Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 270457
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1157 PM CDT Sat Jul 26 2014

.DISCUSSION...
ISSUED 901 PM CDT Sat Jul 26 2014

Already made one update to remove the watch, but will need to make
another to try to better represent expected conditions overnight.
Cold front is still northwest of the area and will be moving
through the area overnight. Some models indicate that some
additional showers and storms could develop overnight as the cold
front interacts with the moist air over the area. With lots of the
airmass worked over from the evening storms, chances may not be
that high for additional pcpn, but it remains a possibility. Fog
will also develop as skies become clear and winds become light.
Some spots already seeing fog, so will making sure this is added
in grids as well. Update will be forthcoming in a while.

Auten

&&

.AVIATION...
ISSUED 1157 PM CDT Sat Jul 26 2014

Fog has developed in areas where there was rain this afternoon.
Some places have gotten as low as 1/4sm. MVFR cigs are developing
in the north and expect this to overspread PIA and BMI during the
overnight hours. The dense fog seems to have developed around SPI
and DEC, and unsure if it will get to CMI since CMI site did not
have a lot of rain. So have tried to forecast for LIFR or IFR
conditions at SPI and DEC overnight, with MVFR at PIA/BMI/CMI.
Then all sites will improve to VFR tomorrow morning with scattered
CU developing for the daytime hours. Skies should clear for
tomorrow evening. Winds will be light and variable overnight and
then become northwesterly after the cold front moves through.
There is a slight chance that some showers will develop along the
front late tonight as it encounters the juicy air. But chances are
low and confidence is low, so will not have any mention in TAFs at
this time.

Auten

&&

.PREV DISCUSSION...
ISSUED 150 PM CDT Sat Jul 26 2014

ILX Local objective analysis as of 18z indicating the cap holding
strong across our northern forecast area where the frontal boundary
has slipped south of early this afternoon. Further south, we have
seen the cap weaken with Mixed Layer Cins down to around 100 along
the I70 corridor with Mixed Layer Capes were up to 3800 j/kg over
far west central IL where temps have climbed into the upper 80s
with dew points in the mid to upper 70s. 18z sounding from ILX and
DVN showing some moisture around 2500-3000 feet with a dry layer
from 850 to 500 mb and the cap holding strong at both locations.

SHORT TERM...Tonight through Tuesday

Storm coverage tonight the main forecast issue as all models weaken
the cap significantly this evening as the main upper level energy
starts to push into the region accompanied by cooling temperatures
aloft. HRRR and WRF-HOP ensembles were indicating the main convection
would be tracking across northern Missouri and into central to southeast
Illinois late this afternoon and evening, along the differential heating
boundary set up by the lower cloud cover. Further south, nothing but
sunshine and temps in the low to mid 90s, so quite a contrast across
central thru southeast Illinois which many times these storms tend to
propagate through. If the cap is breached there is plenty of CAPE and
Shear to interact with this evening with a fast moving QLCS still looking
more likely at least over our southern half of the forecast this evening.
Damaging winds and large hail will be the primary threats but enough
low level shear prevalent, especially near the boundary across our
northern counties, that a tornado could develop with a persistent
rotating updraft. Some of the storms could start to back-build later
this evening as the low level jet starts to back more into a southwest
to west direction increasing the threat for locally heavy rainfall.

Storms should start to edge out of our forecast area Sunday morning
as the front settles to our southeast by afternoon. Will still keep
low chance pops going, especially across the east but some fairly
decent dry air will be advecting in on a gusty west to northwest
wind during the afternoon. Cooler and much less humid air will filter
southeast into our area Monday and Tuesday as an unseasonably deep
trof settles in north of the Great Lakes.

LONG TERM...Wednesday through Saturday

The deep h5 trof will be the main weather story for much of this
period bringing rather cool temperatures for the first few days of
August, although latest guidance was not quite as cool as previous
runs as we see daytime highs edge back to or just above 80 degrees
starting on Wednesday. Rain chances remain a challenge as models
diverge with respect to timing of individual shortwaves that drop
southeast into the region bringing mainly diurnally driven shower
and thunderstorm chances, especially on Friday and Saturday.

Smith


&&

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

$$







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