Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 122012

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
212 PM CST Sun Nov 12 2017

117 PM CST

Through Monday...

Precipitation will exit to the east this afternoon as our compact
and fairly potent upper wave continues into the Ohio valley.
Biggest question for the night is how quickly clouds will clear.
We are seeing a steady erosion of the lower clouds which linger
behind the higher precipitation-producing cloud shield. Light
winds with the high moving in and some recent precip may result in
a little fog. RAP does suggest a gradual thinning of the cloud
shield which may slow some at night, so will continue the general
clearing trend.

Monday looks like one of our nicer days of the week after a gray,
cold, and damp weekend. High pressure across the upper midwest
will become centered across northeast Illinois by Monday mid to
morning before shifting to the eastern Great Lakes region. This
should result in sunshine, light winds, and warmer though still
seasonally cool temperatures. Highs will reach the lower to mid
40s. As the high shifts east Monday afternoon, some increase in
higher clouds is expected.



211 PM CST

Monday night through Sunday...

High pressure expected to still be in place at the start of the
period, but will shift east Monday night into Tuesday. Southerly
flow/WAA will support continued warming trend with highs in the
upper 40s expected Tuesday. However, sky cover will increase
during the day Tuesday ahead of the next system to affect the
region. Next chance of precip arrives Tuesday night into Wednesday
with the approach of a deeper trough and surface trough/front.
All rain expected, and with increasing WAA and instability, slight
chance thunder wording still seems reasonable. Some slight and
brief cooling expected behind this system but once again only
brief, as WAA ramps back up in advance of the next system.

This system looks to arrive late in the work week into the early
part of the weekend. There are still some timing and placement
differences with this anticipated system, however, wet conditions
appearing likely for most locations within the CWA during this
time. Confidence with overall thunder trends still low. However,
did add slight chance thunder mention Thursday night into Friday.
It`s conceivable that at least a narrow moisture/instability axis
could be in place ahead of the strong/dynamic system, with thunder
a definite possibility. Will need to monitor the possibility for
more robust development somewhere in the region, given the
potential strength of the system. Anticipate colder air to move in
behind this system into next weekend.



For the 18Z TAFs...

The main precipitation shield is reaching the Chicagoland
terminals as of 18z. Low level thermal profiles are warm enough to
support rain. As the columns cools a bit some snow flakes will
probably mix in for an hour or so of the increased precipitation
rate. Snow upstream across north central Illinois will wind down
shortly as well with IFR visibilities, and accums possible still
on grassy surfaces.

Ceilings will continue to fall with LIFR across north central
Illinois, and expect MVFR to drop across the Chicago area as well,
possbily getting close to IFR as well.

Confidence on specific clearing times overnight is not super high,
so have kept the overnight clearing in at this point in time.
Variable NE-N winds will shift to NW this afternoon and evening,
though remain fairly light. High pressure will result in calm
conditions on Monday.



211 PM CST

With a relaxed gradient in place, relatively lighter winds have
been in place today. Expect this overall trend to continue into
Monday with the arrival of high pressure. This will change going
into the middle part of the week as winds turn southerly and
increase ahead of the next system to affect the region. The
strongest southerly winds during this time expected to be Tuesday
night. Expect winds to mainly stay at or below 30 kt, however,
will need to monitor the possibility for at least a small window
of gales. Winds diminish after this system departs, but will once
again see an increase by late in the work week. Still some likely
variability with the forecast in the coming days, but at this
time, guidance indicating the possibility for higher end gales.






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