15 replies to this topic

[Stormchaser]

As we move into the beginning of December, wavelengths continue to increase and the mid latitude jet continues its seasonal descent southward; however, where will large scale ridges and troughs position themselves over the next couple weeks? Well, we have some fairly strong evidence in that global indices are in the process of a significant shift in modality -- namely the NAO and AO, both of which are progged to head into the tank as we progress through the next week to 10 days.







Heights will increase dramatically in northern latitudes with a large positive anomaly positioning itself near Alaska/Western Canada, in conjunction with increasingly negative NAO values by the end of this week. The inland runner on Thursday will be a catalyst in terms of changing the upper air regime -- a rapidly intensifying low propagating NE up the appalachains should send temps well through the 50s Wednesday night with even the possibility of some elevated thunder in association with the frontal passage. It's a fairly dynamic storm overall, which should bomb sub 985mb over northern New England Thursday afternoon, before shooting into the north atlantic. This is when the important part comes in -- this powerful cyclone will aid in mechanically forcing a height rise over Greenland and thus sending the NAO negative at least for the time being. The negative AO is able to come about via a weakening polar vortex in arctic -- which by the way, is very likely due to the easterly QBO this winter. Anyway, this regime shift brought on partially by the big, wound-up late week storm will shift the mean trough axis eastward, allowing continental polar air to finally reach the east coast. A couple of models are already detecting a shortwave rolling around the base of this trough and near the benchmark position for this weekend (Dec 5th/6th). Could this short wave produce the first accumulating snowfall in many Northeast coastal areas? That remains to be seen, but the pattern this weekend will be more conducive for snow due to some semblance of blocking upstream. Now, as we head out further into the future, we run into some problems. The ECMWF and GFS to an extent are indicating that the mean trough will retrograde westward into the Plains/midwest after this weekend, allowing the next series of arctic outbreaks to spill into that region initially. This is not surprising and it could very well play out as depicted by the ECMWF for a number of reasons.

Tropical forcing right now is not that favorable for a sustained mean trough along the east coast, rather, the MJO argues for the axis further west in the Plains. Note the following phase diagram of current MJO wave progression in the tropical pacific:



Phase 6 right now - expected to return to the "circle of death" for a little while before possibly heading back into phases 5 or 6. But there is no signal for the MJO moving into phases 7, 8 or 1 on any of the modelling, which is a bit disconcerting as those are the more typical phases for sustained troughiness in the Eastern US.

Take a look at phase 5 and 6 diagrams respectively for the MJO in December. These are average 500mb composites one would tend to see in these two phases.







Even heading into phase 7 for the 500m composities, the signal in December is for some SE-ridge resistance. And that does appear to be what the ECMWF is portraying down the road in Days 8-10. Just to clarify, the upcoming pattern will definitely NOT be one that blowtorches the east coast, but at the same time, I'm not confident we'll be very cold either considering unfavorable tropical forcing. The PNA is now progged to decrease to around neutral/slightly negative over the next week which also indicates the retrograding of the mean trough axis into the Rockies/Central US.

In summation -- the next 5 days will be mild, with an intense, warm inland runner Thursday which will aid in forcing the NAO negative. Our first potential snow threat is this weekend w/ a numer of models keying in on a short wave near the east coast. As we move into next week, Dec 7th-12th, the bulk of the bitter cold air should be contained in the Upper Mid-west, although the Northeast will also see some cold air intrusion. However, I'm worried another inland runner or two may impact the region after this weekend's potential snow threat. Overall -- a seasonal temperature pattern through December 15th, with a chance for snow this weekend. Moderate nino climatology says we wait until Jan/Feb for the real fun stuff, but I do think December will offer some snow opportunities as well, just not nearly as cold as it'll be further west.

[Desnowlover]

Thank you for the great write-up.
It was easy for me to understand!

[stormy]

Stormchaser, on Nov 30 2009, 11:58 PM, said:

As we move into the beginning of December, wavelengths continue to increase...

Appreciate the discussion. Seems JB is onboard for snow later Saturday in the NYC/Metro area. It'll be interesting to see how this unfolds. The system for tomorrow night/Thursday morning could also be interesting. Strong SE winds are expected along with the possibility of an isolated t-storm.

An active pattern shaping up for the beginning of December, I for one like it! It's been boring for too long.
North Jersey Weather

[Stormchaser]

Thanks for the comments guys. I have no changs to this post -- although the NAO and AO will be heading strongly negative, the PNA will also dip neg, thus the retrograde westward of the mean trough axix. This should dump most of the polar air into the Rockies/Northern plains through next week. As I noted above, if we miss out on the snow opportunitiy this weekend, the pattern is not conducive the next 7-10 days.

Snow threat for Saturday cannot be written off yet as most modelling has the hvy pcpn shield just 300 miles to our SE.

[metfan4life]

Stormchaser, on Dec 2 2009, 12:16 AM, said:

Thanks for the comments guys. I have no changs to this post -- although the NAO and AO will be heading strongly negative, the PNA will also dip neg, thus the retrograde westward of the mean trough axix. This should dump most of the polar air into the Rockies/Northern plains through next week. As I noted above, if we miss out on the snow opportunitiy this weekend, the pattern is not conducive the next 7-10 days.

Snow threat for Saturday cannot be written off yet as most modelling has the hvy pcpn shield just 300 miles to our SE.

Storm, do you see the models shifting west or do you think the eastern solution will verify?

[metfan4life]

[lab94]

metfan4life, on Dec 2 2009, 01:30 PM, said:

If you are going to play connect the dots. Try this on, you will like it better!!! LOL

[vascudave]

lab94, on Dec 2 2009, 02:59 PM, said:

If you are going to play connect the dots. Try this on, you will like it better!!! LOL

lmao!! where the hell do you find this stuff?

[metfan4life]

lab94, on Dec 2 2009, 01:59 PM, said:

If you are going to play connect the dots. Try this on, you will like it better!!! LOL

Buy me the book. It looks interesting.

[vascudave]

metfan4life, on Dec 2 2009, 03:42 PM, said:

Buy me the book. It looks interesting.

http://www.amazon.com/Erotic-Dots-Carlton-..._pr_product_top

[lab94]

vascudave, on Dec 2 2009, 02:14 PM, said:

lmao!! where the hell do you find this stuff?

Bedroom Google is my friend. LOL

[terryjohnson16]

Bring on the 50s and 60s. I hope the ocean is still warm to prevent snow.

[NittanyLion]

vascudave, on Dec 2 2009, 02:54 PM, said:

http://www.amazon.com/Erotic-Dots-Carlton-..._pr_product_top

Haha I like how there is a "used" version.

[jjvesnow]

terryjohnson16, on Dec 2 2009, 09:08 PM, said:

Bring on the 50s and 60s. I hope the ocean is still warm to prevent snow.

You post the same thing every time. So annoying. Is there a way to hide certain post from people?

[terryjohnson16]

jjvesnow, on Dec 2 2009, 04:27 PM, said:

You post the same thing every time. So annoying. Is there a way to hide certain post from people?

By your screen name, I can tell you love snow. Whats the big dead? You like cold/snow, while some people like the warm weather.

One thing you should be happy about is that the cold weather lasts longer than the warm weather.

[GameOfLove]

Give me about 3-4 6+ all snow events and I'm happy.

What is with people and snow and the cold? Seems like some people want it to snow once a week at least - maybe more.