6/19-6/23 Severe Weather Risk

[nwburbschaser]

Wow, that is a strongly worded outlook too. I'm actually a touch surprised how far north it is.

I did not expect that at all. Interesting. 

 

Edit: Just read the last lines of the outlook so that explains it. 

[OceanStWx]

Wow, that is a strongly worded outlook too. I'm actually a touch surprised how far north it is.

 

I know my own personal bias is to hedge too much towards the CAPE. Sometimes that warm front retreats northward faster than anticipated.

[HillsdaleMIWeather]

That Day 2 literally made me choke on my coffee and spill it.

Holy hell SPC

[Stebo]

I know my own personal bias is to hedge too much towards the CAPE. Sometimes that warm front retreats northward faster than anticipated.

If there was a case for it to happen, this sort of setup would so it. Such a strong LLJ is going to be in place.

[snowlover2]

I thought it should be more NW-SE oriented. But they said it could change.

[Hoosier]

I guess the potential magnitude is trumping the uncertainty about how the morning activity could affect the setup.  Though as was mentioned earlier, you would not necessarily expect a lollygagging warm front with this type of setup.  

[Stebo]

I thought it should be more NW-SE oriented. But they said it could change.

Nah the mean flow is W-E. It makes complete sense.

[Stebo]

I guess the potential magnitude is trumping the uncertainty about how the morning activity could affect the setup. Though as was mentioned earlier, you would not necessarily expect a lollygagging warm front with this type of setup.

Makes you wonder if we have a chance to go up from here even...

[hlcater]

West got trimmed much to my dismay but saying I didn't expect it would be a straight up lie. Still kinda sad to see my ENH go though :'(

[Hoosier]

Probably been a while since the last day 2 moderate risk in this region, especially on the first day 2 outlook.  11/17/2013 had it but there's gotta be something since then that I just forgot about.

[Powerball]

Pretty bullish day 2 outlook, at least in terms of northward extent.

[RCNYILWX]

Probably been a while since the last day 2 moderate risk in this region, especially on the first day 2 outlook. 11/17/2013 had it but there's gotta be something since then that I just forgot about.

7/13/15 got a d2 MDT with the 1730z update.

[Hoosier]

Makes you wonder if we have a chance to go up from here even...

 

 

I'm of the view that any day 2 moderate risk is a candidate to potentially go high risk. 

[HillsdaleMIWeather]

I'm of the view that any day 2 moderate risk is a candidate to potentially go high risk.

I'd probably say the Chicago area into Northwest Indiana would be the most likely candidate like during the first High Risk outlook on 11/17

[Hoosier]

Not a huge moderate risk area but targeting some big population areas

 

 

[Powerball]

Nah the mean flow is W-E. It makes complete sense.

 

The mean flow for complexes is W-E, but the thing is the stronger cells within the complex(es) will propagate SE along the instability gradient. 

 

What I will say that the models ALWAYS go overboard with accelerating this gradient too far to the NE too fast (especially in our region with the lake waters and all), so I wouldn't be surprised if they back track some from the last couple of runs we've seen.

[andyhb]

The possibilities of a high for wind seem pretty reasonable at this point. Reminder that we haven't seen pink since 6/3/2014. Longest drought in the modern era for SPC.

 

But actually, the thing that's giving me pause regarding the wind threat, besides early convection, is the amount of directional shear. That doesn't exactly favour MCS evolution quickly (and obviously might raise the tornado threat).

 

I do think they shifted a bit too far N/E with this and trimmed a bit too much off the western end, but one can't be too thrilled with Chicago's position in all of this.

[cyclone77]

West got trimmed much to my dismay but saying I didn't expect it would be a straight up lie. Still kinda sad to see my ENH go though :'(

 

CR is still possibly in the thick of it.  4km NAM hangs the WF up and keeps it further south, as does the new Euro.  Shows the surface low closer to I-80.  Best shot for largest severe coverage will end up being to the east after the MCS matures, but east Iowa still has a good shot at the earlier sup stage.

[OHweather]

I know time of year and overall pattern may suggest linear stuff, but I'm struggling to wrap my head around i .

Strong vertical shear that is also veering, great low level moisture, relatively steep lapse rates given location, height rises/no real height falls/mid level warming (there is no real mid level cooling or large scale ascent outside of the warm front WAA regime)... I am struggling to see, aside from the cold front, what particularly screams MCS/Derecho. This isn't a strongly forced trough we're dealing with, aside from perhaps a strong jet providing forcing for ascent. There are no real height falls, at least from what I saw earlier. Was inferred that warming was taking place earlie . Perhaps 00z changed it up a little.

So you have strong shear, lapse rates/instability that I would guess is in the upper end of what this region typically sees in severe/tor producing environments... You have lift, but you also have capping/no really strong height falls... And finally, you have moisture. I tend to think this will be more of a supercellular event than some seem to currently think but I may just be missing something.

