These late winter/early spring storm systems can be very interesting while coming off of a La Nina winter and this current storm system is a prime example of what can happen. One typical feature of the La Nina is ridging in the Eastern Pacific which sends cold air masses down it's eastern side into western and central Canada then into the northern US. We also have a negative NAO leading to a strong Omega blocking ridge over central Canada. A very energetic jet stream flow continues south of all of the blocking over Canada and The Northern Atlantic from over the top of the ridge in The Gulf Of Alaska into California then eastward across the lower 48 exiting off the east coast.

This is a very ominous pattern really as there is a very large contrast in temperatures from north to south across this storm track. Our latest storm has one center back in the Ohio Valley with a developing storm farther east over northern VA. These lows are along a very strong boundary between warm and moist air to the south and cold air to the north. The boundary stretches this evening from the mouth of The Chesapeake bay to the secondary north Virginia low then back west to the primary low near Cincinnati. We find temperatures in the 20s with snow over New York State contrasted by temperatures near 80 degrees in North Carolina! This extreme contrast helped to fuel thunderstorms, some of which produced hail and strong winds back through the Upper Ohio Valley into southwest PA earlier where funnel clouds were spotted as well. One tornado ripped the roof off a high school and damaged 10-20 homes in Hempfield 5 miles southwest of Greensburg, PA. This is also southeast of Pittsburgh. Some of this convection is pushing across The Tri-State area at this hour with heavy downpours, sleet, snow and some thunder and lightning. The mixed precipitation should eventually change to just snow by midnight as that warm layer of air up at about 5-6 thousand feet goes below freezing but by that time, the second storm center will be pushing off the coast and precipitation rates will be diminishing.

I expect a coating to an inch of snow in the city & LI with a couple of inches near, and around I-80 in NJ. Hudson Valley could also see light additional accumulations. The precipitation should diminish to spotty snow showers a few hours after midnight.

Much colder air aloft will come across the region Thursday as the main short wave crosses the area and this will give us the possibility for a rain or snow shower in the morning. As the wave axis exits to the east of our area a colder but dryer northwest surface flow will probably break the clouds for a little sun tomorrow afternoon but highs will run about 10 degrees below where they should be this time of year. This "locked in" blocking pattern insures that our temperatures will stay below normal for several days with the active jet stream running to our south. Friday and most of Saturday will offer some quiet weather with some sun but those beloved below normal temperatures then the next system tracking farther south then our current system will bring us the chance for some more snow Saturday night into Sunday if the moisture gets this far north.

Posted by Lee Goldberg on March 23, 2011 | Permalink


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