Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 181918
Area Forecast Discussion
National Weather Service Lincoln IL
218 PM CDT Fri Apr 18 2014
ISSUED 218 PM CDT Fri Apr 18 2014
Models in very good agreement today well into next week. Looks
like a nice spring weekend on tap.
SHORT TERM...Tonight through Wednesday
High pressure building into the Midwest will continue to advect a
dry airmass into Illinois through much of the weekend.
Temperatures at 850 mb will climb 4-8 degrees C between this
morning and Saturday afternoon which should be reflected by
temperatures significantly warmer on Saturday after a cool start.
Boundary layer moisture does increase somewhat late Saturday Night
into Sunday and will likely lead to some cloud development which may
inhibit further warming on Sunday, but for now it does appear
that a warmer start to the day and a reasonable amount of sun
should allow temperatures to climb into the 70s.
A northern-stream shortwave approaches late Sunday Night into
Monday. This system will be moving into a very dry air mass and
will likely take a while to saturate the column. Instability will
be somewhat limited due to the dry air in place. CAPE values of
200-400 J/kg max are the highest the operational models expect
and that should be after sunset. However, there are some SREF
members with higher CAPES to around 800 J/kg. Some scattered
thunderstorms may be possible, but should be limited in coverage
and intensity. Models may be a bit overdone in total QPF, but some
local amounts of 0.50 may be possible in locations that are
impacted by the thunderstorms.
Cold advaction behind the system should be limited as shortwave
ridging moves in quickly and 500 MB heights climb quickly almost
100 meters between 12z Tue and 00z Thu in reaction to a stronger
system approaching late in the week.
LONG TERM...Wednesday Night through Friday
A stronger system is progged to move out of a broad trough along
the Pacific Coast for the later half of next week. The models do
begin to diverge with the strength and timing of this system. As
often is the case, the differ on the amount of the overall energy
of the trough is associated with each ejected wave. ECMWF is
faster and weaker with this initial wave, while the GFS suggests a
more dyanmic system holding off until late Thursday. The GFS would
suggest quiet a warm day Thursday with clouds and only a slight
chance of thunderstorms, while the ECMWF has a broad precip field
moving in early Thursday keeping temperatures on the cooler side.
Timing of this system will also have a huge impact on the
strength of convection. ECMWF suggests a lower potential for
strong storms given the ongoing precip on Thursday, while the GFS
suggests a more stormy Thursday late afternoon and evening.
For now will stick with a compromise as we are looking six days
out and will focus on run-to-run consistency as we look to
determine the overall trend.
ISSUED 1223 PM CDT Fri Apr 18 2014
High pressure ridge keeping VFR through the pd. Some cu
indicated, but may not have enough moisture to work with for much
in the way of cloud cover. Keeping the cu in CMI and DEC to the
south and east closer to the cu rule max value axis for this
afternoon. Other than that, light winds with a northerly component
becoming more easterly after sunset, and more southeasterly