Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville, Illinois
634 am CDT sun Jul 24 2016
318 am CDT
Feeling much more confident with the today's forecast versus the
past couple of days due to clearer forcing for storms. First things
first, issued a heat advisory for the I-88 corridor south including
Northwest Indiana. Heat indices will reach 105-110 degrees quickly.
On to convection...a few showers are visible over southern LaSalle
and Grundy counties this morning with the rain from the evening mesoscale convective system
shifting east into central and eastern Indiana. Additional
convection over eastern WI and along the Minnesota/WI state line will
remain north of US. The latest CR-hrrr suggests that the convection
over Minnesota will build south and pass over the Illinois/WI state line this
morning. I am not buying this progression because storms are not
building south and storm movement is due east.
Thinking the atmosphere will recover this morning with no precip
expected. Meanwhile the cold front currently stretching from
eastern Minnesota through Iowa will shift east reaching the Rockford area
early this afternoon. The atmosphere should recover enough for
storms to sprout along the cold front. Guidance features cape
around 3000 j/kg, 0-6 km bulk shear of 20-30 kt, and pwats around 2
inches. Steering flow is a bit faster today around 30 kt. Therefore
expecting a scattered storms to develop ahead of the cold front with
a more solid line of storms along the front. Hail and damaging winds
are the main severe threats along with localized heavy rain. Storm Prediction Center
mentions that supercells may be possible in their discussion, but
thinking supercells will be more common to our north in WI where the
shear is greater. The line of storms shifts southeast through
318 am CDT
Monday through Saturday...
Any lingering storms dissipate early Monday morning as cooler and
drier air spread across the region along with high pressure. Have a
dry forecast through Tuesday with high temps only in the mid 80s.
Cooler conditions are expected along the lake.
An upper level wave passes over southern WI and northern Illinois
Wednesday. Thinking the majority of storms will form over WI, so
only have a low chance of storms along the Illinois/WI state line. A
stronger upper level wave arrives late Wednesday night into Thursday
morning bringing showers and storms to the entire region. The
storms should also limit warming Thursday leading to highs only in
the low 80s.
The pattern remains busy through the end of the week with chances of
showers and storms. However, the good news is the cooler temps with
highs in the low 80s continue through late this week as well.
for the 12z tafs...
630 am...thunderstorms are most active across the lake and over
northern Wisconsin ahead of more pronounced upper level
shortwaves. Farther south across Iowa there have been occasional
showers or storms popping up but have been more limited a forcing
is weaker and there is capping in place. We have some instability
available, but feel the capping will hold for much of the area
this morning, though an isolated shower or storm is possible.
Additional thunderstorm development is expected this afternoon
into Sunday evening ahead of an approaching cold front. Coverage
looks to be isolated to scattered so will continue with thunderstorms in the vicinity
mention for now until trends develop. Timing in the Chicago
terminals is around 20-21z based on latest short term convective
allowing models for a few hours. South/southwest winds will gust
to the lower 20s today, with winds easing and shifting to the
northwest later tonight.
252 am CDT
Southwest winds will increase today to around 25 kt ahead of low
pressure that will move east through northern Ontario today. A
cold front behind this low will move south across the lake tonight
with modest northwest winds behind it. High pressure will take
control through mid week with fairly benign conditions across Lake
Michigan. Thunderstorm chances exist today and then return later
in the week.
Sunday to 7 PM Sunday.
In...heat advisory...inz001-inz002-inz010-inz011-inz019...11 am
Sunday to 7 PM Sunday.
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