Area Forecast Discussion
Issued by NWS Chicago, IL
FXUS63 KLOT 172340
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
640 PM CDT Mon Oct 17 2016
228 PM CDT
Surface low centered over the mid-Missouri Valley this afternoon
continues to result in strong southerly flow across northern
Illinois and northwest Indiana. Forecast soundings are a bit
divided between the various models on what degree we decouple
this evening, but either way breezy conditions should continue
through the overnight hours and decent chance we see gusts
of 25 to 35 mph continue through late tonight. Breezy conditions
along with unseasonably moist air mass with dewpoints in the mid
60s will help keep temperatures propped up overnight with lows in
the low to mid 60s northwest near the Rockford metro to near 70
south of I-80 for east central Illinois and northwest Indiana.
Meanwhile, a strong upper jet punching from the west coast across
the Rocky Mountains will continue to translate east with an
amplifying lead shortwave trough lifting across portions of the
upper midwest overnight. This will result in strong surface
cyclogenesis across Wisconsin and the Great Lakes tonight, with
the low lifting to near James Bay midday Tuesday. A trailing cold
front should push across the Rockford area around sunrise, and the
Chicago metro area by mid to late morning. Could see an increase
in stratus in the WAA out ahead of the front, but very poor
mid/upper level lapse rates and fropa occurring at diurnal min
will not be conducive for any precip. Also, there is not a sharp
contrast in air masses with this front, and it looks like
temperatures will continue to run well above normal behind the
front. Expect highs in the low to mid 70s north of I-80 and mid to
upper 80s south with a few spots touching 80.
256 PM CDT
Tuesday night through Monday...
The current 140 knot jet oriented west to east from northern
California to southern Minnesota will transfer eastward to southeast
Canada by Wednesday and fragment into more of a trough pattern
across the center of the US for the middle of the week. A cold
front will be draped across the Middle Mississippi Valley into the
Ohio River Valley, but will remain parallel to the upper flow.
This will allow the front to become stagnant through the middle of
the week and may just provide some light showers across central
Illinois/Indiana. A surface low does appear to re-emerge in the
right rear flank of the jet stream (southern Illinois) Thursday.
That feature will be further amplified by the deepening
approaching trough, but that would just bring a glancing blow of
showers to southeast portions of the CWA. That feature will be the
main threat of precipitation for the next five days.
As far as temperatures go, northern Illinois will see fluctuations
back down to near normal as the afore-mentioned upper trough makes
its way to the region. A couple of weakly-forced cold fronts and the
associated air masses will also support northerly winds and cool
things down from the current near-record values. Looking past
Saturday, the latest model suite indicates a ridge pattern will
set up warmer temperatures once again for the extended period.
325 AM CDT
Record/near record high minimum and maximum temperatures are
possible Today and tonight based off the current forecast. Below
are the current records that could be threatened.
Record High Min for Rockford: 65 in 1968 (*Tied yesterday*)
Record High Max for Chicago: 86 in 1950
Record High Max for Rockford: 87 in 1950
Record High Min for Chicago: 63 in 1998
Record High Min for Rockford: 61 in 1998
For the 00Z TAFs...
Main concerns this forecast period will be with the persistent
strong southerly winds and LLWS this evening, and with FROPA and
possible MVFR ceilings Tuesday morning. VFR conditions in place
at this time and expected to persist, with dry conditions likely.
However, there does appear to be a window of MVFR ceilings Tuesday
morning post FROPA, and did include during that time. Despite
strong winds and gusts this evening, even stronger flow aloft will
still allow LLWS to be present. Winds turn west and northwest on
Tuesday, but with speeds diminishing throughout the day.
246 PM CDT
A warm front lifting through northern Lake Michigan has helped
create some instability across land portions of Wisconsin and Upper
Michigan for the afternoon. This instability will help for
thunderstorm development through the evening as low pressure draws
nearer to northern Lake Michigan. Thunderstorms will track eastward
across northern portions of the lake through the evening. In
addition to the thunderstorm threat, winds are expected to reach
close to gale force associated with a trailing cold front that will
cross the lake overnight. While there is a threat for some 35 knot
wind gusts, the short threat window precludes a gale warning at this
time. Southwest winds will turn more west-northwesterly behind the
front overnight with winds and weather subsiding for daytime
Tuesday. Waves over 4 feet will be possible until they wane in the
afternoon hours Tuesday. Benign marine conditions are expected for
the remainder of the week with winds generally northerly under 25kt.
LM...Small Craft Advisory...NEARSHORE WATERS
UNTIL 10 AM Tuesday.
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