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Feb 28th - March 1st Severe Weather Outbreak


andyhb

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Following this loosely, hate to sound like a downer, but my confidence is low in anything directly for the Chicago metro. It's been cloudy, cold and windy all day in my area. I feel well south of here towards Champaign it will be a different story. 


As I mentioned before, destabilization is advection driven, meaning you don't need sun. With the warm front lifting into the area, the entire LOT CWA is at risk for scare.

And lol at temps around 60 being cold...let alone in Feb.
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4 minutes ago, buckeye said:

ILN :  Haven't seen a discussion like this in some time....just a portion:

 If storms come
through while still somewhat elevated, the tornado threat would
be reduced. However, if the boundary layer warms/saturates and
allows for surface-based parcels, the tornado threat could be
significant. Thus, this will be a crucial part of mesoscale
analysis going through the evening. Shear profiles of this
magnitude do not frequently combine with perfectly favorable
low-level thermodynamics, but when they do, the results speak
for themselves. This is the biggest potential threat that will
have to be examined tonight into Wednesday morning -- a
conditional not-just-low-end tornado threat, combined with a
slightly greater level of confidence in large hail potential,
and some attendant damaging wind potential as well (depending on
boundary layer destabilization). 
.........

In terms of messaging, it is very important to get the word out
that these threats will be occurring at non-standard times,
continuing through the night, and quite likely into Wednesday
morning (details of which are covered below). Given that there
is a risk of severe weather that may be greater than just a
low-end marginal event, it is crucial for people to have ways
of receiving warning information during the off-typical-peak and
extended hours that this severe weather may occupy.

Yeah, not liking how this is shaping up; when I expect things to moderate a more balanced direction...they come out with the FD of the decade compared to the minimal version they constantly put out....concerning....and in the f-ing middle of the night? no thank you.

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29 minutes ago, Chicago Storm said:


As I mentioned before, destabilization is advection driven, meaning you don't need sun. With the warm front lifting into the area, the entire LOT CWA is at risk for scare.

And lol at temps around 60 being cold...let alone in Feb.

Yeah, just need a bit more warming and if dews can get to around 60, the tor threat goes up dramatically.

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LOT should be firing off frequent mesoscale updates

 
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
349 PM CST Tue Feb 28 2017

.MESOSCALE DISCUSSION...
349 PM CST

Convection has been developing and steadily intensifying over
eastern IA and northwest IL. Both ILX and DVN afternoon special
soundings indicated a formidable capping inversion. Continued low
level theta-e advection combined with increasing ascent has been
gradually eroding the cap and given intensity trends, its likely
storms are solidly surface based.

Over our western CWA, surface obs show slightly cooler temps and
slightly lower dewpoints, so current environment is possibly a bit
less favorable for surface based storms now. Short range guidance
continues to forecast environment to quickly improve and will
likely grow increasingly favorable for maintaining storms over
western IL as they move east. Given their fast movement, it is
possible they could eventually outrun the better air as they get
east into NE IL, but that is still a couple hours out and we`ll
need to closely monitor.

Given the favorable instability and extremely strong deep layer
shear profiles would anticipate a continuation of the transition
of this activity to supercellular. Strongest low level shear
profile is over central and north central IL, with the current
best co-location of most favorable low level shear and instability
over north central IL, mainly south of I-88. This would suggest
that in the next couple hours the highest tornado threat would
exist with the storms developing from Bureau Co southwest to near
Burlington, with the highest short term threat likely to spread
into LaSalle and Livingston Counties.

Large hail, damaging wind, and perhaps a tornado risk cannot be
ruled out north of this area into Ogle and Lee Counties in the
next couple hours, but the greatest area of concern appears to be
LaSalle and into Livingston Counties. Extrapolation of storms
moving into Bureau County suggest the threat should move into
LaSalle County toward 430 PM.


Izzi
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