Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 201102

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
602 AM CDT Tue Mar 20 2018

328 AM CDT

Through tonight...

Generally quiet, but blustery, weather expected today.

Brisk northeasterly winds should continue through the day today as
low pressure moves through the Upper Ohio Valley while strong high
pressure remains parked over Ontario.  A complex series of
shortwaves over the Middle Mississippi and Upper Missouri Valleys
are spreading increasing and thickening cirrus over the region, but
will, otherwise, have little impact on local weather conditions.
With persistent flow off of Lake Michigan, some increasing lower
level cloudiness is expected across nern IL/nwrn IN through the day
as well as keeping temperatures 5 to 10 degrees below seasonal
normal levels today.  Highs closer to the lake should top out in the
middle to upper 30s, while only reaching the low to middle 40s well
inland.  Lows tonight should be in the middle to upper 20s under
mostly cloudy skies.


328 AM CDT

Wednesday through Monday...

Little change has been made to the going longer term forecast as
general trends remain consistent with previous forecasts.  The
latest longer range model runs continue to indicate a period of dry
weather into Friday night.  Temperatures should remain a bit below
normal through Wednesday, but then trend closer to seasonal normal
levels as the upper level pattern trends more progressive with upper
level ridging moving out of the Rockies and over the Central Plains.

The longer range models are beginning to come into better agreement
on handling the next system to impact weather over the local area,
with low pressure developing over the Central Plains Friday night
and then tracking through the Middle Mississippi Valley Saturday and
then continuing through the Ohio Valley Saturday night and Sunday.
There are still some timing and intensity differences among the
models, but the general track is coming into a little better
agreement with the low center moving through srn IL/IN.  Pcpn is
likely with the system across the entire CWA, with the main concern
being p-type.  Thermal profiles are looking marginal for snow and
much of the pcpn being rain or a rain/snow mix, though there may be
short periods of wet snow during the diurnal min temp hours.  By
Sunday, the ECMWF continues to trend slower with upper ridging
building across the region behind the exiting system, so there is
still some concern that some pcpn could linger into Sunday morning.
there should be a short dry period as the upper ridge quickly moves
across the area, but another wet period looks to be setting up for
Sunday night and into early next week shortwave energy lifts through
developing swly flow aloft ahead of a longwave trough deepening over
the Rockies.


For the 12Z TAFs...

For today and tonight`s aviation forecast, the element of interest
remains the northeast wind speed. There will also be some MVFR
cloud potential.

Gusty northeast flow continues today. Given the gusts have
already been in the mid 20 knot range early this morning, see no
reason why they will not frequently be to that level today, with
some gusts in the upper 20s through early afternoon. Confidence is
highest in the 030-040 degrees direction for today. Late this
afternoon into this evening, some guidance is indicating slight
backing to 020 or even 010 degrees. Winds are likely to be closer
to due north during the Wednesday morning rush but less in speed
than today.

The flow off the lake has developed patches of 1500-3000 ft clouds
per webcam imagery near the lakefront. It is challenging to say
how persistent this will be today. The air temperatures over the
lake are marginal for lake effect clouds but since they are
already being generated, cannot rule out some broken MVFR at ORD
and MDW through Wednesday.



101 AM CDT

Strong northeast flow will continue over the lake today with a
gradual weakening tonight. Gusts to around 30 kt will be frequent
across the south today, and occasional for central and northern
parts of the lake. Frequent wave action to near 10 ft with
occasional higher is forecast today in the Illinois and Indiana

With low pressure deepening off the Northeast U.S. shore on
Wednesday, the winds over the region will turn more due north and
remain somewhat elevated (15-20 kt gusts). This likely will
continue Small Craft Advisory waves, or at least near it, in the
Indiana and possibly the Illinois nearshore through the day
Wednesday. Ridging will then move over the lake during Wendesday
night-Friday bringing quieter conditions.

The next low is expected to move eastward into the Ohio River
Valley this weekend, bringing stiff east to northeast winds once



LM...Small Craft Advisory...IN nearshore waters until 10 PM

     Small Craft Advisory...IL nearshore waters until 4 PM Wednesday.




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