Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 210450
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1150 PM CDT Sun Apr 20 2014

.DISCUSSION...
ISSUED 900 PM CDT Sun Apr 20 2014

High clouds continue to blanket the sky over central and southeast
Illinois this evening. This will continue overnight as well. Just
like last night, dewpoints are quite low, but blanket of clouds
will keep temps from falling too far by morning. Current forecast
of lower to middle 50s overnight still looks good. Therefore no
update required at this time.

Auten
&&

.AVIATION...
ISSUED 1150 PM CDT Sun Apr 20 2014

VFR conditions will still prevail at all sites next 24hrs. Mid
clouds around 15kft will overspread the area overnight in advance
of the next system approaching from the west. As it gets closer
tomorrow morning, cigs will fall some, reaching to around 8kft.
Models indicate there could be some light showers or sprinkles
from this, but confidence is not very high given how dry the lower
levels are. So will just have VCSH for late morning at each site.
Then as the front gets closer, cigs will drop a little but will be
adding a scattered deck at around 3.5-4kft. Precip should be
ongoing and there is a chance that thunder could be there as well.
Again with dry surface levels, do not expect much reduction in vis
when showers are occurring. So only going with 6sm. As the front
moves in during the early evening hours, pcpn will end and
expecting cigs to rise back to around 10kft for remainder of the
night. Winds will be south to southwesterly overnight, but then
become west-southwesterly during the afternoon when the showers
arrive. West to northwest winds can be expected after the front,
though CMI will likely switch closer to 06z than the others.

Auten
&&

.PREV DISCUSSION...
ISSUED 235 PM CDT Sun Apr 20 2014

Another pleasantly mild day continues to unfold across central and
southeast Illinois. As expected, temperatures are a little warmer
than yesterday thanks to increasing southerly flow in advance of a
developing storm system in the plains. Main forecast concerns today
revolve around shower/storm chances tomorrow with the passage of
the plains system, as well as with a stronger system for Thursday.

SHORT TERM...Tonight through Wednesday:

The approaching plains system is still expected to produce showers
and a few thunderstorms as it passes through Monday into Monday
night. However, it will not be a significant system in terms of
precipitation amounts or storm intensity.

The forcing with this system will come courtesy of loosely phased
northern/southern stream waves, but the more vigorous forcing with
these features should stay north/south respectively of the
forecast area. In addition, only modest instability (CAPE values
AOB 1000 j/kg), and weak bulk shear (less than 20 kts) are
anticipated.

The precipitation threat will come to an end fairly quickly Monday
night as the system pushes east of the area. Quiet weather and more
seasonable temperatures (highs in the 60s) will accompany the
upper/surface ridging that will build in behind the system into
midweek.

LONG TERM...Wednesday night through Sunday:

The next, more vigorous, system is still on track to bring
showers/storms to the area for Thursday into Thursday night, mostly
associated with the passage of the system`s cold front. However,
can`t rule out a stray shower or storm in the pre-system warm
advection regime as early as Wednesday or Wednesday night. However,
most of this precipitation should occur north of the forecast area.

After a brief surge of warmer air ahead of Thursday`s system,
temperatures will cool back to normal levels, possibly colder, for
the weekend. Model agreement and run-to-run consistency with the
overall weather pattern for the weekend is not very good. While
they generally agree on a cooler trend, they don`t agree with how
quickly we get there. The timing differences are also reflected in
how quickly precipitation chances return. The ECMWF has been most
aggressive by far with the arrival of the cooler air and wetter
conditions, although the latest GFS has trended closer to the
ECMWF. Plan to keep PoPs on the lower side, and temperatures a bit
more moderate, until a better model consensus is reached.

Bak


&&

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

$$







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