Blocked Up Weather Pattern Ahead

By: Chief Meteorologist Eric Fisher
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From the ‘it could be worse’ files – check out the scene above 6,000′ on Thursday! The Cog Railway is doing some excavation work on the summit of Mt. Washington, and a rime ice event struck the rockpile while all the equipment was up there. Certainly not the first time this has happened, but always an amazing sight. Supercooled water droplets in the air, flying past the summit, freeze onto anything they come into contact with. The result is an ice covered wonderland. I guess the 50s here at sea level aren’t so bad.

car Blocked Up Weather Pattern Ahead

Photo courtesy Katie Brace, WBZ-TV

The one thing that was a universal issue in New England the past couple days was wind, which lead to several scenes like this one on Charles Street in Boston. Never a happy surprise when you return to your car with a tree on top of it. Several large trees came down with a few scattered power outages, but thankfully those winds are now gone. Just a breeze today, which will be a lot easier to take.

In fact, today is THE day to enjoy for the next 7-10. Certainly my top pick for best one to be outdoors, with highs reaching above 60º inland and lots of sunshine. Some high cirrus clouds will advance during the afternoon, but that’s the only game in town. A sea breeze will develop along the coast, so areas near the water will fall through the 50s and perhaps even into the upper 40s by the afternoon and evening. TGIF!

By late tonight and into Saturday morning, a quickly advancing storm system should bring a dousing of rain. Right now, I’d plan on sleeping in and making pancakes. Best use of a rainy morning (real maple syrup of course). Looks like a solid 0.5 – 1.25″ of rain across the area as a coastal low takes over and also keeps chilly air locked in place. In fact, many towns should stay in the 40s on Saturday. This first batch may end by midday, and hopefully we will manage a break in the action for part of the afternoon. However, a vigorous short-wave will dumbell around this first area of low pressure, and come diving across SNE by the evening/overnight. This piece of energy looks potent, and could spark some downpours/thunderstorms during that time frame. Small hail may again be in play as a very chilly pocket of air aloft will come along with this system. So if you’ve got Saturday evening dinner plans, you should keep in mind that we could get some wild downpours and lightning mixed in!

There’s also a slight chance that it will be cold enough for some wet snowflakes at this time. I don’t think it will add up to much, and may not even materialize. The air aloft is definitely cold enough, but the layer of above-freezing air near the ground should be deep enough to melt most of the flakes. In any case, we’ll keep an eye on this for sure. Not too often you get any flakes around here in late April. The highest risk areas for snow would be into southern NH and across northern New England. Why close up the ski areas? May as well get a couple more runs in.

weekend Blocked Up Weather Pattern Ahead

Some slight disagreement exists in the models for how quickly this low will depart. I’m leaning toward a less progressive idea, which would keep mostly cloudy skies around on Sunday and some more scattered rain showers, particularly far eastern MA. Highs should stick in the low/mid 50s, a little below average for this time of year. The wind will also pick up, gusting out of the NNW. Even still, compared to Saturday, it should still be the better of the two weekend days.

block Blocked Up Weather Pattern Ahead

A huge sprawling area of high pressure is forecast to materialize across Canada by early next week, blocking in a pair of cut-off lows to the south of it. Source: WeatherBell

Blocking is the weather vocab word for next week, and will be the main weather story for the entire country. Essentially, the whole flow of the jet stream will meander and become disjointed, forming what we call a ‘Rex block.’ A Rex block is when you have a high-amplitude ridge with a storm stuck underneath it. The high almost ‘protects’ the low from moving on, and this will have several ramifications.

1) A lot of rain will fall in the middle of the country. Bands of rain rotating around this storm system will continue to pour down on similar areas, so flooding will end up being a concern.

rain Blocked Up Weather Pattern Ahead

7-Day rainfall forecast from the WPC. It’s a pretty safe bet that locally higher amounts will certainly occur, dependent on where training rain bands set up. Source: NOAA

 

2) Cool air will stay in control, with temperatures below average east of the Rockies for an extended period of time

gefs t2anom by5 conus 41 Blocked Up Weather Pattern Ahead

GFS Ensemble Mean 2m temp anomalies for days 5-10. Source: WeatherBell

 

3) Severe weather will be a risk as vort-maxes rotate around the eastern flank of this low for multiple days. Saturday, Sunday, and Monday all look like they should produce strong to severe storms and potentially quite a few tornadoes too.

spc Blocked Up Weather Pattern Ahead

Several Days to Watch, Via the Storm Prediction Center. You can get their latest outlooks and forecasts from www.spc.noaa.gov

 

4) We get mired in an onshore flow here in New England for many days.

So overall, not a lot of good comes from a setup like this. It definitely will not be a warm end to April and start to May, but I suppose we’re ‘due.’ There hasn’t been one of those weeks this April where it’s just cold every day and gray. Some short stretches here and there, but it could be worse. The month overall is still running above average in terms of temperature, and will probably end up just about average by the close. With such a blocked up pattern, I’m thinking the significant rain from this middle America storm will take its sweet time getting here, and may wait as long as Thursday to reach the Boston area.

AO NAO

The Arctic Oscillation and North American Oscillation will go negative, and so in general the idea is just that not much will change in the overall pattern for the better part of a week. Source: WeatherBell

 

 

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