Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 171738

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1138 AM CST Fri Feb 17 2017

954 AM CST

Have upped already forecast record high temperatures for today
another 2-3F degrees across most of the area. The 925mb
temperatures of 13-14C observed on 12Z morning soundings
correlates to lower to mid 60s areawide on local climatology and
upstream conditions yesterday. Well-performing short range
guidance this week is also indicating mid 60s over most of the
western/central/southern CWA.

Dew points have increased a tad early this morning but should
flatline in the mid 30s and then drop into the lower 30s per
mixing current soundings, with minimum humidity falling out near
35 percent. Afternoon wind gusts of 19-23 mph are expected. These
conditions are closer to critical fire weather conditions but we
look for humidity under 25 percent. Nonetheless, the first of
these types of the days in the spring /or winter in our case/ can
sometimes catch some off guard.



248 AM CST

Through tonight...

Didn`t make many changes to the going forecast as near to possibly
record breaking warmth is expected today. High temps will soar
into the low 60s after a warm front surges north this morning.
Southwest winds will gust to around 20 MPH. Low temps will be
around 40 tonight.



248 AM CST

Saturday through Thursday...

Above normal temps continue into early next week. However, a lake
breeze is expected Saturday and Sunday, and temperatures along the
lake will fall into the 50s if not upper 40s Sunday thanks to cool
lake temperatures.

A low pressure system forms over the northern plains Sunday night
and lifts to Hudson Bay Tuesday night. The low`s cold front is
progged to bring rain to the region Monday night into Tuesday
morning.  Winds remain southwest, and there isn`t a significant cold
push behind the front. Highs on Tuesday will be in the upper 50s to
low 60s.

Zonal flow sets up aloft keeping systems to our north and south
through the middle of the week.  Blend of models kept a chance of
rain in the forecast for Tuesday night, but currently only one model
is featuring precip at that time. Lowered precip chances across much
of the area and have low confidence in precip occurring.

The next strong low forms over the plains Thursday and travels over
the forecast area late next week.  Will keep an eye on this system
due to it`s dynamic nature. While it`s much too early to discuss
specifics, models suggest thunderstorms may be on the horizon.

Outside of lake breezes, high temperatures remain in the 50s to 60s
throughout the forecast period. Low temps vary from the mid to upper
30s Saturday night to near 50 Monday night.



427 AM CST

We will be heading into an unseasonably warm stretch of weather with
near to possibly record breaking warmth at times. Here are some
statistics on daily records, and consecutive days of 50+, 60+ degrees.


Chicago:                         Rockford:
      High:      High Min:       High:      High Min:
2/17: 60 (1880)  42 (1890)       59 (1981)  39 (1961)
2/18: 62 (1981)  45 (1981)       58 (1981)  38 (1997)
2/19: 65 (1930)  51 (1994)       63 (1930)  42 (1994)
2/20: 64 (1930)  49 (1930)       61 (1983)  46 (1930)
2/21: 67 (1930)  47 (1930)       64 (1930)  42 (1930)

For more, see our web top news headline or Public Information



For the 18Z TAFs...

The weather pattern provides limited concerns and those are only
low-level wind shear tonight and the possibility of a lake breeze
Saturday afternoon.

Southwest winds will show more gusts beginning by 19Z as mixing
deepens. The pressure gradient remains strong enough this evening
to keep surface sustained speeds at 10-12 kt though gusts should
be more sporadic. A stout southwest low-level jet is forecast to
develop tonight with 40-45 kt forecast between 700-3000 ft. Given
the jet within a 1000 ft of the surface and surface speeds easing,
have included LLWS in the TAFs for late this evening into
overnight. This should ease quickly during the pre-dawn hours as
the jet translates east of the area.

Westerly surface winds on Saturday will be less in speed than
today`s winds, presenting the potential for lake breeze
development Saturday afternoon. However, we expect enough of an
offshore component in the wind to keep the lake breeze close to
shore, thus not forecasting a wind shift at the TAF sites.



148 AM CST

Southeasterly winds of 10 to 20 KT over the lake early this
morning will gradually veer southerly during the day today as a
warm front shifts northward over the lake. A period of
southwesterly winds are then expected to set up over the lake
tonight before a weak cold front shifts over the lake early
Saturday setting up light westerly flow. Wind speeds look to
abate Saturday afternoon over southern Lake Michigan as a surface
high approaches the western lakes, and this could allow the
afternoon winds on southern Lake Michigan to turn onshore as a
lake breeze tries to develop.

The main period of potential higher impact winds and waves during
the period looks to be Monday and Monday night. During this
period, some strong southerly winds, potentially up to 30-35 KT
will be possible as a storm system shifts northward into south
central Canada. Following this, it appears the weather pattern
could get more active later next week, and this could result in
another potent storm system impacting the Great Lakes region late
in the period.






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