November 5th, 2017 Severe Weather Event

[Jim Martin]

It could be an instance tomorrow where there is action on/near the warm front, and in the warm sector itself, at the same time.

[snowlover2]

23 minutes ago, Jim Martin said:

0z 3k NAM showing potential for an active warm front tomorrow afternoon.

Seems to be showing lots of action for IN/OH tomorrow night.

[HillsdaleMIWeather]

27 minutes ago, Jim Martin said:

0z 3k NAM showing potential for an active warm front tomorrow afternoon.

Even though it's not having the best parameters over us, I wonder if having the front over us might give us some wind and hail 

[Jackstraw]

2 hours ago, IWXwx said:

Unfortunately, in my position with EMA, I won't be able to chase since there's still a slight possibility of severe hitting in the FWA and just south area. I would love to be able do a little chase. Good luck Jack and the others that are going out. I'll just be waiting for them to come to me here in Huntington County.

Might be the best strategy if anything really gets going!  KIND has been ramping up the rain totals to close to 3-3.5 inches during the roughly 24 hr. event.  Ground around here is already saturated, flash flooding is definitely an ever increasing concern. 

[OHweather]

Wouldn't be surprised to see a moderate risk for flash flooding from the WPC and some flash flood watches issued by morning.  The front moves slowly for a few hours, with near record high PWATs for the time of year, unseasonably strong instability, storm motions parallel to the front, and a strong low to mid-level theta-e gradient and nose of the low-level jet helping to generate strong low-level convergence.  Although the upper-level dynamics are lacking some when compared to past big November tornado outbreaks in the region, that's still a really nice right-entrance quadrant of an upper-level jet streak over the front over eastern IN and OH for several hours tomorrow evening into tomorrow night.  The front does sag south gradually, so it may not be more than a potential few hours of heavy rain potential in any given spot, but it's been a bit of a wet week for parts of the region.

[IllinoisWedges]

SPC went 10 tor, 15 wind, 30 hatched hail. 

Quote

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   FAR EASTERN MISSOURI...SOUTH-CENTRAL ILLINOIS...INDIANA AND
   WEST-CENTRAL OHIO...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
   ENHANCED RISK AREA ACROSS PARTS OF THE MID MISSISSIPPI VALLEY...OHIO
   VALLEY AND LOWER GREAT LAKES...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
   SLIGHT RISK AREA FROM PARTS OF THE OZARKS EAST-NORTHEASTWARD TO
   WESTERN NEW YORK...

   ...SUMMARY...
   Severe thunderstorms capable of large hail, damaging winds, and a
   few tornadoes, will be possible from parts of the mid Mississippi
   Valley east-northeastward into the lower Great Lakes this afternoon
   into tonight.

   ...Mid Mississippi Valley/Ohio Valley/Lower Great Lakes...
   A subtle upper-level trough will move eastward across the central
   and northern Plains today and into the mid to upper Mississippi
   Valley tonight. At the surface, a cold front will move southeastward
   across the western Great Lakes extending southwestward into the mid
   Mississippi Valley. Elevated convection may be ongoing along parts
   of the front this morning from northern Illinois eastward into
   northern Ohio. As the front moves southeastward into central
   Illinois, north-central Indiana and north-central Ohio during the
   afternoon, surface-based thunderstorms should develop. By early
   evening, a large part of the front should be covered by
   thunderstorms. These storms are forecast to become organized and
   move southeastward across the mid Mississippi Valley and Ohio Valley
   during the evening.

