A Nasty Mess For Interior Areas
A double barrel system is very likely to bring snow, sleet, freezing rain and rain to the state for Tuesday into Wednesday. This “inside runner” system spins off a coastal low which may add problems for areas away from the immediate shoreline. Heavy wet snow, ice, sleet appear to impact interior areas, with rain the precipitation form for the shorelines.
An Inside Runner Equals A Mixed Bag
As it appears for now, the coast appears mostly rain and the northwest crown around Allagash appears all snow. Sandwiched in the middle is a blend of the four precipitation types, with areas close to the coast may see some rain, further north and east, snow.
I will be right up front with you, forecast models are all over the place with this event. It’s this kind of inconsistency this close to a storm that gives forecasters fits. My discussion here leans on previous history for these kind of events, as recent as within the last 2 weeks. We’ve seen this movie many times in the state, and there is always an element of surprise.
Timeline Depends On Location
It appears at this point that the mountains of western Maine get in on the game first with snow showers Tuesday morning. Any sunshine over the rest of the state will give way to increasing clouds. Precipitation will begin to build over western & southern areas during the day and slowly take over to the north and east. It may be midnight before the northeastern crown around Caribou up to Van Buren may get in on the action.
End times Wednesday appear between 7 AM – 10 AM for areas from Bangor to Coburn Gore south and west, and early afternoon for the far northern crown.
One Model Idea To Get A Perspective On Recent Events
The recent storm that dumped epic snow over western & southern Maine, caused angst as the forecast track abruptly shifted east within 12 hours and in many cases changed the entire ballgame for the southwest coast & interior. This situation is a bit similar, however, it appears to be later in the event for Maine where the coastal low forms. The developing coastal low always raises the red flag for potential last minute forecast shifts and surprises, and this case is no different. I will use today’s 12z RGEM Canadian short term model as a case study, and pinpoint where it predicts the action will take place at 4 AM Wednesday. This one model idea and should be viewed as such. Forecasts are a blend of model ideas, not based on one model solution.
Cold Air Damming Is Always A Challenge
Exhibit A above sets the stage for us: A weakening low just east of Lake Huron and a developing low over the Gulf of Maine. Since low pressure in the Northern Hemisphere operates counter-clockwise (or anti-cyclonic) the wind is generated from the southwest and wraps around to the northeast. Those little wind flags show the direction and intensity. It’s south / southeast over the Gulf of Maine, then transition to the northeast and north over land. Over land is below 32° cold, over water is 40-50° warm. Cold air doesn’t move as fast since it is more dense. Warm air is more active since it has more energy, making it less dense. Simple law of meteorology and physics. Unfortunately, it is a character flaw in model guidance. It is that character flaw where more forecasts go up in smoke because the models want to treat cold air at near the same level as warm air. It doesn’t work that way. This is why long term models fail consistently in winter, and short term models have the same error. They are most always too progressive with their ideas of air movement with air pressure and temperature. More times than not, forecasts bust because of this element, and it is by respecting cold air where I proceed.
Same map I started with above, but this adds 2-meter (~6 ft) temperature to the view. Cold air to the north, warm air to the south. As far as I am concerned, I see this as a battlefield for ground supremacy. Given the position of the intensifying surface low over the Gulf of Maine, the area within 25 miles around the anti-cyclone is believable. Where I become concerned is in the areas to the west. Low pressure is essentially driving cold air from the northeast back around to the west.
This was the set up for the most recent snowstorm last Thursday afternoon. Models had +32° in similar fashion as the RGEM model idea above. We know how that ended up, and it did not end up good as far as the forecast is concerned for southwestern Maine. Models disrespected the cold air, forecasters (myself included to a certain degree) disrespected the cold, and with a more easterly track (a result of the cold) the forecast blew up for the coast.
What is different this time is the coastal low isn’t going to bomb out at the velocity the storm did last week. Models can’t handle rapid intensification, either, but that is story for another day.
Western Maine from around the foothills over to Southern Aroostook / Northern Washington Counties almost always get bit by this by poor model output. This is cold air damming, and unless it is getting a significant push, it’s not going to move. It needs wind, and plenty of it.
Warmer Air Moves In Easier Aloft
Since there is no mountains or any of other obstruction, warmer air with aid of the wind has a much easier time taking over the air battle. That said, warmer air has more moisture and the drier colder air will slow it down by eating up the moisture. Ever seen a forecast call for 2-4″ of snow and it ended up less? There you go. Cold air dries out warmer air. The snowfall to water ratio is usually far different for the mountains & north since the air is drier than the ratio for the coast. Fluffier snow north, more watery coast. One inch of water may mean 12-16″ of snow in the mountains and 4-8″ for the coast.
One thing with this event, the intensifying low will tap into warm Gulf of Maine moisture and throw it inland. The problem is that the temperature may be above 32° at 5,000 feet where it is below 32° at the surface. It is this type of warm air inversion that can cause sleet, and pending on how low the inversion goes will depend on it landing in frozen form, or liquid in the form of freezing rain.
In this image it shows the temperature and wind at roughly the 1,700 foot level and in comparing the 850 mb (5,000 ft) level above, it shows discrepancy of how far inland warm air at that level has gone in comparison. Pending on velocity of the falling precipitation, sleet is the likely form of precipitation since it may refreeze before contact with the surface.
Again the red flags show colder air closer to the shoreline at the 1,700 foot level and northeast flow at 20 knots just helps aid cold air at the surface to stay locked in. There is plenty of moisture to work with. Folks in the Fryeburg to Gilead over the Vanceboro to Calais (Augusta, Waterville, Bangor, you as well) could get a solid shot of sleet, which is a plowing and shoveling nightmare.
Lessons learned from the big snow event from last week looking at this event Tuesday & Wednesday: Respect cold air. More easterly track near Bangor means more cold for Western Maine. A more west track closer to Portland means warmer air has a better chance of moving inland over the southwest coast and does not invade as far over Coastal Hancock & Washington Counties.
Now onto the outlook for accumulations.
Ice Threat For Interior Areas
As it stands for now based on current trends, the Allagash region and the coast appear to escape the ice threat. Further inland, this forecast clearly depends on just how low the warm air can invert at a low level above the surface. If it does not, this could very easily turn into sleet show. Freezing rain & drizzle is the toughest form of precipitation to forecast. Given the fact that heavy wet snow is likely to fall and ice may form to go over it, keep in mind that winds are picking up Wednesday night into Thursday as the departing storm blows up over Atlantic Canada. There could be power outages in areas that don’t rise above freezing given the weight of snow and ice. Models think the temperatures will rise above freezing for most areas except the crown in the afternoon. After this lesson on cold air damming, I’ll let you be the judge if you live around Carrabassett Valley, Greenville & Millinocket.
Snowfall Maybe Inhibited By Sleet & Freezing Rain
Given all the various dynamics at play here, it’s real tough to nail down a specific amount of snow. Northern Maine has better chance of falling in lines with these numbers. This forecast considers the threat for sleet & freezing rain, but actual results are likely to vary pending on how much sleet & freezing rain falls. If the mid-level air is colder, more snow. Warmer mid-level air, more sleet & ice potential.
The plan is to update on this Tuesday afternoon.
~ Mike Haggett
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Special thanks to Tropical Tidbits and Pivotal Weather for their written permission to use their graphics in this post. Use of WeatherTAP images used within their written permitted terms of media use policy. Additional forecast information supplied by the National Weather Service, WeatherBELL Analytics and AccuWeather Professional.
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