Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 220414

Area Forecast Discussion
National Weather Service Lincoln IL
1114 PM CDT Mon May 21 2018

Issued at 845 PM CDT Mon May 21 2018

Weak cold front pushing across far west central Illinois early
this evening with only isolated showers noted along and just
to the east of the boundary. Despite some good instability this
afternoon, the mid levels of the atmosphere dried out significantly
after our shortwave from this morning shifted off to our north
and east. Had some decent cumulus development just to the east of
the boundary, with a second band along an old outflow boundary
that shifted along and just to the east of the I-55 corridor.
However, once the updrafts initiated, they were only able to get
to around 10,000 feet before running into the dry mid levels and
thus, not much organization to the showers late this afternoon and
evening with only a few lightning strikes noted over far southeast
Illinois. Will continue to carry the slight chances further east
into the CWA just ahead of the weak cool front.

As the weak surface low along the boundary to our north shifts a
bit further east, the large band of low clouds and fog to our
north should settle south into parts of our area after Midnight.
The main question is how far south. Based on the current trends,
it appears about the northern half of the forecast area should see
the lower clouds by sunrise Tuesday along with some patchy fog.
That should gradually dissipate by mid to late morning allowing a
sun-cloud mix for the afternoon along with pleasant temperatures
with readings climbing into the upper 70s north to the middle 80s
in our southern counties. Have adjusted the POPs a bit further
west closer to the cool front this evening, otherwise, the rest of
the forecast is in good shape. We should have the updated ZFP out
by 9 pm.


.SHORT TERM...(This evening through Tuesday)
ISSUED AT 313 PM CDT Mon May 21 2018

Low pressure is currently centered over west central IL with a warm
front extending east along I-74 and cold front working its way
through the Illinois River valley. Considerable cloudiness over the
warm sector in central IL is limiting destabilization this
afternoon, and weak lift seems to be focusing near the IN state line
with a few thunderstorms forming there. Nevertheless, could see
thunderstorms anywhere ahead of the front late this afternoon and
there is a recent trend toward a line of weak radar echoes forming
just east of I-55 which could turn into some thunderstorms. Have
therefore kept a mention of thunderstorms over most of central IL
for late afternoon, ending from west to east through to the IN state
line by 11 p.m.

Overnight, high pressure building into the area along with moist
conditions from significant rainfall up to an inch or two from
Jacksonville to Lacon should allow patchy fog to develop and
spread through much of central IL overnight. Lows expected to
range from 57 in Galesburg to 66 in Lawrenceville. Tuesday should
end up partly cloudy with warm temperatures ranging from around
80 along I-74 to the mid 80s south of I-70, along with light NW

.LONG TERM...(Tuesday night through Monday)
ISSUED AT 313 PM CDT Mon May 21 2018

Much drier air should move into central IL through midweek as an
upper level ridge builds over the central U.S. Highs should climb to
the mid and upper 80s midweek through the weekend. A couple of upper
level troughs looks to struggle across the central U.S. ridge late
in the week through the weekend to potentially produce chances of
thunderstorms over portions of central IL, but model inconsistencies
point toward low predictability on any of these features. A more
predictable feature appears to be low pressure developing over the
southeast U.S over the weekend, but this appears to stay out of the
central/SE IL forecast area.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1106 PM CDT Mon May 21 2018

MVFR and IFR cigs/vsbys just to our north with the main forecast
challenge through 15z just how far south the lower vsbys and
clouds will go overnight. Surface and low level flow quite weak
despite a cool front pushing across the forecast area tonight. The
stratus deck and lower vsbys were slow to advect south this
evening but looking at our current temp- dew point spreads suggest
the lower cigs and especially vsbys may develop across our area
during the early morning hours, especially in the areas that
received the significant rainfall over the past 24 hours.

If the clouds do indeed advect south into our area, not sure how
low our vsbys will get overnight, while at the same time, if the
lower cloud deck is slower to arrive, we may just drop down more
quickly with our vsbys during the early morning hours. Any IFR/LIFR
or MVFR cigs/vsbys will gradually dissipate by 15 or 16Z Tuesday
with a sct-bkn deck at 2000-3000 feet in the late morning and then
scatter out in the afternoon with cloud bases in the 3500 to 4500
foot range by 20z.

Light south to southwest winds will shift into a light westerly
direction after FROPA late tonight with a northwest wind at 8 to
13 kts from mid-morning thru late afternoon Tuesday.




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