A Glancing Blow Sunday Night Into Monday

Hello everyone!

Boy has this been a fun one to forecast. As one of your sources for weather information (you should always consult the NWS and local media too!), the last thing I want to do is lead you on a roller coaster ride in terms of the forecast. To flip flop the forecast each day heading into a storm is something I hate doing. I want to give you a good idea of what to expect a few days out and then fine tune the details as we approach the event. With that said, this storm has led me on a wild goose chase in that every day, everything I look to points to something different. This isn’t just the whims of the model guidance I use to make forecasts, this is observations and satellite imagery painting completely different pictures. There are many moving pieces and it’s hard to figure out where they’re all going to go and what they’re all going to do. If life was full of easy forecasts, I wouldn’t be doing this. With all that out of the way, let’s try to figure out the forecast.

Evening Water Vapor Satellite Showing Many Moving Pieces (Including Lots Not Annotated!). Image Credit: SSEC
Evening Water Vapor Satellite Showing Many Moving Pieces (Including Lots Not Annotated!). Image Credit: SSEC

Water Vapor satellite imagery this evening shows all the parts of our storm. I’ve marked the disturbances and where the surface low will form and where it could possibly track (approximately). The ULL over Iowa is diving SE and will merge with a weak disturbance embedded in a deep plume of subtropical moisture which is marked in Green. Their interaction is beginning to form a storm over the SE US. When they merge, the storm will intensify a little bit as it begins to move NE. The real question has to do with Polar energy dropping down from the Western side of Hudson Bay. It has until Sunday night to get all the way to NY (about 1500 miles). It’s a race against time. If that energy crosses the finish line in time, it intensifies the storm, helps tilt the upper trough negative, and in turn wraps heavy precip back into our area. If it doesn’t, the storm continues at a moderately weak intensity ENE out to sea leaving us with but an inch or two.

BUFKIT Profile For Portland Showing Approximate Start/End Times As Well As The Mechanics Of Snow Growth.
BUFKIT Profile For Portland Showing Approximate Start/End Times As Well As The Mechanics Of Snow Growth.

It is becoming more and more clear that this storm isn’t going to drop a lot of liquid. However, given cold temps and a reasonably solid snow growth setup (see right), the snow could fluff up enough to lead to a couple of inches despite a lack of liquid. I don’t think this will be pure powder snow, but I also don’t see it being cement. Look as much or as little as you like at the image above, it shows/explains a little what you need for snow to form and what we have. Much like a Venn diagram, where they all intersect is where the snowflakes are forming. Based on this info, expect snow to start tomorrow evening. I suspect this may be a little late as the mid level dry air isn’t too stubborn compared to some other events. Snow looks to be light to moderate through the event before ending midday Monday. The ‘heaviest’ of the snow will be during the Monday AM commute though I don’t see it being all that heavy.

My Snowfall Forecast
My Snowfall Forecast

Here are my thoughts on snowfall. Earlier today, I was ready to pull the trigger on lower snowfall amounts but afternoon guidance and a couple of things I noticed on the WV satellite and in the observations this afternoon have led me to remain more or less unchanged with my snow map from yesterday. I cut back a little on the back edge of the precip as all indications are that this will feature a sharp cutoff. I bumped up snowfall a little along the midcoast where the heaviest snow looks to fall. While 8″ seems like a stretch, 5 and 6″ amounts seem very reasonable along the Midcoast. Unfortunately for ski areas looking to refresh the base, this one looks a little too far east. Thankfully for skiers, both Sugarloaf and Sunday River have fired up the snow guns again! With cold temps lasting through midweek next week, snowmaking will remain possible for a solid few days.

A warm up is in store headed towards the end of next week and some wild temperature swings are looking likely heading into April.

I’ll have another storm forecast tomorrow evening.




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