Fall 2020 Discussion

[Carvers Gap]

Time to wake this place up after a few days nap.  Looks like LR models are again signaling a cool-off in the East just after ten days(we know the drill when we hear "ten days").  Anyway, I suspect modeling is on to another shot of BN air entering the Lower 48 in the d10-16 time frame - maybe even a bit earlier.

edit: Euro OP has it inside of d10.

[weathertree4u]

On 8/25/2020 at 11:29 AM, AMZ8990 said:

4 weeks until fall y’all,  We are getting closer!!  Fun fact- in Memphis we’ve had four LA Niña winters since 2010.  3 of those 4 years produced measurable snow days.  1.8in on January 16th, 2018.  2.0in on January 6th, 2017.  And 3.1in on February 11, 2011.  January has been the best winter month for Memphis in La Niña setups over the last ten years statistically. ENSO neutral conditions have favored more December snows with 2 separate systems dropped .9in on December 26th, 2012, and a trace amount on December 30th, 2013.  The daily snowfall record in Memphis of 14.3in also fell during a moderate La Niña on December 22, 1963.  Long story short- La Niña winters are historically good for west Tn.  Soon I’ll crunch some numbers and see how that translates to east and middle Tennessee winters.  

The 1960's were great winters in the Mid-South; Nashville area got some great snows December that year as well. The big boy was on New Years that year that went just to the south of Nashville, we got snow but Huntsville and southern TN got hammered. 

[nrgjeff]

I saw some 1965 hype, but didn't check snow. Severe wx that spring, lol!

My guess is Memphis and Nashville will do OK this winter. Southeast Tenn will be blanked, or have an upper low surprise. All or nothing, lol!

[weathertree4u]

7 minutes ago, nrgjeff said:

I saw some 1965 hype, but didn't check snow. Severe wx that spring, lol!

My guess is Memphis and Nashville will do OK this winter. Southeast Tenn will be blanked, or have an upper low surprise. All or nothing, lol!

Well, it doesnt take much to be a better season that the last several lol

[Carvers Gap]

We have been fooled once already this season, but the EPS is showing what I consider to be a significant pattern shift over NA with a big ridge holding out West with a low over the Aleutians.  Not wasting much time going into the details.  Pattern change is now within seven days though.  Maybe those CPC maps are on the money.  If so, we have MUCH cooler temps on the way and soon.

[dwagner88]

On 9/12/2020 at 6:40 PM, Carvers Gap said:

We have been fooled once already this season, but the EPS is showing what I consider to be a significant pattern shift over NA with a big ridge holding out West with a low over the Aleutians.  Not wasting much time going into the details.  Pattern change is now within seven days though.  Maybe those CPC maps are on the money.  If so, we have MUCH cooler temps on the way and soon.

  Not good news for firefighters out west. 

[Carvers Gap]

14 hours ago, dwagner88 said:

  Not good news for firefighters out west. 

Yeah, coastal states in the West are getting torched, literally.  The recent snows and rain really helped the intermountain West.  It was within about 48-72 hours of getting scary bad there.  The snow storm put a dent in that danger.  Now, does that threat come back in the intermountain West as that ridge rebuilds?  IDK - maybe.  The good things is that the days are getting shorter and temps at high elevation will start to cool off.  For places like California and Oregon, not good at all with very little relief in sight.

[John1122]

Looks like we may dodge the hurricane rains for the most part. I know MRX was initially showing 2 to 3 inches across the area. I'm actually running BN for the month with only 1.3 inches. Creeks and streams are still over full but it feels almost strange to be getting so many dry days, even though it did rain this weekend. 

MRX also has my highs in the upper 60s late this week. That will feel awesome Friday night after last Friday's humidityfest at Seymour. 

[Carvers Gap]

Some beautiful weekend wx upcoming once this tropical system exits.  TRI is forecasting highs in the 70s with lows in the 40s.  Much different than last Sept where we hit 90+ for roughly 14 days with multiple record highs. We have hit 90 only one time during this Sept.  We are four degrees above normal right now, but that number should come down quickly after today.  

[Holston_River_Rambler]

Yum:

The more interaction between Teddy and the mid latitudes pulls down more cooler and drier air for us. Saw some DPs in the 30s on the 12z run. 

[John1122]

Last time we had such an active tropical season in 2005, we were basically normal for October and November, slightly BN for December, January was an unrepentant blow-torch that finished +7. February was 3 degrees BN and I had 7 inches of snow during the month. January will probably match this year with how our luck has gone. Not sure if the others will or not. 

That September was much drier and much hotter than this one has been so far. It didn't rain at all until September 15th. It was 4 degrees AN with 7 days in the 90s. We haven't been above 87 this month here and it's rained some. September 2005 didn't see a day in the 40s until the last day of the month. We should get there this weekend. 

[Carvers Gap]

The Weeklies can easily fool me at this time of the year...but that is some crazy blocking in the HB and Greenland area at times during that run.  Looks like the eastern trough amplifies fairly regularly with a few bouts of a ridge rolling through, but popping again out West.  Jeff, feel free to add or subtract from those brief comments....I always look forward to the "Jeff update" on the Weeklies!

