November 5th, 2017 Severe Weather Event

[Stebo]

26 minutes ago, OHweather said:

A little cap can be good, as it can limit weaker convection from firing too early and can keep storms that do fire discrete for a longer period of time.  Obviously, too much can completely kill a threat.  The models generally do have storms firing with the cold front itself, so it's possible (if not likely) the frontal circulation is enough to lift parcels above the cap...but that would certainly limit the tornado threat to more of a brief/spinup type with any forced line segments along the cold front near or after dark. 

I think instability or lack thereof won't be an issue, as the current projections for instability are plenty good when compared to other outbreaks in this region in November.  Veered surface winds area concern with a lack of a progged deep surface low.  There's decent UL divergence over the Great Lakes Sunday afternoon/evening, but the jet streaks aren't the strongest and as has been mentioned height falls aren't impressive given the time of year.  That said, the models still generate enough SRH when combined with low LCLs for a decent tornado threat, but I can't recall any big tornado events this time of year with such a weak surface low.

I have to think that given the seasonably strong instability and more than adequate shear that it'll be hard to avoid some severe weather.  Ingredients for a big tornado outbreak may be missing...namely good evidence for discrete warm sector convection and somewhat veered surface winds.  With such a strong LLJ there could be a half decent coverage of wind reports either way.  I also wonder if elevated convection can fire along the warm front with a hail threat as the EML advects in. 

The thing to watch too going forward is if we get an increase of instability, this is mid-level lapse rate driven as we are getting the values shown with essentially mid 60s temps and dews. If we were to realize something closer or above 70 the instability would go up substantially.

[OHweather]

Just now, Stebo said:

The thing to watch too going forward is if we get an increase of instability, this is mid-level lapse rate driven as we are getting the values shown with essentially mid 60s temps and dews. If we were to realize something closer or above 70 the instability would go up substantially.

It seems fairly common for surface temps to be low-balled by the models in warm sectors (esp with strong WAA) during the cold season.  As we discussed earlier I think there may be some more breaks in the clouds, as the mid-levels are quite dry and any mixing below the EML would likely produce some clearing...so I agree that's something to watch.  Anything to potentially lead to a weaker cap and pre-frontal convection could increase the tornado threat...the one downside is, the soundings Quincy posted have a fairly robust cap that may not be completely broken on its own by somewhat warmer low-levels.  

[Stebo]

Just now, OHweather said:

It seems fairly common for surface temps to be low-balled by the models in warm sectors (esp with strong WAA) during the cold season.  As we discussed earlier I think there may be some more breaks in the clouds, as the mid-levels are quite dry and any mixing below the EML would likely produce some clearing...so I agree that's something to watch.  Anything to potentially lead to a weaker cap and pre-frontal convection could increase the tornado threat...the one downside is, the soundings Quincy posted have a fairly robust cap that may not be completely broken on its own by somewhat warmer low-levels.  

Yeah if the NAM's cap is realized it would be very tough to get anything in the warm sector.

[Indystorm]

1 hour ago, Hoosier said:

Thing is, what is an "outbreak" anyway?  I think the old accepted definition was >5 tornadoes within x amount of time, but that seems outdated with increased reporting these days.  A large tornado outbreak looks unlikely, but a smaller one may be possible.

Agree with you on the numerical definition from earlier times.  Don't know what it might be today.

[HillsdaleMIWeather]

0Z NAM is even more unstable, particularly near the triple point

[Hoosier]

00z GFS actually looks slightly deeper.  Also holding onto a more northwest track.

[Stebo]

1 minute ago, Hoosier said:

00z GFS actually looks slightly deeper.  Also holding onto a more northwest track.

Yeah it isn't backing down, will be interesting to see what the Euro does, if it blinks again or goes back toward GFS.

[Hoosier]

5 minutes ago, Stebo said:

Yeah it isn't backing down, will be interesting to see what the Euro does, if it blinks again or goes back toward GFS.

The NAM and GFS differences are enough to have significant implications around the LOT cwa, so some clarity would be nice. Either way, setting up to possibly be a local-ish chase day.

[HillsdaleMIWeather]

1 minute ago, Hoosier said:

The NAM and GFS differences are enough to have significant implications around the LOT cwa, so some clarity would be nice. Either way, setting up to possibly be a local-ish chase day.

