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Area forecast discussion
National Weather Service Lincoln Illinois
1247 am CDT Thu Jun 20 2019

Update...
issued at 926 PM CDT Wed Jun 19 2019

Cancelled some of the counties out of the flash flood advisory with this update, as
rainfall is beginning to diminish in southern Illinois. Also
updated pops to account for the decreasing threat of rainfall
across the southern County Warning Area overnight. Rain will continue throughout
the northern cwa, tracking eastward overnight. Therefore the flash flood advisory
remains in effect the northern counties, where around 2 inches of
rain have fallen, with up to an additional 0.50-1.00 inches
expected. Behind this system, drier conditions will arrive
Thursday, lingering into Friday...however another system will
arrive later on Friday and last through the weekend.

&&

Short term...(this evening through thursday)
issued at 309 PM CDT Wed Jun 19 2019

The short term will be dominated by a shortwave that has the
potential to produce locally heavy rainfall and flash flooding.
The instability parameters are marginal at best, with the MLCAPE
of 1500 j/kg and weak shear not able to support much in the way of
severe wind/hail. However, the non-supercell tornado (nst)
parameter on spc's website is showing increased potential for a
few quick spin-up tornadoes under some of the stronger updrafts.
So far, only a couple of funnels have been reported. Circulations
are being monitored, and the trends are for a quick
intensification and then weakening. That is supported by the lower
cape values present. The Severe Thunderstorm Watch just south of
our area has better instability and is also in the path of
stronger 500mb speed Max, increasing shear in that area.

The main push of rain and storms for areas south of I-74 looks to
continue through around 03z/10pm, then advances into Indiana. The
northern counties look to remain under the influence of the 500mb
shortwave through around 09z/4am, before the steadier rains shift
east into northern Indiana. Precipitable water values of 1.5 to 2"
will support very efficient rainfall production from any stronger
storm cells. Therefore, the Flash Flood Watch was expanded northward to
include the counties of Peoria, Woodford, Tazewell and McLean
earlier this afternoon. The watch ending was kept at 18z tomorrow,
but most areas should be able to be cancelled early, if current
model solutions are correct about a dry Thursday morning.

Long term...(thursday night through wednesday)
issued at 309 PM CDT Wed Jun 19 2019

The extended forecast will be dominated by rain chances through
Sunday night, as the forecast area remains under the influence of
the back side of an upper level trough. The area will experiencing
a warming trend and increasing humidity, as the upper ridge inches
into Illinois from the west. However, the storm track will remain
active on the leading edge of that ridge, guiding several waves of
energy across central Illinois from Friday afternoon through
Monday night. The target periods for more widespread rain/storms
looks to be Friday night, Saturday night-Sunday, and in eastern
Illinois on Monday. While the models have generally overdone the
coverage of 2+" rainfall areas that far out, we are seeing more
potential for widespread 2" rainfall amounts across all of our
forecast area during the Fri night-Monday time frame.

Increasing heat and humidity will be noticeable on Saturday and
Sunday, when heat indices climb into the mid to upper 90s in some
locations. Those numbers are highly dependent on if any extended
periods of sunshine can develop. In any case, dewpoints in the 70
to 75 deg range will be well above anything we have seen in quite
a while.

A break in the rain chances looks to develop for Wednesday, as a
progressive trough shifts east of Illinois and upper level ridging
becomes established farther north into Illinois.

&&

Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1243 am CDT Thu Jun 20 2019

Light rain showers will continue to impact cmi and bmi over the
next hour, as the system moves eastward out of the region.
Ceilings will remain in MVFR to IFR overnight, as moisture remains
throughout the area. A frontal boundary is shifting through the
region, just passing through spi, heading toward Dec within the
next hour...increasing and shifting winds from the west-northwest. As
daylight arrives, ceilings will begin to lift and break apart.
Sustained winds will remain below 10kts throughout the period,
however some gusts could top out near 15kts.

&&

Ilx watches/warnings/advisories...
none.
&&

$$

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