Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 230825

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
325 AM CDT Sun Oct 23 2016

300 AM CDT

Through Monday...

Sunny, windy, and unseasonably mild conditions are on tap for
today. Models generally prog 925mb temps to climb to around +15C
which would support highs around 70. Forecast soundings this
afternoon indicate that the boundary layer will mix up into the
25-30kt southwesterly flow just off the deck, so gusts to 30 mph
this afternoon are a distinct possibility. Cold front will move
through the region tonight with little fanfare. Behind the front
winds will shift to the north allowing cooler (more seasonable)
temps to filter into the region to kick off the work week, but
still with abundant sunshine.



300 AM CDT

Tuesday through Saturday...

Attention by Tuesday will quickly turn to the rather sharp
shortwave trough forecast to amplify as it tracks east into our
region by midweek. Warm frontogenesis will take place in advance
of this wave with guidance consistently breaking out WNW-ESE band
rain in the strengthening WAA regime. Have seen some run-to-run
waffling of the medium range guidance with respect to the exact
track of this system and location of where the WAA wing of precip
sets up. Latest guidance suggests most likely location of WAA
breaking out over southern WI into far northern IL later Tuesday
and especially Tuesday night as LLJ strengthens nocturnally.

Track of the surface low Wednesday will dictate how potentially
crummy of a day weather-wise Wednesday will be. The ECMWF/GEM have
trended farther north with the surface low track which would place
most of our CWA in the warm sector Wednesday, which would mean
largely dry weather with just some showers and perhaps t-storms
late as cold front moves through. The GFS tracks sfc low across
downstate IL and would keep CWA socked in with steady rain through
the day in the WAA wing then deformation zone of the system. The
GFS solution would likely mean highs barely reach 50 in the rain
over northern CWA, while the ECMWF/GEM solution would support
highs in the 60s in the warm sector. Will need to watch trend in
guidance the next day or two and will fine tune forecast as it
becomes clearer where this low will track.

In the wake of this midweek system look for seasonable temps and
dry conditions for the end of the week. Some decent size
differences in handling of potential northwest flow shortwave
which could bring some rain to the area in the Friday night
through Saturday night time frame. Medium range models haven`t
shown great run-to-run consistency and some big differences in the
amplitude of the wave exists between the ECMWF (more amplified)
and the GFS/GEM (weaker/less amplified). Blended model
initializations in the grids came up with very low pops and given
low confidence saw no reason to make any big adjustments one way
or the other for now.



For the 06Z TAFs...

VFR conditions in place this morning will likely persist through
the period. Do expect a front to move through the area later
today/evening with a possibility for a period of VFR or MVFR
ceilings. However, with low confidence, have left out at this
time. Light southwest winds will steadily increase later this
morning, especially early this afternoon when gusty conditions
are expected. With FROPA, winds will turn north northwest.



311 AM CDT

A ridge of high pressure centered over the central Great lakes
will shift to the east today as low pressure over the northern
Plains quickly moves southeast to southern Lake Michigan this
afternoon. With these two surface features moving through the
region today, expect widely varying wind directions and speeds. It
does appear that the strongest winds will initially be over the
southern end of the lake and nearshore waters for much of today.
With these higher winds, hazardous conditions for small craft will
develop this afternoon. This low will then quickly move east of
the lake tonight with winds shifting more northerly tonight into
Monday. Higher speeds of 15 to 25 KT and even 30 KT winds/gusts
will help waves build, with hazardous conditions for small craft
continuing tonight into Monday morning. Have issued an advisory to
cover these hazardous conditions today through Monday morning, but
could possibly see higher waves lingering slightly longer over the
Indiana shore on Monday. Winds will then diminish with building
high pressure Monday night into Tuesday. Next area of low pressure
expected to move towards the lake through mid week with higher
winds and waves returning. Will continue to monitor this period as
gales are still appearing possible on Wednesday.






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