Of course the cold front could have something to say about everything and the warm front could get messy... Even with a linear mode I think there are going to be embedded supercells capable of producing tornadoes. Easily a moderate risk setup if ATM recovers behind morning activity. Just my opinion and I have not sat down to really interrogate dat .

I definitely agree with the risk for tornadoes early on with supercells near the surface low in far eastern IA/northern IL/far southern WI late Wednesday afternoon/evening, as the shear and instability clearly are supportive of strong, rotating updrafts...there appears to be a narrow zone near the surface low and along/just south of the warm front where there will be strong surface based instability with little to no CIN...on top of strong lift on the nose of the LLJ and in the right-entrance quadrant of a departing UL jet streak. The strong ascent/instability combined with weak CIN should allow storms to grow upscale here. A strong LLJ/strong instability has been associated with strong MCSs before, and most derechos this time of year are associated with rather subtle shortwaves. Regardless of if things go linear quickly or are messy due to the strong LLJ nosing in, which both appear possible/likely, as I mentioned in my post 30+ knots of 0-1km shear is associated with non-supercell spinups in squall lines IIRC...so we could see a fair number of tornadoes for a late June event, assuming the early stuff clears quickly enough.

[HillsdaleMIWeather]

IWXs thoughts are echoing the SPC

SHORT TERM...(Today and Tonight)

Issued at 340 AM EDT Tue Jun 21 2016

...moderate risk of severe weather Wednesday afternoon and evening...

Drier and somewhat cooler air mass has settled into the region for

today and tonight.

This will change rapidly wednesday.

A warm front and moisture surge will overspread the area early

Wednesday and this will set the stage for the afternoon and evening

convective development. Westerly flow and a pronounced shortwave

trof will lead to intense and rapid cyclogenesis over Iowa during

the early morning hours Wednesday. Ahead of this expect to see

strong LLJ formation across the Mississippi and Ohio River Valley

and this will help to trigger convective development along the

frontal boundary. While the severe threat with this initial round of

convection is relatively low for our area...this will help to set

the stage for the late afternoon/evening severe threat.

Convective destablization over IA/IL/WI during the afternoon

coincident with the surface low will likely form in to a well

organized MCC/MCS. This will likely track rapidly along the warm

frontal boundary into the IWX area. Given the shear and instability

the potential for widespread damaging winds. This pattern favors

squall line and bowing segments...which would also support the

development of weak tornado formation along and embedded in these

lines. Additionally there will be an abundance of boundary layer

moisture and expect that rainfall amounts will easily exceed 1 to

1.5 inches in many locations...especially during the evening and

overnight period.

[Indystorm]

From LOT

 

The focus for a potentially more significant heavy rain and severe
threat will come in the later afternoon and evening hours. Several
factors are coming together to support that. The NW-SE oriented
warm front should be pulled northward ahead of the surface low to
our west which most guidance holds at a bit higher than 1000 mb
and track it directly across our CWA. Instability will ramp up
significantly as this occurs with a plume of upper 60s to lower
70s dewpoints moving in, while low and deep layer shear increases
even more ahead of the next mid level speed max.

A near 1000 mb low is pretty impressive for mid to late June, but
some uncertainties how far north as to where the more significant
severe threat will lie and will likely need refinement as we see
how the storms evolve during the day, and if this has any
appreciable affect on the northward movement of the low. SPC has
upgraded most of our area to a Moderate Risk for severe weather in
the Day 2 outlook. This does not occur very often for us. And
while this Moderate Risk is largely for damaging winds, strongly
curved hodographs coupled with strong mid and upper level lapse
rates and shear in the hail growth region, and 2 + PWAT values
suggest that all severe weather threats are possible including
heavy rain, very large hail, and even some embedded tornadoes.
There could also be some capping in place given the expected
storms and cloudiness during the day, but forcing does appear
strong enough to overcome this. Supercellular mode is likely
initially given the strength/balance of the instability and shear
with a transition to an organized MCS, though where this
transition occurs is still not clear. Again the expected time is
late afternoon and evening for the more widespread chance of
severe weather across Northeast Illinois and Northwest Indiana.

[A-L-E-K]

IMO the limited westward extent is a good call (they're going to get trained tonight anyways), the morning convection along the warm front is going turn hard right and fester into much of the day. It will be tempting to cry bust when it's overcast and raining everywhere still at 16z. (Same morning convection is going to leave a mess of boundaries). That said, the low looks strong enough and the deep instability will be lurking close enough by that the WF should make an aggressive jump north along with extremely rapid destabilization.

 

Re: timing, at this point i'd look for initiation with the main show anywhere between RFD and GYY (where as 6/13 was a bit further west)...so depending on how the mesoscale details shake out, there could easily be a line of tornadic sups initiating just outside the metro and peaking right over the population center (easily worst case scenario, most of the recent high end threats have been just west or south of the city center) or initiation just east of the city.

