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John1122

Spring/Summer 2018 Mid to Long Term Discussion.

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It's looking like a cold spring, technically it already is since meteorological spring starts March 1st. Will we continue the trend of below average severe weather seasons? These threads in warm months don't see the activity that the winter thread does, so I figured this would handle summer as well. I guess because summer is normally benign in our part of the world outside the occasional heatwave, pop up storm or rare tropical remnant. 

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Glad that you started this thread.  Weeklies will roll tonight.  I will add a spring update unless @nrgjeff updates first.  My Weeklies spring updates are not "winter focused" though there certainly could be some snow for the mountains.  So, when I mention cold it is not "winter cold" but just against the norms.  Like @John1122, I think we are cold for a bit.  I wonder how the transition to a neutral ENSO state will impact things.  The models are hinting at some warmth building from the south/southwest.  To close out the winter thread, I mentioned that it will be interesting to see if the Greenland block re-establishes(not that it really leaves) and if the building warmth in the aforementioned areas can "win" the battle.  By warmth, I mean AN temps.  Obviously it is spring, and warmth of a seasonal variety will win at some point.

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The CPC 8-14 day outlook favors BN for the NE Valley,  near normal for the remainder, above normal just to our south along the Gulf Coast. This may set up a battle ground, energy is there. AN precip is favored over the entire forum area. 

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Over the next few days we may still see some energy rotating through the trough in the East, probably producing snow showers at times in the Eastern forum areas. I don't expect much more than a roof top duster but sometimes these March snow showers can be very convective and cause whiteout driving conditions for 10 or 15 minute periods.  Not to say these showers will produce that but they are something to look at in a lost winter season for us in the Eastern Valley.  

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3k NAM and RGEM are bullish with these snow showers and both want to show them coming in overnight which will probably help the areas normally favored. I've been surprised in Knoxville a few times by a good overnight snow shower (a decent dusting).  Energy looks nice and the fetch is from lake Superior onto Lake Michigan and then SSE.  

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Euro weeklies want to continue the SSW hangover for a few weeks. CFS is warmer, hinting a brief warm interludes. My gut says hard to verify an AN 7-day period. Most may verify slightly BN. Ohio River Valley boundary looks nearby some of those weeks, which would add variability - also could be dreary. Still that SSW hangover...

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Great discussion everyone and thanks.  Great read.

MRX evening disco snippet...

LONG TERM...(Tuesday night through Monday)...A vort max rotating
around a closed upper low will drop southward into our northern
sections on Tuesday night, bringing steep lapse rates and a NW
flow that will generate scattered to numerous snow showers in SW
VA and NE TN. Saturation in the dendrite growth zone and cold
temps aloft will begin in our area around 03Z Wed and continue
until around 15Z Wed. With surface temps in the 20s, 1-2 inches of
accumulation may be possible in the mountains of TN and SW VA,
with under an inch expected in lower elevations of NE TN and SW
VA. Highs on Wednesday will be well below normal, only in the
upper 30s and 40s.

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Looking at the EPS at 240, one thing that intrigues me is that the renewed -NAO (if it verifies) seems to be a slightly different critter than the one we just saw.  The recent one was driven by the strat and seemed to retrograde as part of a general pattern across the North Atlantic.  While it was very strong, if I remember correctly it also was limited to northern latitudes for most of its life cycle. (See my image on page 79 of the Winter Speculation Thread for the recent -NAO)

This one seems to have more of a equator-ward connection.  At this point not really chasing any snow, but more interested in storm track for future winters.  Does the type of NAO have a correlation to a storm track? If there were a fuller latitude Atlantic block, does it change things up as it weakens? If we can get something like what the 10 day EPS shows, let's see.  

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The type of -NAO forecast is similar to that in winter 2010-11 when we got some good snows. Note it was not as cold as winter 2009-10 but at least Chattanooga did better with snow 10-11. I would say the current -NAO is a little more traditional than the oddball previous one.

Generally -NAO is a cold snowy signal for our part of the world. However other pieces need to be in place for snow. Bone chilling northwest flow only helps the mountains. Need a westerly component to the jet stream.

Unfortunately in spring the only result of this -NAO is dreary cool weather. It becomes not cold enough to snow in the valleys and not warm enough for interesting severe. Air mass dividing line looks to set up in the Tennessee and Ohio Valleys. In May that's severe. Now it's just rain and clouds.

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The angle and origin of the  snow on the way favors SEKY and SWVA but it looks far enough west to hit back to my area on radar. It may bend a bit before it can though. The NAM has it angling north of me, the RGEM has my area in 1-2 inches. The HRRR is in line with the RGEM and hits my area with 1-2 inches as well. 

