Northeast Weather Blog

Last Updated: 12:41 AM GMT on November 24, 2009 — Last Comment: 6:56 AM GMT on November 25, 2009

	Grey days and pink nights

Posted by: sullivanweather, 12:41 AM GMT on November 24, 2009

Current watches, warnings and advisories.

Fig.2 - Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.

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Forecast Discussion

Synopsis - Issued 11/23/09 @7:50pm

A weak coastal low will spread showers north along the coastal plain and southeastern interior of the Northeast through Tuesday. A brief break in the action on Wednesday before a trough developing over the center of the nation pushes east into our region for the Thanksgiving holiday and Black Friday. Multiple pieces of energy within this trough should consolidate into quite a potent storm by Friday afternoon over the interior of the Northeast. Progressive flow should keep low pressure moving along and out of the picture for the weekend with seasonable temperatures left in its wake. More pronounced changes commence at the beginning of next week as a northern stream trough pushes a cold front through the Northeast.

Near-term - Issued 11/23/09 @7:50pm

A sliver of fair weather remains this evening extending from northern Maine southwestward along the Canadian border into the Adirondacks of New York, then back into the Finger Lakes region. Clear skies and light winds across this region will allow temperatures to fall quickly during the evening hours towards the freezing mark. Elsewhere across the region skies are considerably cloudy as low level flow from the southeast is advection a marine layer across the southern three fourths of the Northeast. This southeasterly flow is in response to an area of low pressure advancing slowly northeast from the Mid-Atlantic region. Scattered showers have broken out in a west-east line across southern Pennsylvania then curving up along the coastal plain into southern New England. Within this band of precip where it isn’t raining it’s likely foggy and drizzly so all in all not a pleasant evening for traveling. The clouds and precipitation will likely keep temperatures holding in the 40’s.

Short-term - Issued - 11/23/09 @7:50pm

The band of showers will continue to lift north tonight, overspreading much of the southeastern half of the region. Rainfall amounts should be on the light side, around a tenth to a quarter inch for most areas. Rainfall may be a bit heavier across southern New England and eastern Long Island, closer to the track of the low moving northeast just offshore. In these areas rainfall may reach a half to three quarters of an inch. A surface ridge axis to the north will limit of northern extent of precipitation as the leading edge pushes into an area of subsidence and slightly drier air. The aforementioned areas currently seeing clear skies are the ones underneath this ridge axis. These areas will cloud over at some point during the overnight, except for perhaps extreme northern Maine, with temperatures rising several degrees once doing so. Winds will be generally out of the northeast at 5-10mph except for along the coastal areas where winds will be in the 10-20mph range with higher gusts due to their proximity to low pressure.

Low pressure will move towards Nova Scotia during the day on Tuesday with much of the heavier precipitation associated with it moving just offshore. However, weak northeasterly flow will continue with plenty of low-level moisture in place over the region. Some weak lift provided by lingering vorticity advection and low-level convergence boundaries should keep light showers and drizzle going throughout the morning and into early afternoon, especially along the coastal plain. Locally dense fog will also be an issue for the morning commute but should abate by the noon hour outside of the higher terrain from the Poconos to the Catskills and Berkshires. Areas to the north ill also see pockets of low clouds and drizzle during the morning hours but as low pressure moves away and the flow turns more northerly, the weak subsidence provided by the lingering ridge axis will eventually act to break up the cloud cover during the afternoon hours. Temperatures across much of the region will reach into the 40’s on Tuesday with a couple 50°F+ readings along the immediate coast and urban centers. Northeasterly wind will gradually turn northerly over the interior and remain on the light side, 5-10mph. Along the coastal plain winds will remain elevated, 10-20mph and will also trend towards a more northerly trajectory by afternoon.

Not much change in the overall weather picture Tuesday night. Plenty of low-level moisture will remain trapped under a modest inversion keeping low clouds fog and drizzle across a good portion of the region. Later on in the night high clouds will begin to advance over the western portions of the region as jet energy rounds the base of a low pressure trough over the Mississippi Valley. The cloud cover will act to keep temperatures elevated overnight, generally in the upper 30’s to mid 40’s. These readings are some 5 to 15 degrees above average for late November.

