Nor’Easter #4: Will this one finally provide?

Well, we know one thing for sure is that the Nor’Easter machine is functioning properly – just somebody forgot to flip the switch for the Mid-Atlantic. And now with a fourth storm on our hands, are our odds on the rise? Probably not. As usual, this storm is going to come down to location/elevation, timing, and amount of cold air – the last two being the most important, but also the most stubborn – and typically do not favor our area. It is March now, and the sun is higher in the sky (more solar energy available), so it’s getting more and more difficult to get accumulating snow in the daytime in low elevation areas. Ideally, we want a night-time event with a storm that tracks to our south with cold air in place before the storm, and an area of high pressure to the north to keep the cold locked in place.

Model Comparison

As of Saturday morning, both the GFS/American and the European models had pretty good agreement on the storm overall – regarding track and timing. The image below shows the Mid-Day Saturday GFS possible solution for this event.

GFS model-precipitation type

If you follow the progression of the red ‘L’ you can see the storm does track to our south. Precipitation begins to overspread the area Monday evening as light rain.  There is a transition to snow overnight, and into Tuesday. What you probably noticed is that the GFS only made the switch to snow over the mountains and Northern Maryland. Why? Cold air, or a lack thereof.

GFSModel – surface temps

The temperature animation above is over the same time period as the precipitation. Notice Monday evening, the GFS has temperatures in the upper 30s and 40s across the area – and that temps really never fall to or below freezing during the entire event. What this says is that the cold air never gets fully established over the region. In fact, if we look vertically, the cold air is not very extensive. On the image below, the left is a map of temperatures about 2000ft above ground, and on the right is about 1 mile above ground – valid 8AM Tue when the best snow chance occurs per the GFS. Notice that the areas that are below freezing (these temps are in Celsius, so below 0, or whitish-green areas), they are not that cold. The atmosphere must be below freezing and especially this time of year the entire atmosphere needs to be below about -3C for best snow opportunities.

So, the GFS has the track and timing (for the most part) of our ideal scenario, but falls short with the cold air, and favors those in elevation. Northern Maryland, gets the best opportunity, while along & east of I-95, this is another rain/snow slop, or just rain.

Now the European Model.

Euro Model – Precipitation type

The European model has a very similar track to the GFS, keeping the low to the south of the area (again, you can follow the red ‘L’ for the track of the storm on the animation above. It begins as rain late Monday night (the Euro begins a few hours later than the GFS), but colder air pours in and a switch to snow occurs overnight. But if you look closely, you’ll notice that the precipitation type pattern is very similar to that of the GFS, with snow to the N&W, rain/snow in the I-95 corridor, and rain S&E. The Euro does persist some of the heavier precipitation and snow into the early afternoon before tapering it off, which makes sense considering the Euro is slighly slower than the GFS with the progression of the storm.

The Euro actually starts out warmer than the GFS, with everyone in the low to mid 40s Monday night. However, the Euro is much colder once the precipitation begins, with most areas dropping to around freezing by Tuesday morning. Temps stay in the mid-upper 30s throughout the remainder of Tuesday.

The Euro is also warmer just above the surface than the GFS, which again supports a rain/snow mix or rain in the I-95 corridor and points east. Areas N&W in elevation have the best shot to see snow, but it will be a very wet snow.

 

I’ll mention the Canadian Model too, since it has a little bit of a different solution compared to the GFS and Euro. But, I’m do not like this model, and rarely use it. But the Canadian, or GEM, tracks the low a little farther north, and has a slightly different evolution – the details of which are more technical than I want to get. Precipitation begins overnight Monday into Tuesday, with the Mountains & Northern Maryland being favored for snow. Once the sun comes up, areas that were seeing snow switch to a mix, before the precip lightens up and mostly tapers.

Canadian Model Animation from Tue 2AM through Thu 8AM

One thing I’ll also note, and the Canadian is the most aggressive model with this. There will be a secondary low that develops off the GA/SC coast and moves north. It’s not going to be a big deal, but additional snow showers are possible Wednesday – no accumulation expected though.

Take Aways

This is probably not going to be a big storm. There is still time for things to change, but in my experience forecasting here, cold air is extremely stubborn to move in to the area in these types of situations. My early guess for this system, is it will probably be mostly snow for the higher elevation areas of northern & western Maryland. In and around the I-95 corridor will be rain & snow, and the further east you are, just rain. I doubt there will be much in the way of delays or closings. The night time snow, if it falls heavy enough, could lead to some slick spots N&W Tuesday morning, but once the sun comes up, roads will be fine.

-Andrew