Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 202335

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

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

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

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.


ISSUED 635 PM CDT Sun Apr 20 2014

VFR conditions will prevail at all sites next 24hrs. High cirrus
will continue over the area, affecting each site this evening.
Then mid clouds around 12kt will begin to advect into the region
from the southwest, starting at PIA at around 07z, then gradually
moving east, reaching CMI around 13z. Then lower clouds around
5kft will move into during the morning hours in the west, to
afternoon hours in the east. Think precip will be scattered
showers or light rain at the beginning, well ahead of the front,
so have just VCSH at all sites during the morning hours in the
west, to afternoon hours in the east. Then more predominate
showers will move in during the afternoon in the west, and late
afternoon in the east. Keeping vis and cigs VFR for now and later
forecasts can adjust if confidence is higher that category will
drop to below VFR. Also have included VCTS with the predominate
showers. Winds will be southerly to start but then become
southwest the remainder of the TAF period. Wind shift due to the
front will likley be after 00z tomorrow. Wind speeds will remain
below 15kts and do not expect any gusts.



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