Mid-term - Issued - 11/23/09 @7:50pm

The trough moving into the Midwest will pull steadily eastward during the midterm portion of the forecast, a period covering the busiest travel day of the year on Wednesday and the Thanksgiving Holiday. Several shortwave disturbances will round the base of this trough, eventually consolidating into a rather formidable area of low pressure by the time Black Friday rolls around. Prior to the major cyclogenesis, the lead shortwave will move into the Northeast on Wednesday with showers spreading into the western half of the region. These showers are expected to be on the light side with precipitation amounts of a tenth of an inch or less. The flow will increase from the south ahead of the trough with milder air spreading over the region along with a continuation of considerable cloudiness. Temperatures will remain above normal with highs on Wednesday running in the mid to upper 40’s across the north with low to mid 50’s south.

The first shortwave will lift north of the region Wednesday night with a lingering trough axis lined up north-south across eastern New York State. In the vicinity of this trough axis light precipitation, mainly in the form of drizzle, along with low-clouds and fog will make for rather murky conditions. Elsewhere skies will be cloudy with pockets of fog, especially along the coastal plain. Temperatures will remain mild, generally in the 40’s with some 30’s across the higher terrain to the north.

Thanksgiving morning will break cloud filled with foggy areas and pockets of drizzle. An ill-defined cold front will begin to slice into the region from the west but will halt its eastward progress as a stronger shortwave reaches the base of the trough, now over the Ohio Valley, and starts to swing the trough axis from a positive tilt to a negative tilt. The flow out ahead of this trough will begin to turn around to the southeast by afternoon, helping to advect milder maritime air over the region. Clouds will persist into the afternoon but precipitation will remain light and scattered with little forcing over the region. Temperatures will be on the mild side, with readings in the upper 40’s to mid 50’s east of the Appalachians. To the west of the Apps, temperatures will be slightly cooler being behind the cold front. But even here highs will be a few degrees above normal with readings in the low to mid 40’s.

Big changes start to occur during the evening hours of Thanksgiving as the shortwave at the base of the trough crosses the central Appalachians inducing cyclogenesis east of Delmarva. Low-level easterly jet will increase to nearly 30kts to the north of the developing low pressure helping to draw Atlantic moisture back across the northeast. Developing deformation axis along the western flanks of the developing low pressure system will cause precipitation to break out across much of New York, New Jersey and Pennsylvania. At first much of this precipitation will be in the form of rain but as colder air drains into the backside of the system and dynamic cooling processes develop in response to the strengthening low/subsequent closing off of mid/upper lows, some of the precip will begin to change to snow. This changeover will occur first across the elevated terrain of the Allegheny’s and Laurel Highlands and eventually will work down to the lower elevations across western Pennsylvania by later in the overnight.

Long-term - Issued - 11/23/09 @7:50pm

Black Friday will be rather stormy across the Northeast as low pressure quickly intensifies in the vicinity of the Jersey shore and moves northeast. Cold air continuing to be drawn into the backside of low pressure will push the rain/snow line south and east, into central New York and Pennsylvania by afternoon and eventually reaching western New England by the evening. Across the higher terrain of the Appalachians and Adirondacks a measureable snowfall of several inches is possible during the daylight hours on Friday, meanwhile points east should see a half inch to an inch of rainfall.

Low pressure will bottom out Friday night at sub 990mb’s along the Maine Coast. Any lingering rain showers should change to snow for most areas save the immediate coastal plain and the State of Maine where milder southerly flow ahead of the low will be in place. Across the higher terrain of the North Country several more inches of snow may fall during the overnight hours while snow may leave a coating across the higher terrain to the south, including the Catskills, Berkshires and Taconics. Deep moist cyclonic flow will keep non-accumulating snow showers scattered about the remainder of the interior with some lake effect action thrown in there as well. 850mb temps are progged to fall to -6°C to -8°C so nothing significant is expected but an inch or so may fall away from the lakes where bands persist. Closer to the lakes themselves temperatures may indeed be mild enough for a mixture of precip types, deterring accumulations.

Wrap-around precip and lake effect snow showers will last through Saturday before gradually winding down as low pressure quickly lifts towards Newfoundland. The second half of the weekend looks splendid with partial breaks of sun but mostly mid/high clouds and seasonable temperatures.

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Radar: Northeast Region Loop

NE radar

Fig.4 - Radar loop of the Northeast region. Courtesy of Weather Underground.

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Local SST's

Fig.5 - Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.

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	Delightful late Autumn weather to continue through midweek

Posted by: sullivanweather, 7:57 PM GMT on November 16, 2009

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Posted by: sullivanweather, 7:50 PM GMT on November 06, 2009

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	Nor'easter to deliver unusually early snowfall

Posted by: sullivanweather, 6:09 AM GMT on October 15, 2009

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