The PSU (Cherry Pie) March 13-15 possible snowstorm

Winter storm watch has been issued for DC metro. 5+ inches of wet snow expected.We will get a storm. The thing is we're walking a tightrope in regards to precip and temperatures. Too far west of a storm and we mix. Too far east or if the low pressure centers fails to consolidate fast enough, precip totals could be lower. There are still plenty of details to hash out.

In case you're wondering where the bar stands for snow:
Exceptional: Top March DC snow event (12.0" to tie 1891)

Excellent: Top 5 March snow event (9.8"+)
Good: Top 10 March snow event (7.5"+)

Also we're at like 2" for the entire season.... Won't take much to double that.

If the NWS issues warnings later, then expect Tuesday off. Maybe a early release on Monday too. We'll see.

Timing:
 Rain/snow in the late Monday afternoon into early evening changing over to snow. Temps in the low 40s, upper 30s. Heaviest snow late Monday night into early Tuesday morning. Temps in the low 30s to upper 20s.  There is some potential for mixing with sleet and rain depending on the exact low track. Light snow diminishes during the day with some steadier snow possible Tuesday night as the upper level low passes

Snowfall:
There is a decent consensus among global models for at least 1" of liquid equivalent precip. If all snow, @10:1 ratios, that would give us 10". Since it's March and March is warm, the snow will likely be wet and pasty, great for snowmen, but also low ratio and naso great for the trees. If heavy wet snow does materialize, power outages could be an issue (look at Jan 26, 2011). As usual with the elevation/temperature gradient of Montgomery County, snow amounts will be significantly higher in the upper part of the county than the lower part, as much as 6" different (rather arbitrary but you get the point).

Another thing is the instensity of the precip. As the storm bombs off the coast, we get slammed by a slug of tropical moisture. Much of our snow falls overnight, in the way early morning hours. This is the highest confidence part of the storm. As much as 10" could fall then, and then as the storm winds up and pulls away, moisture throw along the backside could bring some more snow. This part is less certain because there will be two initial lows, one well NW and one a coastal. Depending on how long it takes for the coastal to absorb the NW low, the NW low could disrupt the circulation of the coastal and therefore prematurely end the snow.

March snow again?

3/9/2017 Update:
Well the sunday storm got squashed
Friday (tomorrow) may bring some light snow

We're looking at Tuesday of next week now. Stay tuned...

Original Text 
Well February was a fail. 8.7 degrees above normal and only a trace of snow measured. But it's March and this is the real winter month. We will get feet and feet of snow. But joking aside, there's not much that could be the failure we called Feb 2017. The month averaged a temperature of 47.7 while the average temperature of March is 46.8 so we were literally a full month early.

There are some indications of March having the potential to be a better month than Feb. A large storm this week is set to develop and sit over Eastern Canada, which would push any following waves under it. In addition, following the storm will be unseasonably cold air. Storms running under us+cold air=possibility of snow.

However, the fast flow under the blocking in addition to the multitude of shortwaves that could interact with each other will likely throw off computer model forecasts. It also means many different chances. Our current window of highest chance is centered around this Sunday, the second shortwave after the cutter.

March Sun Angle

Ever since the winter solstice, the sun has been climbing higher and higher into the sky day by day. As we approach the equinox (and therefore spring, unless you're a meteorologist, the spring started when March did), the sun is getting stronger faster every day. One can feel the sun beating down on their backs now, especially near noon when the sun peaks at about 40 degrees in elevation. The higher the sun, the more direct the sunlight hits the surface of the Earth and the more energy is transferred.

 

An easy way to look at the energy of sunlight is to look at snowmelt patterns. The other day I noticed that the shadow of the trees were protecting snow from being zapped by the sun, even tracing out its major branches. Mind you it was in the mid 20s outside at the time this photo was taken. The sun at this point can easily warm the soil surface by 10 degrees F. This kind of freeze thaw typically does not go very deep but in the case where concrete or other heat absorbing materials are involved it can get interesting.

A Red Oak on Tower Road shelters some snow with its shadow.

One of my plant science professors Dr. Rossi once talked about how freeze thaw cycles induced by sun shining on concrete killed the grass around them. Grass around pavement really has a hard time. Foot traffic, salt, and heat all damage them. But his research showed that the sun does the killing, not the salt like many believed. The funny thing is at one point a critical amount of concrete is reached an one can have a consistent heating effect even at night and then you can zone push plants. Although Ithaca is officially zones 5b/6a, there are some small places, usually sheltered by well heated, concrete buildings that can harbor zone 6b or even zone 7a plants. It's all or nothing I guess.