Nor'easters The storms that cause the Great Blizzards of the Northeast and some of the greatest one-day snowfalls. Mike http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2012/04/120423_g13_wv_anim.gif By: Michael Vuotto and Jake Mulholland

Blizzard of 2010- December 27th at 1am and then at 9am Mike Blizzard of 2010- December 27th at 1am and then at 9am

What are Nor’easters? “A name given to a strong, steady wind from the northeast that is accompanied by rain/snow and inclement weather. It often develops when a storm system moves northeastward along the East Coast of North America.” (Ahrens, 2009) Any development or strengthening of a mid-latitude cyclone is called_________. Jake

Where do they tend to form? East Coast of the United States off Cape Hatteras, NC. When air flows westerly across a north-south mountain range– this allows air to curve cyclonically. This curving of the air allows for developing or strengthening of a cyclonic storm. These are called lee-side lows or lee cyclogenesis. Think of the gulf stream as well … lots of latent heat release! (baroclinic zone) Also, when a storm drops 24 mb in 24 hours…. What is it called??? Hint: you can give it two different names. Jake

How do they form? -Baroclinic instability- “A type of instability arising from a meridional (north to south) temperature gradient, as strong vertical wind speed shear, temperature advection, and divergence are in the flow aloft.” Mike

Background on why Nor’Easters form? Initial development appears to be influenced by the land-sea interface between the East Coast and the Appalachian mountains as well as the Atlantic Ocean. Once these storms move out over the open waters of the Mid- Atlantic they tend to rapidly intensify. Coastline serves as a focal point for cyclogenesis as the coastline is where the cold air trapped over the coastal plain and east of the Appalachian mountains and boundary layer are moistened by the Atlantic. The influence of the Appalachian mountains on cyclogenesis has a small, but significant impact on the path of a storm forcing the storms to track farther south and east of its initial track. Absence of cold-air damming causes the surface lows to develop farther south along the cyclones front in the lee of the mountains. When cold air damming is present, lows tend to form farther east near the coastline. Processes related to the presence of the mountains are important factors in maintaining cold air over the coastal plain, contributing to the enhanced low-level baroclinicity at the coastal-ocean interface required to get cyclogenesis. Jake

What ingredients are needed for a Nor’easter to take shape?? -Cold air coming down from the arctic to the northwest of the storm system being drawn into the low pressure . -High pressure to the northwest of the storm system to filter in the cold air as highs have clockwise flow around them. Most favorable place for a high to be centered is over Northern Ontario to the northwest of Ottawa. -”Isentropic lift”- important because this is where the heaviest banding features for snow in the storm will take shape. -NAO, -AO, and +PNA. Jake

Example of a developing Nor’easter March 1993 superstorm 500mb chart of the superstorm of 1993. 7am EST March 13, 1993 -Deep, negatively tilted, digging trough in the east Divergence is present where?? Where do you think cold advection is?? Warm advection? Mike Cold Advection Warm Advection Divergence

Background (cont.) Two types of storm paths on the East Coast: Miller Type A- look for a surface low that might try to develop along a frontal boundary separating the cold continental air from the warmer maritime air. Miller Type B- the more classic type of scenario- features the development of a secondary area of low pressure along the East Coast to the southeast of an occluding primary, or initial, low pressure center that moved to and filled over the Ohio Valley, west of the Appalachians. Mike

Jake

Jake

Primary lows - develop further north in Canada -“Alberta Clippers” -Amplify upper level troughs , which initiate East Coast cyclogenesis - Bring in reinforcing shots of colder air = spark east coast development either near the coastline or most of the time out to sea. (Baroclinc zone) Mike

Explosive Cyclogenesis -Sanders and Gyakum (1980)- said that the term explosive cyclogenesis is systems exhibiting a central sea level pressure decrease greater than specific threshold of 1 Bergeron which is equivalent to a 24h deepening rate of 24mb at 60˚ latitude. -1b= 24mb [sin((phi))/sin (60˚)] 24h^-1 -Regions favored for explosive cyclogenesis- the East Coast of the United States. Mike

Climatology of Nor’easters Hoskins and Valdes found that diabatic processes serve to replenish the baroclinic zone on the east coast of the U.S. Cold continental air flows over the warm waters of the ocean which allows latent heat release and diabatic warming to take affect. Chang (2009)- identified extratropical heating exerts an important influence Jake

Review *For a surface mid-latitude cyclone to develop or intensify (deepen), the upper-level low must be located to the west of the surface low. *For a mid-latitude cyclone storm to form, there must be an area of upper-level diverging air above the surface low. (“mass evacuation”) *For the surface storm to intensify, the region of upper-level diverging air must be greater than surface converging air. *When the upper-air flow develops into waves, winds often cross the isotherms, producing regions of cold advection and warm advection, which tend to amplify the wave. Also, vertical air motions begin to enhance the formation of the surface storm as the rising of warm air and the sinking of cold air provide the proper energy conversion for the storm’s growth. (QG theory……) Jake

What to look for when forecasting a Nor’easter Look at current observations for the Northeast. Look at what is coming in from the Midwest … for example … a trough digging into the East. Blocking up in Greenland to make sure that the storm doesn’t just race out to sea. Cold air being filtered in due to a strong high pressure to the northwest of the coastline. NAO= negative (-), AO= negative (-) and PNA= positive (+) Look for meridional flow and not zonal. Look at GARP and Bufkit to see isentropic lift, temperatures, dew points, mixing ratio. Where there is the highest isentropic lift, that’s where the heaviest bands in the storm may set up. (typically on the northwestern side of the storm  “pivot position”) Mike