Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260834

Area Forecast Discussion
National Weather Service Lincoln IL
334 AM CDT Wed Apr 26 2017

.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 06Z TAFS through 06Z Wednesday night)
Issued at 1240 AM CDT Wed Apr 26 2017

Line of showers/storms taking shape across Missouri and now
brushing the Iowa/Illinois border at 0530Z. Concern initially will
be with how far east this makes it, as the line will be running
into some dry air this far east. In the short term, only have VCTS
mention at KPIA/KSPI toward 11Z and have kept the thunder mention
out further east through the morning. Second surge of showers and
thunderstorms will move in from the southwest after 18Z. By 00Z,
main threat of thunder will be east of a KBMI-KDEC line and will
likely be east of the TAF sites by 03Z.

Ceilings are high so far, but initial surge of showers will bring
MVFR conditions to KBMI/KPIA after 12Z. Ceilings dropping
elsewhere into MVFR range by midday or early afternoon, and likely
will be near IFR levels by mid-late afternoon as the storms
arrive. These lower ceilings will linger into Thursday evening.




SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Geelhart is the U.S. government's official web portal to all federal, state and local government web resources and services.