Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 270201
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
901 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 645 PM CDT Sat Jul 26 2014

Cluster of storms pushing east of CMI early this evening with
mainly stratiform rains to its west. A mix of VFR with some MVFR
cigs in the wake of the rains over the remainder of the forecast
area this evening. Still have the cold front to our northwest and
that won`t be pushing thru until Sunday morning. May see some addl
development late tonight as the front approaches late tonight but
the latest short term models are not very aggressive with any
redevelopment. One other possible concern will be with the potential
for fog to develop across the northern TAF sites just ahead of the
front as winds drop off to nearly calm for a time after 05z. What
fog and stratus that does develop late tonight should be gone by
15z as drier air filters southeast into the area behind the cold
front late Sunday morning into the afternoon hours. Surface winds
will be light southwest tonight and then switch into the west and
then northwest behind the cold front in the 14z-16z time frame.
We should see some gusts up to 20-23 kts by Sunday afternoon out
of the northwest as the much drier air moves in.

Smith
&&

.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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