Mar 17, 2016 11:04 PM
NH1 Chief Meteorologist
Canadian high pressure will be settling in for the weekend with below average temperatures in the 30's to near 40. The high will be a good supply of cold as all eyes are focused on the upcoming storm. While the calendar will say Spring on Sunday we will be tracking a developing Spring Nor'easter which will be coming off the Carolina coastline and intensifying into a larger storm and tracking close to New England Monday Morning. Earlier this week, there was the potential that this storm could stay out to sea, then it looked like a big storm, now the out to sea option is still on the table! We should see snow out of this, but there are still many questions which need to be answered before we have an answer. In some circumstances, that answer will only be known once the storm is happening.
This storm is likely going to come close enough to New England to provide snow for parts of New Hampshire. The models have shifted east Friday, with some of the information showing a storm just providing a light graze of snow and even missing us! If this jog to the east persists, this would mean less of an impact for New Hampshire with lighter snowfall totals. Any further jog to the west,would bring heavier snow inland. As it stands right now, it appears eastern New England, specifically the coastline, could end up being one of the places which should get into some heavier bands of snow. Amounts could drop of sharply farther inland. We are watching the changes.
This is critical. If the storm speeds up with snow falling during Sunday afternoon, radiation from the sun along with temps in the mid 30's, this will keep accumulations down and roads wet. Plus, it would likely be a weaker less phased storm. If the storm arrives at nightfall, with the heaviest snow falling Sunday night and early Monday, this will be snow falling during the coldest part of the day. The snow will have a better chance to accumulate and road conditions could be a problem especially for the Monday morning commute.
Perfect snow growth is when temperatures run about -5 to -10 degrees celcius at 850 mb. Will there be good snow growth in this storm? Decent. All areas will be cold enough for snow. No mixing at the coast. And with the snow falling at the coldest time...we have a chance. But High pressure just may be strong enough to our N & W to suppress some of the snow south of us. Temperatures will be in the 20's when the snow could be falling so that is plenty cold enough.
Once we take these variables into consideration, we see what sort of moisture will be available and do the math. Usually 1" of precipitation is equal to 10" of snow in a typical snow storm. While most of NH will have that typical 10-1 ratio or less, along the coast we will be looking for some heavier bands of snow to develop along a coastal front. One of our more bullish models has printed out estimated precipitation of about 1.2" of total precip which would be close to 12" of snow Thursday. Today, there is less moisture to work with printing out between .5-.8" of precipitation which could mean 5-8" for the seacoast, but that is the heaviest model. Most have shifted to lesser amounts of moisture now between ,10-.5"...if that. Some have nothing! We'll see if there is a trend back west Saturday...if not...snow forecasts amounts will go down in a hurry.
HOW LOW WILL IT GO? The stronger the storm, the slower the storm, the greater the potential for heavier snow in bands and for snow to add up in optimal temperature conditions.
This low is going to come off the Carolinas and deepen into a strong storm as it tracks just off the coast of New England Monday morning. The peak of the snow should be Sunday night and early Monday morning which would not be good for Monday morning commuters. As stated, the time can change slightly. Another change is the storm does no look as strong. It will deepen into an incredibly strong storm in the Canadian maritimes as it pulls away, but here off the coast of New England, it does not look as impressive as it once did. The storm will begin to pull away Monday morning. Most of the snow will be over by Monday midday. The afternoon will be dry, breezy with highs in the 30's near 40. So it's a fast moving storm, with a small window of snow. Another reason for low estimates.
On Friday night, it was a low confidence forecast with a variety of solutions which could happen with this storm. Winter is playing hard to get even in these waning moments. The forecast will be evolving for better or worse this weekend. You will want to know the changes. Slight jogs east or west are huge to what happens here.
Stay tuned to NH1 News today for the latest updates and information.
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