Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 190719
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
219 AM CDT Thu Oct 19 2017

.SHORT TERM...
219 AM CDT

Through Friday...

The stretch of mild October weather will continue, with a fairly
warm day in store on Friday. Current surface analysis depicts a
weak cold front across central Wisconsin. Temperatures are not all
that colder behind the front, but there is significant dewpoint
gradient across the boundary. This front will graze the area
today, providing a wind shift to the north through the morning.
Behind the front weak high pressure will collapse the pressure
gradient which will keep winds fairly light today. With the weak
gradient, there could be a secondary lake breeze surge today, but
will be somewhat masked by the synoptic flow. Satellite pictures
of higher clouds and upper flow being out of the northwest today,
expect some passing clouds and some dip in highs today for areas
north of the front in northern IL.

The high will become reestablished across the Ohio Valley tonight
and Friday. A strengthening upper ridge ahead of low pressure across
the west and increasing southwest low level flow will pump up
temperatures some 15 degrees above normal. Certainly below records,
but still rather warm for late October. Winds will not be as strong
as the past few days.

KMD

&&

.LONG TERM...
219 AM CDT

Saturday through Wednesday...

Saturday still appears to be a fairly nice day across the region in
spite of steadily increasing cloudiness. Mild southwest flow will
continue with some upper level energy spreading in ahead of a deep
upper trough across the west. Some of this energy splits between the
northern and southern jet streams, but there is a pacific origin
surface front that will support a steady blossoming of rain and,
given modestly impressive mid level lapse rates ahead of the front,
even a few embedded thunderstorms Saturday night into Sunday, with
Sunday still holding the better chance for rain.

There are some pretty significant model differences in how each
model handles the eastward movement of the upper trough. The general
idea is a trend toward a cooler and showery pattern given the
influence of a deep upper low, but the way the guidance develops the
precipitation is not all that consistent as a farther western
solution will place the region under more significant rain chances
per the EC/GEM whereas the GFS which is a bit quicker with the
deeper souther track surface low. At this point chances of showers
and slightly below normal highs generally tell the story, but expect
some tweaks to the forecast in the farther extended once a better
sense of the low progression becomes apparent.

KMD

&&

.AVIATION...
For the 06Z TAFs...

There are no significant weather concerns expected through the
period. A surface ridge of high pressure will set up over the area
today, and this will result in light and somewhat variable winds.
However, the winds will likely fall into a more east-
southeasterly direction this afternoon albeit light (below 10 kt).

Otherwise, expect VFR conditions to continue through the period.

KJB

&&

.MARINE...
225 PM CDT

No significant changes to the forecast this afternoon into this
evening, which includes the Gale Warning and Small Craft Advisory.
Southerly winds have increased across the entire lake today,
ahead of strong low pressure to the northwest. At this time, gales
are likely over the north half, with speeds up to 30 kt now in
place over the south half. In the nearshore waters, southerly
winds of 20 to 25 kt are being observed. Expect these trends to
remain in place for the rest of the afternoon into this evening,
with an increasing trend likely becoming more of the trend over
the open waters. This will increase the gales more towards higher
end gales, up to 45 kt. While gales are still not expected over
the south half, occasional gale force gusts are a possibility. As
this low lifts further to the north and an associated frontal
boundary moves across the lake tonight, expect speeds to diminish
across the entire lake especially after the midnight time frame.
However, speeds approaching 25-30 kt may still persist for a time
on Thursday across the north half.

Rodriguez

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...nearshore waters
     until 3 AM Thursday.

&&

$$

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