Warming Trend + Weekend Trouble?
Almost there people….the warmer air is coming. Worcester’s streak ends either Thursday or Friday
The storm has come and gone, but there’s still plenty of reminders along our streets and sidewalks that this December has been busy. Boston saw 6.4″ of snow from the event (at Logan) – which set a daily snowfall record for December 17th. It also is more than the past 2 Decembers combined! (3.4″). On top of the snow, it’s been quite cold out there. Most of the region has now seen 12 straight days of below average temperatures, the longest such streak this year. We may add one more to that streak tomorrow before finally working some milder air into Southern New England for the weekend.
We’re also now well entrenched in the freeze-thaw cycle, so just keep in the back of your mind that all the melting during the day will immediately be followed by water freezing up once the sun goes down. Some icy patches on roads, decks, and sidewalks are certainly expected. Tonight is another night spent in the 10s and 20s. Out ahead of an advancing front, some high and mid level clouds will pass overhead late.
Tomorrow and Friday are similar, with nothing major going on across the region. A quasi-stationary front will be setting up and essentially hanging out through Sunday just off to our north and west. We’ll live on the mild side of this one, but barely. Highs will sneak into the upper 30s/low 40s tomorrow, and most everyone should make it into the 40s on Friday. Most of the shower activity and lowest cloud decks will stay to our northwest to end out the week. Thursday looks brighter (and breezier) than Friday, while a few showers may start to encroach on us with a wave of low pressure by Friday evening. The snowpack that’s nearly a foot deep in some towns currently will slim down heading into the weekend, but not completely disappear.
Cold air locked up north with the deep snowpack, while warm air surges in the Mid-Atlantic. 70s may make it into the NYC area!
The weekend forecast is a tricky one, particularly for northern MA and southern NH. An anomalous pattern will set up, with extremely warm air aloft screaming in overhead and a column of air that will have moisture content WAY above normal (some models have PWATs at 300% of normal in the area). Now for most of southern CT/RI, and MA – it looks like a high confidence forecast. Warm air will win, it may jump into the 60s by Sunday evening, and you’ll be looking at rain. But the situation farther north is a tougher call.
Check out Sunday 850mb Temps (ECMWF)… +19C in MD/VA is absurd for this time of year. If it were July and sunny, that would translate to highs roughly in the low 90s. The NWS says the highest 850mb temp at Dulles ever recorded (since 1961) in December is 20.6ºC
Essentially, a warm front will be draped somewhere across New England (likely central/southern NE). This will be the boundary between very mild air (45-60º) to the south and very chilly air (25-35º) to the north. With temps that cold in New Hampshire, Vermont, and Maine you’d probably think it would be all snow. But the problem is that the very warm air pictured above will be moving in about 3,000′ up in the atmosphere. That means that as snowflakes fall, they melt on the way down. Once they run into the cold air near the ground, they supercool and then freeze on contact, giving us freezing rain. There’s pretty much nothing good at all about freezing rain. You can’t drive in it, it causes power outages, and generally wreaks havoc if >.25″ of it can cling to branches and limbs.
Wednesday 18z GFS forecast for precipitation type. Note all the pink – that’s the potential for freezing rain it’s picking up on. Courtesy: WeatherBell
Now it’s still several days out and so things will change before we get to the weekend. But the setup is certainly one with the potential for a significant icing event in parts of New England and New York State. At the moment, I’d say this potential lurks as far south as the Merrimack River Valley. The threat is also highest in the valleys, *not* across the higher terrain. The warmer air aloft will be so strong that peaks will be much warmer than the lower elevations for this one.
GFS sounding for Burlignton, VT Saturday night into Sunday. Illustrates what we’re talking about when we say warmer air aloft. You can see the temperature line (white) go on the warm side of 0ºC above the ground, but much below it at the actual surface. So water drops supercool on the way down, then freeze on contact. Also, the precipitable water value of 1″ is quite high for an ice event! Courtesy: Wright-Weather
Moral of the story is to check in for updates on this setup as we get closer, and start to think about how much firewood, water, and other supplies you have handy in the event of prolonged power outages heading toward Christmas. Since it’s a ways out and low confidence for now – all I’d ask is to think about those things. But in the next two days if the forecast stays similar – you’ll likely need to take some action.
At the same time that we’re watching this wintry potential, the Patriots will be soaking up the warmth again! Even with a post-sunset start time, temperatures should be WELL into the 60s in Baltimore this weekend. It ain’t Miami and the mid 80s, but hey that’s comfortable stuff for this time of year. Rain may also be a factor for the huge match-up.
We’re also looking forward to the big holiday next week of course. As of right now, it looks cold and quiet for Christmas Eve and Christmas Day. All the wet/wintry mess of the weekend will head out by Monday evening, and a blast of Arctic air will follow. Temperatures probably won’t head out of the 20s on Christmas Eve – along with gusty winds. And below is our first crack at the Christmas forecast one week out. Looks cold but bright, with no major travel issues for you or St. Nick.
And hey, I couldn’t let a winter storm in Boston go without a shout-out to the big guy, Jim Cantore from The Weather Channel. He was in town covering our terrible evening commute on Tuesday, and I’m sure you spotted his mug on the front page of the paper on Wednesday. If you’re a snow lover, I’m sure you hope to see more of him around town this winter. I know I do – one of the biggest weather geeks and nicest guys you’ll ever meet! Not to mention a great former colleague.
Couple of dudes, just talking about the weather after work. Courtesy: Eric Fisher