   Forecast soundings along the front at 00Z from southern Illinois
   northeastward into central Indiana show surface dewpoints in the mid
   60s F and MLCAPE values around 1500 J/kg. In addition, 0-6 km shear
   is forecast to be from 50 to 60 kt which will be favorable for
   supercell development. Large-hail formation will be aided by steep
   700-500 mb lapse rates of 7.5 to 8.0 C/km. Hailstones greater than 2
   inches in diameter will be possible with the more dominant
   supercells. The potential for large hail is forecast to be greatest
   during the late afternoon and early evening when instability will be
   maximized. The tornado threat is forecast to be greatest during the
   early evening as supercells ahead of the front interact with a
   strengthening low-level jet. 0-3 km storm relative helicities of 300
   to 400 m2/s2 and low LCL heights should support a conditional
   significant tornado threat with cells that remain discrete ahead of
   the front. As convection fills in along the front, the potential for
   wind damage should increase. A mixed model of convection should
   exist along the front. The faster moving bowing line segments will
   have the greatest potential to produce wind damage. The wind-damage
   threat should persist during the early to mid evening as an MCS
   becomes organized and moves southeastward across the region. 

   The severe threat should extend northeastward into northeast Ohio
   and western Pennsylvania but weaker instability should keep the
   severe threat isolated there. A severe threat will also be possible
   in south-central Missouri but the potential should drop off quickly
   with southwestward extent due to a capping inversion in the Ozarks.
   As the front moves southeastward into the Ohio Valley during the
   overnight period, the severe threat should become isolated.

[Chicago Storm]

SWODY1 answers my earlier question, they're gonna ride and die with an overly bullish outlook.

10% tor is comical. Broyles gonna Broyles.

[RCNYILWX]

SWODY1 answers my earlier question, they're gonna ride and die with an overly bullish outlook.

10% tor is comical. Broyles gonna Broyles.

Given how far south the boundary is gonna be, I'm astonished (well, can't be too surprised with Broyles) how far north the 2% tor extends and the 5% wind for that matter.

Sent from my SM-G935V using Tapatalk

[Stebo]

1 minute ago, RCNYILWX said:

Given how far south the boundary is gonna be, I'm astonished (well, can't be too surprised with Broyles) how far north the 2% tor extends and the 5% wind for that matter.

Sent from my SM-G935V using Tapatalk
 

Yeah it is too broad brushed of an outlook, I definitely agree there.

[Hoosier]

The undercutting issue seemed less on the 00z NAM compared to earlier runs.  I haven't had a chance to look at other models yet.

That being said, I'm probably a little more surprised at how far south the 10% tornado area goes than there being a 10% area.  I agree with the conditional sig tor wording but no hatching.

[OHweather]

I'm sort of meh on the SPC tornado risk.  Some obvious cons are lack of low-level backing to the winds in the warm sector, ongoing convection potentially limiting instability, and not much of a window for discrete or semi-discrete convection.  Some arguments for are despite the lack of turning, the low-level wind fields are still strong enough to generate more than enough storm-relative helicity and LCLs will be low, so it won't take an extremely persistent or strong meso to get a possible tornado. 

The cap overall looks a bit weaker on forecast soundings than it did a day or so ago, which while possibly allowing for a somewhat better shot at some development in the open warm sector also increases the odds of storms growing upscale too quickly.  There's a ton of lift, both large scale and mesoscale near the warm front (or outflow boundary) and cold front, which when combined with storm motion and shear vectors nearly parallel to the front and less cap than before suggests that there will be a lot of storms and things won't stay semi-discrete for very long.  

I'd personally go with a broad 5% area (and cut it off farther south than the SPC as it looks like ongoing convection will limit the northern extent of the best threat area).  I've seen worse setups get 5% risks before, sure, but a lot of arguments against a lot of tornadoes.  MLCAPE over 1000 J/KG and the expected shear (both bulk shear and low-level SRH) along with the low LCLs are adequate for a strong tornado threat, as mentioned in the outlook and in the discussion here, but you really need a prolonged and more robust supercell for that to happen.  Not impossible but it may be a situation where one or two cells are able to pull it off while everything else fails.  Given the shear, I'm sure a lot of cells will have transient/weaker rotation and fail to produce tornadoes but have an accompanying hail/wind risk.  There will be a brief tornado risk with more robust bowing structures too well into the evening given the strong low-level shear, though those usually are weaker and very hard to chase. 