 

Re: storm mode, sups are going to dominate at onset but given the environment, i'd expect the playing field to get crowded relatively quick, so evolution into an MCS might be a bit quicker than some of the shear profiles would otherwise suggest. (which is why the potential initiation right on the western edge of the metro is so concerning.

[cyclone77]

Nice disco from DVN.  They believe the warm front will hang up a bit further to the south, putting the I-80 corridor in the game for later tomorrow...

 

From DVN..

Wednesday 12z, ongoing convection will likely be across the CWA in
close proximity to the warm front. Ongoing severe weather potential
and possible flash flooding event could be ongoing during at 12z.
outflow boundaries will likely litter the warm sector for
afternoon heating and destabilization. H7 temps ranging from 10C
to 14C advect into the area, aiding in capping the warm sector. A
speed max and sfc low are prog to move through the area in the
afternoon. Impressive response in the surface mass fields will
lead to deep layer shear of 50+ knots and llvl bulk shear in the
40 kts region. Model soundings are textbook severe weather for the
area, with backed sfc winds increasing the threat for supercells
and tornadoes. Again, these supercells should grow upscale to a
large MCS with a wind threat for the evening and overnight over
the Great Lakes. The thermodynamic and kinematic fields are in
place for severe weather across the area Wednesday afternoon. Two
parts of this puzzle are less clear. 1. The cap. 2. The position
of the warm front and sfc low. The cap is sufficient to hold
convection in the warm sector at bay for most of the day. With the
speed max and possible ourflow boundaries across the area, think
the cap will be broken, especially along and north of interstate
80 in the current runs. Looking at model soundings, even though
there are warm llvl temps, the high sfc temps will likely lead to
little to no cap. This needs to be looked at closely in later
forecasts. 2., the fronts and low. Models continue to push this
warm front north with ongoing convection. With the lack of a vort
max to pull the low north, think that the current positions of the
low and warm front are too far north. If there are clouds to the
north of the warm front all day, it will be difficult to mix the
front north. However far the front gets tonight will likely be
close to where it will stay during the event. This also needs to
be watched as a change in the low placement and warm front could
mean that we could see a better/worse chance for severe weather.
Hires CAMs are starting to depict isolated cells near 00z across
the eastern CWA. With all of that said, it will be important to
pay attention to future forecasts today and tomorrow about this
system.

[purduewx80]

It seems to me at this point the warm front is going to struggle to get much farther north than DVN to IKK-ish, given persistent warm advective activity through the morning and perhaps early afternoon - which is modeled similarly on a lot of CAMs.  PM initiation will be close to Chicago if not overhead, but I'm thinking more of an extreme hail and heavy rain threat from HP supercells than tornadoes or wind damage in the city proper. Will be a different story for cells that root right along the warm front, where dewpoints should pool in the mid-70s to near 80. 

 

There are still plenty of mesoscale details to sort out, some of which will not become clear until we see how the morning activity plays out.  Still leaning towards 2 or more derechos from Iowa to West Virginia, one Wednesday morning and one Wednesday evening/night. If these details stay similar on today's guidance, I'd expect the northern edge of the mdt risk area to be nudged back south closer to the IL-WI and IN-MI borders.

[A-L-E-K]

catching up on overnight models but something like the NMM is probably the worst/best case scenario for chicago (depending on your preferences) with explosive initiation over S. WI riding SE and dews pooling across the metro area

 

definitely got that messy HP look

 

[Radtechwxman]

I definitely think this could setup a bit further south than what SPC is depicting. If the models are right about the lingering morning MCS that wf will be held south most of the day and may make a slight north movement as low approaches and llj responds. I'm def wanna be near or just south of wherever that wf sets up to get a shot of tornadic supercells early on. As far as the damaging wind threat I can see that materializing near or over Chicago if not further east. Does anyone remember that high risk we had for wind years ago? It took a while for storms to congeal and organize a cold pool. If we keep storms semi discrete in this environment watch out

[King James]

Nice to have a system that has you boys engaged and posting. Looking forward to the discussion and forecasting

 

-edit: Local WGN Met, Mike Hamernik, has first round coming through Chicago between mid morning and lunch time and second round coming through during the evening hours

[CoalCityWxMan]

The new NAM has the warm front further south than before. According to that run, if a supercell can ride the front for a long time, it could take a similar track to how the 6/22/15 cell did...depending on how fast it would evolve into an MCS of course.

[Hoosier]

Doing a dprog/dt as the 12z NAM is rolling in suggests a slight slowing trend in the last few runs.

[A-L-E-K]

4km NAM has initiation very similar (timing and location) to the NMM i posted above

 

Thinking the highest severe threat stays just southwest of the loop/city proper (over the favored local southwest suburban tornado alley into hoosiertown) but it's certainly going to be within striking distance