This morning we have an excellent example of why winter storms are so hard to come by in the northern Mid Atlantic and why all features must be in place just right. In this case, the Sub Tropical disturbance certainly delivered with an energetic and impressive storm developing off the North Carolina coast. A well defined precipitation shield has formed just off the southern New Jersey coast and the surface low pressure system is ranging from 995 to 998 MB over the past three hours, fluctuating through this morning. Frustratingly for snow lovers in the Philadelphia and New York City metropolitan areas, this time the Polar jet stream was just in the wrong position with the trough axis over eastern New England and no blocking over the North Atlantic. As a result, the upper level winds from the Great Lakes to the New Jersey coast was from northwest to southeast, suppressing the advance of moisture to the north and forcing the surface low pressure system due east. Even still, the air mass in place was marginal at best so even if a phase had occurred with the Polar jet stream, the boundary layer would have ended up too warm to support frozen precipitation for many locations.
Surface high pressure currently over Ontario will build south this afternoon and evening, promoting clearing skies for tonight. A very nice weekend is setting up for the northern Mid Atlantic as high pressure slides just to the east of the region, supporting dry conditions, clear skies, and moderating temperatures to near and above normal levels. In fact, Sunday afternoon will have many locations along the coast approaching 50 degrees. A strong southwesterly flow will develop on Saturday night into Sunday as the high moves into the Atlantic and a strong cold front approaches the East coast. Changes are certainly on the way, and this January thaw is about to come to an abrupt end.
Note the 500 MB pattern by Sunday night from the ECMWF guidance. A negative EPO pattern is rapidly developing due to the changes in the stratosphere (rapid warming, which has been covered for several weeks in variouspremium discussions) and a crashing negative Arctic Oscillation supports a new Polar Vortex developing over central Canada. The MJO wave, currently in stage 6, strongly supports a changing pattern, which is exactly what happens as a new trough axis is repositioning towards the Eastern third of the nation rather than the Rockies. As a result, at the surface an impressive cold front will march through the eastern third of the nation. The strong southwesterly winds at the surface and mid levels will pull a significant amount of moisture northward along the cold front supporting periods of heavy rainfall on Monday morning. I’m concerned that the Monday morning rush hour will be significantly impacted with flash flooding and poor visibility, and I can’t rule out a few thunderstorms embedded in this rainfall to make conditions rather interesting to say the least. In short, Monday morning is going to be rather wet and stormy.
The push of cold air at the surface is going to be slow, thus the real impact of the new Arctic/Polar air mass sliding south from Canada will first be felt over the Plains and Great Lakes before reaching the northern Mid Atlantic. Temperatures on Tuesday will still push into the 40 early in the afternoon before rapidly declining in the evening. As the trough is established with an axis over the Ohio Valley on Tuesday through Thursday, a series of weak disturbances or cold fronts will move through the region introducing a fresh cold air mass and a few scattered snow showers. High temperatures Wednesday through Friday will be hard pressed to break through the lower 30’s along the coast and will likely remain in the 20’s just away from the coast. So the cold air is back and well sustained at the 850 MB, 500 MB, and even stratospheric levels.
By the end of the week, a very interesting set up is starting to come to light. The Polar vortex slides east over Ontario and Quebec, supporting a developing negative NAO pattern, thus leading to convergence over Ontario and a surface high pressure locking in over the St. Lawrence Valley. Meanwhile, the Sub Tropical jet stream remains active and sends an area of low pressure into the Tennessee Valley by Friday night. With cold air in place along with an established blocking pattern intensifying over the North Atlantic, there is a significant threat for an accumulating frozen precipitation event for Friday evening through Saturday. I am using a combination of the Canadian, ECMWF, and Ensemble guidance that continues to point to this threat for three model runs thus far.
By the end of next weekend, in a span of 10 days, a dramatic shift in the pattern will have taken place. With the MJO finally moving towards the more El Nino enhanced stages 6 and 7 in this time period, the Southeast ridge is gone and a trough is in place as a series of Sub Tropical disturbances cut through southern California and towards the Gulf Coast. The negative EPO/negative AO pattern is established and the growing warming in the stratosphere will support the high latitude blocking pattern to become established. The NAO pattern wanes from neutral to negative and back to neutral, supporting a higher potential for storms to move northward along the coast rather than be forced into the Atlantic like what was seen in early January. Further, the heart of the Arctic air mass will be reestablished over eastern North America with the boundary setting up over the Mid Atlantic coast. All of this will unfold if the majority of model guidance, teleconnections, and observed atmospheric data is correct. So those expressing doubts that winter will return, will get their answer ten fold by the time February starts.
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