[andyhb]

Should note that the bullishness of the 06z SPC outlook may stem partially from the fact that the majority of the 00z CAMs (and recent runs of the HRRR) were rather impressive through the 10% tor corridor with pre-FROPA (from the looks of it anyway) supercells/etc. 03z SREF continues to be rather stout as well and took a step up from the 21z run. Dewpoints are already in the mid to even upper 60s in S IL and mid 60s all the way east to ILN so moisture should, as expected, not be an issue.

Despite the lack of substantial backing of the surface winds, there still appears to be sufficient low level hodograph curvature and critical angles (>50˚ in basically all of the soundings I've pulled from different models), to pull tornadoes out of any supercells that become well established within the warm sector boundary layer.

Proximity of the weak frontal wave/surface low may also yield an appreciable tornado threat in western Ohio (yes tornadohunter, perhaps Van Wert/Lima, although long tracked F4 I would certainly not expect) assuming enough buoyancy can reach there in time and at least transient supercell structures.

Still does irk me that this is November and we have summer-like amplitude/southward extent to this overall trough, a bit more amplitude and we'd be really talking something significant here in all likelihood given the widespread extent of quality low level moisture and solid lapse rates.

[snowlover2]

Wow never expected to wake up to being in a 10% tornado area.

[IWXwx]

Mile Ryan at IND lays out his thoughts nicely concerning Central IN in the longest Near Term AFD I've ever seen lol. And yes, he is bullish.

.NEAR TERM /Today and Tonight/...
Issued at 311 AM EST Sun Nov 5 2017

Warm front progressing north through the forecast area early this 
morning with convection developing along it. Have not seen any 
lightning strikes to this point...but have seen brief heavy rainfall 
within the convective band as it streaks northeast. Temperatures 
have been steadily warming through the night as the warm front lifts 
north...with 08Z temps now firmly into the 60s and near 70 in the 
lower Wabash Valley and a noticeable increase in dewpoints.

Active 24 hours forthcoming for central Indiana as the presence of 
the frontal boundary followed by several surface waves tracking 
along the boundary later today and tonight will bring a multifaceted 
severe weather and flooding event into the forecast area through 
predawn Monday. 

Model guidance continues to zero in on the details through tonight 
with the warm front currently tracking through northern portions of 
the forecast area set to eventually align from central Illinois into 
northeast Indiana by midday before a series of surface waves track 
along the boundary and begin to shift it back southeast as a cold 
front late today into tonight. This system is missing some of the 
key features historically common with bigger fall severe weather 
events...especially the presence of a deeper and singularly dominant 
low pressure. That being said...there are several pieces present 
that support the severe weather threat over the region through this 
evening before transitioning to a greater flooding threat. 

Low level forcing remains impressive as the day progresses... 
highlighted by a maximized jet peaking at 50-60kts by early evening 
from southern/central Indiana into Ohio. Forcing aloft present as 
well with speed shear in the mid levels and a dual jet structure 
diverging in the upper levels and presenting a diffluence signature 
over the area. At the surface...a nice moisture surge south of the 
warm front ongoing this morning and will continue through the day as 
dewpoints likely peak in the 64 to 67 degree range. While the NAM in 
particular is likely overdoing instability values later today 
somewhat...expected MLCAPEs in the 1000-1500 j/kg range remain 
climatologically impressive for early November by this afternoon. 

Strong support continues for all modes of severe weather being 
present later today...but can be more detailed on timing and extent 
of impacts as the convective scenario evolves. Model soundings 
continue to favor sharp lapse rates in the mid levels in excess of 7 
C/km during the afternoon and early evening in the warm sector. This 
combined with wet bulb zero values at 9-10kft and a broad hail 
growth zone aloft support large hail likely serving as the primary 
threat initially as supercellular structures develop...especially 
across the western half of the forecast area. The presence of such a 
deep hail growth zone alone presents an argument for stronger cells 
to carry a potentially significant hail threat during the second 
half of the afternoon through about 23Z.  

