Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 192027

Area Forecast Discussion
National Weather Service Lincoln IL
327 PM CDT Sat Jul 19 2014

ISSUED 326 PM CDT Sat Jul 19 2014

A weak mean trough remains over the eastern U.S. with Illinois in
a light and relatively featureless northwest flow aloft. The main
change over the next several days will be an amplifying ridge over
the West...initially extending into the Midwest increasing
temperature and humidity over Illinois. Midweek...a shortwave
will propagate over the western ridge pushing a cold front through
Illinois for a good chance for thunderstorms followed by a cooldown.

SHORT TERM...Tonight through Tuesday

Scattered cumulus development based around 4000-6000 feet covers
most of central and southeast Illinois as expected today. This
will diminish overnight with the loss of surface heating.
Overnight expect patchy fog mainly over areas east of I-57 as
easterly surface winds pull a more moist air mass in from Kentucky
and Indiana as seen on satellite trends and depicted on HRRR
model. Sunday and Monday a strong 500 mb ridge is progged to
develop over the West and extend into the Midwest. This will bring
a warm and stable air mass over Illinois. Southerly low level flow
will bring an increase in moisture yielding dewpoints over 70 by
Monday and Tuesday and heat index values approaching 100 by
Tuesday afternoon.

LONG TERM...Tuesday Night through Saturday

A shortwave propagating over the western ridge will flatten the
ridge somewhat and bring a cold front through Illinois. Models
tend to depict this scenario early Wednesday morning at this point
but there is still plenty of room for uncertainty in timing. This
will bring a good chance for showers and thunderstorms followed by
a cooldown and dry conditions by Thursday.

A stronger low pressure system moving in from the Pacific
Northwest looks to break down the ridge significantly late next
week. This should bring another surge of cooler air southward,
though not as cool as this past week.



ISSUED 1248 PM CDT Sat Jul 19 2014

High pressure ridge keeping TAFs contained to diurnal cu and light
winds. Mostly easterly/southeasterly flow...though some variability with
winds less than 5 kts or so. Diminishing cu and light winds
continue into the overnight hours. With slowly increasing boundary
layer RH, will maintain a continuity forecast and keep some MVFR
vis in for the predawn hours.




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