Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 221840

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
140 PM CDT SUN MAY 22 2016

138 PM CDT

Through Monday Night...

Sunshine and warmth will be the main story in the near term as high
pressure is sprawled across the Great Lakes and portions of the mid
to upper Mississippi Valley. The ridge axis is centered just to
our north this afternoon allowing a light northeast breeze to keep
the lake front cooler while temperatures inland warm into the low
80s. The ridge axis will slide to our southeast overnight
allowing southerly flow to overspread the forecast area tomorrow.
Temperatures tomorrow are expected to be similar to today...except
the warmth should spread across much of the Chicago metro with
south flow. Parts of Lake County and northern Cook County will be
the main areas of concern where an afternoon lake breeze will
keep temperatures cooler.

Monday night...low level jet ramps up across portions of the mid
Missouri Valley which will be the focus for initial nocturnal
convection.  As the low level jet veers late into the overnight
hours...several models indicate that convection will spread into
northwest and north central Illinois late Monday night. With the
main instability axis focused well to our west and veering/weakening
low level jet by the time precip approaches the local area...would
anticipate any convection to be weakening if and when it enters the
CWA. Maintained some slight chance/low chance PoPs mainly along and
west of the I-39 corridor and focused them towards the pre-dawn
hours early Tuesday morning.




Monday night through Saturday...

300 am...The high will slowly move southeast Monday night into
Tuesday as an upper wave approaches the area late Monday night
into Tuesday morning. This has been a fairly consistent feature
but there still remains uncertainty regarding precip coverage and
timing. Added slight chance for the far west late Monday night.
But as has been seen in the models...its possible this activity
lifts northeast Tuesday morning leaving much of the area dry. Too
much uncertainty to remove low chance pops for Tuesday...but if
trends continue Tuesday could end up mainly dry for much of the

Low pressure forming over the southern plains Tuesday lifts
northeast to the upper midwest Wednesday and Wednesday night and
during this period appears to be a better chance of showers/
thunderstorms and if things are slower...perhaps centered more on
Wednesday though low confidence on timing. Precipitable water
values reach 1.5 inches during this time and locally heavy rain
will be possible. Models then push dewpoints into the mid...
possibly upper...60s on Wednesday.

Another low develops over the southern plains Thursday and lifts
northeast Friday into Saturday basically repeating the cycle with
a possible lull in the precip Wednesday night into Thursday or
Thursday night with more widespread activity later Thursday night
into Friday. Too early for specific timing but trends seem to be

High temps each day likely to be lower 80s unless any daytime
periods remain cloudy with prolonged precip. Days with less
precip/more sunshine could potentially allow highs to reach the
mid 80s. While surface winds currently appear strong enough from
the southwest to prevent any lake cooling/lake breezes...and thus
warm temps all the way to the lakeshore...any thunderstorm
outflows could turn winds onshore and as the second low approaches
late in the week...gradient could weaken enough to allow winds to
turn onshore Thursday or Friday. cms



Very quiet weather expected to continue through the remainder of
the TAF period with VFR conditions and generally light flow
under the influence of high pressure. Ridge axis is currently
centered just north of the terminals stretching from near James
Bay southwest into the Upper Mississippi River Valley and allowing
light northeast flow across northern Illinois and northwest
Indiana. The ridge axis will settle to our southeast overnight
into Monday allowing southerly flow to overspread the region.
Outside of the winds gradually veering...conditions will remain
unchanged with Mostly Sunny/Clear skies and VFR.



108 AM CDT

Continued quiet conditions prevail over the lake today as a high
pressure ridge moves across. This could bring calm winds at times
especially late this afternoon into this evening. With the slow
movement of the pattern this week...a prolonged southerly flow
regime will establish itself. Multiple low pressure centers are
forecast to migrate from the Central Plains to the Upper
Mississippi Valley. As these reach the far western Great Lakes
enough of a pressure gradient may exist for higher than 20 kt
gusts including Small Craft Advisory conditions...but at this time
most of the wind forecast is 10-20 kt. Thunderstorm chances will
also increase over the lake during the middle to latter part of
the week.






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