Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 261802
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
102 PM CDT Wed Apr 26 2017

.UPDATE...
Issued at 1025 AM CDT Wed Apr 26 2017

Have made several adjustments to today`s forecast. A surface cold
front has pushed into parts of western Illinois, including far
western portions of the forecast area. The thermal gradient along
this boundary is significant, and high temperatures have likely
been reached in areas along/behind the front. Additional
temperatures rises to the east of the front should also be
relatively small. Also had to increase winds in the warm advection
regime to the east of the front where some gusts over 30 mph have
been seen this morning.

PoPs also needed quite a bit of adjustment. General subsidence in
the wake of the area of showers/storms that moved through the
area early this morning, coupled with a lack of instability and
upper-level forcing, has kept additional rainfall development to a
minimum. Expect these trends to last until late afternoon when
the mean upper-level trof, currently tracking east across the
Plains, pivots to a more northeast track toward the forecast area.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 334 AM CDT Wed Apr 26 2017

Convection in Missouri is marching northeast early this morning
and has recently passed Columbia. A narrow axis of showers and
isolated storms extends northeast along the Illinois/Iowa border.
High-res short-range models lift the Missouri convection to the
northeast across areas mainly along and west of the Illinois River
through about 9-10 am, before the next round begins moving in from
the southwest toward midday as the cold front starts to move into
the forecast area. Extent of the early morning convection has
disrupted the amount of instability that was originally projected
to be ahead of the front. However, some CAPE of around 1000 J/kg
is still indicated ahead of the front in the afternoon with some
impressive bulk shear values of 50-70 knots in the 0-6km layer, so
some strong to isolated severe storms still are not out of the
question. Nice plume of moisture, with precipitable water values
of around 1.5 inches, will surge northeast into the forecast area
ahead of the front, so heavy rain remains a significant threat.
Latest indications are 1.5 to 2 inches or so remain possible along
the I-55 corridor. Conditions in this area have been fairly dry
recently, so the ground should be able to absorb a good chunk of
this, and will not go with any headlines at this time.

While the front does not fully go through the forecast area until
after midnight, main threat for heavy rain and stronger storms
will generally be through about mid evening.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 334 AM CDT Wed Apr 26 2017

Not much in the way of any dry periods is in store for this part
of the forecast. Main focus remains with the heavy rain threat for
Friday into the weekend.

Lingering showers on Thursday morning will pull out as the upper
wave swings east, but the next system will already be taking shape
over the central Plains. The first round of showers will mainly
pass through Friday morning, as the first wave of low pressure
rides northeast along the front. However, the main period of
concern is from Friday night into Sunday morning, as the front
becomes nearly stationary for a time, before a large upper low
forms over the central Plains and the associated surface low pulls
the front northward. An extended period of PWAT values of 1.5 to
2 inches will ensure some rather hefty rain totals, the highest of
which will be dependent on where exactly the boundary becomes
stationary. A few inches of rain are likely, which the ground will
less readily absorb after the current system. Will continue with
the hydrologic outlook to discuss the issue, but as the event gets
closer, flood headlines may be needed.

The upper low will continue to strengthen as it lifts northeast,
and should be located near Wisconsin by midday Monday. With the
strength of the low, wraparound showers will still continue into
Monday evening.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 100 PM CDT Wed Apr 26 2017

A disturbance, and accompanying area of showers/storms, will
spread across the central Illinois terminals late this afternoon
into tonight. This precipitation will degrade conditions to at
least MVFR, with IFR conditions likely later tonight. A slow
improvement is expected Thursday morning.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Bak
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Bak



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