February/March 2021 - Frigid or Flop? Pattern/Longterm Forecast Thread.

[BNAwx]

3 minutes ago, TellicoWx said:

Posted by Alan Gerard on Twitter..excellent example of how globals near surface resolution don't allow them to see shallow level cold that well.

Great example.  And depending how cold the upper levels are, that could mean the difference between ice, sleet or snow...or just plain rain.

[CG2]

1 hour ago, TellicoWx said:

While the NAO can assist the TN valley (more the eastern side vs western side), the Pacific still/ and will always rule the roost. Until we can get the ridging off the west coast nudged closer to shore (GFS hints at that evolution toward day 7-8 beyond), I'm not that confident the cold will get shoved far enough east for the eastern valley..(different story for the western areas). Due to the shape of the state (horizontally oriented), it's what makes getting a statewide event so difficult. Place the ridge far enough offshore (west thrives), right against shore (east thrives/but systems can't get the moisture far enough back to help the west side. 

You have ventured into the great Atlantic vs Pacific argument in the forum.  LOL!  I would probably disagree on the PAC always ruling the roost, especially for MBY and for TYS.  I think that would depend on how close one is to the Atlantic and which side one is on the valley.  You all on the west slopes really need NW flow.  Doesn't work here at all.  We need SE flow which mostly comes from coastals which are nicely correlated to periods of blocking over Greenland (even if the blocking only lasts for a few days).   I wholeheartedly agree that under the current AMO setup that the Pacific is the best driver, even in Kingsport.  However, prior to the AMO flip during the last century, -NAO winters were often attached to some fantastic winters(not all for sure).  IMBY, I don't get a lot of snow unless the NW flow is has sort of a long track northern system OR coastals.  Our annual snowfall totals at TRI have dropped steadily as coastals have diminished due to less blocking during this AMO cycle.  The problem with proving this, is having to go back to every, single storm and check blocking - meaning some months may be a positive NAO but the storm during that month may have occurred during a brief -NAO.  Now, John's neck of the woods is highly correlated to PAC stuff.  

And yes, there are no certainties once past the Plateau for the upcoming overrunning event(s).  Though, I do think the boundary does press eastward over time - but slowly.  

[CG2]

What the NAO provides is confluence.  The Pacific has been pretty much awful all winter which is no surprise give the La Nina state.  However, we still have had chances at snow. Confluence is every bit as important as cold IMBY.  When I see DC getting excited about a storm, I perk up.  We often score up here when the wx pattern is good for them.  But if you had to make me choose between a great Atlantic and a great Pacific...I take a great Atlantic.  If a lived on west facing slopes of the Smokies or anywhere from the Plateau west...my answer would likely be the opposite.  The problem with the Pacific IMBY is that systems often move too quickly to overcome the downslope.   Confluence produces storms which allow systems to pivot up the coast.  That sets up SE flow here.  This winter, though I have only two systems which have gone over two inches, we have been nickel and dimed with multiple systems.  I have run in the snow more times this winter than I can remember.  TYS does especially good with -NAO setups.  All of that said, I think there are exceptions to each rule.  I get excited about either setup!  I think next winter we have a favorable Pacific BTW.  

[CG2]

As for ENSO and MJO driving models...both are generally good predictors.  Note that I say generally.  There are definitely exceptions as to when the MJO orbits warm phases, and it stays cold.  I think North Carolina has a correlation between winter storms and maybe phase 3?  - Our SE folks can correct me there.  The ENSO is also a great driver.  Again, the SST gradient in the Pacific(see my quotes which paraphrase Typhoon Tip) has made analog work very murky business.  The SST gradient has to be present for analogs to work effectively IMO.  Also, one new driver (probably has been present all along) is the IO.  Jeff uses that really effectively.  I mean it may be that we take a favorable IO over all other drivers.  When the IO is firing, the MJO generally makes a mess of wx here.  I am not sure that I paid a lick of attention to the IO until a couple of years ago.  The problem this winter is that the cold in the northern hemisphere went to Siberia and a low over AK blocked cross-polar flow until recently.  If the cold had been in NA all winter, the -NAO would have provided a memorable winter, and it may still yet.  Hopefully we are going to re-enter a time frame when NAOs are more frequent - I have zero idea if that happens or not BTW.  I think we are about ten years out on that, but just using the AMO pattern for that really broad guess.   That said, we are about to see what a -NAO can do when cross polar flow is present.   That is not guarantee for anyone, but action in parts of the forum is potentially about to pick-up quickly.

[CG2]

With a cold source lacking, TRI has a real shot at recording two BN months in terms of temps for winter.  December was 0.4 below normal.  February is now 3.1 BN.  Now, that could be La Nina related.  Many of you will recall that I actually prefer a weak La Nina winter(not strong) pattern.  Not all La Nina winters are cold, but the analogs which are cold...are often impressive.  That said, I think the -NAO has not allowed a persistent SER.  SERs are often present during long spells of many La Nina patterns.  The weaker presence of that SER(this weekend is probably not a great example of that) has likely contributed to TRI being BN in both December and now February(so far).  If anyone had told me that we would have been BN with a rotten Pacific pattern, I would have really questioned that...but here we are.  So, thus continues the Atlantic vs the Pacific annual discussion....LOL.  Please know all of that is said in good spirits!!!!

[CG2]

1 hour ago, TellicoWx said:

Posted by Alan Gerard on Twitter..excellent example of how globals near surface resolution don't allow them to see shallow level cold that well.