It is during this time when the tornado threat will be maximized as 
well with BL shear and 0-3km SRH values well within the range to 
support rotating storms. Think two potential areas could see a brief 
tornado threat enhancement in the 18-23Z time period. The first will 
be near the slowly sagging frontal boundary over far northern 
portions of the forecast area. The front and the individual waves 
riding along it may serve to enhance backing flow in the low levels 
and overall SRH values through the lowest 1-3km. The second location 
will be across western portions of the forecast area where 
directional shear maximizes for a couple hours around sunset and 
aligns with the expected area of greatest instability. Any 
individual cells developing in this area could carry an enhanced 
tornado threat for a short period of time. With that being
said...still feel a more substantial tornado threat over the
forecast area is limited by the lack of more substantial backing 
flow in the lowest levels that a strong surface wave would bring. 

As we move into the evening...should see convection gradually 
transition into a linear mode with the potential for bowing 
structures. As is often the case with QLCSs...a brief spinner threat 
will linger with the linear convection through much of the evening 
as it moves southeast...but the main severe threat will shift to 
damaging wind gusts. Much of the severe weather potential should be 
over by 03-05Z with heavy rain and flooding eventually becoming the 
primary concern overnight as the frontal boundary becomes more 
parallel to the flow regime aloft. In addition...the low level jet 
will align immediately ahead of the slow moving front and continue 
to pump deep moisture into the area. Precip water values peak near 
record levels at this time of year around 1.5 inches as well. 
Considering the high potential for efficient rainfall...will be 
introducing a Flash Flood Watch for the northern half of the 
forecast area beginning at 17Z and continuing through the predawn 
hours Monday. Confidence highest over this area to see rainfall 
amounts of 2 to 3 inches by Monday morning with locally higher 
values most likely northeast of the Indy metro. Will leave it to 
later shifts today to determine if the watch would need to be 
expanded further south.

So to summarize...scattered convection remains possible over 
primarily northern counties this morning. Severe storms become an 
increasing threat after 18Z and continuing through the evening. 
Large hail and tornadoes are greater threats through early evening 
with damaging winds becoming the primary threat during the evening 
and early overnight as convection becomes linear. Heavy rainfall and 
flooding will be a growing concern this evening into the overnight 
before storms gradually end from west to east late. 

Temps...despite thick cloud cover all day...expect highs to warm 
into the lower and mid 70s over much of the area. The passage of the 
cold front after midnight will ensure lows dropping into the 40s 
over much of the region by daybreak Monday.

[Quincy]

Tornado potential will likely come down to storm mode and interactions. Two regimes will be favorable, assuming cell(s) can remain at least somewhat isolated. 

Midday through mid-afternoon favors central IN to western OH along an effective warm front/moisture gradient. Here, shear looks to be greatest, both in terms of stronger 0-2km flow and vectors being more orthogonal than points west. With that said, instability appears to be on the lower end of the spectrum, in the range of about 500-1000 J/kg. Cells may tend to outrun the favorable thermodynamic environment.  

Mid to late afternoon targets the southern third of IL and possibly into portions of eastern/southeastern MO. Model data and trends suggest unseasonably robust instability will develop immediately ahead of the frontal boundary, with 1500-2500 J/kg CAPE and dew-points in the upper 60s (a tick higher than IN/OH). With that said, angles created by the shear vectors and front will be smaller than points east, but will be conditionally favorable for tornadic supercells. 

It's one of those events where the ceiling is fairly high, but only if storms remain discrete. There is not much room for error, but one cannot help but be intrigued by this sort of parameter space in the region in November. One scenario features messy storm modes with too many storm scale interactions for a widespread tornado event. There could also be a rogue cell that either fires in the warm sector/near the warm front and goes to town. Cells along the western portion of the front will probably be at least semi-discrete to start, but if storm mode trends toward more isolated, watch out. 

[Quincy]

Not only are steep mid-level lapse rates noted across MO/IL, but the 12z SGF sounding sampled nearly dry adiabatic lapse rates from 800-550mb, supporting a mean 850-500mb LR of 7.8 C/km.

Seasonably large CAPE profiles will easily be realized downstream as a result, even if there is only partial sunshine today from MO into central/southern IL.

