Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 192001

Area Forecast Discussion
National Weather Service Lincoln IL
Issued by National Weather Service CHICAGO IL
301 PM CDT Mon Mar 19 2018

.SHORT TERM...(This evening through Tuesday)
ISSUED AT 300 PM CDT Mon Mar 19 2018

Afternoon GOES water vapor imagery depicts a strong mid-level
short wave/closed low feature over southern MO, with an associated
998 mb surface low analyzed along the AR/MO border. Regional
radar mosaic indicates rain spreading across southern/southwestern
IL, just southwest of about a Hannibal MO to Taylorville and
Effingham line as of 250 pm. This area of rain will continue to
spread east across the southern half of the ILX forecast area this
afternoon/evening, mainly along/south of the I-72 corridor.
Heaviest rainfall is expected south of the Taylorville and
Charleston areas, with amounts around an inch possible before
ending Tuesday. The northern periphery of the rain shield will
likely be a sharp cutoff, with dry air on east-northeasterly low
level winds leading to quick drying north of I-72.

After highs today in the 50`s and lower 60`s, colder air will
spread into the region tonight into Tuesday as winds turn more
northerly with time as the low passes south of the forecast area.
Temperatures are expected to dip below the freezing mark by
Tuesday morning, which may result in a precipitation changing to a
mix of rain/snow except far southeast (Lawrenceville area) toward
sunrise. Forecast soundings do suggest that mid-level drying may
limit ice nucleation over a portion of the mixed precip area,
which could potentially support some patchy light freezing rain as
surface temps hover around 32 F.

Otherwise, windy/blustery conditions will continue, with
northeast winds gusting 25-30 mph turning more northerly Tuesday,
and gradually easing later in the day. Highs Tuesday are expected
to be in the low-mid 40`s across the forecast area.


.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 255 PM CDT Mon Mar 19 2018

Main forecast concerns/challenges are with low chances for lingering
precip early Tuesday evening, a chance of precip Thursday/Thursday
evening, and then with more widespread chances for precip Friday
into the weekend.

Expect mainly dry conditions Tuesday evening, however, there remains
a slight chance for some lingering precip for east central IL close
to the IL/IN border. While main upper level low and surface low will
be well east of the area, upper level trough will remain in place.
This along with potential for inverted trough to still be in place,
could support the western extent of the precip shield to be near the
area mainly in the evening. Thermal profiles during this time could
be supportive of at least a rain snow mix, if this precip were to be
in place. However, the bulk of any precip should be to the east, and
if any precip were to occur it would be brief and light. So, don`t
anticipate any impacts at this time.

With a large trough now situated over the eastern CONUS, northwest
flow looks to be in place on Thursday. In this pattern, it is
possible for upstream energy to move across the region. Guidance
continuing to indicate a shortwave diving southeast during this
time, with resultant precip pushing through the MO/IL areas. While
guidance is indicating the bulk of this precip should once again
stay away from the area, the southwest portion of the CWA could
briefly observe the edge of this precip mainly during the day on
Thursday. Thermal profiles during this time would support rain.

Continuing to monitor more widespread precip chances returning
Friday into the weekend. A brief period of upper level ridging gets
replaced with an approaching trough and potentially strong vort max
at the start of the weekend. Ahead of it, additional short wave
energy and increasing WAA will support increasing ascent which will
support developing precip shield to move across the region. This
will especially be the case Friday night into Saturday morning.
Precip still appearing to be all rain during this time. Also keeping
an eye on thunder potential during this time, as increasing LLJ and
WAA could provide a window of thunder potential initially Friday
night into early Saturday morning. However, with confidence lower at
this time, have not included thunder. Saturday will also need to be
monitored for thunder as some guidance is bringing low pressure and
a surge of warmer and more moist air across the area. In this setup,
a window of stronger development could occur. However, confidence is
low, and it is still quite possible for this low to track further to
the south. If this were to occur, the threat of stronger storms
would also be to the south.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1218 PM CDT Mon Mar 19 2018

Primary aviation concern is with gusty east to northeast winds
approaching 30 kts at times this afternoon, and an area of rain
which will spread across areas along/south of an SPI-DEC line.

Mid-high VFR clouds were spreading into central and southern IL
from the west at midday, in association with an area of low
pressure over southwest Missouri. VFR ceilings will lower to the
6000-8000 ft range by late afternoon for SPI and DEC, while
remaining generally above 15 kft for terminals farther north. Rain
will also spread across southern IL during the afternoon, and will
likely come close to the SPI/DEC areas. Dry east-northeast low
level flow will likely result in a sharp cutoff to the rain along
the northern periphery, and at this time have maintained just a
VCSH mention for SPI/DEC, but could foresee potentially having to
add a period of VFR rain at those locations if precip extends
farther north. Rain should pull off to the southeast of SPI/DEC by
mid-late evening.

Otherwise, strong surface pressure falls were developing into
southern IL ahead of the approaching low, helping to tighten up
the pressure gradient and increasing wind speeds. Forecast
soundings support east-northeast sustained speeds in the 15-20 kt
range with gusts 25-30 kt this afternoon and early evening,
gradually decreasing and becoming more northeasterly overnight.
Winds will continue to slowly diminish from the north-northeast
Tuesday morning.




LONG TERM...Rodriguez
AVIATION...Ratzer is the U.S. government's official web portal to all federal, state and local government web resources and services.