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I don't know how much moisture will be left by tomorrow around 7 AM, but a 18z, NAM 3k sounding over SW VA (from Tropical Tidbits) is showing a DGZ between 850 and 950 mb, but an associated dry layer. Sounds pretty low though and maybe able to squeeze that last bit of moisture out for NE sections. 

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4 hours ago, John1122 said:

Kudos to the RGEM/HRRR they nailed the 1-2 inch snow amounts in my area when the NAM was only showing them in NETN/SWVA. The RGEM is very good with northern stream/clipper type disturbances.

I agree.  It did a great job.  Has been pretty good over the past week w a few expected hiccups.

Edit:  MRX did a great job as well w their disco Monday evening.

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EPS agrees with the operational in that there is a big 500mb trough over the eastern US around next Wednesday, but there seems to me to be a wide spread in the individual placements of multiple pieces of energy at 500 mb in that trough across the EPS members. If you thought the last one looked complicated (not the nice NW flow event, but the long suffering storm track we consummated last week) you ain't seen nothing yet. 

GEFS and GEPS 500 mb geopotential height means seem to agree with EPS means. I'm just too lazy and worn out right now to dig much deeper in these other ensembles' individual members, but the ops show a wide spread of energy pieces across the eastern US. I have included an image of the GFS of 500 mb relative vorticity at the beginning of the evolution of this storm just to illustrate how much energy (numbers 1-6) is rotating and interacting. I know most of you know how to read this, but there maybe someone lurking here like I did who might like to see what I'm talking about. Also, I don't necessarily favor the GFS here, but just want to show how complicated all this is. "Just in time..." as Jeff has said is not good for lower elevations and southern areas even in mid winter.  

What a weird set up though!  All major models have primary surface low below 1000mb meandering across the TN Valley and then dying in southern WV as it transfers to the coast. That would always scream to me (in every situation I can think of aside from there being an exceedingly cold antecedent air mass in place) horrible set up for any type of winter weather in our area.  I think it looks really complicated and marginal for areas outside of maybe 2000 feet and up and especially southern areas.  And that's if it works out at a 5 day lead as it has been modeled over the past couple of days. 

Bottom line for me:

At this point I'm burnt out for winter, but I thought I'd give it a day yesterday and see how things began to break. Not in any way hopeful for any type of winter in my neck of the woods, but wouldn't mind a flake or two if its going to be cloudy and cool. It also seems like such an unusual evolution for a storm if it occurs, that it might turn out to have a surprise or two for someone at elevation and NE as most of these upper lows seem to have lately, even if it doesn't have one for me.  Complicated and difficult things interest me, and the whole evolution just seems that way to me. High fail potential, even if it is just for a 500 mb setup = high learning potential. Also there seems to be some talk in some of the other subforums that this may be a bigger storm further north that helps boot out the -NAO and usher in a more significant pattern change. I think we can all get behind that at this point.  

By the by John, I do not mean this as a direct response to anything you've posted. My interest has been piqued though, so these are just my overall thoughts on the set up. 

500 mb GFS.jpg

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........My mind says that last third of March is just a "no go"...but the overnight runs at 0z and 6z at least have my passing attention.  So, proceed at your own risk from this point forward in this post.  The event looks a bit too complex on the 21st of next week, and complex can be a pain even during the heart of winter....but most global operationals are showing some variation of the same thing.  SLP crosses the TN Valley and a slp forms in the lee of the Apps or Piedmont and then slows over the Chesapeake area.   I can definitely see a scenario of cold chasing rain...but that slp forming as one exits has been depicted for several runs.  To me, spacing seems to be an issue, but there could also be an issue of the models not knowing which piece of energy to accentuate and/or have difficulty w those interactions once formed.  Again, NE TN and SW VA seem to be in an area that could possible see winter precip....at this point ANY snow is bonus, even flurries.  I think this is a very good write-up by MRX.

This Spring type weather
will give way to a colder regime to end the long term period as two
or three short wave features dive into the back side of an Eastern
United States long wave trough resulting in a rather amplified
pattern Wednesday and Thursday. Model solutions indicate these short
wave systems may have enough moisture for a chance of rain showers
mainly on Wednesday with decreasing probability Wednesday night into
Thursday. The temperature profile could be cold enough for the
possibility of some snow showers in the higher terrain during this
period, and maybe even in valley locations across Southwest Virginia
and Northeast Tennessee as the system gradually moves away to the
east Wednesday night and Thursday morning. Forecast highs will be
near normal for mid March early in the long term, but will be a good
ten degrees below normal during the end of the period.

