6/19-6/23 Severe Weather Risk

[purduewx80]

18Z RPM keeps the warm front even farther south, with no morning convection for Chicago and a miss well to the south in the evening. 

[Stebo]

18Z RPM keeps the warm front even farther south, with no morning convection for Chicago and a miss well to the south in the evening. 

That doesn't make any sense, no morning convection yet the front stalls south?

[HillsdaleMIWeather]

4KNAM now has a pretty decent MCS on it

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[buckeye]

any similarities between tomorrow's set up and the June 29th 2012 derecho?    Now that was a show.

[purduewx80]

That doesn't make any sense, no morning convection yet the front stalls south?

No, the warm advective precip in the morning affects northwest to central IL, holding the warm front farther to the south. It models the derecho from its beginnings near the Quad Cities to maturity near central/southern IN/OH late evening.

[purduewx80]

Point is, there are a wide range of possible solutions on the table depending on what happens overnight into midday tomorrow. 

[RyanDe680]

Flood watch through LOT CWA now

[CoalCityWxMan]

Flooding could be a real issue tomorrow as well. The 4km NAM has been consistently showing scattered areas seeing 4-6" of rain between tonight's convection and tomorrow evenings. Yikes.

[A-L-E-K]

I'd put very little stock in the rpm verbatim

[RyanDe680]

Also a little convection popping up in western IA.

[JasonOH]

any similarities between tomorrow's set up and the June 29th 2012 derecho? Now that was a show.

Tomorrow actually has storms modeled, so that's a major difference.

[Stebo]

I'd put very little stock in the rpm verbatim

Same, it isn't that good of a model.

[chase_stormz]

The DVN afternoon AFD is wow...

 

 

 

Wednesday: The flash flood threat wanes while the severe weather
threat ramps up big time in the afternoon. There is the potential
for a strong tornado or two and possibly long track. Operational
models similar in taking a surface low across central IA in the
morning and then along Highway 20 in the afternoon. The triple
point is expected in that area with backed surface winds ahead of
the low and warm front. A hot and capped airmass will be spreading
over most of the cwa which should limit the severe potential to
mainly extreme northeast IA/northwest IL north of I-80. By mid
afternoon severe thunderstorms should explode near the triple
point with strong deep layer shear, a backed surface wind and
sfc-3km helicity of over 600 m2/s2. Even in the sfc-1km the
helicity is over 400. SBCAPES are expected to be near 4000 J/kg.
With a 500 mb wind of 65 knots and strong shear this increases the
potential for intense supercells and strong tornadoes during the
initial convective development.

[purduewx80]

I'd put very little stock in the rpm verbatim

in general, i agree with this. however, it is good for watching trends. there are no real trends with the past ~6 runs, which have had wildly varying solutions. 

 

the RPM is a slightly varied version of the WRF-ARW, btw. it's going away soon and will be integrated with what is apparently a much more powerful tool from IBM called Deep Thunder. 

[andyhb]

LOT discussion (can someone tell the forecaster that it's "tornadoes" not "tornados):

 

The severe weather event is currently forecast to unfold during the

mid-late afternoon through the evening Wednesday. However...as is
typical with thunderstorm forecasting this far out...the main
challenge forecasting this severe threat later in the
afternoon/evening will be with regards to how much recovery occurs
in the afternoon...along with the placement and behavior of any
residual mesoscale boundaries from the expected morning convective
activity. There are some minor differences in the placement of the
warm frontal boundary...and track of the surface low over the area
Wednesday evening. However...in spite of these slight
differences...there is a general corridor across northern Illinois
into northwestern Indiana...where hires guidance is suggesting that
strong backed surface flow will set up later in the afternoon...in
the vicinity of a surface warm frontal boundary. With strong veering
flow expected within the lowest 1 km...very impressive low-level
shear/helicity...is forecast. Because of this, there is a real
threat of strong tornados over northern Illinois Late Wednesday
afternoon/evening. The main challenge at this range is the exact
placement of this surface boundary as convection develops.

Given that recovery is expected following the morning
storms...storms are expected to redevelop...possibly over or near
north central/northwestern Illinois (near the triple point) by mid
afternoon. With deep layer shear likely to support rotating
updrafts...super cells...with all severe hazards...will likely be
the initial storm mode. With time...expect the storms to begin to
grow upscale into a southeastward moving MCS with Strong damaging
winds...and possible embedded tornados over the area into Wednesday
evening.

[buckeye]

Tomorrow actually has storms modeled, so that's a major difference.

