Area Forecast Discussion
Issued by NWS Chicago, IL
FXUS63 KLOT 291130
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
630 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
318 AM CDT
Monday Night through Saturday...
Mild conditions...in the low to mid 80s...are expected to
continue on Tuesday and Wednesday. However...a potent storm system
is expected to move across the Dakotas and Upper Midwest by late
Wednesday. This storm system promises to push a rather decent cold
front across the area by Thursday morning. Cooler conditions in
the 70s are likely to follow for Thursday through Saturday.
Onshore flow on Friday and Saturday could even keep temperatures
in the 60s along the lake shores of Lake Michigan.
While the later portion of the forecast period...particularly
Thursday through Saturday...looks to be mainly dry but cool across
the area...the same cannot be said for midweek...during the
transition period to this cool and drier air mass. The chances for
showers and thunderstorms will be on the increase Tuesday as better
moisture begins to filter in over the area ahead of the storm system
taking shape over the Dakotas and Upper Midwest. However...it
appears the best chances for thunderstorms will be Wednesday into
Wednesday night as the cold front gradually approaches the area. Due
to the fact the deeper layer steering flow looks to be somewhat
parallel to the approaching surface front...there could be the
potential for some training storms and some heavy rain threat given
increasing PWATS. Also cant rule out the potential for a few
stronger storms on Wednesday...though deep layer shear looks
marginal. The threat of storms looks to end by Thursday following
the frontal passage.
For the 12Z TAFs...
Minor aviation forecast concerns this morning include a brief
period of MVFR ceilings later this morning primarily for KRFD...
and breezy west-southwest winds today with gusts 20-25 kts.
Surface low pressure was northwest of Lake Superior this morning
with a trailing cold front moving east across the Mississippi
River. Ahead of the front...clouds had cleared out across the
forecast area in the wake of last evenings showers and
thunderstorms as drier mid-level air had wrapped around an upper
disturbance tracking across the upper Midwest. Satellite and
surface obs did indicate a patchy area of MVFR ceilings over
northeast IA/western WI behind the cold front however...which
model forecast soundings indicate may work into the KRFD area
after about 14z. Diurnal warming is expected to allow the MVFR
bases to rise and scatter prior to moving into Chicago terminals
after 16z. Thus have included a period of BKN 1500-2000 ft for
KRFD this morning. Otherwise...winds will shift southwest and
eventually more westerly as the front moves through and the mixed
layer deepens this morning. West-southwest winds are expected to
gust around 20 kts from mid-morning into the afternoon before
diminishing this evening.
There is some model support for VFR ceiling development overnight
tonight as warm/moist ascent redevelops across the Plains to our
west. Current indications are that any precip/convection should be
focused west/south of the terminals through the period.
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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