Yes, Virginia, there really is snow coming

1:14 PM, Apr 11, 2013   |    comments
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Before I dive into the details of this late season snowstorm, let me throw two disclaimers at you. (Actually two phrases for the same disclaimer, just to make sure I cover all age groups)

"Don't shoot the messenger." Or, alternately, "Don't hate the playa, hate the game".

Ok, now that we got that out of the way, let's move on.

Today: The vast majority of the state will see a mixture of sun and clouds through the afternoon, making for a pleasant Thursday. However, down across southern Maine there are some showers pushing in from New Hampshire. Most of these showers aren't being reported as reaching the ground, indicating to me that dry air is eating the drops up on the way down. Still, I'm inclined to leave in the chance for a shower across York and Cumberland counties through the afternoon because there are some pretty healthy looking radar echoes to the west. High temperatures will end up in the upper 40s for most, with only low 40s in the mountains.

Tonight: A fairly deep low pressure system will approach from the west this evening, leading to the entire state becoming cloudy from southwest to northeast fairly early on. After that an area of snow and sleet will develop over southern New Hampshire and push into southern Maine. The timing on this is a little tricky since I was originally thinking nothing would arrive until well after midnight, but seeing the warm front showers knocking on our doorstep already pushes the timeline up. So, look for a shower or flurry early in the evening across the southern 1/3 of the state, but the real bulk of the precipitation shield will hold off until 3-5 AM. The initial "thump" of precipitation will be snow and sleet, even along the immediate coastline. Temperatures will drop off considerably through the night, into the upper 20s to low 30s. This is going to be a HUGE factor in how the storm plays out on Friday.

Friday: From Berlin, NH to Camden, ME and all points south will deal with a wintry mix for the morning commute. Most of the precipitation will be wet snow, but there will be some mixing with sleet across York and southern Cumberland county as early as 7 AM. The precipitation shield will push northeastward, reaching Bangor by about noon as all snow. Meanwhile the sleet and snow will become heavier over southern Maine as the storm redevelops into a coastal low southeast of Cape Cod, MA. By the afternoon the entire state will be involved in some sort of precipitation: Snow from Bangor northward, sleet across interior and central Maine and a mix with rain along the southern coast and into the Midcoast.

Without a doubt the biggest challenge with this storm is how quickly the coastline changes over to rain. At first glance a screaming east wind off the water in mid April should mean a VERY quick transition to rain. BUT WAIT THERE'S MORE! In this particular setup we have a strong high to our north, providing cold air at the surface on a north wind. We call this "cold air damming" and it's something the computer models have a very hard time picking up on. I see a classic signature for strong cold air damming all the way into Friday afternoon, so that makes me think the rain/snow battle will be fairly hard fought even close to the coastline.  Bottom Line: I don't think the coast changes over until early afternoon, at that point they should have 1-2" of snow/sleet mixture. Is there a high bust factor here? Sure, but that's the whole fun of it!

Sleet will continue through the afternoon and into the early evening before the storm tapers off from southwest to northeast on Friday night.

I've made a snowfall map so you can find your town and then latch onto the high number of my forecast range while ignoring the low number; but here are a few extra tidbits:

1) I know a "Coating to 2" is a fairly big swing but I don't see much of a way around it. As I described before, the rain/snow line battle is a delicate one and I DO believe the cold air at the surface will be stubborn to leave. But I don't feel SO strongly about that that I'm inclined to put 1-3" along the coastline in April.

2) The snow will probably be slow to accumulate at first. The temperatures at the surface will be borderline so much of the first wave of precipitation will probably melt on contact. No worries, once the precipitation rate increases, the melting will stop. (It's not that "the ground is too warm". That doesn't exist, trust me).

3) Sleet will be an usually predominate type of precipitation for this storm. That's because the "cold air damming" I described before only applies to the surface. So you have all this warm air at the mid levels of the atmosphere that is still able to move in. As a result the snow melts on the way down, and then re-freezes into sleet as it enters the cold surface layer.

The system will pull out of Maine on Saturday morning, leaving us a few leftover showers and flurries. We should get into some sunshine by Saturday afternoon however.

The remainder of the weekend looks a bit unsettled with an upper level low stalled on top of us. That should provide partly sunny skies with a chance of showers on Sunday.

Things look a bit warmer for next week, but still nothing that screams "early summer tease" to me.

Twitter: @KeithCarsonWCSH. I'll tweet the latest on this storm. More importantly, I'm like 50 followers away from being the first to hit 3,000 at WCSH. The bragging rights would be enormous. Let's do this.


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