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Weather Threats: Winter 2020-21 Edition

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With many members highlighting the first week of December as wintry for the interior and NNE, and potential for a wintry 12/8 -12/15 period for the MA& NE in general, I thought now might be a good time to break out the discussion a bit.


The “Pattern Drivers” thread should be reserved for more technical long range discussion.


We can use this thread going forward to highlight specific threats within the aforementioned period. Let’s see where we started, and where December is headed!









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  • 33andrain changed the title to Weather Threats: Winter 2020-21 Edition
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8 minutes ago, Allsnow said:

I like where we stand currently with respects to the ensemble guidance for the first half of December. As many have stated the period from 7th-11th needs to be watch. The first two systems are being cutoff from the flow with a putrid airmass. They don’t have much of a chance to produce snow outside of the lakes. 

In the extended range i don’t see a typical Niña look coming. That is the look we had in late October/early November that had a dateline ridge with troughs diving into the west. The 12z eps has a +pna/-epo with a hint of -nao. 
12z GEFS 



We do run the risk of cutters if a system gets to wound up out west. We can hope a -nao can keep any Atlantic ridge at bay. We should have colder air in Canada after next week which could set the stage for overrunning type systems.


We are early in the season so let’s practice patience as the pattern evolves. I wouldn’t expect to track anything wintry for the northeast until the 2nd week of December. 

Let It Snow! 

We can always run the risk of cutters.  Even in the best winters, there are cutters.

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Now starting to see the northern stream shortwave appear (N of MT) in this loop, and the southern stream is looking impressive as well. The ULL there has continuously gotten stronger, and is producing some weather over OK/KS mostly right now. Might see a little more coherency at the sfc level very soon as something tries to form in the Gulf. Still, it'll be relatively sloppy before the phase, then be able to strengthen with a more conducive upper air look. 




As we all know this doesn't really look like a NE event as the upper low will set up far too west and induce lots of southerly flow in the area, and put the temperature gradient well to the west meaning this will just be a rain event for the area where the majority of the regulars here live. 





I believe eastern Michigan and southern Ontario will end up cashing out most from this once all is said and done, probably the most on the Canadian side of the border. These areas will mostly be west of the rain/snow line (though only the former seems like it will totally miss any rain), and the spot where the surface low stalls out and tries to couple with the ULL will be interesting as it could keep snow over one spot for a while. Guidance suggests that this will occur north of Lake Ontario near the Quebec/Ontario border, and as such will produce some more lasting snowfall in that eastern Michigan/southern Ontario area. 


Cool early season event to watch! We'll see if the NE sees something other than rain in that Dec 9-13 period

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6 hours ago, Analog96 said:

I am REALLY starting to like what I see for mid December.

Yeah that period around Mid December looks really good for you guys. I'm going back east on the 17th to the 28th so count on storms on the 16 into the 17th and 29th. In all seriousness that period around 12/11 to 12/14 or so looks really interesting. 

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We're getting closer to the phase, with the northern stream shortwave diving SE to meet the southern stream ULL. In fact, this is causing some of the upper divergence fueled rising air and cloudiness to get pulled NE due to the flow. Tonight into tomorrow morning, they are expected to phase.




Then looking at the surface, observations in the NW Gulf where we are watching for sfc cyclogenesis show that there is a circulation forming there and pressures are getting lower. We'll see this feature get pulled NE for a little bit but remain disorganized, then when the phase happens and the sfc low is closer to a stronger upper level low and a stronger temperature gradient the low will deepen into the 990ssfcplot_latest.png

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On 11/25/2020 at 8:29 PM, CCB! said:


As the low occludes, I wouldn't rule out some rumbles of thunder with the strong SW flow & resultant warm front pushing through the area either. 


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3 hours ago, IsaacWxObserver said:

Now the second storm has trended weaker. Euro has a great track. There is just no cold air to work with. Lets hope the following chances produce


the upper level pattern is no good on the euro even with that track

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2 minutes ago, DualJet said:

the upper level pattern is no good on the euro even with that track


Yeh these aren't the ones in the pattern, it's one of SW inside the following 7 day period.


Just have no way of knowing who one IMO. 

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8 minutes ago, DualJet said:

the upper level pattern is no good on the euro even with that track

In Mid-January, you might be able to squeak out a moderate snow event with that setup.

But this is not Mid-January.

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1 hour ago, NorEaster27 said:

I know it’s super far out OP run but talk about the pattern repeating itself




I guess we can ignore 7 days prior that has 2 coastals and 1 Clipper in the flow.

Not sure if any actually produce but I do think one of the coastals throw snow back, but that cutter just ushers in BN air behind it.


You do realize you will cut in every winter especially ones that are not forecast to be cold and snowy.


Hope something in that 7 day stretch gets you.


Don't sweat 16 day operational runs.




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