Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS63 KLOT 260748

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
248 AM CDT Thu Apr 26 2018

210 AM CDT

Through tonight...

Another quiet weather day is in store across the area as a surface
and mid-level ridge slowly exit to the east. Expect mostly sunny
skies this morning to give way to filtered sunshine this afternoon
as widespread cirrus spread across the area. Temps today will be a
few degrees warmer than on Wednesday, with mid to upper 50s along
the immediate Lake Michigan shore to the mid 60s inland.
Additionally, with rather dry conditions aloft, daytime mixing
should produce minimum RH values of 25-30% across much of the

A cold front and associated mid-level trough axis extending from
Hudson Bay to the central High Plains will track southeastward
across the CWA during the early morning hours Friday. Given a very
dry antecedent air mass and limited deep forcing, only some very
isolated light showers/sprinkles are expected for an hour or two
along the front. Otherwise, conditions will be mostly cloudy with
NNW winds gusts of 20 mph to possibly 25 mph overnight.



244 AM CDT

Friday through Wednesday...

Amplified upper level pattern in place will bring large
temperature swings during the extended timeframe. Initial cold
front that pushes across the region Thursday night into Friday
should pass through mainly dry given the unfavorable diurnal
timing. Expect a modest cool-down with the first front. North
flow through the day Friday will keep temperatures in the upper
50s to low 60s across northern Illinois and northwest Indiana,
except for low to mid 50s near the lake with onshore flow through
the day. Meanwhile, a vigorous shortwave will dig into the western
Great Lakes Friday afternoon and evening bringing a reinforcing
shot of cold air. Steep low level lapse rates will be in place
with passage of the upper level disturbance which should allow for
scattered showers to form and couldn`t rule out an isolated low-
topped thunderstorm or two as well. Cold air mass behind the front
will push across the Ohio Valley Saturday encompassing the entire
midwest. Locally, expect highs only in the low to mid 50s for
much of the CWA, but again cooler by the lake with persistent
onshore flow that will limit temps in the 40s. An expansive
surface high will build across the Upper Midwest on Saturday
resulting in a modest northerly breeze locally, but otherwise
expect dry and sunny conditions.

By Sunday, surface high will build southeast towards the Ohio
Valley with winds flipping to southwest across the CWA which
will help moderate temperatures closer to, but still likely below
the seasonal norms. This begins to change as we head into the
upcoming week, though, as strong upper ridge translates east
across the plains into the Great Lakes. Low-mid level flow
increases out of the southwest as this transition occurs which
will transport an increasingly warm and moist air mass into
portions of the Midwest. After a warming trend with nice weather
Monday into at least part of Tuesday when temperatures could top
out near the 80F mark, a more active pattern sets up midweek.
Surface high settles over the southeast allowing ample gulf
moisture to stream north into the midwest. Meanwhile, a series of
shortwaves rounding the base of the upper trough over the
southern plains and lifting into the mid/upper Mississippi Valley
will result in periodic chances for showers and thunderstorms. Way
to early to get into the details with these low amplitude waves,
but large scale pattern does look stormy with potential for strong
to severe storms in or near the local area.



For the 06Z TAFs...

VFR conditions are expected through this evening at all sites. Light
winds will become SW less than 10kts this afternoon as a surface
ridge shifts to the east. A lake breeze may move far enough inland
to briefly reach MDW early this afternoon before increasing SW winds
push the lake breeze east of the terminal by late afternoon. A cold
front will then reach RFD late this evening and ORD/MDW during the
early overnight hours Friday, bringing a period of gusty N winds and
MVFR ceilings. An isolated -SHRA will be possible for an hour or two
with the cold front passage.



244 AM CDT

Light flow is in place across Lake Michigan this morning under
the influence of high pressure just south of the lake, but
southwest to south winds will gradually pick up through the
afternoon ahead of an approaching cold front. The front will sweep
down the lake this evening and overnight leaving north winds
gusting to 30 kt in its wake. Conditions appear briefly close to
small craft criteria late tonight into early Friday, mainly for
the Indiana nearshore zones where the fetch is longest, but will
not hoist any headlines at this time. A stronger cold front will
push down the lake Friday evening and night and will provide
another period of north winds gusting to 30 kt that will gradually
ease through the day Saturday. A small craft advisory will likely
be needed for this time frame. Winds should diminish later in the
day Saturday as high pressure builds towards the region and
remain light on Sunday.






WWW.YOUTUBE.COM/NWSCHICAGO is the U.S. government's official web portal to all federal, state and local government web resources and services.