 20s inland, however this dry period will not last for long before yet another storm moves in, with more snow, ice and rain.

Tuesday – Wednesday Night: Snow, Ice And Rain

Looking at the latest models, there are no significant changes from the forecast yesterday, and I have decided to issue an Ice Storm Watch for the interior parts of the area and a Snow Watch elsewhere. For today’s forecast, I mainly used the 12z NAM and 12z/18z GFS runs. The 18z NAM came in much colder, with as much as a foot of snow for northern New Jersey and over 6 inches of snow in NYC, however as of now it has little support, and I am waiting to see tomorrow’s runs to determine whether this is a new cold trend or just an off run.

Tuesday Storm: Snow To Sleet

The storm will start on Tuesday morning with an overrunning event. Light snow will overspread the area during the early morning and will become moderate by the mid to late morning hours from east to west. By the late afternoon, the 850 mb zero degree celsius line will begin to move north through the area, however cold air will remain in the surface, preventing a changeover to rain and instead resulting in a changeover to sleet from south to north between 2 and 6 PM.

By then, at least 2 to 4 inches of snow are expected in Long Island, 3 to 5 inches for southern Connecticut and the immediate NYC area, and 4 to as much as 7 inches of snow for the western parts of the area. There is some uncertainty with exactly how much snow falls, and these amounts may have to be slightly lowered or raised. Stay tuned for more information on Tuesday’s event.

Tuesday night into Wednesday: Bigger Storm, Significant Ice Possible

On Tuesday night, a break in the precipitation is expected with occasional light sleet as a bigger storm develops to the west of the area. While the low will track towards Illinois, it will be blocked from moving further north with a high pressure to the north of the storm, which will also help supply the storm with a lot of cold air, and will be forced to move east through Pennsylvania and into New Jersey.

Precipitation will move in from west to east on Wednesday morning. 850 mb temperatures will be above 0c in most of the area, though surface temperatures will still be below freezing, resulting in freezing rain developing for the area. As temperatures warm up from south to norh, the coast will quickly change over to rain, with New York City also changing over to rain by the mid morning hours. Places north and west of NYC, however, will deal with a more prolonged ice event, with NE NJ and southern Connecticut changing over to rain by the late morning with the potential for 1/4 inch of freezing rain.

The interior parts of the area may never change over to rain at all, though there is some uncertainty as some models bring in enough warmth to change the interior parts of the area to rain in the afternoon while other models keep enough cold air to prevent a changeover to rain. This potential will be watched, however if precipitation type fails to change over to rain, as much as 0.5 to even 0.7 inch of freezing rain may be possible, which may result in significant damage.

In the immediate NYC area, heavy rain will fall by the mid and late afternoon hours, with at least 1 inch of rain possible. This may lead to significant flooding, especially with snow cover over 15-20 inches in some spots. By the time that the storm ends overnight, temperatures will quickly drop into the 10s and 20s with the entire area changing over to light snow. In places where heavy rain falls, black ice could form by Thursday morning.

This will be a dangerous storm for the East Coast, with impacts ranging from as much as 12-24 inches of snow for the interior Northeast, a major ice storm for parts of the northern Mid Atlantic, and flooding in places that see heavy rain. Stay tuned for more information on this storm over the next few days.

Longer Range: Tomorrow’s update will have a little more on the longer range, including the potential for colder temperatures in the late week and another rain or snow storm for Saturday.

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