Cool and dry weekend, snowstorm threat looms

Canadian model (CMC) showing a significant snowstorm impacting the area on Monday. The CMC remains one of the farther north models within the envelope of guidance.

Canadian model (CMC) showing a significant snowstorm impacting the area on Monday. The CMC remains one of the farther north models within the envelope of guidance.

Not only is March madness taking place in the college basketball world, but it’s also taking place in our world of meteorology. Cooler than normal air remains well settled into the region to begin the weekend, as historically strong blocking near Greenland and the North Pole as well as a historically negative Arctic Oscillation (AO) has led to a late-March pattern that feels more like mid-February. High temperatures in the 40’s and cold westerly winds have been a staple in the area weather the past few days. Much of the same is expected through the first half of the weekend, with cooler and dry conditions prevailing. Attention will then turn to a potential snowstorm (yes, snowstorm) on Monday. Forecast models are struggling with the track and intensity of the system as well as the resulting impacts on our area. We’ve detailed the entire threat below.

SREF ensemble mean showing a significant snowstorm on Monday.

SREF ensemble mean showing a significant snowstorm on Monday.

It’s Spring. What is causing the threat for the snowstorm? Historically strong blocking over the high latitudes (extending from Greenland to the Pole) is displacing unseasonably cold air into the Northern 1/3 of the US. At the same time, a strong disturbance is ejecting out of the Pacific Northwest into the Central United States. Such a storm track could occasionally cause a rain storm in our area, especially this time of year, with the surface low tracking to our west. However, the presence of the unusually strong blocking is forcing the system farther south, to redevelop off the East Coast. The presence of cold air to the north and throughout our area is increasing the likelihood of snowfall if precipitation makes it to our area.

What are the uncertainties with the system?  One reason why blocking patterns can be so unseasonably cold is the fact that they force powerful Upper Level Low (ULL) pressure systems to meander at latitudes just to our north and northeast, which are a great source of cold air. However, when an ULL is too powerful and too close to our area, it can compress the height field out ahead of our storm and force it drift eastward instead of turning the corner and heading up the coastline. We do know that eventually, the storm will run into a brick wall and be forced to drift eastward. However, will it do this after it gets to only Ocean City Maryland’s latitude, south Central Jersey’s, or somewhere in between? This is the difference between a graze, a moderate rain to snow event, and a major snowstorm.

Over the past several model cycles, we have seen a slow, not necessarily linear trend, for the guidance to leave more room between our main storm and the ULL to the northeast. This is because models have shifted the ULL further northeast and have weakened it a bit. This allows our main storm to generate more height rises out ahead of it, leading to a more amplified pattern, as opposed to the height rises being compressed. Mid and upper level winds have shifted from the ESE to the E in Northern New England, and E winds will not act to suppress the storm to the south nearly as much as ESE winds would. That being said, the ULL is still positioned in an area a bit to the southwest of what is ideal for major east coast cyclogenesis.

We’ve also seen a more mature and organized area of vorticity with the main storm a bit to the west of previous runs, since the pattern has trended more amplified, and thus, slower. The storm does not race east and have a corresponding secondary low to the southeast; it’s able to slow down, and have a secondary tucked in towards the coast and gain latitude before being shunted to the east. This is also why the timing of the storm has slowed down from Sunday night to a Monday and Monday night event.

Obviously, uncertainty remains very high in whether or not the storm will come far enough north to bring heavy precipitation to the area. A stronger upper level low to the north of our area will compress the storm to the south and east, while a trend towards a weaker upper level low will allow the storm to track near the New Jersey coast and bring significant impacts to the area.

What can we expect if the system comes far enough north to bring heavy precipitation? If the farther north model guidance verifies, the potential for a significant late-season snowstorm throughout the area would be rather high. In addition, gusty winds would be likely as the storm passes very close to the area. Although it is too early to talk about specific accumulations, a farther northwest track would (As stated above) increase the likelihood of significant (6″+) accumulations for a good majority of the area.

Stay tuned over the next day or so as we get more details and analyze new data. We’ll be updating throughout the weekend on our Facebook and Twitter accounts.