Same, I'm either going to stay in my county or drive down towards Angola to chase if the GFS verifies,

[Stebo]

13 minutes ago, Hoosier said:

The NAM and GFS differences are enough to have significant implications around the LOT cwa, so some clarity would be nice. Either way, setting up to possibly be a local-ish chase day.

Yeah idk what I am going to do but I would like to be out because it is rare for a Sunday chase.

[Hoosier]

The NAM forecast soundings are pretty nasty, especially the closer you get to the warm frontal zone.  Would look even more impressive if it's underdone with sfc temps.

[HillsdaleMIWeather]

Lows even further south on the 0Z Euro

[Stebo]

4 minutes ago, HillsdaleMIWeather said:

Lows even further south on the 0Z Euro

Yeah I don't get it because it was going good until 12z Sunday then the wheels flew off. I guess several days of model consistency is evaporating in one day.

[HillsdaleMIWeather]

Just now, Stebo said:

Yeah I don't get it because it was going good until 12z Sunday then the wheels flew off. I guess several days of model consistency is evaporating in one day.

Agreed, It just suddenly started going south while the GFS has been consistent. It's weird.

[Stebo]

Just now, HillsdaleMIWeather said:

Agreed, It just suddenly started going south while the GFS has been consistent. It's weird.

The GEM is with the GFS as well, the NAM and Euro are in other camp. I mean both still have severe weather potentials but the locations and timing are all different.

[Hoosier]

Not sure but I wonder if the subtle nature of the upper level disturbance is causing these model differences.

Often times you end up with some kind of model compromise in the end.  Whether it's 60/40, 70/30, 80/20 and which direction is what remains to be seen.

[Stebo]

2 minutes ago, Hoosier said:

Not sure but I wonder if the subtle nature of the upper level disturbance is causing these model differences.

Often times you end up with some kind of model compromise in the end.  Whether it's 60/40, 70/30, 80/20 and which direction is what remains to be seen.

Yeah since there is no real distinct vort lobe and it is just small ripples the models are having a hard time, not to mention the energy is just now coming ashore too

[HillsdaleMIWeather]

LOT sounding MUCH more concerned in their morning AFD compared to the afternoon one yesterday, mentions sig. tors.

[IllinoisWedges]

5 minutes ago, HillsdaleMIWeather said:

LOT sounding MUCH more concerned in their morning AFD compared to the afternoon one yesterday, mentions sig. tors.

Could you supply a link? I don't see anything of the sort. 

 

Edit: Scratch that, found it on CoD. 

[HillsdaleMIWeather]

Just now, IllinoisWedges said:

Could you supply a link? I don't see anything of the sort. 

https://mesonet.agron.iastate.edu/wx/afos/p.php?pil=AFDLOT&e=201711030715

 

 

"* impressive EML progged to advect over the warm sector with h7-5
  lapse rates >8 C/km 
* rich low level moisture, warm sector already has Tds well into
  the 60s, and that juice will not be shoved very far south before
  being pulled back north Sunday
* weaker shortwave/large scale forcing combined with favorable
  shear vector orientation and forecast storm motion w.r.t. to
  originating boundary would favor a potentially sizable time
  window with the potential for discrete supercells
* kinematic field is seasonably impressive for November, with
  strong low level winds resulting in large area of >250 m2/s2
  background environmental 0-1km helicity in the warm sector

While the above would suggest a non-trivial significant tornado
potential, it is important to note we are still 3 days out and how
the atmosphere looks on Sunday could be vastly different than how
the models are currently saying it will look."

[Stebo]

6 minutes ago, HillsdaleMIWeather said:

LOT sounding MUCH more concerned in their morning AFD compared to the afternoon one yesterday, mentions sig. tors.

Yeah that was a strongly worded AFD by Gino Izzi. He does highlight the potential caveats well too.

Going to add it to the thread because it really is a masterful job of outlining everything at this junction:

Quote

Sunday through Thursday...

Primary forecast concern in the longer range will be with the
system moving through the area Sunday. Big picture-wise, it is
worth noting there are some notable differences in the various
models w.r.t. the track and to a lesser extent the intensity of
the surface wave progged to ride the baroclinic zone across the
region Sunday afternoon. The GFS is the northern most outlier with
the GEM farther south, but still in the northern camp of
guidance. The camp of the southern solution is led by the ECMWF
and NAM, both of which suggest the surface low will track south of
Chicago and I-80 Sunday afternoon.

