Friday, May 12, 2017

Nor'easter Expected to Impact the Northeast Mother's Day Weekend

Brian Donegan
Published: May 12,2017

A Mother's Day weekend nor'easter will bring a combination of rain and wind to the Northeast, resulting in a second consecutive wet weekend.
The term "nor'easter" most often is used for strong winter storms crawling up the Northeast coast, but, in fact, snow isn't a requirement for such a storm.
Nor'easters are simply stronger areas of low pressure along the Eastern Seaboard of the U.S. featuring winds typically from the northeast. They're usually strongest from fall through early spring, but can happen any time of the year.
(MORE: What is a Nor'easter?)
This year, it will likely include mid-May, unfortunately.
This Mother's Day weekend, low pressure should form somewhere off the Northeast coast.
This area of low pressure will then intensify as it tracks northeastward. There will be plenty of moisture from the Atlantic and Gulf of Mexico, which will increase the chance for moderate to locally heavy rain in some areas.
The exact track and strength of this low-pressure system is still uncertain, which will determine where the heaviest rain and strongest winds will occur. But rain, wind and coastal impacts are likely this weekend across the region.
(MORE: Stunning Contrast Between the Worst and Best U.S. Drought Monitor Conditions)
In general terms, here is an outlook for the region through the weekend:
  • Low pressure is expected to develop near or just off the mid-Atlantic coast.
  • The best chance for rain is along the coast from the mid-Atlantic states to southern New England, extending inland to Pennsylvania and New York state.
  • Winds will increase along the coast, with gusts up to 35 mph possible.
  • Some coastal flooding is also possible north of the low.
  • Chilly temperatures are expected with highs generally in the 50s.

Saturday's Forecast
Mother's Day:
  • The area of low pressure will track near or off the southern New England coast.
  • The best chance for rain and wind is from New England westward into upstate New York.
  • Windy conditions will persist for much of the Northeast, with gusts up to 40 mph possible.
  • It will remain cool, especially in New England and New York, with highs in the upper 40s and 50s.

Sunday's Forecast
This low-pressure system will be slow moving and will continue to bring showers to portions of New England into Monday.
To complicate things further, another system may swing through the Great Lakes and interior Northeast Sunday into Monday, prolonging rain showers in those areas into Monday.
(MAPS: 7-Day Forecast Highs and Weather)
The entire weekend won't be a complete washout, though.
For instance, parts of northern New England may escape much of Saturday without rain. Parts of the mid-Atlantic states may also dry out a bit by Mother's Day, as well.

Rainfall Forecast
A widespread area of 1 to 3 inches of rain is expected from the mid-Atlantic into New England, with locally higher amounts possible, especially toward the coast. Heavy rainfall over a short period of time will also bring the potential for urban and poor-drainage flooding.

Blame the North Atlantic Oscillation (NAO)

Last weekend's gyre of low pressure was cold enough to produce snow Monday in parts of upstate New York and New England, even as far south as northwest Connecticut. In fact, there were still flurries falling Tuesday morning in Saranac Lake, New York.
The North Atlantic Oscillation (NAO) – an index based on the pressure difference between typical Atlantic subtropical high pressure and typical low pressure near Iceland and southern Greenland – has turned negative so far this month. In fact, it was a record low for the month of May in 69 years of records, according to Dr. Phil Klotzbach, atmospheric scientist at Colorado State University.
When the NAO is in this negative phase, blocking high pressure in the upper atmosphere near Greenland causes the jet stream over North America to plunge southward across the eastern half of the United States, resulting in a period of cooler-than-average temperatures.
This is a typical setup during the negative phase of the North Atlantic Oscillation (NAO).
There is some good news. This negative NAO should finally relent next week, but it won't do so before this next gyre of low pressure affects the Northeast on Mother's Day weekend.
Be sure to check back to in the days ahead as the details of this complicated forecast are ironed out.
MORE: Winter Storm Stella (PHOTOS)

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