Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 200642

Area Forecast Discussion
National Weather Service Lincoln IL
142 AM CDT Sun May 20 2018

.SHORT TERM...(Today and tonight)
ISSUED AT 140 AM CDT Sun May 20 2018

Several boundaries in place across the Midwest this morning which
may become important as the mesoscale situation evolves over the
next 24 hours. One boundary extends across the northern edge of the
forecast area and is evident as a focus of low-level convergence.
The second boundary is located over southern Illinois and has been
the focus for convective development on Saturday.  Activity over
Missouri has been advecting down this southern boundary leaving
much of central Illinois dry this past evening/this morning.
Isolated convection has developed near the northern boundary, but
with surface-based parcels capped per KILX sounding coverage has
been limited. Will have to monitor storm near the Missouri/Iowa
border that is moving along this boundary. Even if storm does not
hold together it may produce additional boundaries that could
trigger convection this morning in the northwest section of the
forecast area.

Lack of overnight convection should keep air mass pristine above the
boundary-layer and provide additional instability when the next wave
approaches during the day Sunday. Latest CAMS suggest that the next
convective surge may move into the forecast area early Sunday
afternoon, but with the upper-level forcing limited and forecasted
mid-level heights rising ahead of the precipitation, there is
significant uncertainty as to how coverage and intensity. 00z NAM (3-
km) forecast sounding for KILX at 17z suggests CAPE values
approaching 1500 J/kg, but little in way of shear and DCAPE
approaching 700 J/kg.  This suggests that any potential MCS may
become cold-pool driven and may have trouble sustaining itself.
Clouds ahead of the system and outflow with the system should keeps
temps cooler than Saturday across much of the forecast area.

Evolution of Sunday system will have big impact on any development
as a stronger short-wave moves into the area Sunday Night. A
stronger system during the day should limit instability available
for the overnight MCS. Although, strong de-coupling of the boundary-
layer is likely in the wake of any daytime convection, moisture
advection above the inversion and resultant elevated instability may
be sufficient for hail with stronger storms.  Again all of this is
highly dependent on the preceding scenario.


.LONG TERM...(Monday through Saturday)
ISSUED AT 140 AM CDT Sun May 20 2018

Energy dives into and reinforces western U.S. trough early this week
bringing increasing mid-level heights to Illinois.  After some
remnant showers and storms on Monday, temps should climb well above
normal for the remainder of the work week and precipitation should
be mostly isolated. As the trough in the west re-develops further
west over the Pacific, northern stream energy may begin to impact
the forecast area toward Friday and into the first part of the
holiday weekend bringing a chance for precipitation for late Friday
and into Saturday.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1045 PM CDT Sat May 19 2018

Mainly VFR conditions to start this forecast period with and then
a low probability for a period of MVFR cigs Sunday morning in the
12z-16z time frame, especially if precipitation occurs late
tonight into Sunday morning. The large cluster of storms to our
south will remain well south of the TAF sites overnight. However,
additional showers and thunderstorms may move northeast into the
area late tonight and especially during the morning hours of
Sunday. However, coverage at this point continues to be limited
so will hold on to the VCTS until we get a better timing on any
storms that may affect one of the TAF sites. Surface winds for the
rest of tonight will be light southeast to south but will tend to
back more into an easterly direction in PIA and BMI. Easterly flow
will continue at PIA and BMI on Sunday with speeds of 8 to 13 kts,
while at SPI, DEC and CMI we look for winds west to northwest by
tomorrow afternoon and then into a northerly direction by Sunday




LONG TERM...Barker
AVIATION...Smith is the U.S. government's official web portal to all federal, state and local government web resources and services.