Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 021753
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1253 PM CDT MON MAY 2 2016

.UPDATE...
Issued at 1020 AM CDT Mon May 2 2016

Another mostly cloudy and cool day is unfolding across central
Illinois, thanks to a slow-moving upper trough extending from
Wisconsin southwestward to Kansas. Weak synoptic lift ahead of
this feature will be enough to trigger isolated showers today.
With cool surface temps and corresponding instability parameters
remaining quite weak, do not think thunder will develop. Latest
visible satellite imagery generally shows overcast conditions:
however, some partial clearing is trying to work into the far
northern KILX CWA from the northeast. Think any clear spots that
develop will fill back in due to adequately steep lapse rates in
the vicinity of the approaching upper trough axis. As a result,
will maintain the mostly cloudy forecast across the board. Thanks
to the clouds and a continued northeasterly flow, high
temperatures this afternoon will remain below normal for this time
of year, mainly in the middle to upper 50s.

&&

.SHORT TERM...(Today)
ISSUED AT 322 AM CDT Mon May 2 2016

While cooler/drier post-frontal air has overspread all of central &
southeast Illinois since yesterday, the threat for a few showers
will persist today. Forecast area remains on the southern side of a
sheared upper-level trof that extends from eastern Canada into the
southwestern United States. Another disturbance within this mean
flow, currently over the central Plains, will track across the area
today. Radar returns associated with this disturbance are already
tracking across Missouri and approaching Illinois. This feature will
have limited moisture to work on today as it moves through, and
limited diurnal instability is expected to develop. With this
thinking in mind, only Slight Chance PoPs and low QPF are warranted
with the passage of this disturbance. Otherwise, abundant cloud
cover and cool northerly low-level flow support cooler than normal
highs today, with most locations topping out in the 50s.

.LONG TERM...(Tonight through Sunday)
ISSUED AT 322 AM CDT Mon May 2 2016

Little change indicated from previous model runs in terms of the
upper air pattern this week, with significant ridging along the
Rockies and a cold core low dropping southward through the Great
Lakes by Wednesday night. The ridge will get squeezed and shift
eastward with time, as a second upper low comes onshore of
California. A slow breakdown of the ridge will take place this
weekend as a more significant trough drops southeast through central
Canada. Although temperatures will be relatively cool for the middle
of the week, a significant warming trend will take place beginning
Friday as the thermal axis approaches from the west.

The presence of the current elongated trough from the Great Lakes to
the central Plains will continue a threat of a few showers on
Tuesday, mainly over the southeast parts of the CWA. Better chances
of scattered showers are expected Wednesday as the upper low moves
in from the north. Have increased the PoP`s late Tuesday night and
Wednesday with the main frontal boundary, with chance PoP`s as far
south as I-70 by late Tuesday night. While showers will taper for
awhile Wednesday morning as the front exits, scattered showers are
again expected in the afternoon across mainly eastern Illinois, as
the upper low arrives. Coldest air aloft will be centered over
Indiana in the afternoon, and have maintained a mention of isolated
thunder over eastern Illinois due to the steep lapse rates expected.

Late in the period, the extended models start to show some
disagreement. While the upper features are similar, with an upper
low over Colorado or eastern Utah and shortwaves rotating through
the Great Lakes, the ECMWF is further south with a surface warm
front connecting the two. This would result in scattered showers
into central Illinois Saturday night, whereas the GFS does not bring
the boundary into the area until late Sunday afternoon. For now have
mentioned only slight chances of showers and thunderstorms until
this starts to clear up a bit.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1253 PM CDT Mon May 2 2016

MVFR ceilings prevail at the central Illinois terminals early this
afternoon. Latest water vapor imagery shows a weak short-wave
trough over west-central Illinois between KSTL and KUIN. As this
feature tracks eastward, the low cloud cover will tend to pivot
southward in its wake, resulting in rising ceilings and eventually
a clearing trend from west to east later this afternoon and
evening. HRRR forecast suggests ceilings improving to VFR at KPIA
as early as 20z...but holding off until 03-04z further southeast
at KCMI/KDEC. Think skies will clear along/west of I-55 during the
evening, then further east late tonight toward dawn Tuesday. After
that, forecast soundings indicate steep lapse rates developing on
Tuesday, which should lead to at least SCT diurnal clouds at
around 5000ft. Winds will be light through the entire
period...initially from the northeast this afternoon, shifting to
the northwest by Tuesday morning.

&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...BAK
LONG TERM...Geelhart
AVIATION...Barnes


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