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Area forecast discussion 
National Weather Service Lincoln Illinois
641 PM CDT Friday Jul 31 2015

Short term...(tonight)
issued at 315 PM CDT Friday Jul 31 2015

19z/2pm surface analysis shows weak cold front settling into central
Illinois...extending from near Rantoul to just south of Quincy.
Minimal convergence along the front and an overall lack of deep
layer moisture has largely prevented convection. The exception has
been further northeast across northern Indiana where a few clusters
of thunderstorms have developed. Hrrr continues to over-emphasize
dewpoint pooling along the front and produces numerous thunderstorms
with its 1 and 2-hour forecast. Meanwhile...the rapid refresh has
consistently presented a more realistic scenario...suggesting only
isolated storms mainly across the east/NE kilx County Warning Area over the next 2-4
hours. Given this is the location where cumulus-field is currently most
pronounced...will continue to follow this solution closely. As a
result...will carry slight chance probability of precipitation along/northeast of a
Champaign to Marshall line through the afternoon. Any isolated
convection that develops will quickly dissipate toward
sunset...followed by mostly clear and dry conditions tonight.
Slightly drier airmass will trickle in from the northwest once the
front passes...with overnight low temperatures dropping into the
lower to middle 60s.

Long term...(saturday through friday)
issued at 315 PM CDT Friday Jul 31 2015

Overall a fairly persistent west-northwest flow pattern will remain across Illinois
and much of the Midwest through the weekend and into early next
week. Quite a bit of model uncertainty regarding a breakdown of the
western ridge and deepening of the eastern trough for the middle of
next week.

In the near term...very warm and increasingly humid conditions will
be on tap for central and eastern Illinois Saturday. An advancing warm
front and a cluster of convection from Iowa/Nebraska is expected to
approach areas west of the Illinois River valley late Saturday night and
into Sunday morning. The remnants of the early morning T-storms are
then expected to spread across most of central and eastern Illinois Sunday
morning and early afternoon. Residual boundaries from this
convection should result in redevelopment of T-storms Sunday
afternoon and into the evening...especially along and north of I-74.
Some of the storms later in the day Sunday could be strong...mainly
due to moderate levels of wind shear and instability.

Most of the forecast area will be in the warm sector of an advancing
frontal boundary...yielding very warm and somewhat humid conditions
Monday. The aforementioned front is expected to slowly move into
central Illinois Monday night and then remain nearly stationary for
much of the week. This should result in a rather unsettled weather
pattern with the potential for several periods of rain from late
Monday...on and off...through the end of the week.

The uncertainty in the models revolves around the details of
possible shortwave energy breaking through the western U.S. Ridge
and interacting with the front. The GFS is a bit more aggressive with
this than the European model. However...the European not only
underplays the affects of this but keeps the surface front farther
north. Until the details are worked out it is hard to pin down
where a threat of persistent...possibly heavy rain may set up the
middle of next week. Thus...will not make too many major changes
to the forecast and keep chance probability of precipitation for thunderstorms across a
large part of the forecast area.

The one thing the models do agree on is that with the periods of
convection and residual cloud cover...temperatures should be below
seasonal normals.


Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 641 PM CDT Friday Jul 31 2015

VFR conditions will continue for the next 24 hours as high
pressure continues over the area with a frontal boundary pushed
just south of the central Illinois terminals. Convection over northwest
Missouri/SW Iowa this evening will cause some middle and high cloud
cover to drift eastward over the southern terminals kspi-
kdec...but dry conditions and VFR flight category will continue.
Winds west-northwest 3-5 kts overnight...becoming SW 8-12 kts after 15z


Ilx watches/warnings/advisories...


Short term...Barnes
long term...Miller

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