Living On The Edge

Hello everyone!

Today’s update will focus solely on the storm tomorrow. The current thinking is that I’ll have time tomorrow evening to analyze our next few storm threats. With that in mind, let’s dig into what is an interesting and dynamic system for the day tomorrow. We will be right on the edge of a rapidly intensifying coastal storm as it moves from the waters off the mid atlantic past Cape Cod and on towards Nova Scotia. There will likely be a sharp gradient associated with snowfall amounts meaning that any shift east or west will have major ramifications for the forecast.

Since I’m short on time, I’ll quickly go through each of the three scenarios: high end snowfall, low end snowfall, and the current forecast.

WPC Probabilistic Guidance Showing Reasonable "Best Case" Scenario. Image Credit: Weatherbell
WPC Probabilistic Guidance Showing Reasonable “Best Case” Scenario. Image Credit: Weatherbell

The first scenario is that the storm doesn’t quite develop in time or the upper level trough can’t pull it back as far west as forecast. This would result in less snow. I doubt this will happen due to the orientation of the upper level trough (very negative with SE winds to feed in moisture)  as well as the current observations of the storm which are in line with the stronger/farther west guidance so far. However, what goes up must come down and it’s possible that part of the area will get stuck in a subsistence zone as powerful snow bands blast SNE. This would also result in these lighter snow totals. Notice though that even with the lighter outcome, Portland is still likely in for a 6″ snow event.

WPC Probabilistic Guidance Showing The Most Likely Scenario. Image Credit: Weatherbell
WPC Probabilistic Guidance Showing The Most Likely Scenario. Image Credit: Weatherbell

Here’s what the WPS thinks is most likely and my thinking (shown in my official snow map below) is fairly close to this idea. The storm will deepen rapidly off the Mid Atlantic coast and move NE towards Nova Scotia. This would result in a fairly substantial snowfall event along the coast with some spots likely seeing up to a foot. The mountains would see lighter amounts with only around 2″ up by the Canadian border.

WPC Probabilistic Guidance Showing A Reasonable "Worst Case" Scenario. Image Credit: Weatherbell
WPC Probabilistic Guidance Showing A Reasonable “Worst Case” Scenario. Image Credit: Weatherbell

Here’s a look at what could happen if things develop a little more quickly. Much of the area would see a serious snow event with much of the coast coming in at right about a foot. Right now this does not look likely but given the steady NW trend in guidance, it remains on the table as a possibility. Dendritic growth parameters give us the green light for fluffy snow that will accumulate quite quickly as the day goes on tomorrow so even with low liquid equivalent, ratios will be the friend of those rooting for heftier snowfall totals.

My Forecast
My Forecast

Here’s my forecast for snowfall tomorrow. Guidance is hinting at a band of heavy snow developing over the coastal plain tomorrow afternoon and before that a band of heavier snow over the mountains during the morning hours resulting in the 4-8″ forecast up there. There may be a lull of lighter totals just away from the coast where subsistence between these two bands results in sinking air and lighter snow.

More tomorrow morning on this storm (we’ll know by then which scenario we’re heading for) and tomorrow evening on all the other storms headed our way in the next 7-10 days (there are a bunch!)

-Jack

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