........Now to the near term.  I thought the disco from MRX regarding severe(prior to the event above) was also interesting regarding Sat night.  I am no fan of large hail which have been a big problem for those of us in NE TN during the past couple of decades.  These comments preceded the comments noted above

or Saturday...Warm front will continue to lift northeast across
the regon with showers and elevated thunderstorms likely for the
first half of the day. For the afternoon, the central and southern
valley will likely have a lull in the convection as the lift moves
north. However, as the upper trough moves toward the east Ohio and
northern Tennessee Valleys late afternoon and evening, scattered
showers and storms will redevelop.

The NAM, GFS, and ECMWF all differ on the amount of low-level
moisture available during the afternoon. Will follow the more
moist NAM/ECMWF solutions for now and expect scattered to broken
convection to develop.

Model soundings show the potential of large hail and damaging
winds. MLCAPES of 1000-1500 J/kg, Hail CAPES of 300-600 J/Kg,
lapse rates near 7 C/km, and WBZ Heights near 7kft support large
hail. The 0-6km shear of 60kts also support rotating storms with
more sustain updrafts. SHIP values between 1 and 1.5.

As for the convective damaging winds, melting hail, plenty of dry
mid-level entrainment and mid-level winds of 30-40kts supports
potential of damaging winds.

The potential strong convection will emain during the evening
hours with showers diminishing after midnight.

 

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Weeklies update....Keep in mind this is not a "winter season" update...but, man, it is cold relative to averages considering these are mean departures for normals.  Temps are BN for most of the 6.5 week forecast...This current week and a timeframe during wks 4-5 depict seasonal to warm temps which eventually gets pushed back.  Precip is BN for the southern areas of the forum and normal for the northern areas...but a generally BN signal overall for precip.  So, some of that does not jive...normally for a cold spring, we see plentiful cold rains.  Time will tell.  The potential for a change in ENSO may be driving some of this.  Have to think during those brief time frames where it warms up...sever could be an issue.   

....This week and next is heaven for basketball fans.  Some great games yesterday.  More on tap today!

edit: Typos fixed.  

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 The 12z suite held check or in the case of the Canadian, upped the ante for potential snow from Clarksville to Nashville and points east. It might be crazy but 12z even gave Chattanooga some snow. You'd think snow would be more clustered in the first 10 days of March in our region, but when I looked back on it it was equally distributed in from 1-10, 11-20 and 21-31 in my area.

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The Euro comes towards the GFS/Canadian a little more. It's more of an elevation event, 1-3 inches on the Northern Plateau/NETN and the mountains get 8-10 inches.  Once again, timing will be key, if we can get this to happen in the dark there's a much better shot at seeing snow stick.

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Interesting and volatile week of weather coming up per the ICON, GFS, and CMC at 0z...The strat warm and subsequent block continue to wreck havoc on spring.


CMC and ICON bury the east coast while the GFS is a whiff for those folks. 12k NAM buries parts of VA east of Roanoke with a foot plus. For us it will be tough to get accumulating snow outside of the higher elevations. Unless the vort can close off and suck the cold air in faster.

Your saying is snow just a few days after thunder and lighting right? Lol

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13 hours ago, 1234snow said:

 


CMC and ICON bury the east coast while the GFS is a whiff for those folks. 12k NAM buries parts of VA east of Roanoke with a foot plus. For us it will be tough to get accumulating snow outside of the higher elevations. Unless the vort can close off and suck the cold air in faster.

Your saying is snow just a few days after thunder and lighting right? Lol

 

Ha!  Well, technically I am not sure that applies during spring....but does anyone have an accumulation map for the 12z Euro for the mid-late week system?

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For my part I'm even less enthused with whatever snow potential there was for my local area (not much to begin with).  I am interested in severe potential tomorrow.  Will still take a few flakes if it I can get em, but trends over the past couple of days seems to be worse for central and southern locations in the eastern valley.  It's still a potentially dynamic upper low, so maybe some surprises (for me a burst of snow for 10 minutes would count). 

In terms of storms tomorrow the 12z RGEM looks rather aggressive for TN and later for N. Georgia and I feel like it was the most conservative with its early depiction of convection yesterday (3/17). I cold also be comparing apples to oranges in trying to compare its depiction of convection to the NAMs. (only looking at the MSLP and precip maps).  Hi-Res models seem to show some early cells racing ahead and eventual consolidation into a line. Hoping for a line by the time it gets across the plateau as those situations seem to be less damaging in my experience in that there seems to be less of a chance for an isolated tornado.  

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