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January 2014 pattern discussion


CapturedNature

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The NAM has been showing potential for some snow showers too tomorrow night. We get some decent lapse rates in the LLS and PVA to try and sustain them, but there's no true instability like in typical WINDEX events since the inversion is pretty low around 800mb, so it would likely remain scattered. Kind of like the November snow showers we had that gave a some people coatings and an isolated inch in a lucky spot or two.

yeah seems that way, NAM had a pretty intense band from the Berks to ORH. TTs are very low though.
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yeah seems that way, NAM had a pretty intense band from the Berks to ORH. TTs are very low though

 

 

Yeah the inversion is very low and sharp (aiding in the low TTs), so you aren't going to see more than a few localized snow showers...and most of them won't be heavy outside of the upslope spots. Maybe a few lucky isolated spots get a burst.

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80% of the next 10-14 days AOA.

Thereafter, back to Leon.

 

That's a helluva long January thaw.......snow pack ftl.

 

Seems like we could have some SHSN traverse the area tonight.

 

Forecast for here is up to an inch today (I imagine back end, but I'm not confident that'll work out) and then 40% chance of snow showers tonight with no accumulation mentioned.

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That's a helluva long January thaw.......snow pack ftl.

Forecast for here is up to an inch today (I imagine back end, but I'm not confident that'll work out) and then 40% chance of snow showers tonight with no accumulation mentioned.

Well I think the real thaw is next week and I'm probably over generous with the duration as signs are abundant that we freeze later January.

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What happened to the n plains staying cold..and us just being in the low 40's for a few days with maybe 1 cutter?

 

No the Plains are expected to get mild for a brief time. I think a few of our days may be in the 40s, but as I said to you a couple of days ago, the real mild weather will be before that cutter. If the euro ensembles are right, it gets near 60 before we cool down.

 

But I like the pattern after that...looks more like a +PNA. After being in the freezer, the nrn Plains could turn mild if that happens as the cold stays more east.

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No the Plains are expected to get mild for a brief time. I think a few of our days may be in the 40s, but as I said to you a couple of days ago, the real mild weather will be before that cutter. If the euro ensembles are right, it gets near 60 before we cool down.

 

But I like the pattern after that...looks more like a +PNA. After being in the freezer, the nrn Plains could turn mild if that happens as the cold stays more east.

Well we're near 60 now..so I guess it can't get any worse.

 

What date are we looking at? You think 15th or not till after the 18th?

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Well we're near 60 now..so I guess it can't get any worse.

 

What date are we looking at? You think 15th or not till after the 18th?

 

It looks like after the 15th is when the 1st shot comes in, but the meaningful stuff might wait until the 18th and beyond.  This is sort of what happens when the PV drops into the US and lifts out. After the big freeze is the bog torch.

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It looks like after the 15th is when the 1st shot comes in, but the meaningful stuff might wait until the 18th and beyond.  This is sort of what happens when the PV drops into the US and lifts out. After the big freeze is the bog torch.

 

 

Euro ens look really good for after mid-month. They have the EPO reloading around the 15th, so I think by the 18-20th we should be in good shape.

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Would one of you guys mind doing a write up on all of this terminology?  We've got a week or more of downtime.   I think it'd help a lot of the newer people and I'd Leon the explanation.

 

A +PNA? I think most know what that is. Basically ridging over the West Coast and Rockies.

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Does EPO and PNA relate to one another? If there is a massive ridge in the eastern pacific, i would think that would lead to a trough over AK and western Canada. So A +EPO would generally lead to a -PNA, correct?

 

No, there is an overlap in the regions. You can get a -EPO/+PNA combo...esp when the EPO is more east based into eastern AK and NW Canada. That is basically what the Euro ensembles are showing.

 

This is the loading pattern for the EPO (positive phase)...you can see that is is almost PNA neutral (heights SW of Aleutions are near neutral and the interior western Canada heights are near neutral to perhaps just a smidge correlated to EPO).

 

 

epo_composite.gif

 

 

 

For the negative EPO, just imagine the negative height anomalies on the map above are positive height anomalies...and vice versa for the positive height anomalies. If you shift the EPO ridge slightly east, you can see how it would teleconnect to a massive PNA ridge...OTOH if you shift it a tad west, you can see how a negative PNA could be supported (something we saw for a time in middle December).

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BTW, the Euro ensembles basically took the GEFS out to the woodshed for this warmup in store before the reload...the EC ensembles had struggled a bit in parts of December with the EPO ridging, but they nailed it pretty good this time to get their mojo back. I was hoping they were wrong since the GEFS showed not much relaxation at all. But revision to the mean was inevitible for each model suite.

 

At least things look to get quite wintry again after mid-month.

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BTW, the Euro ensembles basically took the GEFS out to the woodshed for this warmup in store before the reload...the EC ensembles had struggled a bit in parts of December with the EPO ridging, but they nailed it pretty good this time to get their mojo back. I was hoping they were wrong since the GEFS showed not much relaxation at all. But revision to the mean was inevitible for each model suite.

 

At least things look to get quite wintry again after mid-month.

 

Yeah I mentioned that a few days ago. I was hoping they would be wrong, but they absolutely nailed it. 

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There's also apparently a seasonal dependence on the correlation between the EPO and PNA.  It's bit more robust in autumn, with +.14 and +.20 positive correlation during Nov and Dec respectively.  But the correlation falls off to +.05 in Jan/Feb, which means very near equal chance for concurrent negative or positive phases of those indices.

 

That's interesting because one might think the opposite to be a better fit for having [typically] shorter wave-lengths in autumn, but it is what it is...

 

******

 

I wouldn't hit the "warm-up" too hard folks.   Just moo but I still see this as a cold relaxation due to the loss of the predominating -WPO/-EPO influence on N/A.  

 

Obviously relaxing the cold is warming things up a bit, but just how much is going to depend upon noise in the L/W jostle as the period unfolds, and whether a surface high happens to retreat when there happens to be a balmier 850mb temperature air mass available to the circulation.   Right now, you have the Euro showing a snow pack eater pattern with perhaps one cold insert period days 6-10, which could very well be typical meridional bias of the extended Euro tainting truth and over-doing that.  Contrasting, the GFS has less impactful warming, and actually more of a transitional type pattern that could even offer a winter storm or two over the next couple of weeks.  Personally I still see this a return to normalcy with some tendency to be above normal; which for our latitude can still mean wintry like events.

 

I am also interested in testing this EC ensemble notion of re-establishing the -EPO mid-month.  The GEF mean has the PNA more than less rising through the period.

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