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12/17 Messy Mix


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During mid week, it became evident that a mixed bag of precipitation would be likely across the area in association with the system poised to impact the region next Tuesday12/17.  Eastern Mass Weather posited that it would be difficult for the majority of the area to remain as snowfall since the surface high pressure was escaping seaward, and the upper level energy was tracking to the north. While this still appears to be the case
Branch.png
 

Some subtle, but important morphologies have taken place over the past 84 hours. Note that the receding high pressure area in the atlantic is now arching more back towards Maine. The impact of this on sensible weather will be that low level cold will now be more difficult to scour out even closer to the shore, thus increasing the risk of more frozen precipitation.
The difference in guidance from this past Wednesday is quite evident, as that appendage of cold +pressure pattern was not apparent.
Mixed.png
The reason that we have seen this trend is very apparent, and one need not take more than a cursory glance at the modeled hemispheric 500mb pattern to understand why this has taken place.
 
Impact of Negative NAO
The aforementioned alterations to the pressure pattern along the northeast coast can be traced back to what will verify as a decidedly more negative NAO than was modeled over the course of this past week. 
Here is the forecast NAO index from Wednesday:
Wed%2BNAO.png
 
While it was technically forecast to be negative, it was only marginally so. However here is the forecast from Friday:
Fri%2BNAO.png
 
The NAO is going to verify significantly more negative than anticipated mid week. While the upper level energy is still going to be track to the north, the more deliberate departure of the cold high pressure area in the vicinity of Maine due to the more blocked downstream heights will force the surface reflection to the south of southern New England, effectively shearing and weakening the system.
H5.png
 
 
The fractured, weaker disturbance in conjunction with the surface system being displaced to the south will allow for a colder solution than otherwise may have transpired, but the mid levels of the atmosphere will still warm considerably across at least the southern half of southern New England. Warmth overrunning cold air entrenched at the surface is a recipe for ice.
 
Storm Evolution and precipitation Types
 
Snowfall should begin to overspread the area from southeast to northeast on Monday evening.
7PM%2BMon.png
 
 
 
Precipitation falls as snow when the entire atmosphere is subfreezing. Snowfall should reach the Mass pike region after midnight, as mixed precipitation already begins working onto the south coast.
 
1am%2BTues.png
 
 
Local climatology dictates that the progression of the sleet should slow considerably as it encounters more resistance in northern Connecticut and Rhode Island from the retreating high pressure area. It may creep to the vicinity of the Mass pike by the Tuesday morning commute. Dangerous icing should be ensuing across much of interior Connecticut and Rhode Island at this point, where the cold layer will be very thin near the surface. North of this region, where the colder layer is thicker, the snowflakes will still pass through a warm layer in the mid levels of the atmosphere, thus melting into rain drops. However the rain will have had more time to refreeze into pellets of ice referred to as sleet, by the time that they reach the surface.
 
winter-weather-rain-freezing-rain-sleet-snow-temperature-versus-altitude-diagram-44223505.jpg
 
 
7am%2BTues.png
 
H85.png
 
 
The heaviest period of precipitation should arrive mid to late morning on Tuesday, as the mid level warm air advection reaches its zenith, potentially promoting a period of sleet to the north of the Mass pike, with freezing rain potentially nearing the pike. Precipitation type will be crucial during this particular time, since it will be steadiest.
 
1pm%2BTues.png
 
The precipitation should taper off throughout the afternoon, as the cold air collapses back to the south and east.
 
7pm%2BWed.png
 
 
First Call:
Relatively signifiant amounts of freezing rain accretion are possible throughout interior Connecticut, and Rhode Island, with less across interior southeastern Mass and south of the Mass pike.
ICE.png
 
First%2BCall.png
 
 
Stay tuned for Final Call on Monday-
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12 minutes ago, Damage In Tolland said:

00z Euro has 4-6” Pike south and 1-3” North. Better thump and colder 

There is definitely some thump potential. 

Definite mid level warmth worries down in SNE, as the thump may already be too warm. Overall if we don't cool the column a bit even CNE and NNE run the risk of a very elevated DGZ and saturation issues. 

F-gen looks nice though. 

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2 minutes ago, OceanStWx said:

There is definitely some thump potential. 

Definite mid level warmth worries down in SNE, as the thump may already be too warm. Overall if we don't cool the column a bit even CNE and NNE run the risk of a very elevated DGZ and saturation issues. 

F-gen looks nice though. 

We’d love a sig icestorm . We’ll see if colder trends continue over the weekend. Off to run 5 miles in a deluge. Awesome 

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16 minutes ago, NYCweatherNOW said:

No you’re right some people get 6-8 there instead. The point here to take is, the run is colder and so is the 06 nam

Yeah this suite got colder, but the shortwave isn't onshore until tonight and I'm not going to bank on this being a long term trend until we sample that with some balloons.

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8 minutes ago, Ginx snewx said:

What did you get done? I mean it was pouring rain, outside cancel, everyone in your house is sleeping,  vacuuming cancel. Lol tell us

I got my 5 mile run in like always at that hour. Exercise portion done for day, load of laundry done and folded, showered and breakfast and now out for errands. The day is already 1/4 over 

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2 minutes ago, Damage In Tolland said:

I got my 5 mile run in like always at that hour. Exercise portion done for day, load of laundry done and folded, showered and breakfast and now out for errands. The day is already 1/4 over 

What time is the Shepherd’s pie early bird special at Bickford’s?

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3 minutes ago, HoarfrostHubb said:

I don’t see anything that screams damaging ice amounts. Slick roads and walkways sure.  
Nice moderate event for some.  Nice write up Ray.  

Agreed.  Only a couple alarmists were hyping that.

The freezing/frozen stuff will likely be good for a nearly region-wide advisory event though.

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4 minutes ago, CoastalWx said:

What time is the Shepherd’s pie early bird special at Bickford’s?

Discounted afternoon lap-dances at the Blue.

I'm up at 4:30 myself.  I'm not doing chores then, but am able to clear my mind as I drink coffee, check email, what's happening here, etc. before the demands of the day take root.

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Just now, moneypitmike said:

Discounted afternoon lap-dances at the Blue.

I'm up at 4:30 myself.  I'm not doing chores then, but am able to clear my mind as I drink coffee, check email, what's happening here, etc. before the demands of the day take root.

Except on days off same here. It’s certainly not my choosing though. Kids still get me up at 5:30-6. :lol:  

Anyways, we’ll see if we can tickle up this thing Tuesday. Part of me wonders about that 6z euro. We’ve seen those WAA thumps before in SW CT and then sort of weakens as it moves northeast before another area north of the pike forms as the warm air aloft stops its push north. Some guidance has shown that scenario. Plenty of time to work out those details.

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