Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 252318

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
618 PM CDT Wed Apr 25 2018

237 PM CDT

Through Thursday...
Surface high pressure stretching from the southern High Plains to
James Bay will settle into the local area overnight. The breezy
northeasterly winds of this afternoon will diminish early this
evening. Expect that temperatures will drop off into the mid 30s.
Am thinking that some of the typically cold areas will see lower
temps than that. With current dewpoints running in the low 30s
will use that as a starting point for the corridor from Rochelle
to Aurora to Kankakee but would not be surprised if a few of these
spots fall below 30 overnight. Winds will be lighter and generally
from the southwest Thursday allowing for temps to recover into the
mid 60s as the high settles south. A lake breeze is likely so
lakeshore areas will only see highs in the 50s. An influx of high
clouds ahead of the next disturbance will arrive for the afternoon
which may keep the lake breeze from working too far inland.



309 PM CDT

Thursday night through Wednesday...

Overview...After a couple of cold fronts, a summer-like warm up is
expected early next week.

A cold front moves through the forecast area Thursday night, and
guidance continues to back off on how much precip will accompany the
front.  I lowered precip chances to slight chance, and I`m not
expecting much rain.

Another cold front and weak low pressure system move through Friday
afternoon/night, and the low could bring a better chance of rain
possibly storms.  Precip is possible northeast of a Dixon to
Rensselaer, IN line with the best chances over the Chicago Metro.  I
kept thunder chances confined to over Lake Michigan, but there`s a
low chance that an isolated thunderstorm could occur over the metro.

Cooler temperatures follow both cold fronts, especially the second
front Friday. On-shore flow will keep lakeside temps cooler Friday
through the weekend.  The coolest day looks to be Friday with lake
side temps in the 40s, and highs in the 50s away from the lake.

High pressure shifts east allowing gusty south winds bring warmer
air to the region early next week. I bumped up high temps, but kept
them lower than what raw model guidance would suggest. 70s are
likely Monday and 80s are possible Tuesday. Increasing cloud cover
may limit warming Tuesday.

Showers and storms are possible mid week, and the ECMWF is quicker
to bring showers into the forecast than the GFS.



For the 00Z TAFs...

Concern is on wind direction and lake breeze on Thursday. High
pressure over the lake will weaken this evening and reduce the
onshore gradient. There is enough of a gradient to support winds
around 9-11 kt for a few hours, but NE winds will slacken and
even go light and variable overnight as high pressure becomes
centered overhead. Weak southwest winds will develop overnight
into Thursday, with a modest increase during the day. A lake
breeze will develop, but at this point most guidance does keep it
east of ORD and MDW, though some guidance does bring it close to
MDW. No guidance is showing a strong surge, but MDW could flop to
more of SE for a brief time later afternoon. A cold front will
approach toward the tail end of the 30 hr TAF cycle (late Thursday
evening) with a sharp shift to a NW wind.



309 PM CDT

North winds will continue to diminish through this evening as
high pressure builds overhead. High waves and hazardous conditions
for small craft in the Illinois and Indiana nearshores will
continue into this evening. After brief southwest winds Thursday,
another cold front will drop over the lake Thursday night with a
push of north winds to 25-30 kt behind it. Yet another cold front
will push through Friday night, though with weaker northerly winds
behind it. Winds become south Sunday into next week. Small craft
advisory conditions are probable in the Illinois and Indiana
nearshores during the days Monday-Wednesday with gusty offshore



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

     Small Craft Advisory...IN nearshore waters until 1 AM Thursday.




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