[nrgjeff]

I saw the same. Weeklies do look blocky; however, we still might have to hurry up and wait on wavelengths and other features. If the Canada ridge goes mega-ridge, we are back in that +ABNA summer weather pattern. Siberia is also doing +ABNA things on the weeklies.

Fortunately in October that's not as humid. Temps near normal, but no big trough either. Also, to give fair time, haha...

There are some 16-30 day analogs with blocking and the +PNA and +WPO that go pretty cool. +WPO might be meh in winter; but at these early fall wavelengths, it's actually cold East. Selfishly I'm hoping for the normal/warm scenario. While I love cool mornings, warm afternoons get me more in the mood for fall foliage.

In the relatively shorter-term there's Wilfred/22 for next week. ECMWF favors a track between that of Laura north and Sally south. Caution a 7 day forecast; but, inland storm chasing hopes always spring enternal!

[Carvers Gap]

That is some pretty strong, high latitude blocking being shown by the operational Euro and EPS.  Catches my attention for sure around the d10 range.  

[Windspeed]

[John1122]

Odds of seeing it in winter .008 percent but it sure would be beautiful. 

Gonna be tough to beat the weather this weekend. 60s and 40s, should really help the leaves here.

[Carvers Gap]

Yeah, there have been some wild looking solutions on modeling since the middle of the week last week.   Odds are it dumps West like it did last time.  LOL.  Models seem to really like an eastern trough, only to back off as we get closer.  That said, there is a pretty strong signal for very cold air to dump into the Lower 48 yet again this fall - already been significant cold into the northern Rockies.  Right now, models are showing a strong amplification of the western ridge nearly into the Arctic on some models.  Now, that sometimes allows the cold to buckle right underneath it into Montana and Wyoming.  For now, modeling is sending it eastward.  Then the fun begins as the pattern seems to hold with a deep eastern trough.  

The Euro/EPS are pretty much at the time of year where I don't trust them as much.  However, what the EPS and operational are doing(and have been doing for a few days...weeklies caught it Thursday) is depicting a blocky pattern which does not want to budge.  They did nearly the same thing a couple of weeks ago, only for it to revert to a western trough that buckled into the Rockies.  That said, it is impressive what is being depicted nonetheless.  

[nrgjeff]

I like John's cynicism. I strongly approve that message!

Remember November 2019 setting the table for this epic snowy below normal temps winter? 

Sure was a nice early spring!

OK I will try to share a shred of optimism. Only takes one day. Chattanooga Magic Saturday February 8.

[Carvers Gap]

Posted this in the obs thread on accident...moved it to here.

If you like a -AO, the Euro Weeklies are your huckleberry.  Nice amplification still being depicted next week w an eastern trough.  Hope that solution holds!!!

[nrgjeff]

I want to be a cynic and say it failed the last two times in the 11-15 day. However this time it has plenty of teleconnection support. Also East Asia looks more friendly upstream. 

That's just for the next 2-3 weeks. For winter, revert to cynical skeptic.

[Carvers Gap]

On 9/22/2020 at 8:31 AM, nrgjeff said:

I want to be a cynic and say it failed the last two times in the 11-15 day. However this time it has plenty of teleconnection support. Also East Asia looks more friendly upstream. 

That's just for the next 2-3 weeks. For winter, revert to cynical skeptic.

For sure...And going back to last winter, it failed even more than that.   Plus it is shoulder season, so plenty of reason for some solid skepticism...see that alliteration?  But yeah, looks like it might verify at least in the short term anyway.    Each run I am just expecting a correction which means the trough to head into the Mountain West.  Sooooo, looks like a period of tough-i-ness followed by a near certain +NAO and SER for winter?  

Total speculation and just spitballing....If we hold to six week weather cycles which I do as a very rough rule....That gives us a trough until late October, then a ridge for six weeks, and a trough back by the end of December.  I mean that kind of looks like what some LR modeling has, especially the Euro seasonal.  But I still think we better score by mid-Jan.  Looks very shaky after that if one is using both modeling and Nina climatology.

That said, I wouldn't be surprised for a pattern with an eastern trough to hang around for some time, and then flip warm right as winter begins.  1989 will forever be remembered for that lesson.  Great start...then torch city.

[nrgjeff]

European weekly charts line up with the cooler than normal outlook through the first 10 days of October. However, it ends there.

Rest of the weeks are slightly warmer than normal. AN heights stretch from the West across Canada. Return of the +ABNA. Cancel winter?

Well, this is the fall thread. Good news is the next few weeks will be good for leaves turning on time.

Just avoid any wet wind storms. Early next week is not an issue. Same system in 15 days would be awful.

