Area Forecast Discussion
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FXUS63 KLOT 012344
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
644 PM CDT FRI JUL 1 2016
211 PM CDT
High pressure is centered across the eastern Dakotas and Minnesota
this afternoon providing fair conditions along with a modest
northerly breeze across much of northern Illinois and northwest
Indiana. A little bit of a lake shadow can be seen on visible
satellite imagery along with some convergence in the winds
stretching from the middle of Lake County, IL south across Cook
County. Northeast flow in place on the east side of the boundary
has kept temperatures in the low to mid 60s immediately along the
lake front with mid 70s in place farther inland. Otherwise, it has
been a quiet day across the region with some afternoon fair
weather cumulus continuing to erode as dry air advects into the
region. Expect skies to go mostly clear this evening and tonight
once the cumulus dissipates. The high center is progged to build
southeast into northern Illinois by the predawn hours and the
ridge axis should settle just to our south during the day
Saturday. Favorable conditions for radiational cooling will be in
place overnight and leaned towards some of the cooler bias
corrected guidance to try to hit the typical cold spots in the CWA
which should cool to around the 50 mark and wouldn`t be surprised
if a couple spots even dipped into the 40s. Most of the Chicago
metro and urban heat island area should hold onto mid even upper
50s though. Expect fair conditions to continue through the day
Saturday with light flow allowing a lake breeze to develop.
Temperatures should warm into the mid to upper 70s with increasing
cirrus streaming overhead.
311 PM CDT
Saturday night through Friday...
The main forecast concerns will center around the potential of
moderate to heavy rainfall over portions of the area Sunday into
A series of upper level disturbances are expected to track eastward
across the Mid-Mississippi valley later in the weekend within a semi-
zonal upper-level flow pattern. Model guidance continues to suggest
that this will help induce and drive an area of surface low pressure
from the Central and Southern Plains across the Mid-Mississippi
valley by Sunday evening. All in all this is shaping up to be a
impressive rain event for some in Illinois and Indiana as a 40+ KT
low-level jet noses into the region by Sunday. With high
Precipitable water values up to around 2 inches, heavy rain will
certainly be an issue Sunday.
The main question, however, continues to be how far north will this
rain get into northern Illinois/northwest Indiana. This is
especially true given there will be relatively dry easterly flow
that will be in place into Sunday as the surface ridge axis
gradually shifts over the eastern Great Lakes region. Ultimately
this could play havoc in how far north the rain does proceed into
Sunday, possibly even resulting in a sharp gradient between areas
with rain and areas with little to no rain. In spite of this, the
latest 12 UTC guidance has shifted the focus a bit farther north
into at least my southern areas (south of I80) Sunday and Sunday
evening. If this pans out, it could be a very rainy and cool Sunday
across my southern areas, with the potential of 1 to 3 inches of
rainfall. Thunderstorms chances look minimal, and likely confined
over far southern sections of the area, if not south of the area
all together, in closer proximity to the nose of the low-level jet.
Following this system it appears that the 4th will be drying out
area-wide and could shape up to be a pretty nice day. High temps on
the 4th look to be around 80, though onshore flow will result in
cooler conditions along the lake.
As we head into next week it still appears that a board flat upper
level ridge will begin to set up over the CONUS. This should help
set the stage for a warming trend through the week as the flow turns
southerly again by Tuesday night. The air mass expected to set up
over the area looks to support temperatures well into the 80s by mid-
week, with some 90s even possible by Thursday and Friday. If this
higher heat pans out, we could also be flirting with heat index
values near 105. However, I have some concerns that this more
extreme heat in the 90s could fail to occur. First, it appears that
the flat nature to the upper ridge will favor a potentially active
period of weather over the Northern Plains and Upper Midwest and is
not out of the question that this could spawn an MCS or two, which
could impact the area later in the week, and impact the magnitude of
high temperatures. Secondly, it appears that a cold front will be
approaching the area by late week, and depending on its timing,
(which could depend on the amount of convective activity) it may
push through and push the heat to our south. All in all, our current
forecast mentions highs near 90, but confidence at this time is
a bit lower than average.
For the 00Z TAFs...
Modest lake induced NE winds will ease at sunset and become
light/variable overnight through midday Saturday before another
lake breeze causes a modest easterly wind again Sat afternoon. VFR
conditions expected through the period.
326 PM CDT
The small craft advisory will continue into tonight as
northerly winds continue to produce waves above 4 ft. Conditions
will improve on Saturday, however, as a surface ridge of high
pressure builds over the southern part of the lake. Light winds
are expected for a couple of days as this high dominates. The
only system of interest this weekend is an area of low pressure,
which is expected to track south of the lake Sunday night. This
low could result in a period of modest easterly winds (~10-20 KT)
along southern Lake Michigan.
IL...Beach Hazards Statement...ILZ006-ILZ014 UNTIL 9 PM Friday.
IN...Beach Hazards Statement...INZ001-INZ002 UNTIL MIDNIGHT Saturday.
LM...Small Craft Advisory...ILLINOIS NEARSHORE WATERS UNTIL 10 PM Friday.
Small Craft Advisory...INDIANA NEARSHORE WATERS UNTIL 4 AM Saturday.
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