The eventual track of this low and how far north the warm
front/warm sector air mass lift will be vital in diagnosing the
location of the subsequent severe weather threat Sunday afternoon
and evening. The 00z ECMWF is consistent with its 12z run, if not
even a bit farther south and the 51 member ECMWF ensemble from 12z
showed strong support for the farther south solution. Given the
forecasted low amplitude nature of the shortwave trough, am
inclined to place more weight on the NAM/ECMWF camp. In addition
to playing a role in the eventual location of the greatest severe
risk, a tightening temperature gradient is expected with low 50s
and perhaps even 40s north of the front and 60s to perhaps low 70s
south. Have tightened up the temp gradient in our area Sunday,
which involved significantly lowering forecast highs north of I-80
and even these highs could end up being too mild.

As has been advertised by SPC for a couple days now, there does
appear to be a sizable severe weather risk with this system, which
should be confined almost entirely to the warm sector. Can`t rule
out a rogue hail report or two north, but by and large the
northern extent of the appreciable severe threat will be
delineated by the position of the frontal boundary. Given the
uncertainty in how far north the boundary will lift, it is too
soon to give the all clear to even our northern CWA given the GFS
solution, however at this point the greater severe weather threat
at this time looks to increase as you head south, with the
southern 1/3rd of our CWA looking most favorable for our area.

The system is still 3 days out, so am reluctant to throw out a
ton of details this far out. However, there is reason to be
concerned, as there are many parameters at this point that do
suggest there could a supercell tornado threat in the warm sector
with this system. A sample of some of the concerning details
include...

* impressive EML progged to advect over the warm sector with h7-5
  lapse rates >8 C/km
* rich low level moisture, warm sector already has Tds well into
  the 60s, and that juice will not be shoved very far south before
  being pulled back north Sunday
* weaker shortwave/large scale forcing combined with favorable
  shear vector orientation and forecast storm motion w.r.t. to
  originating boundary would favor a potentially sizable time
  window with the potential for discrete supercells
* kinematic field is seasonably impressive for November, with
  strong low level winds resulting in large area of >250 m2/s2
  background environmental 0-1km helicity in the warm sector

While the above would suggest a non-trivial significant tornado
potential, it is important to note we are still 3 days out and how
the atmosphere looks on Sunday could be vastly different than how
the models are currently saying it will look. Given the potential,
if not likelihood, that the forecast will evolve and require some
adjustments between now and Sunday, it is strongly advised that
everyone pay attention to later forecasts and outlooks regarding
Sunday`s severe weather potential.

 

[HillsdaleMIWeather]

[IllinoisWedges]

30% hatched. 

 

Quote

STRONG EFFECTIVE SHEAR ASSOCIATED WITH THE PREVIOUSLY MENTIONED   SOUTHERN-STREAM MID/UPPER-LEVEL JET WILL FAVOR SUPERCELL STRUCTURES   WITH ANY INITIAL CONVECTIVE DEVELOPMENT ALONG THE WARM FRONT AND   ACROSS THE OPEN WARM SECTOR. GIVEN THE STEEP MID-LEVEL LAPSE RATES   AND RICH LOW-LEVEL MOISTURE THAT WILL BE PRESENT ACROSS THIS REGION,   POTENTIALLY MODERATE BUOYANCY SHOULD DEVELOP BY SUNDAY AFTERNOON   EVEN WITH ONLY MODEST DIURNAL HEATING. SCATTERED LARGE HAIL, SOME   POSSIBLY SIGNIFICANT, MAY OCCUR WITH THESE SUPERCELLS, PARTICULARLY   ACROSS PARTS OF CENTRAL/EASTERN IL INTO WESTERN IN WHERE BUOYANCY   SHOULD BE GREATEST. DAMAGING DOWNDRAFT WINDS WILL ALSO BE A THREAT   WITH ANY SUPERCELL AS LOW-LEVEL LAPSE RATES STEEPEN WITH DIURNAL   HEATING. THE TORNADO POTENTIAL SHOULD BE MAXIMIZED ALONG THE SURFACE   WARM FRONT AND EAST OF THE LOW WHERE LOW-LEVEL WINDS WILL BE LOCALLY   BACKED TO A MORE SOUTHERLY DIRECTION (VERSUS GENERALLY SOUTHWESTERLY   ELSEWHERE).    

