Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 192331
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
631 PM CDT Wed Jul 19 2017

.SHORT TERM...(This evening through Thursday)
ISSUED AT 306 PM CDT Wed Jul 19 2017

High-res visible satellite imagery is showing an enhanced Cu field
along the I-80 corridor and east of I-55 this afternoon. Isolated
thunderstorms will develop across these areas over the next couple
of hours...as per the ARW/NMM/HRRR. Any convection that fires will
rapidly dissipate by sunset, leaving behind mostly clear and dry
conditions early this evening. The next short-term forecast
concern will be the track/timing of a cluster of thunderstorms
currently ongoing over southwest Minnesota. These storms initiated
over the western Dakotas this morning and have been tracking
southeastward throughout the day. Think they will continue in this
general E/SE direction along a stationary frontal boundary through
the evening hours. Most recent runs of the HRRR show the cluster
entering north-central Illinois later this evening, brushing the
far northern KILX CWA after 03z/10pm.  Have therefore updated
PoPs to include low chances along/north of I-74 tonight.  While
this initial round of storms will diminish as it drops
southeastward into the area, a larger MCS will likely take shape
further north across Minnesota into Wisconsin. These storms will
also track E/SE, but will remain north of central Illinois later
tonight into Thursday morning. Will continue to carry slight
chance PoPs along/north of I-74 into Thursday morning, but think
the system will stay north of the CWA. Once the morning MCS drops
into northern Indiana, another hot and humid day will unfold
across the region. High temperatures will rise into the lower to
middle 90s, while heat index readings reach the 105-110 degree
range. The morning convective complex will push the synoptic
frontal boundary further south, with most models showing it along
or just south of I-80 by Thursday afternoon. With a boundary in
the vicinity, decided to carry slight chance PoPs across the N/NE
Thursday afternoon.

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 306 PM CDT Wed Jul 19 2017

An active weather pattern will persist through the end of the
week, with several nocturnal storm complexes expected to develop
and ride along a stationary frontal boundary draped across
northern Illinois. Hot and humid weather will prevail across the
KILX CWA, with afternoon highs climbing into the middle and
perhaps upper 90s Thursday through Saturday. With dewpoints
remaining in the 70s, peak afternoon heat index values will reach
105-110 degrees...prompting the continuance of heat headlines
across the entire area through Saturday evening. Storm chances
will generally be confined to the north through the period, as
strongest forcing will remain across northern Illinois.

A significant short-wave will push the frontal boundary southward
by Saturday, setting the stage for a round of showers and
thunderstorms across central Illinois. With strong instability as
characterized by both NAM and GFS CAPE values in excess of
4000J/kg, strong thunderstorms with torrential downpours will be
likely. Main mitigating factor for widespread severe weather will
be weak wind-shear, with most models suggesting the strongest
shear will lag well to the north of the primary instability axis.
Nevertheless, think thunderstorms are a good bet Saturday
afternoon and evening.

The cold front will drop southward into the Ohio River Valley by
late Sunday, triggering a few additional storms across the
southern half of the CWA Sunday afternoon. After that, a
cooler/drier airmass will settle into the region for early next
week...with high temperatures dropping into the lower to middle
80s by next Monday and Tuesday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 631 PM CDT Wed Jul 19 2017

Expecting skies to be clear most of the evening at all TAF sites.
However, a line of convection occurring in northeast IA, headed
for northwest and northern IL has the potential of sliding more
southeast than currently and could bring some thunderstorms to the
northern three TAF sites later tonight. Will have VCTS at PIA/BMI
and CMI tonight and lasting about 4hrs at each site. Beyond this,
high cirrus is expected remainder of the overnight hours and
through tomorrow. Winds will be light and variable tonight, but
then become southwest tomorrow at less than 10kts.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM CDT Saturday for ILZ027>029-
036-037-040>042-047>054-061-062-066>068-071>073.

Heat Advisory until 8 PM CDT Saturday for ILZ030-031-038-043>046-
055>057-063.

&&

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Auten



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