We are about to embark on a little storm and an active pattern that brings the best potential for universal snow to central Maryland in two years. After a forgettable performance last winter, the last time Baltimore measured 2 inches or more of snow was in January of 2011. The 11th had a 2 inch snowfall, but the 26th was our last big one at 7.6 inches. Perhaps this is payback for the record winter of 2009-2010. So it is understandable that any prospect has heightened the anticipation.
Winter not done, or going out with a fight
There has been some disappointment today with a few computer models losing sight of the expected larger storm this weekend. Not all have lost it. See the video clip below showing the Canadian Computer Model showing 3 potential storms between Feb 13-20 2013 for the eastern US. The first one appears weaker with rain and snow, but there is more on the way for this weekend and then again next Tuesday with colder air in place.
Forecast: In short, it will snow even with temps above freezing. That is part of the problem with how much will accumulate. The track of the storm will be to our south, and it will bring colder air with it. So don’t be lulled by the recent mild air. However that has warmed the ground and will play a role in how much of those flakes will be wasted and others counted.
See the slide show for computer model images, forecasts, and my first call for snowfall. I may be higher with my amounts than what you might have seen, but I still think I am playing it conservative, at least for Baltimore and Annapolis.
Note that the models are based on a set of temperatures that may end up being too warm.
- The GFS Model is projecting s high temperature of 46F for BWI and a total of about 1 inch of snow.
- The NAM Model is projecting a cooler high temperature of 41F for BWI with a snow total range of 3-5 inches.
The arrival of the clouds and wind speed may play a role in holding actual high temperatures a little lower. That would be crucial in how warm the ground is when the storm arrives and getting the colder air in sooner.
My call is based on potential stickage and assuming that this storm may end up with the recent trend just a little farther east. That would allow slightly colder air to build in sooner.
How Much? Temperature, intensity, and timing
Temperature plays a big role. While I expect snow to fall above freezing, it will drop colder west and north of Baltimore sooner. That will allow for higher amounts. Even in places that snow falls with temps lingering in the mid 30s.
The intensity of the snow can do two things. Heavier snow can actually drag down colder air with it from the clouds. That can be enough in some places to drop it to or below freezing, then warm a degree when the snow is lighter. Heavier snow also can overtake the warmer ground and where it is just when, initiate stickage.
The timing of the snowfall or change over from rain and a mix to snow after dark will allow for the maximum potential with marginal temperatures.
Timing:
Arriving: Mid Afternoon. This will be rain in southern Maryland, rain or a mix in central Maryland, and a mix or snow from the start in the mountains and our northern counties in to Pennsylvania.
Ending: It is likely that this ends from west to east between midnight and 5 am. So waking up on Valentine’s Day the storm should be off the coast and done for us.
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Definitions
I would love to describe the entire event and truly ‘geek out’, but I will save that for tomorrow. For now I just want to keep it simple and try and cut through some of the confusion. First a few definitions and descriptions that I often use which may help elaborate my thoughts.
Stickage- This is the process of snow reaching the ground and sticking. It can be crucial with marginal temperatures on the ground. This upcoming storm will display stickage on the grass long before we see it on the roads. Yes, this is my word I’ve used for over a decade, but it seems to have caught on (finally).
“Lays and Stays”- This goes along with stickage, but a step further. It is possible for snow to fall from colder clouds and reach the ground, then melt. While stickage overcomes the melting process, there can still be a battle depending on how heavy the snow rate is. When snow lays and stays, that is when it can finally accumulate.
*I remember one year a storm at the end of February and early March was expected to drop 3-6 inches of snow. Schools closed, but the roads were wet all day. There was enough snow to pile up that amount, but even on the grass, some melted and only showed about 1 inch. After dark however a burst of snow verified the forecast. In all actuality it snowed more than expected, but what laid and stayed was within the expected range. A lucky forecasting victory.
Dynamic Cooling: Heavy snow can actually drag down colder air with it from the clouds. That can be enough in some places to drop it to or below freezing, then warm a degree when the snow is lighter. Heavier snow also can overtake the warmer ground and where it is just when, initiate stickage.
Snow Ratio: This is a measure of the water content of the snow. On average, 1 inch of water would produce 10 inches of snow.
Colder air would be a fluffier flake and drier, so 1 inch of water could produce 15-20 inches.
Warmer air would produce a wetter flake. Sounds off, but true. With temperatures at or above 32F (yes snow is possible) the ratio can be 1 inch of water producing 8 inches or snow or less. Heavier flakes will compact and weigh down on the pile.
I have been asked to simply define our forecast regions in Maryland. I will try to do that tomorrow. A lot is based on geography, with many boundaries running along major roads or county/state borders. You can see more on my Winter Precipitation page
For more on my forecasting platform, please read My Winter Forecasting Manifesto
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