Northeast Weather Blog

More flooding rains likely

By: sullivanweather, 10:21 PM GMT on September 03, 2011

Current watches, warnings and advisories.


Eastern US current watches/warnings
Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.

Your Northeast Forecast


Synopsis

A rather complicated forecast is shaping up for the Northeast this upcoming week and much will be dependent on the behavior of two tropical systems, Katia in the Atlantic and Lee currently along the Gulf Coast, and their interaction with the mid-latitude flow. Tropical storms aside, our region will have its own issues as a slow-moving cold front taps into some of that deep moisture streaming out from the Gulf ahead of Lee and deposits it onto the region in the form of heavy rain and thunderstorms Sunday through Tuesday. This alone will have the potential to reinitiate flooding given the over-saturated soil and rivers still running quite high. Beyond Tuesday all bets are off as model consensus completely breaks down in their handling of Katia and Lee, especially. Some models merge Lee with the stalled front bringing yet another round of heavy rain for mainly the southern and eastern portions of the region, though a few models manage to bring Lee's remnants as far west as Michigan. Other models loop Lee back into the Gulf where it then meanders and strengthens into a hurricane. While all this uncertainty exists with Lee during the midweek timeframe, Katia will be swinging between Bermuda and the US East Coast. Most models bring the storm completely around the high missing the coast but allow for some indirect effect between itself and a stacked low pressure over the Ohio Valley. Other models build the high to the north of Katia just enough to bring the western half of the storm into at least a portion of the region along the coast by the end of the week into next weekend.



Daily soil-moisture percentiles. Nearly all of New Jersey, eastern Pennsylvania, southeast New York and western New England are at record high soil-moisture content levels. Credit: CPC/NOAA


Unfortunately, this uncertainty in the forecast couldn't have come at a worse time given the ongoing clean-up and reconstruction efforts following Irene. Irene's rains on top of already record to near-record levels of soil-moisture content provided for record flooding and only further bolstered the high soil-moisture contents across the region. With one round of heavy rain virtually guaranteed to occur with the stalling cold front centered on Labor Day and others possible from midweek on, additional flooding is all but sure to occur. Having just experienced a devastating flood, many of the same areas could very well flood again. So if you live in a flood-prone area and are recovering you may need to prepare once again.


Short-term forecast

Warm, muggy, summer-like weather will persist this weekend for the Northeast as a deep-layer southwesterly flow emanating from the scorched Southern Plains advects their hot airmass into the region. Temperatures in the 80's and low 90's are common across the southern two-thirds of the region this Saturday afternoon, with dewpoint temperatures well into the 70's. Further north, more clouds have kept temperatures cooler, mainly in 70's across northern New England. Though warm temperatures aloft have capped much of the surface-based instability a few thunderstorms have managed to pop and will continue to do so into the early evening hours across central Pennsylvania and New York.

A very warm night for Northeast with temperatures remaining in the 70's for much of the southern two-thirds of the region, excluding the higher elevations which will drop into the 60's. With lots of low-level moisture expect areas of locally dense fog to develop overnight. Across the northern third of the region it will be a bit cooler, with lows in the 60's. This region will also stand a chance of being grazed by a MCS moving east-northeast from the Great Lakes region along a warm front draped along the US-Canadian border. A quick inch of rain is possible from this system but most places will see amounts under a half an inch. This batch of showers and thunderstorms will weaken towards daybreak as it moves into Maine.

Sunday begins very warm with any fog quickly burning off. Convective debris from the Great Lakes region may provide for varying levels of mid/high clouds across the region but most places will see filtered sunshine at the least through late morning, helping to warm things up back into the 80's for most places from I-90 south. To the north 80's will be found in the St.Lawrence and Champlain Valleys with 70's elsewhere. The very warm and humid airmass will give rise to afternoon shower and thunderstorms as a pre-frontal trough moves into western Pennsylvania and New York ahead of a cold front across the Great Lakes. Some of these storms have the potential to become severe but the bigger concern will be the expected slow-movement of these thunderstorms along a line. The individual cells will move northeastward rather quickly but training of cells and slow forwards progression of lines of storms may present a problem with flash flooding, especially across northern New York during the day on Sunday. This threat will slowly shift southeastward Sunday night into Monday as the cold front pushes into the region, further aiding in lift. Once again, Vermont and the northern Catskills/Mohawk Valley/southern Adirondacks look to receive the heaviest rainfall from this first event. The rainfall will be convective in nature throughout the event so the biggest threat will be from flash flooding, though larger rivers will once again see significant rises as well. Rainfall of 2-4 inches is possible with much higher amounts possible in areas of training cells. Along the coast any activity is expected to be widely scattered as the heaviest stuff will hold off until Monday night. Highs here on Labor Day will climb into the 80's.


Mid-term forecast


Monday night through Tuesday night the front slowly sags to the coast and stalls. Heavy rainfall and thunderstorms will continue to stream along it with the tropical moisture feed well-established between itself and Lee. Rainfall will average an additional 1-3 inches with higher amounts. These amounts could easily lead to flooding. Further north rain will begin to taper to lighter showers and eventually end by Tuesday. Additional rainfall of a half inch to an inch is possible. Temperatures behind the front will run 15-20 degrees cooler than those out ahead of it.

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Tropical Update


Coming soon...



IR Satellite image of Tropical Storm Katia. Credit: SSD/NOAA




IR Satellite image of Tropical Storm Lee. Credit: SSD/NOAA






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Radar: Northeast Region Loop

NE radar
Radar loop of the Northeast region. Courtesy of Weather Underground.


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Local SST's

Northeast SST's
Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.


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About sullivanweather

Thomas is an avid weather enthusiast, landscaper and organic gardener. This blog is dedicated to Northeast and tropical weather forecasting. Enjoy!

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