[geddyweather]

Convection already ongoing across West Central IN. So out of place to see early in the morning in November, seems more appropriate in the spring. Widespread dew points in the 60-65 degree range building up so far in IN, west central OH. Already reaching close to 70 in parts of srn IL.

[Jim Martin]

[Jim Martin]

[HillsdaleMIWeather]

I'm surprised there's no SPC MCD out yet

[OHweather]

11 minutes ago, HillsdaleMIWeather said:

I'm surprised there's no SPC MCD out yet

For now I think those SVR warned storms in NE IN are still elevated, so we're still a little ways away from a more substantial risk. 

EDIT: A couple of wind damage LSRs just came in so they may be getting close to surface based.

[geddyweather]

Wow. SPC 1630z takes the ENH all the way to Eastern OH. No joke.

[geddyweather]

30% wind introduced into Srn IN, most of OH. 10% Tor and 30% hatched hail trimmed a bit, now mostly in just Srn IL and IN.

[MattPetrulli]

What a technical and in deph discussion by SPC. *Sarcasm* 

 ...SUMMARY...
   Severe thunderstorms capable of large hail, damaging winds, and a
   few tornadoes will be possible from parts of the mid Mississippi
   Valley east-northeastward into the lower Great Lakes this afternoon
   into tonight.

   ...IN/OH/PA...
   Have expanded the EHH risk area eastward to include more of central
   and eastern OH.  Trends in surface observations and satellite
   imagery suggest destabilization will continue over this region, with
   12z CAM solutions indicating robust thunderstorm development through
   the afternoon and evening.  Forecast soundings show substantial low
   level wind speeds and vertical shear, promoting a squall line with
   embedded bowing/rotating storms capable of damaging winds and
   isolated tornadoes.  Large hail may also occur in any supercells
   that can become established.  The threat should slowly diminish as
   the storms move into a progressively more stable air mass over
   western PA.

   ...IL/IN...
   Another area of intense thunderstorm development is expected this
   afternoon along the primary cold front sagging into parts of MO/IL. 
   Most model guidance suggests development will begin near the STL
   area and spread eastward across parts of southern IL into central
   and southern IN.  Thermodynamic parameters will be stronger in this
   area compared to farther northeast, promoting a greater risk of
   large (possibly very large) hail.  Model guidance along suggests a
   slightly higher probability of discrete supercells in this area,
   with a few tornadoes expected.  Eventually, these storms will also
   congeal into a squall line as they build southeastward toward the OH
   river.

[Jim Martin]

[geddyweather]

Mesoscale Discussion 1754 NWS Storm Prediction Center Norman OK 1048 AM CST Sun Nov 05 2017 Areas affected...portions of southern Indiana Concerning...Severe potential...Tornado Watch likely Valid 051648Z - 051745Z Probability of Watch Issuance...80 percent SUMMARY...A warm-sector supercell risk is increasing across the lower Wabash Valley. A tornado watch will likely be issued soon. DISCUSSION...Radar trends over the past 30 minutes have shown the development of a sustained/robust updraft over Lawrence County, IL. The airmass downstream over this intensifying thunderstorm is moist/adequately unstable with surface dewpoints in the middle 60s degrees F and temperatures are slowly rising into the lower 70s. Objective analysis fields indicated around 750 J/kg MLCAPE and KVWX VAD data shows a strong wind profile supportive of low-level updraft rotation. Given the low CAPE/high shear setup, expecting a gradual intensification of warm sector storms and low-level mesocyclones potentially capable of a few tornadoes.

[Chambana]

Storms really starting to fire along the boundary. Looked like for a split second partial clearing. 70/67 here. Very heavy rainfall and small hail primary threat. 

 

Was weird, weather channel actually mentioned champaign earlier and gave us a TORCON of 5. 

[HillsdaleMIWeather]

Tornado Watch issued

[geddyweather]

2 minutes ago, HillsdaleMIWeather said:

Tornado Watch issued

Looks like they just decided to cover both MDs, as well as the area in between. 50/20 TOR probs to go with 70/10 wind and 70/40 hail.

[CoachLB]