Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 201201
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
701 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 12Z TAFS through 12Z Monday morning)
Issued at 658 AM CDT Sun May 20 2018

An unsettled pattern will cause periodic showers/storms through
the 12z TAF period. CAM models are varying in solutions to storm
timing, but overall consensus is showing some early morning storms
for SPI to DEC, then a break in storm coverage until early this
afternoon. That wave of storms should last 3-4 hours as it tracks
across the area. Then another line of storms is forecast for later
this evening, passing from west to east.

For the first half of the 12z TAFs, VFR conditions should
prevail, with brief periods of MVFR ceilings and vis during
rain/storms. BMI is starting out with some IFR fog, but that
should improve to VFR by 15z or so. If any storm goes over a
terminal site, IFR vis and cigs could result during very heavy
rainfall.

MVFR and IFR clouds are forecast to develop late tonight,
especially north of a frontal boundary from PIA to BMI.

Winds will vary from easterly north of a stationary front (PIA,
BMI), to southeast or south winds to the south of the front (SPI,
DEC, CMI). Low pressure drifting to the south of our counties
will cause winds to become SE overnight.

&&

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

$$

SHORT TERM...Barker
LONG TERM...Barker
AVIATION...Shimon



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