Area Forecast Discussion
Issued by NWS Chicago, IL
FXUS63 KLOT 290756
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
256 AM CDT SUN MAY 29 2016
252 AM CDT
The remnants of the line of storms that impacted northern Illinois
yesterday evening has abated to only a few spotty showers entering
northwestern Indiana at this hour. A weak surface cold front will
move across the area this morning. In spite of this cold frontal
passage...temperatures today will not be more than a couple degrees
cooler than Saturday. As such...another day in the low 80s looks in
store for the region. The main difference today will be the
humidity. With dew points in the wake of this front expected to
settle down into the upper 50s...although it will still be mild
today...it will feel more comfortable than Saturday.
Overall I have opted to go with a dry forecast area wide today with
the drier air moving over the area. However...following the passage
of the main upper trough this morning...guidance is suggesting that
another...much weaker mid level disturbance...currently over
NE...will shift eastward across northern IL this afternoon. Guidance
is not suggesting any precip will occur with this disturbance...and
this may very well end up being the case. However...I cant totally
rule out an isolated shower or thunderstorm developing over northern
Illinois later this afternoon...but due to low confidence in this
actually occurring...I have kept a dry forecast with partly cloudy
to mostly sunny skies.
Memorial day looks to be another decent day...though could be a bit
warmer in the middle 80s...especially inland from Lake Michigan.
Weaker westerly winds on Monday could allow for lake breeze
development...and slightly cooler conditions on the lake shores.
There will also be a small chance of thunderstorms over western
Illinois late tonight into early Monday as better moisture tries to
shift eastward atop a surface ridge over the south central CONUS.
This small chance of thunderstorms will extend farther east over
northern Illinois Monday afternoon as diurnal instability builds.
However...it does not appear that there will be much low-level or
upper level support for widespread thunderstorm development Monday
afternoon. However...due to weak capping an isolated storm or two
cannot be ruled out...though I tend to think most areas will stay
204 PM CDT
Sunday night through Friday...
The upper low will dampen and shift east of the region Sunday night.
Broad surface high pressure will form in its wake and bring a
generally drier start to the extended period. A subtle trough/weak
cold front will move through overnight with weak energy sliding
southeast in slightly more progressive WNW flow aloft. Most
guidance is dry with its passage but we cannot rule out an
Memorial Day is shaping up to at least start off fairly nice
and stay that way for most areas in spite some increasing clouds.
After the weak trough passage, a ever so slightly cooler and less
humid air mass will remain in place. To our west warm moist
advection will resume after the gulf of Mexico is temporarily cut
off by the transient surface high. Most of the convection looks to
be tied to daytime heating. Some guidance including the GFS/GEM
attempt to bring some of this into our area. The NAM shoves the
moist air mass south suggesting a better push with the front, and
the EC keeps convection to our west. Given the mixed signals but
favoring a drier solution as is currently forecast, have trended
Model guidance does show a diurnal weakening Monday evening, but
suggests some overnight development again to our west that will
attempt to push into our area into early Tuesday, but chances
remain tempered given the weak ridging, southeasterly drier
surface flow. Better chances for showers and thunderstorms returns
Tuesday through midweek in response to a storm system that will
move east through the Dakotas Tuesday. A warm and humid air mass
will return in the southwest flow ahead of this system with an
undisturbed feed from the gulf of Mexico. Shower and thunderstorm
chances appear highest Wednesday and Wednesday night as forcing
from the low is much closer to the region. Cooler and drier
weather will eventually take hold for the latter half of the week
as a modest cold front shifts in with dewpoints dropping back
through the 50s making it feel comfortably and seasonably cool.
For the 06Z TAFs...
Only aviation weather concerns through Sunday night is a brief
period of showers and possibly an isolated embedded thunderstorm in
the next 1-2 hours for Chicago terminals...then breezy west-
southwest winds through the day Sunday.
Low pressure was over the upper Midwest at midnight...with a cold
front trailing southward across east-central Iowa and into
Missouri. A decaying area of showers and a few lingering
thunderstorms was well ahead of the front across far eastern WI
and eastern IL. Activity has shown a marked downward trend in
lightning over the past couple of hours...with most of the
remaining thunder located in the vicinity of KBMI. An area of
showers roughly from KARR-KJOT-KIKK was lifting northeast...and
will likely bring a brief period of light rain to the Chicago area
terminals prior to about 07z. Once this passes...dry weather is
expected to persist through the remainder of the taf period.
South winds near 10 kts expected for the remainder of the night...
becoming west and gusting 20-25 kt by mid-morning as cold front
moves east across the area and boundary layer mixing deepens after
sunrise. Breezy westerly winds to continue through the afternoon.
254 AM CDT
Marine forecast concerns on Lake Michigan include lingering areas
of fog/dense fog over central and northern portions of the
lake and breezy west winds along the western shore today.
An area of low pressure will move north of Lake Superior today...
with a trailing cold front pushing east across Lake Michigan this
morning. South winds gusting around 20 kt will eventually turn more
west-southwest behind the front later today...though relatively warm
air over cool lake waters will maintain a very shallow and stable
marine boundary layer. This will keep stronger winds from mixing
down near the water surface...though westerly winds will gust 20-25
kt within a couple miles of the IL/WI shores on the west side of
the lake. It will remain fairly humid over the lake because of the
shallow mixing...with areas of fog expected to persist during the
day especially on the central and northern portions of the lake.
Fog should become more restricted to the eastern shores of
central and northern lower Michigan by tonight however...as winds
turn more west-southwest. Showers and a few thunderstorms may
linger across the northern parts of the lake through the day
too...as an upper disturbance moves through the region.
Relatively quiet weather is expected Monday as high pressure
drifts across the lake. Another low will track across the
northern lakes Tuesday through Thursday. Thunderstorm potential
will return especially late Tuesday and Wednesday as an associated
cold front moves through. South winds will increase to 15-20 kt
ahead of the front Wednesday...eventually turning west-northwest
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