THERE IS AT LEAST SOME POTENTIAL FOR ISOLATED ELEVATED CONVECTION TO   BE ONGOING AT THE START OF THE PERIOD ACROSS IL/IN IN ASSOCIATION   WITH A SOUTHWESTERLY LOW-LEVEL JET. THIS ACTIVITY, SHOULD IT OCCUR,   MAY DELAY DIURNAL DESTABILIZATION OF THE WARM SECTOR, AND COULD   RESULT IN LOWER SEVERE POTENTIAL THAN CURRENTLY INDICATED.   CONSIDERABLE UNCERTAINTY ALSO REMAINS CONCERNING THE NORTHWARD   EXTENT OF THE WARM SECTOR SUNDAY AFTERNOON/EVENING, AND SEVERE   PROBABILITIES WILL LIKELY NEED TO BE REFINED ONCE MODEL AGREEMENT   INCREASES IN THE LOCATION OF THE WARM FRONT AND BEST POTENTIAL FOR   SURFACE-BASED CONVECTION. EVENTUAL UPSCALE GROWTH INTO ONE OR MORE   BOWING LINE SEGMENTS MAY OCCUR ALONG THE SOUTHEASTWARD-MOVING COLD   FRONT BY SUNDAY EVENING, PROBABLY POSING A RISK FOR STRONG TO   DAMAGING WINDS. DECREASING INSTABILITY DUE TO THE LOSS OF DIURNAL   HEATING WITH EASTWARD/SOUTHWARD EXTENT SHOULD RESULT IN A GRADUAL   REDUCTION IN SEVERE POTENTIAL BY SUNDAY NIGHT.

 

[Stebo]

Discussion:

..SYNOPSIS     A SPLIT MID/UPPER-LEVEL JET STRUCTURE WILL LIKELY BE PRESENT OVER   MUCH OF THE WESTERN/CENTRAL CONUS ON SUNDAY, WITH MODEST 500 MB   HEIGHT FALLS FORECAST TO SPREAD ACROSS THE MID/UPPER MS VALLEY AND   GREAT LAKES REGION THROUGH SUNDAY EVENING. LARGE-SCALE LIFT   ASSOCIATED WITH THE STRONG SOUTHERN BRANCH OF THE MID/UPPER-LEVEL   JET (100+ KT AT 250 MB AND 60-70+ KT AT 500 MB) SHOULD PROMOTE   CONVECTIVE DEVELOPMENT ACROSS PARTS OF THE LOWER GREAT LAKES,   MIDWEST, AND OH VALLEY BY SUNDAY AFTERNOON. AN ELEVATED MIXED LAYER   WITH STEEP MID-LEVEL LAPSE RATES (GENERALLY 7-8 C/KM IN THE   700-500-MB LAYER) EMANATING FROM THE CENTRAL/SOUTHERN PLAINS IS   EXPECTED TO OVERSPREAD THESE REGIONS THROUGH THE PERIOD.    

AT THE SURFACE, A BROAD MOIST WARM SECTOR WILL BE IN PLACE ACROSS TX   AND THE LOWER MS VALLEY INTO PARTS OF THE SOUTHEAST, TN/OH VALLEYS,   MIDWEST, AND LOWER GREAT LAKES. SURFACE DEWPOINTS REACHING INTO AT   LEAST THE LOW TO MID 60S SHOULD BE COMMON ACROSS THE WARM SECTOR   SUNDAY AFTERNOON. A WEAK SURFACE LOW SHOULD DEVELOP NORTHEASTWARD   ALONG A WARM/COLD FRONT TRIPLE POINT FROM THE VICINITY OF EASTERN   KS/WESTERN MO TO THE LOWER GREAT LAKES BY SUNDAY EVENING. A TRAILING   COLD FRONT SHOULD PROGRESS SLOWLY SOUTHEASTWARD ACROSS THE MID MS   VALLEY AND PARTS OF THE MIDWEST/OH VALLEY THROUGH EARLY MONDAY   MORNING.  