 

true.... the derecho was the most fantastic severe event I had ever personally experienced and I had no idea there was a threat until the sky turned.  

[buckeye]

LOT discussion (can someone tell the forecaster that it's "tornadoes" not "tornados):

 

apparently had the same spelling teacher as Dan Quayle

[Geos]

Flooding could be a real issue tomorrow as well. The 4km NAM has been consistently showing scattered areas seeing 4-6" of rain between tonight's convection and tomorrow evenings. Yikes.

 

Yeah definitely. The ground up this way is pretty dry and hard.

[Geos]

I honestly don't know what to expect, it could be a near miss or a very dangerous situation over here and near the heart of Chicago. We will have to carefully watch the models tonight and tomorrow morning's situation

 

South is probably the way to go, but things could bust with the warm front position. Scary situation for populated areas for the City, western and southern suburbs more so.

[Harry Perry]

GRR discussion pretty bold about the severe weather staying entirely out of the forecast area. Mentioned it a few times. We could use the stratiform rain, that's for sure.

[Hoosier]

EF4/EF5 tornadoes are pretty rare once you get into late June but tomorrow's setup is about as good as it gets to produce one at this time of year, imo. The spatial extent/width where that would be a real possibility probably isn't that large (most likely near the front) and generally speaking, it takes some luck as it needs to hit a structure capable of revealing that type of damage so I'm not saying it's likely or that it will happen, just that there's an elevated possibility. Area to watch would be northern IL and possibly into northwest IN but storm mode is more in question by that time.

[Louieloy102]

MKX adds in:

18Z NAM model run now is trending a little further south with the
low and warm front for the Wednesday afternoon/evening period,
mainly over far northern Illinois. This is following the trend of
the GFS/ECMWF/Canadian models, which have been showing a more
southerly track into northern Illinois.

Thus, it appears that the trend toward a northern Illinois track
seems more likely. However, given how close these features remain to
the area, a little shift back to the north would have a big impact
on severe chances over the area. Some uncertainty with the severe
weather potential still exists as a result.

The 12Z NAMNest is showing convection developing quickly by 00Z
Thursday in the counties along the Wisconsin/Illinois border area,
before sliding southeast into northeast Illinois by middle evening.
The 12Z WRF/NMM and WRF/ARW runs show this development a bit further
to the south in northwest/north central Illinois. This would be near
the triple point.

Given the strong low layer and deep layer bulk shear expected, and
increasing mean layer CAPE, any storms will rapidly become severe
with supercells likely during the afternoon into the evening. The
CAPE is dependent on the clouds moving out of the area from the
morning convection, allowing for decent daytime heating.

Given the close proximity of the expected low track and warm front,
all severe hazards remain possible, including tornadoes, large hail,
damaging winds and heavy rainfall. A strong tornado is possible,
given the related tornado parameters being relatively high in the
southern portions of the area.

The transition to a widespread damaging wind event may happen near
or just to the south of the Wisconsin/Illinois border area in the
evening. Thus, think the Moderate Risk and surrounding risk
categories look good at this time from the Storm Prediction Center.
Keep up with the forecast.

[purduewx80]

GRR discussion pretty bold about the severe weather staying entirely out of the forecast area. Mentioned it a few times. We could use the stratiform rain, that's for sure.

not bold. good meteorology.

[geddyweather]

Short and sweet IWX AFD for Wednesday night as the MCS rolls out of IL:

 

 

 

Sharp wmfntl bndry will focus stg-svr convection wed evening esp
wrn areas in the evening where best overlap of potential
instability/shear parameter space exits. Sig wind damage and
tornado risk appears most present invof of highway 30 south acrs
IN where composite outflw fm morning storms likely to lay out and
interact w/apchg upscale conv line shifting out of IL wed evening.

[weathergy]

Was fun while it lasted. Another tease. Punt.

[Chambana]

That is a gnarly look for LOT.

[Boettger64]

That is a gnarly look for LOT.

Yeah that's looking real rowdy.

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[Geos]

4km NAM late afternoon, storms fire off along the NW tollway.

 

[Harry Perry]

not bold. good meteorology.

Ok then, blunt. Blunt/bold... It all means the same thing. I wasn't implying that it was a bad call. Geesh.

[btcs31]

Sorry if this is OT - mostly a lurker and not an expert.

 

I seem to recall a lot of these big setups for the area are always competing with earlier convection from an overnight / morning system. Is that just coincidence or is it a contributing factor to the afternoon conditions?

 

Recently moved to a location with lots of trees so I now have conflicting feelings about these severe events....