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December Medium/Long Range Discussion


yoda
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6 hours ago, Ji said:
6 hours ago, psuhoffman said:
GFS really isn't far from something Monday...its got a kicker right on its tail...need that to either back off or dig more and amplify the trough.

Ggem does it but no cold again

With a persistent vortex in/near the WPO domain, and a strong Asian-Pacific jet, it wont be easy to get super cold air in our source region. We probably need the AO to be significantly negative to mitigate that somewhat, and allow TPV lobes to break off and come south.

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12 hours ago, psuhoffman said:

Yes this. Wes did an amazing correlation chart and DC snow correlates to the AO more then any other single factor. Adding to this...if you want a HECS then you need a -NAO. Only one of our region wide 18”+ storms in the last 50 years didn’t have a killer block and that one PD2 featured a perfectly timed Arctic high. We got kinda lucky. But that still changed to a LOT of sleet...so had timing been any less perfect...you get it. But oddly the really big ones that feature a great block also usually feature what under a non blocking regime would be a bad pacific. I talked about this some in the snow climo thread. Our HECS look is a weird combo that doesn’t work under normal circumstances. That kind of block would often suppress an event...but a trough near AK that amplified the ridge/trough downstream or a trough crashing the west that tries to ridge in the east actually helps get something to force its way up into what is likely locked in cold and a high pressure due to the confluence. It’s a weird combo that leads to those crazy anomaly storms. But if we just want snow...a good old fashioned warning event snowstorm, a -AO and a PNA or EPO ridge are the way to go. 

That's cool. Wow, I didn't know we only had one HECS in 50 years without a -NAO. Geeze.

Timing seems to almost always be a must at my latitude, but it's fascinating that if you just go 50-70 miles to my northwest, you can score with with a less than perfect solution.

I really feel like our snow success this year (as well as many other winters) is especially linked to how the PNA performs. We all know that a +PNA can influence higher chances for gulf moisture, and of course features an above avg chance we see some cooler temps on this side of the country. With that said, I also have a sense that we see (hopefully) a few periods of blocking, especially into the early part of January, as ridging in (or near) our ideal NAO space seems to be (possibly) the preferred position this season. I noticed back in October that the north Atlantic was rotating higher heights through Greenland/N. Atlantic, at least more than I have seen prior to the last couple of winters. I always feel like October through early November can give us a glimpse of some of the pieces that become featured during winter. Totally anecdotal though. I can't prove it.

Long and short - I'm really hoping for a PNA that cycles through some stable + periods. I feel like we will we get a couple "hum-dingers" if we get this.

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27 minutes ago, WxUSAF said:

November 2018...:whistle:

 

24 minutes ago, osfan24 said:

I don't remember that one.

That was a good early season snow boom. 12z RAOB from IAD show the mid levels were about 2 or 3 degrees colder than even the meso guidance. Everyone wet bulbed right down towards freezing and held there and it was a clusterf*ck on the roads. We had like a 15 car accident on I-270 in Hyattstown that jacked everything up.

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35 minutes ago, WxUSAF said:

November 2018...:whistle:

I remember that, too.

Was the March 2015 event (6.5" where I'm at, general 4-8" area-wide) also a case of a low forming along a cold front?  Front went through in the early morning I recall, and a decent wave moved up shortly after during the day.  Or that's how I recall how that evolved.  I sort of remember @Deck Pic telling people beforehand to not freak out when they woke up in the morning and it's not snowing yet, because there was going to be a "lull" between the front going through and the main show.  And like clockwork of course, people freaked out early that morning when nothing was happening.  And sure enough, it began snowing like crazy starting around 9AM.

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