Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 261921

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
221 PM CDT Sun Mar 26 2017

204 PM CDT


Around sunrise tomorrow the area will be sitting between two
closely spaced low pressure systems, one over Lake Huron and
another moving into southwest Missouri. The low to our northeast
would be the one that was responsible for the wet start to today,
but most of the activity with this system has already lifted
north and east of the area as of mid afternoon. The exception
would be the lingering activity in northwest Indiana and some
isolated showers over Illinois. This too would be expected to
taper off or lift farther northeast along with the departing low
this evening.

Under persistent overcast the area will begin to dry out a bit
overnight as winds turn northwest and dewpoints drop into the mid
40s, but this will be short lived before the upstream low reaches
the area tomorrow. There was some question about fog development
overnight with the relatively light winds, especially given the
recent rainfall, but the overall downward trend on low level
moisture makes this a tougher call. For now we will opt not to
mention fog except in the marine areas, but this will be
something to continue monitoring.



245 AM CDT

Monday through Saturday...

Upper low that provided wet conditions over the weekend is progged
to open up and shift to New England early next week with a brief
lull in precipitation first half of Monday as a transient upper
ridge builds across the Midwest. Meanwhile, water vapor imagery
this morning indicates another upper level disturbance over the
Desert Southwest which will eventually lift across the Plains and
Midwest through the day Monday. A modest surface reflection will
move from Oklahoma late tonight to central/downstate Illinois
Monday afternoon with precipitation overspreading the CWA
associated with a corridor of mid level WAA out ahead of the low.
Soundings indicate fairly shallow moisture this far north with
weak instability only clipping areas east of the I-57 corridor.
This system will quickly depart to our east Monday night with high
pressure building from the Canadian Prairies across portions of
the Upper Midwest Tuesday and Wednesday. Expect dry conditions
during this timeframe but north to northeast winds will suppress
temperatures near the lake front, keeping those areas in the low
to mid 40s while farther inland temperatures warm into the 50s.
Models continue to struggle handling track and timing of low
pressure late in the week. The GFS has a southerly track that
keeps some of the local area dry late in the week while the ECMWF
and GEM lift the low across portions of the midwest which would
result in showers and possibly thunderstorms locally. While the
details are still way out of focus at this distance, the GEM and
ECMWF have been more consistent over the past few days and will
lean on those solutions with at least high chance PoPs late in the



For the 18Z TAFs...

The midday radar shows a few isolated showers across northern
Illinois, with more widespread activity across northwest Indiana.
Trends generally should be on the dry side this afternoon, though
some brief showers certainly are possible. There is even a low
chance of an isolated thunderstorm, but confidence on timing and
location are far too low to warrant mention in the TAF at this
time. As for ceilings, despite some hint of clearing or at least
VFR skies, most locations remain solidly in MVFR and given the low
pressure system parked overhead, that is the favored trend
through the afternoon.

The remaining question is how winds will evolve. A fairly light
gradient has been allowing for some variability in direction so
far today, but the overall flow supports a southwesterly trend
going foward, with turning to northwest overnight and eventually
around to northeast tomorrow ahead of the next approaching system.

Rain and low conditions appear to be on the way again for tomorrow
afternoon. Confidence in timing and exact cig/vsby trends is not
high at this range.



405 AM CDT

Low pressure continues to slowly lift northeast through the mid
Mississippi valley this morning, with more of an easterly wind in
place. This low will move into northern Illinois today, and then
across the lake early this evening. This will provide highly
variable winds over much of the lake today into tonight, however,
do expect speeds to diminish today into tonight. The higher speeds
which provided conditions hazardous for small craft across the
Illinois nearshore have diminished. Higher waves are still in
place, and so have continued the Small Craft Advisory today. Will
monitor for a possible early end time though. Continue to monitor
fog over the south half of the lake, and at this time, it still
appears that the more dense fog is situated over the western
shores of the lake. It does look like this dense fog will continue
for much of today, and quite possibly expanding over much of the
southern half of the lake. Will monitor the possible need for
expansion of the dense fog advisory to remaining areas over the
south half of the lake.



LM...Dense Fog Advisory...LMZ740-LMZ741-LMZ742-LMZ777-LMZ779 until 7
     PM Sunday.




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