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John1122

Fall 2017 Great Tennessee Valley Outlook

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A few days ago Accuweather released it's Fall 2017 outlook. It seems to be on the rain train for fall 2017 and that's certainly been the pattern this year. We've busted the drought wide open with several flooding events and no long interludes of drought. The temperatures are much less warm than last year as well. After a warm winter we've seen a mild spring and summer 2017. Will that continue through fall? Will we have an early frost or freeze or will it be extremely late arriving like fall of 2016? Time will tell, but I'm very happy we've survived another summer season in the Great Tennessee Valley and escaped some of the extremes we can face at times in the region. 

Accuweather Fall 2017 outllook. 

 

https://accuweather.brightspotcdn.com/dims4/default/ec7a292/2147483647/resize/590x/quality/90/?url=http%3A%2F%2Faccuweather-bsp.s3.amazonaws.com%2F8e%2F9d%2Fd3a3bf2c458f8f498c2346abde99%2F2017-us-fall-forecast-final.jpg

Current drought monitor for August 2017 vs 2016. We are starting off much better as we head into fall. Especially given the balance of the next 2 weeks are supposed to be at or below normal on temps with normal or above normal rainfall. It naturally dries out in fall but last fall it was unnaturally warm and the soil moisture was gone by the time we started September.

 

000August1st2017.png

000august2016.png

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They are going for a persistent trough in the central US. I infer that from the Highlights. It is great for fall severe. Continuation into winter would be frequent SER and Apps runners. Thankfully it is just a fall forecast.

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Most of the NMME'S show a more Nina SST in Nov.with a ridge into the Atlantic,possibly.We haven't had a real fall weather severe season in some time here in the Valley

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Last two weeks ending yesterday and the forecast for the next two weeks. Will this set up the fall pattern? The coolest Tennessee August on record was 1967 and that led into a very cool fall. September-Nov of 1967 was the second coldest on record behind 1976. In 1976 August was 3 degrees below normal, the 7th coldest August on record. The second coolest August was 1950, it led into the 7th coolest fall on record.  Will have to look at more years but there does seem to be some correlation between warm August/warm Fall and cool August/cool Fall.

20170808.14day.mean.F.gif

 

 

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We're in a more Nina pattern than Nino.The SOI has been showing this much of the summer.So much for the earlier seasonals showing a Nino.The IMME  doesnt show this breaking down,well not by much the enso in 3.4 &3 are being shown negative through out the winter,right now anyways with 1.2&4= ,with a weak +PDO. Probably will change again.Like to see the enso though the next run in fall with a more Ninaish look it has in Oct lasting into Nov into severe season:D

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I always look forward to that first fall cold front that sends temps into the 40s. The ensembles are predicting BN to persist over the next two weeks. Not sure what effects Harvey may have on our region yet or when it might be felt. GFS seems to keep it confined to the deep south and Texas, the Canadian finally moves it more towards our area and dumps 4-8 inches of rain over a good portion of the region.

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Still major model differences in the track of Harvey next week between the GFS and the Canadian. GFS essentially keeps it confined to Texas and moves it west. Canadian brings it directly over our region with flooding rainfalls. It's such a contrast that the GFS has 0 rain over NW Tennessee and the GGEM has 8-10 inches over the same time frame.

Canadian through Sunday Morning next week.

gem_apcpn_seus_32.png

 

GFS

gfs_apcpn_seus_32.png

 

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Need that ridge off the Fl coast to develop like the CMC shows that would help pull the storm into the Valley.Probably need to watch the system crossing N/FL and where it goes and how strong it gets as the CMC is the strongest with it right now.Lots of moving parts by the looks.

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12z Euro has the second landfall idea and now brings Harvey into the western forum area in 5-7 days.  John, looks like the Canadian has company now.

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European model has 2-5 inches of rain for the Tennessee Valley this week, with 7-8 inches in the mid-Mississippi Valley. GFS has almost as much. Canadian is notoriously fickle on QPF both rain and snow. I favor the Euro. In a true rarity, I'm thinking greater than WPC guidance.

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Time to take a stab at fall and winter. First, August will be cooler than normal. September may very well follow. Without causation, at the risk of voo-doo meteorology, the correlation to a cold winter is surprisingly strong following such a scenario. Will it be so this year?

The +AMO remains about the only warm signal left. The -QBO is no head-fake; it is tanking. The +PNA seems to be happy where it is now. ENSO will be weaker this winter, so expect variability with the MJO. CFS has slightly Nina side of neutral. Euro actually drifts slight Nino side by last winter. I'll go near neutral, and check the week-by-week MJO.

Big question: How fast will the remarkably warm global atmosphere cool off? Keeping warm a year past the super Nino is no surprise. However this is the second winter and anything can happen. So, I will go near normal which is significantly colder than last year. Best chance of cold is probably back half of winter. 

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1 hour ago, nrgjeff said:

European model has 2-5 inches of rain for the Tennessee Valley this week, with 7-8 inches in the mid-Mississippi Valley. GFS has almost as much. Canadian is notoriously fickle on QPF both rain and snow. I favor the Euro. In a true rarity, I'm thinking greater than WPC guidance.

Only concerning thing in my mind, particularly for eastern forum areas is subsidence behind departing coastal cutting amounts.

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If only we could be so lucky... 

40 minutes ago, Daniel Boone said:

Only concerning thing in my mind, particularly for eastern forum areas is subsidence behind departing coastal cutting amounts.

TPC's #10 will be long gone before Harvey approaches. Keep in mind Monday rain is a separate mid-latitude front. Blue Ridge could be hit hard late this week if upslope flow persists for several hours and days.

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Yeah,I kinda used the wrong word(concerning) there Jeff,lol. See what u r saying irt Harvey. That se coast system has helped keep hp over the area and Harvey from coming ne. Yeah,if #10 moves along as per guidance Harvey should move forward but will residual atmospheric affects from departing coastal still weaken it enough to not be too significant,especially in the great E. Tenn. Valley. At any rate, as u said, eastern slopes should amass a good amount with downsloping cutting down amounts in the great valley in the eastern area of t.valley forum. Btw, agree with u on the Winter being colder this year. Only difference, I'm thinking early cold and possibly, depending on enso, moderating back end. Actually, I think there's potential for a solid wall to wall rather cold one this year.

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The NAM is moving Harvey more east and faster than the GFS still. GFS paints the heaviest precip across Arkansas with a general 2-5 inches across most of the Valley. The NAM, through half the time of the GFS (84 hrs vs 168) advances Harvey and it's axis of heaviest rain across the Western Valley with Memphis picking up 6-8 inches of rain with the remnants sitting near Jackson TN by hour 84. By contrast the GFS has Harvey over Southern Arkansas moving more northerly vs the NE movement depicted by the NAM. Looks like the Canadian is going to follow the NAM vs the GFS on placement.  As of now all models show quite a few days in a row of rain coming as Harvey moves very slowly.  The GFS gives the region rain from Wednesday-Monday. In that rain we see a lot of well below normal day time highs.  The GFS is putting out some upper 60s and lower 70s highs in the area on Thursday and Friday. Very similar to today here, we had a high of 72.

 

As I mentioned, below normal August often leads to below normal fall temps and Jeff mentioned that below normal fall temps often show up with below normal winter conditions.

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Weeklies have seasonal rainfall and BN those through 46 w a pronounced warming trend during the last three weeks of the time frame.  The trend during its past few runs is to bring AN temps into the area for late September into October.  BN continues for the first three weeks and is strong enough to skew the entire time frame to BN.  But definitely warm temps showing up late.  The 500 pattern over NA looks very similar to last winter during that AN time frame.  Far western trough, mid/eastern contingent ridge, trough over Greenland.  Tough to tell if it is modeling a pattern flip or just rolling the pattern forward into the current pattern again.  The -QBO (in my opinion) will knock down that look if it becomes reality.  Either way, this has been a great August and looks like the first three weeks of September will be nice as well.  Going to be some nice football temps.

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2 hours ago, Carvers Gap said:

Evening model runs spitting out some hefty rainfall, totals for west TN w the remnants of Harvey.

Yeah, doesn't bode well there as much of that area received heavy rain yesterday. Just nw of Jackson a cocorahs report of over 4 inches.

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There wouldn't be much left of the Bahamas in the GFS scenario, it turns Irma into the 2nd strongest hurricane of all time as it crosses there at 884. Cat 5 Wilma was 882. I sincerely hope the GFS is very wrong, not just for the Bahamas but for Myrtle Beach and points north and east of there. It's a cat 2 hurricane by pressure in Southern Virginia. Would be a devastating landfall.

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The warm SST's it's fixing to endure is not a good thing.The latest EPS shows the storm going through Florida and coming out into the GOM around Tampa then coming back up through N/Fl,that would pose a good tornado threat as well for Florida

Michael Ventrice   MJVentrice    Twitter.png

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Pretty potent cold front on tap Tuesday, strong t-storms possible then a brisk cool down. Possible upper 50s to mid 60s for highs and upper 40s to low 50s for lows Thursday and Friday. This with clear skies and sunshine. 

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If the track/speed from the 00z gfs came to pass elevated areas in East Tennessee would have exceptional winds. 925 mb winds are in the 60mph range and they are close to 100mph at 850. 925 is 2500 feet and 850 is roughly 5000. So I'd peg major tree damage in the Smokies, as well as peaks in SWVA, SEKy and parts of the Plateau.

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Models are definitely southwest today.  They seem to be struggling on whether to go west of the Florida peninsula or just to LF in south Florida.  Still a lot can change in seven days...but a landfalling hurricane seems a bit more likely.  The forum area definitely needs to monitor the situation as several runs on several models really want to track Irma north/northwest once a potential LF is made.  Remind me are landfalling hurricanes more likely during a Nino, Nada, or Nina....?

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