If there was any type of trend to convey regarding our upcoming Friday storm it would be "less bad". It's really no consolation however because "bad" is bad. We've had worse thaws around Christmas both in duration and intensity. This one will feature a little over 12 hours of above freezing temperatures and a small window where temperatures approach 50 along with a burst of heavy rainfall. By Friday evening the rainfall is done and temperatures will again support snowfall if we can get any.
A friend at the National Weather Service made an interesting point to me the other day. He suggested that sometimes the presence of a polar jet can at times have a detrimental impact on a promising storm track. Jet stream impulses with in a polar jet are more dynamic and have the power to amplify storms so ferociously that they are unable to make a clean transition to the coastline and will run up through the Great Lakes sucking warm air into New England. This case would certainly underscore the point although arctic cold is an important ingredient for snow producing storms on the east coast so its presence is important though I suppose it needs to be the right kind of presence.
After several days of sub-freezing temperatures atop last week's two foot snow storm, the big push of warm air should initially bring a period of snow to northern Vermont very early Friday morning. I like to refer to this warm advection snow as a "front end thump" but unfortunately it won't be much of a thump. A few hours of snowfall before dawn and a few inches. At daybreak on Friday temperatures will be moving past the freezing mark and any wintry mix will become mostly rainfall. Models are beginning to sort out the ugly details which include only a few hours of heavy rainfall sometime between noon and 5 pm. This is a very strong storm and I expect the high winds to remain off the ground until late on Friday when we will see wind gusts of 30-40 mph in the valley's and upwards of 50 near the summits. If there's been a positive trend over the past day or so it involves the possibility for some anafrontal precip Friday evening in the form of snow. The drop in temperatures is expected to be very dramatic and capable of flash freezing some standing water late Friday evening. By Saturday we should see some intervals of sunshine, a cold southwesterly wind along with snow flurries. If the flow was better or more northwesterly, we might have snow shower activity of more significance, but this southwest flows confines the heavy snow showers to areas like Jay Peak over the weekend. The arctic outbreak is substantial for the Ohio Valley, Kentucky Tennessee and even areas further south though short-lived. In Vermont however, the cold is very garden variety with high temperatures in the teens on the mountain and morning temperatures in the single numbers. Expect some ugly wind chill values Saturday to go along with those teens and this will only very slowly improve Sunday into Monday.
Most of the holiday week following Christmas is expected to remain sub-freezing in Vermont but the pattern is expected to undergo some material changes with the polar jet and its associated arctic air gradually retreating. A softening pattern can create the opportunity for storminess along the east coast and there are hints of this on the Euro/Canadian models on Tuesday or Wednesday of next week. We should more clarity on how realistic our snow chances are in this time frame within the next 48 hours or so.
After Wednesday the Pacific is expected to really intensify and the entire North American continent outside the southwest U.S. is expected to see moderating temperatures. As bad as the Pacific appears for a few days, and as detrimental as that is for the buildup of cold across North America as a whole, I've seen worse January weather patterns. Both the NAO/AO are expected to remain on the favorable side of neutral and even the PNA index (a measure of ridging on the western North America) isn't all that terrible. Remember, by January, we don't want to be overwhelmed with arctic air as that can really dry things out at our latitude. We would prefer a stormy pattern with a bit more available arctic cold than what's indicated. So the pattern at face value doesn't look great at the start of '23 and quite terrible if you want snow along the coast or in NYC and points south, but there's room for some hope in Vermont.
Will Friday’s warm, windy rain eat all the snowpack or will we still have a white Christmas? Thanks for your updates!
ReplyDeleteThink we are wounded but not dead on that front
ReplyDeleteEPO looks to go positive...your evil empire's construction maybe well under way by the New Year.
ReplyDeleteThe EPO is barely positive according to several models around the new year. We've seen a lot worse honestly with that index in the past several years. At face value though models aren't painting a pretty picture however.
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