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Area forecast discussion 
National Weather Service Lincoln Illinois
309 PM CDT Thursday Oct 8 2015

Short term...(tonight)
issued at 309 PM CDT Thursday Oct 8 2015

Cold front approaching the western border of Illinois this afternoon
and will be the main story in the short range as the eastern half of
the Continental U.S. Is dominated by quasi zonal flow aloft. Winds shifting to
more northwesterly behind the boundary and the pressure gradient is
weak, but enough to keep it a little breezy in the overnight hours.
Mostly cloudy, with some scattered showers and thunderstorms before
midnight. Since most of the showers will require at least a little
bit of an assist from the heat of the day, after sunset, the showers
should slowly lose coverage and intensity. Overnight lows drop into
the lower 50s for most areas northwest of the Illinois River valley... and
areas south of I-70 staying warmer under more persistent cloud cover
and a slower moving front in the early morning hours.


Long term...(friday through thursday)
issued at 309 PM CDT Thursday Oct 8 2015

By early Friday morning, the cold front will have progressed near I-
70. The shortwave that will be fueling the showers early Friday
along the front is approaching from South Dakota/north Nebraska. The
relatively weak wave will have limited low level moisture and
instability to work with, so we reduced the chance pops in our
southeast to slight chance 20%. We also limited the area to S of I-
70 and mainly in the morning.

Cool high pressure will be arriving Friday afternoon behind the cold
front. Breezy north winds of 10 to 20 mph will usher in 850 mb temps
down around 4c. High temps on Friday will be about 15 deg cooler
than thurs, with readings mainly in the mid 60s. The wind add some
fall chill to the air, along with a lack of sunshine for most of the

The cool conditions will continue on Saturday as the surface ridge
axis and cold pool pass across and eventually southeast of Illinois.
Highs will reach into the upper 60s with the help of sunshine, and
lighter winds. On Sunday, the surface ridge will pull farther away
to the east, setting the stage for southerly return flow and a
warming trend. Highs will climb well above normal on Sunday, with
highs in the upper 70s to around 80. The warmer temps will be west
of I-55, where the mid-level thermal ridge will enter Illinois on

The next cold front is projected to push across Illinois early
Monday morning. It will be moisture starved over Illinois, with the
best forcing for precip remaining closer to the surface low in north
Wisconsin and Michigan. The front appears to get more support from
the heat of the day in the afternoon over Indiana, and we kept a
Narrow Channel of slight chance pops east of Champaign to Mattoon.

A brief cool down will occur behind that front, with highs on
Tuesday around 70. The GFS quickly brings another cold front across
Illinois Tuesday night, and a small surface low and cold front into northwest Illinois
Wed night/thurs. The European model (ecmwf) keeps high pressure in place across Illinois
until a low arrives Thursday afternoon. Will keep a dry forecast
tues-thurs going for now, as each of the potential waves are showing
limited moisture availability. Temps will climb above normal for
Wed and Thursday.


Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1255 PM CDT Thursday Oct 8 2015

Keeping the VFR forecast for now. Scattered low/broken high through the
afternoon with southwesterly winds gusting to 20kts at times ahead
of the approaching front. Vcsh mention this evening...losing even
the mention after loss of day time heating. Better chance for
showers and thunderstorms to the north, showers at ilx terminals
will have a large diurnal component. Hrrr is still somewhat bkn
with depiction of precip. Will update as necessary, but confidence
is not high enough to warrant a predominant mention at this point.


Ilx watches/warnings/advisories...


Short term...hjs
long term...shimon

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