Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 230800

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
300 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.




217 pm...A ridge of high pressure will move east of the lake this
evening as low pressure over the western Dakotas moves east and
crosses Lake Michigan Sunday afternoon. As high pressure builds
across the northern plains Sunday night...the gradient will
tighten behind this front with northerly winds increasing up to 30
kts quickly Sunday evening. The high will settle over the lake by
Monday evening with northerly winds steadily diminishing Monday.

Another area of low pressure will develop over the central plains
Tuesday and move east Wednesday...crossing southern Lake Michigan
Wednesday night into early Thursday morning. Strong easterly winds
are expected to develop Tuesday night into Wednesday as this low
approaches. Gale force winds are possible...especially over
southern portions of the lake. Winds will shift northerly and then
northwesterly as they diminish...behind the low as it departs. cms





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