 ..LOWER GREAT LAKES/MIDWEST INTO THE OH VALLEY AND MID MS VALLEY     STRONG EFFECTIVE SHEAR ASSOCIATED WITH THE PREVIOUSLY MENTIONED   SOUTHERN-STREAM MID/UPPER-LEVEL JET WILL FAVOR SUPERCELL STRUCTURES   WITH ANY INITIAL CONVECTIVE DEVELOPMENT ALONG THE WARM FRONT AND   ACROSS THE OPEN WARM SECTOR. GIVEN THE STEEP MID-LEVEL LAPSE RATES   AND RICH LOW-LEVEL MOISTURE THAT WILL BE PRESENT ACROSS THIS REGION,   POTENTIALLY MODERATE BUOYANCY SHOULD DEVELOP BY SUNDAY AFTERNOON   EVEN WITH ONLY MODEST DIURNAL HEATING. SCATTERED LARGE HAIL, SOME   POSSIBLY SIGNIFICANT, MAY OCCUR WITH THESE SUPERCELLS, PARTICULARLY   ACROSS PARTS OF CENTRAL/EASTERN IL INTO WESTERN IN WHERE BUOYANCY   SHOULD BE GREATEST. DAMAGING DOWNDRAFT WINDS WILL ALSO BE A THREAT   WITH ANY SUPERCELL AS LOW-LEVEL LAPSE RATES STEEPEN WITH DIURNAL   HEATING. THE TORNADO POTENTIAL SHOULD BE MAXIMIZED ALONG THE SURFACE   WARM FRONT AND EAST OF THE LOW WHERE LOW-LEVEL WINDS WILL BE LOCALLY   BACKED TO A MORE SOUTHERLY DIRECTION (VERSUS GENERALLY SOUTHWESTERLY   ELSEWHERE).    

THERE IS AT LEAST SOME POTENTIAL FOR ISOLATED ELEVATED CONVECTION TO   BE ONGOING AT THE START OF THE PERIOD ACROSS IL/IN IN ASSOCIATION   WITH A SOUTHWESTERLY LOW-LEVEL JET. THIS ACTIVITY, SHOULD IT OCCUR,   MAY DELAY DIURNAL DESTABILIZATION OF THE WARM SECTOR, AND COULD   RESULT IN LOWER SEVERE POTENTIAL THAN CURRENTLY INDICATED.   CONSIDERABLE UNCERTAINTY ALSO REMAINS CONCERNING THE NORTHWARD   EXTENT OF THE WARM SECTOR SUNDAY AFTERNOON/EVENING, AND SEVERE   PROBABILITIES WILL LIKELY NEED TO BE REFINED ONCE MODEL AGREEMENT   INCREASES IN THE LOCATION OF THE WARM FRONT AND BEST POTENTIAL FOR   SURFACE-BASED CONVECTION. EVENTUAL UPSCALE GROWTH INTO ONE OR MORE   BOWING LINE SEGMENTS MAY OCCUR ALONG THE SOUTHEASTWARD-MOVING COLD   FRONT BY SUNDAY EVENING, PROBABLY POSING A RISK FOR STRONG TO   DAMAGING WINDS. DECREASING INSTABILITY DUE TO THE LOSS OF DIURNAL   HEATING WITH EASTWARD/SOUTHWARD EXTENT SHOULD RESULT IN A GRADUAL   REDUCTION IN SEVERE POTENTIAL BY SUNDAY NIGHT.    

[RCNYILWX]

Great stuff by Gino. I was his shift partner so had the chance to discuss things. Obviously still time for things to change but we roughly went with a 2/3 Euro and 1/3 NAM blend in the forecast with the trends of the Euro and its ensembles continuing from 12z run and the NAM the closest to Euro/EPS consensus. The SPC day 3 outlook is quite reasonable considering the lingering uncertainty.

Sent from my SM-G935V using Tapatalk

[CheeselandSkies]

If the NAM is to be believed it looks like EC IL into WC/NC IN is the place and I am out for chasing due to having work in Madison at 3AM Monday. See you in the spring.

[tornado_junkies]

6 hours ago, RCNYILWX said:

Great stuff by Gino. I was his shift partner so had the chance to discuss things. Obviously still time for things to change but we roughly went with a 2/3 Euro and 1/3 NAM blend in the forecast with the trends of the Euro and its ensembles continuing from 12z run and the NAM the closest to Euro/EPS consensus. The SPC day 3 outlook is quite reasonable considering the lingering uncertainty.

Sent from my SM-G935V using Tapatalk
 

Another beautifully written AFD by Gino. Props. 

[Quincy]

For what it's worth, not only does the 12z GFS remain north, but the SREF mean is also a bit slower and farther northwest. Some of it may be a resolution issue, but it appears to keep areas as far north as Chicago in the warm sector, given dew-points and 10m wind vectors:

SREF severe probabilities are also maximized from central IL into western IN.

[Hoosier]

GFS did come south though, so we'll have to see if that's it or if it's still in the process of trending that way.

[Stebo]

NAM keeps going south, could pretty much eliminate everything North of 80 if that's right.