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Area forecast discussion 
National Weather Service Lincoln Illinois
859 PM CDT Friday Apr 17 2015

issued at 859 PM CDT Friday Apr 17 2015

High pressure over the Midwest resulting in relatively clear
skies over central Illinois this evening along with light winds. High
clouds will generally increase across the area tonight as a low
pressure system over The Rockies slowly approaches from the
west...but no major impacts from this system are expected
overnight due to the relatively slow approach of this system. With
afternoon dewpoints in the low to middle 50s...fog should be minimal
as lows in the middle 50s are expected. No updates needed at this
time as forecasts are in good shape with these features.


Short term...(tonight) issued at 256 PM CDT Friday Apr 17 2015

Quiet weather is expected across central and southeast Illinois
tonight with high pressure and the associated dry airmass in
control. We've had more insolation today than yesterday, despite
the robust cumulus field, and forecast soundings suggest the low level
moisture will be fairly well mixed out. So, do not expect fog to
be as much of problem later tonight as it was in some areas this
morning. Otherwise, light winds and minimal cloud cover should
allow for good radiational cooling tonight. Expecting overnight
lows mainly in the middle 50s, warmer than last night, thanks to
airmass modification/higher dew points.

Long term...(saturday through friday) issued at 256 PM CDT Friday
Apr 17 2015

The cutoff upper-level low, currently beginning to lift northeast
out of The Four Corners region, is still expected to gradually
spread showers and a few thunderstorms into the region as it moves
through. However, as is often the case when dealing with cutoff
upper lows, the model guidance has been trending slower with its
expected arrival (some solutions are still faster than others).
Given the slower expected arrival, have pretty much removed probability of precipitation
from Saturday, and greatly lowered them Saturday night. If slower
trends persist, they will need to be lowered further through at
least Saturday night. Still looks like Sunday and Sunday night
should end up fairly wet as the upper low remnants get absorbed in
to a digging northern stream trough. While one might expect the
surface low to weaken as the upper feature it is tied to diminishes,
the latest model runs suggest that will not happen in this case.
Recent guidance digs the northern stream trough more than previous
solutions, and the jet streaks associated with the digging trough and
dissipating upper low are working in concert to strengthen the
surface low. That being said, the consensus track up the eastern
border of Illinois is not conducive to US getting into the warm
sector and/or severe weather on Sunday.

Some Post system showers are possible on Monday, possibly a greater
risk than before if the system slows much more than current
indications. However, otherwise Monday should be the first day of
what looks to be a prolonged period temperatures on the cooler side
of normal. The weekend system continues to evolve after it leaves
the area, taking up a fairly steady residence as a relatively deep
trough over eastern North America for the rest of the week. Periodic
disturbances moving through this trough may pose an occasional risk of
showers, but guidance agreement with respect to these discrete
features is poor at best. Have kept probability of precipitation on the low side through the
extended range of the forecast as a result.


Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 629 PM CDT Friday Apr 17 2015

VFR conditions and light winds in place across central Illinois this
afternoon with surface high pressure and a high pressure ridge
aloft approaching from the west. Overnight...scattered shallow
afternoon cumulus clouds will dissipate while high clouds
associated with a low pressure system to the west begin to spread
over the area. Dewpoints generally in the low 50s this afternoon
should be low enough for only light fog/haze in MVFR category
developing overnight. For Saturday...increasing cloud cover
expected along with increasing southeasterly breezes...but VFR
conditions expected through 00z.


Ilx watches/warnings/advisories...


short term...Bak
long term...Bak

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