Great find.  Looks like it found the boundary pretty well...missed by about one layer of counties?  But whew, it is significantly colder behind the boundary than what was modeled there!

[John1122]

0z GFS is further east with deeper cold vs 18z. Long duration freezing rain and sleet event unfolding mid state and west. Cold doggedly banks up against the Plateau and sits there.  

 

[John1122]

6-12 hours later it clears the Plateau and freezing rain to sleet happens there as moisture is pulling out Valentines day.

[John1122]

Not a lot but the cold is 2-3 degrees colder and further east by the day after V-day and something is cooking in Texas/Oklahoma. 

[John1122]

Big winter storm deep south Louisiana. May be suppressed vs the 18z run that brought snow. 

[John1122]

Looks like it's going to head east vs NE like last run. 

[John1122]

Yep,  weird Miller B that transferred from the gulf to well off the South Carolina coast. 

[Daniel Boone]

Models clearly MJO 7ing it with the trough in the Rockies & Plains i.m.o. We'll see how well the blocking can cause the cold to come further SE than a typical Ph. 7 pattern.

[John1122]

Very rare case where the Canadian is way warmer than the GFS. Yet it still has more frozen precip. Has the storm the gfs lost but after front end frozen warms the whole forum and switches to rain but not before front end snow and freezing rain. 

[Matthew70]

Right when you then we’re moving in right direction. Whip lash back other way.  

[John1122]

The Euro gets Western areas with the first wave of ice, then is suppressed until the 16th timeframe when a major winter storm slides across the South. Heavy snow in the mid-state, snow in the far west and ice in the east. My terribly drawn map below gives an idea of which wave delivers which on the ice. 90 percent of the ice in the 1&2 section is from wave 2. Middle Tennessee is blank because wave 1 misses it on the Euro and wave 2 is snow. It would be more than what the map is showing for snow. That's a 10:1 map. I think it's only 23 degrees in Nashville when the snow is falling. The wave 2 ice starts with temps in the 20s and freezing rain falls for about 10-12 hours then the central and NE areas of the east get a warm nose. The Plateau switches to snow. There's some sleet in the east as well. The ICON was just a massive miller A snowstorm. I've heard it's doing well this year but I rarely look at it. It's map is the last one, it's still snowing from the Jackson area all the way to Tri/SWVA at the time it ends at 180.

[John1122]

06z GFS gets the storm back that it lost at 0z. Looks like a less amped Euro with snow from the Plateau west and freezing rain far east. 

Wave 1 is a major ice event out west. At this point its going to be hard for some part of our western areas and Kentucky to avoid a major ice storm. 

[Carvers Gap]

6 hours ago, Daniel Boone said:

Models clearly MJO 7ing it with the trough in the Rockies & Plains i.m.o. We'll see how well the blocking can cause the cold to come further SE than a typical Ph. 7 pattern.

Agree.  

[Carvers Gap]

Memphis is under a Winter Storm Watch as well as much of far western TN, SW KY, and eastern Arkansas.

[Icy Hot]

So once again the cold gets pushed back for East TN. MRX a.m. disco-  "Models are keeping more of the colder air to our north and northeast"

[CG2]

Models looks quite similar to yesterday.   Modeling is pretty much set on a western TN and KY event for the the first round.  Still possible it may push more than modeled for this first round, but looks pretty well set.  I have noted multiple times that this likely affects middle/west TN first and then each event slowly pushes the front/boundary eastward.   My thoughts are still the same on this.  Think the next window is around Valentine’s Day for E TN.  That system will likely be stronger.  There does exist the potential it may cut through E TN.  If so it is rain or ZR.   The MJO is a wrecking ball for eastern troughs.  We need it to move from the 6/7 it was in yesterday.   Glad folks in the western areas of the forum have something to track - hate that it is ice though.  

[CG2]

The change in modeling is directly correlated to modeling seemingly making an error in taking the MJO into 8.  Now, IMO we will see the MJO maybe scoot over to the cold phases at some point.  Will look at today’s updates.  Forecasts for OLR maps show the MJO not stuck in phase 6/7.  
 

MRX actually did mention yesterday evening that they felt like the GFS was too fast but would keep an eye on it.  They noted that all other modeling was slower including the blend of global models.  As noted many times, getting this boundary right is very difficult.  Highly doubt modeling changes (to the good and bad) are over...but for now this is a west and middle TN pattern.  Think that threat moves slowly eastward.  

[Lodelwayne01]

Time for some East TN snow!!

[Holston_River_Rambler]

6z Euro for interested parties:

 

probably good to keep in mind, as was posted yesterday, Euro has been underestimating the surface cold push with the front

[codgator]

Let’s get some better model runs today pushing that boundary east and south. 

[Holston_River_Rambler]

RGEM for interested parties:

 

[Kentucky]

For once, the warm nose would be much appreciated. 

[Daniel Boone]

Ive saw this setup so many times before. Patterns set up in a way that it allows that Great Valley gap to be even more prominent irt cold/snow void. MJO really hurt us royally at a crucial time. Can u imagine had the MJO stayed dormant and the pattern we had stayed in place, with the Arctic air being incorporated ; we'd all been digging out for weeks.

[Matthew70]

It was 46 at Clarkesville state line at Hopkinsville it was 44 now at Cadiz Kentucky it’s 35.  I’ve been watching my thermostat on my truck now two more miles north is 33

[Holston_River_Rambler]

12z Euro for ice event one. I don't have access to a total ZR panel, so I tried to make the gif go slow enough that a person could add it up for their location: