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AMZ8990

December/January 2019/20 Winter Speculation Thread

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Local NWS at Nashville calling it a non-event which is a sure sign it will snow; seems like almost every time they approach something in a dismissive nature it backfires on them. 

"This continues to look like a non-event for most locations in terms of wintry accumulation. At first glance, the ECMWF/GFS 850mb 0C isotherm does not reach Middle Tennessee until 00z or later on Wednesday."

https://forecast.weather.gov/product.php?site=OHX&issuedby=OHX&product=AFD&format=CI&version=1&glossary=1

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LR...tough call.  Yet again, LR models are depicting a fairly strong ridge to return to the East during the third week of December.  Why do I say "tough call?"  Well, interestingly ensembles also showing AN heights over Greenland during the same time frame.  Way out there...it looks like the Aleutians trough returns(that we lose around d10 and replace with an eastern Pacific ridge starts to push inward) - meaning that may not be a permanent feature.  I do know one thing, ridges that get established in the East are tough to move once there.  On a sour note, the CFSv2 has flipped to a warm January after weeks on end of depicting that month cold.  It could easily flip back as it is a "flavor of the month" type model anyway.  Just thought I would give a heads-up that it appears that the warmth that was shown for mid-month has re-appeared on ensembles, just one week later.  Will it hold?  No idea.  It hasn't for a few weeks.  But anytime models are in "lock step" probably best to at least throw some shade their way.  It is possible that the trough out West could correct eastward, but we will see.  Finally, there was a lot of talk yesterday about a potential PV split - maybe at 50 mb?  If that happens...modeling should start to really jump around.  Maybe that is why we are seeing blocking showing up out of the blue in Greenland.

As for Tuesday, tough call yet again...probably cold chasing rain but we had a similar set-up in mid-November that worked out quite well.

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Keep an eye on the ridging out ahead of the front (models keep trending stronger each run)...causes the NW trend. Similar to the Nov event except favors Nashville west. Unless modeling flips on the ridge breakdown, dont see this doing much east of the plateau, outside some token flakes. 3 day trend GFS:

 

3a513d8b3d61013c0fb0291ed79ab12e.gif&key=f48b88d4fb7a4f47d01a50ec2a1e51b79444c4dda4170844207be57ca31b5026

 

Sent from my SM-S767VL using Tapatalk

 

 

 

 

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12 NAM snowfall amounts are true statistical outliers compared to other guidance.  Either it scores an VERY unlikely coup or is just further evidence that it amps systems up far too much.   I have seen it amped...but this is even a bit much in relation to itself.  We will need to tread carefully with that model this season.

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12z GFS and CMC very poised to unleash bitterly, bitterly cold air around d10.  4 hours ago...I warned about a warm-up.  You can thank me later - like washing my car in the middle of a drought.  LOL.  We will see what the ensembles say...but I think the operationals since October have actually led the way in finding cold after d10.  The ensembles in that range have been playing catch-up for about two months.  

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5 minutes ago, Carvers Gap said:

12z GFS and CMC very poised to unleash bitterly, bitterly cold air around d10.  4 hours ago...I warned about a warm-up.  You can thank me later - like washing my car in the middle of a drought.  LOL.  We will see what the ensembles say...but I think the operationals since October have actually led the way in finding cold after d10.  The ensembles in that range have been playing catch-up for about two months.  

Can you post a map of how cold those models are?

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If you all get a chance, take a look at the surface temps on the last few frames of the CMC.  -45F air coming down the Plains.  GFS has that to some extent as well.   May or may not verify, but that type of cold never ceases to amaze me.

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Just now, Runman292 said:

Can you post a map of how cold those models are?

Man, I am about out of memory on my account.  Tropical Tidbits has it.  If you don't have access...let me know and I will post it here.  It is almost post worthy anyway.  That was extreme stuff.

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6 minutes ago, Holston_River_Rambler said:

@Runman292

Here is the 850 anomaly on the CMC:

giphy.gif 

True "Barney" cold

And the GFS:

giphy.gif 

No problems with a cold source on those maps.  I have been kicking this around...how many of you feel like the operational have been sniffing out cold in the LR compared to ensembles.  The GFS operational was the first operational to catch the flip from extreme heat to record cold during the four week progression of October to November.  The CMC was next if I remember correctly.  Do you have the actually surface temps for the CMC(not just the departures)?

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The Euro is a nice event from Memphis to Sevier County and basically everyone 60-100 miles north and south of 40.  Not elevation driven particularly. Some of the better totals show up in the high spots, but also nice totals show up around the Tennessee/Miss border areas with some 3 inch dollops. 

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2 minutes ago, Carvers Gap said:

What do you all think about firing up a thread for the Tuesday event?  I don't mind discussing it here either.  Just thinking that it might be thread worthy at this point.

I second that. Been following this thread for weeks but finally logged in. Models definitely have been agreeing on somewhat of an event.

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What little I have been able to see...looks like GFS was a tad stronger wave on 12z. Anyone able to post a vs for the euro (12z vs 0z). NAM still strongest looking...but good to see if others are slowly trending that way.

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Short-term I like the Morristown discussion issued Sunday pre-dawn, digging into type of precip. Partial thickness and temperature profiles support the forecast disco. I also agree non-event though.

Mid-term the Ensembles have gone all mild. I really doubt it lasts, but could be a mild Holiday. How do you say Merry Christmas in Hawaiian? Mele Kalikimaka! Even the cluster with AK ridging has the PNA backwards for the Southeast, giving the Rockies/Plains the cold instead. Again, I figure it won't last forever. This year the see-saw goes both ways.

Long-term I would not worry that the Strato did a major head-fake. Even if it had been jostled, it's normally not too impactful anyway the first tries of the season. Maybe next time will work out closer to the core of winter.

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MRX latest disco, less surface cooling but also less 800mb warm nose. Says that cold will have a hard time getting into the valley from the Plateau, but expects a change from rain to snow rather than any mixed precip for any length of time. Still going with only impacts at elevation NE/SWVA.

 

As a note, MRX has made a top 10 snow events list on it's page for Tri/Knox/Chatt. I appreciate the effort, even though it's laughably wrong in many cases. I think it has my area in the Nov 1952 event with something like 3 inches. For most of my young life prior to the blizzard of 1993, I'd heard of that event as being the king of snow events, described as well over the knees and over bumpers on cars by a multitude of adults.  Neither the Feb 1996 event or the dynamic cooling monster of 1998 are mentioned at Tri. Even though snow depth at Tri goes from 0 to 13 inches from 1-31 to 2-2. It lists 7 snowfalls of 13 inches or less in the top 10. I would have sworn the 1998 event put down 16-24 inches in that area as well. It's a good 10 inches off for a lot of areas for the 93 blizzard as well.

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National Weather Service Nashville TN
207 PM CST Sun Dec 8 2019

.DISCUSSION...

It`s fairly breezy this afternoon with quite a bit of cloud cover
scattered over the area. The southerly breeze is pulling moisture
northward as a broad area of low pressure is organizing over the
Rocky Mountain foothills. That is in response of a negatively-
tilted longwave trough digging into the western CONUS. Closer to
home, a stray shower can`t be ruled out through the rest of the
daylight hours as moisture advection continues. The broad area of
low pressure will slide east this evening before lifting northeast
through the day tomorrow. Models have cut back on the QPF and
coverage of shower activity tonight through the first half of
Monday. Coverage will increase ahead of frontal passage which will
occur Monday night.

Behind the cold front, things get interesting. Models are
producing quite a bit of post frontal QPF thanks to southwesterly
upper flow and a strong jet streak to the north of the area. This
will leave Middle Tennessee in the right entrance region of that
jet streak Tuesday/Tuesday night. Temperatures will drop through
the day on Tuesday and rain will transition to snow with a period
of sleet possible in between. Models, besides the Euro, seem bullish
with the snow amounts. There`s a couple of reasons for that.
Omega in the snow growth region is quite impressive for the
Tuesday time frame and frontogenesis is strong due our positioning
relative to the jet streak.

With any winter weather setup in Middle Tennessee, there are
always some potential red flags. First and the most frequent
question with post frontal snow events around here is how long
will moisture stick around. Model soundings show the low levels
beginning to dry out a couple hours after the rain to snow
transition. Seeder feeder processes may prolong the snow a couple
more hours, but it is something to take note of. Second, it will
take some time or decent snowfall rates to get snow to begin to
accumulate given warm, wet surfaces. Lastly, if there is a
prolonged transition from rain to sleet to snow, that will
obviously cut down on snow amounts. All this leads to a low
confidence forecast at this time, but we trended toward a slightly
snowier forecast. For most of the area, the current forecast is
for less than an inch. The northern Plateau and along the Kentucky
border could see a little more than an inch. There is plenty that
could change over the next 24-48 hours so stay tuned.

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2 minutes ago, jaxjagman said:
National Weather Service Nashville TN
207 PM CST Sun Dec 8 2019

.DISCUSSION...

It`s fairly breezy this afternoon with quite a bit of cloud cover
scattered over the area. The southerly breeze is pulling moisture
northward as a broad area of low pressure is organizing over the
Rocky Mountain foothills. That is in response of a negatively-
tilted longwave trough digging into the western CONUS. Closer to
home, a stray shower can`t be ruled out through the rest of the
daylight hours as moisture advection continues. The broad area of
low pressure will slide east this evening before lifting northeast
through the day tomorrow. Models have cut back on the QPF and
coverage of shower activity tonight through the first half of
Monday. Coverage will increase ahead of frontal passage which will
occur Monday night.

Behind the cold front, things get interesting. Models are
producing quite a bit of post frontal QPF thanks to southwesterly
upper flow and a strong jet streak to the north of the area. This
will leave Middle Tennessee in the right entrance region of that
jet streak Tuesday/Tuesday night. Temperatures will drop through
the day on Tuesday and rain will transition to snow with a period
of sleet possible in between. Models, besides the Euro, seem bullish
with the snow amounts. There`s a couple of reasons for that.
Omega in the snow growth region is quite impressive for the
Tuesday time frame and frontogenesis is strong due our positioning
relative to the jet streak.

With any winter weather setup in Middle Tennessee, there are
always some potential red flags. First and the most frequent
question with post frontal snow events around here is how long
will moisture stick around. Model soundings show the low levels
beginning to dry out a couple hours after the rain to snow
transition. Seeder feeder processes may prolong the snow a couple
more hours, but it is something to take note of. Second, it will
take some time or decent snowfall rates to get snow to begin to
accumulate given warm, wet surfaces. Lastly, if there is a
prolonged transition from rain to sleet to snow, that will
obviously cut down on snow amounts. All this leads to a low
confidence forecast at this time, but we trended toward a slightly
snowier forecast. For most of the area, the current forecast is
for less than an inch. The northern Plateau and along the Kentucky
border could see a little more than an inch. There is plenty that
could change over the next 24-48 hours so stay tuned.

They like to play their cards pretty close to their chest most times. 

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11 minutes ago, weathertree4u said:

They like to play their cards pretty close to their chest most times. 

Yeah you can't blame them.I remember a couple/ few ago we was  in a WSW,it did nothing but rain from a unexpected warm nose the models never picked up on

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Just looking at the 18z GEFS and 12z EPS and 12z GEPS...that is a significant pattern change being advertised.  As Bob Chill mentioned(and I also alluded to this earlier today), that is warm pattern.  Hopefully, models whittle this down to nothing as they have done with this upcoming week's.  But what is depicted doesn't look like a passing ridge in the East...it locks in.  If this "warm up" fizzles...have to think that any warm air forecasted for winter in the LR has to be viewed suspiciously.  Stinks that is over the holidays, but the tendency so far is for those long term patterns to fizzle.  Man, I hopes so...cause that is an ugly, ugly look and if it verifies...a pattern that is very stubborn to uproot.  Maybe the strat split comes to pass and bails us out.  I could happen.  That said, what is being shown is pretty much torch city.  Need that look to go away fairly soon.  Either way, need this week's storm to perform...might be the last for a decent bit IF the ensembles are true.  I suspect they are correct this time...they have been trying to flip for about two weeks on LR modeling.  Sometimes, models just get ahead of themselves or sometimes they constantly portray a change that never comes like last year. I lean warm...

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Of particular intrigue just tagging onto my most current post(besides this one), the 18z GFS looks nothing like the 18zGEFS for days 10-15.  They could not be more different over the Western Hemisphere. Also, as noted above, the operational runs have often (IMHO) been out-doing the ensembles in the d10-15 range.  So interesting test coming up as the operational has not really agreed with the ensemble at 12z and 18z of the GEFS.  That said, the MJO might be about to get more active as evidenced by a more active eastern Indian Ocean.  That might be something to watch as an MJO which is in the COD...might work its way around.

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The 18z GFS has a textbook winter pattern with blocking in both oceans.  I don't like the ensembles...they get better at this time of the year.  But the operational run cannot be discounted due to its recent ability to sniff out blocking...

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