Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 212337

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
637 PM CDT Fri Oct 21 2016

235 PM CDT

Through Saturday...

High pressure continues to nose in from the west this afternoon.
Cloud cover across northwest Indiana and east Central Illinois is
a result of lake effect process with additional diurnallly driven
clouds moving in from the northwest. Lake effect rain showers
continue to shift east of the area though still remain possible
along the lake and on the Porter/Laporte county border and
eastward. Convergence in observation is decreasing as a boundary
from the northwest moves southeast and is scouring out the
easterly component to winds over the lake. There have been a few
funnel cloud reports over the southern tip of the lake today, but
no reported waterspouts. Will maintain the mention this afternoon
across the nearshore but then with expected decrease in lift and
more uniform wind field the threat will shift east and diminish.

Expect that this lower cloud field will erode after sunset with
the exception of lingering lake effect clouds in nw Indiana. With
warm advection aloft we will have some mid and higher clouds
rolling through tonight. In spite of high pressure leading to some
clearing and light winds, have held off on a frost advisory
tonight with the uncertainties in cloud cover as temperatures are
forecast to be in the 34-38 degree range for most areas away from
the urban corridor. Therefore, patchy frost is possible with
local areas of frost in any sheltered areas and could be more
widespread if clouds are thin.

High pressure will shift east Saturday and return southwest flow
will allow for a mix of sun and some clouds with highs back near
normal - upper 50s to low 60s, warmest southwest.




Saturday night through Friday...

216 pm...Two main forecast concerns this period...first high temps
Sunday with a cold front late afternoon/early evening...second is
precip/thunder chances with a storm system middle of next week.

High pressure will be departing to the southeast Saturday night as
low pressure moves from the Dakotas Saturday night to lower MI by
Sunday evening. A trailing cold front will move across the area
Sunday afternoon into Sunday evening. Timing of this front will
have a large impact on temperatures...with possible quickly
falling temps behind the front but also how warm temps rise Sunday
afternoon. Ahead of this front...temps will warm well into the 60s
and some lower 70s are also possible especially across the
southern cwa. Possible front may accelerate down the lake into
far northeast IL with a wind shift more off the lake. An earlier
arrival would limit how much high temps rise across the north.

A fast moving high pressure will build across the area Monday into
Monday night with high temps Monday/Tuesday near seasonal levels...
upper 50s/lower 60s. Another low will develop over the central
plains Monday and Tuesday and move across the area Wednesday
afternoon into Wednesday night. This timing and track has been
fairly consistent for several runs now. There is a chance of
precip along a warm front Tuesday afternoon/Tuesday night which
sets up mainly over southern WI...possibly affecting far northern
IL. But the bulk of the precip will hold off until Wednesday and
Wednesday evening as the low moves across the area. Chance of
thunderstorms also likely Wednesday along with gusty southeast
winds as the low approaches. Flow quickly turns back southerly
Thursday night into Friday with high temps possibly remaining in
the 60s for the end of the week. cms


For the 00Z TAFs...

High pressure is moving across the midwest while low pressure sits
off of the Atlantic coast. Wind direction is nwly arnd 10kt, but
will diminish and back to swly overnight and into tomorrow
morning. Expect that the VFR deck arnd 5-6 kft will erode and
diminish through the night and operationally insignificant cloud
cover will prevail through tomorrow. The lake effect cloudiness
will also diminish at GYY as winds turn swly.



216 pm...Northerly winds will slowly diminish tonight into
Saturday as a ridge of high pressure approaches the lake tonight
and moves over the lake Saturday. Winds will then turn west/
southwest ahead of low pressure which will move across the lake
Sunday afternoon. This low will be absorbed by stronger low
pressure over Quebec Sunday night but strong high pressure will
build across the plains Sunday night and then across the Great
Lakes region Monday. The gradient will tighten Sunday night with a
brief period of northerly winds to 30 kts possible...mainly on the
south end of Lake Michigan. These northerly winds should steadily
diminish Monday as the high moves across the lake. Another low
will move from the central Plains Tuesday to southern lower MI
Thursday. Southeast winds will increase as this low approaches and
may reach 30 kts on Wednesday. Winds will then shift to the north/
northeast Wednesday night into Thursday as the low shifts east.


LM...Small Craft Advisory...INDIANA NEARSHORE WATERS UNTIL 4 AM Saturday.

     Small Craft Advisory...ILLINOIS NEARSHORE WATERS UNTIL 7 PM Friday.




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