[Carvers Gap]

I actually wasn't discouraged in regards to the Euro Weeklies, but I am only a hobbiest so maybe ignorant is bliss!  LOL.  Looks like the western ridge indeed rolls eastward around the 12th and then ridge gradually rebuilds out West around the 24th with the Aleutian low re-establishing itself after a period of AN heights which coincide with the warmth mid-month in the East.   I don't look at Euro temps after week 3...they are nearly always warm.  I just look at the 500 pattern.  I did notice an area of blocking beginning to re-develop and was centered just north of HB late in the run.  Honestly, looks like the high latitude pattern tries to roll forward mid-month and actually retrogrades back to a cooler look at 500 for the East.  After listening to Jeff for many years, I have learned that the Weeklies give us a pretty good look at week 3 and have some skill during week 4.  After that, just very broad generalizations.  So take the reforming Aleutians low and HB block with a huge grain.  With shoulder season now in full swing, the Euro Weeklies might struggle.  All of that said, a warm time frame during Fall and during La Nina is well within the wheelhouse of climatology.  I am actually pretty happy to see summer end on time for once.  I will gladly take AN temps during October vs September.

[nrgjeff]

Yeah the +ABNA does have some blocking as Carvers notes. However the Alaska / northwest Canada source region is on fire. +ABNA can get it done down here locally with split flow, but that's not usually good for Region wide fun.

Plus I'm just a very skeptical bear. If I can find just one reason to go warm, against 3 cold, I'll go warm. It is the South. Everything lines up, or cue up Toad the Wet Sprocket 1992, something's always wrong. 

Given a decent La Nina and QBO fail I'm seriously warm winter at work, no joking. However fall leaf season looks superb!

[John1122]

At this point we should be about to enter a new 30 year climate normal. It's been so warm for so many winters in there that it will be harder to be much above average soon! That's probably not that good a point for the snow lovers across the valley. Fortunately we may be able to cash in at some point even without extended cold. Almost all of our snow comes down to timing anyway. 

[Carvers Gap]

Yeah, not really talking winter in my comments above.  Just really looking at Oct and early Nov.  Interestingly the 12z EPS AO/NAO couplet is negative for most of the run with not a lot of let-up.  That said, it is really important to note(for newcomers) that EPS modeling is notoriously fickle at this time of year, even when there is consensus.  What I do see is a GOA low which is going to have to "battle it out" with the AO/NAO couplet on modeling during mid October in order to see the primary driver.  

If the Nina is moderate, I don't disagree at all on a warm generally warm winter.  My thoughts on winter are in the winter thread(I have a warm winter as well), and I don't have many changes at all up to this point.  Now, if the Nina is weak AND cools MJO regions just west of the equatorial dateline...that might allow for periods of extreme cold to make it into our forum area.  My theme is cold(even severe cold) 2-3 times this winter with long periods of AN temps in between.  1989 was a Nina year that was incredibly cold in December, and broke warm in Jan.  It never let up.   It can snow like crazy during weak La Nina winters in NE TN with lots of upslope snow.  Moderate to strong La Nina's are generally busts.

[Carvers Gap]

Been quiet in here of late, so I will throw in some recent model observations and thoughts....

Looks like the expected ridge in the middle and eastern areas of NA(as the Euro Weeklies have shown) is likely by the second week of October and indeed fits Nina climatology.  Seems like it will be at peak strength by mid-month.  The really question is whether it holds or not.  Lows in the GOA can be stubborn to move, but the Euro Weeklies do imply that a trough may re-emerge by the end of the month or the beginning of November.    Again, it should be noted that the EPS and Euro Weeklies have struggled during the last few fall shoulder seasons.  So, take with a HUGE grain of salt.  Still, some nice weather on tap.  Looks like Jeff may get his wishes with some beautiful weather for the leaf season.

Wild card....As that ridge rolls eastward, that might open the door for tropical development.  And we know that tropical development during October has yielded some crazy weather here.  I would not be shocked if that occurred yet again.  Seems to be a pattern of late.  

[Carvers Gap]

Was a fairly noticeable break in continuity beginning at around d8 on the overnight EPS.   While not surprising given how far out that time frame is,  both the 0z GEFS and EPS have changed how they are handling the eastern ridge/western trough scenario beginning around d8.  Instead of lifting a trough out of the West(and re-establishing another trough there), the trough continues eastward and establishes itself in the East.  Lots of upstream stuff going on which is causing that.  So, basically after d8-9 we begin to see a near reversal of what has been depicted for several days.  Will it hold?  Absolutely no idea.  However, we have seen the EPS miss cold shots during shoulder season in recent years.  I have low confidence in the overnight look other than the Weeklies (derived from a warm run yesterday morning) seem to revert to something similar, and have for a couple of runs - the EPS was just about a week quicker on this run.  I don't want to write-up a long post, just giving a heads-up that modeling was a bit different overnight in the LR.  Wouldn't surprise me to see it revert back, but that is a pretty big move....so worth at least a look when the West Coast trough is replaced with a ridge during the aforementioned time frame.  Plenty of time for that to work itself out.

[Carvers Gap]

For kicks and giggles and nothing else, take a look at the block over the Davis Straits on the 0z EPS control @282.  

[The unknown]

Hopefully the Euro does pan out cause things could definitely get interesting. However like Carver said we still need a couple more runs to dissect before we can get excited. It would be a pleasant and welcome surprise if blocking was a reoccurring theme this fall and winter.