Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 200203

Area Forecast Discussion
National Weather Service Lincoln IL
903 PM CDT Mon Mar 19 2018

Issued at 850 PM CDT Mon Mar 19 2018

An upper-level low is centered over southern Illinois this
evening, with the associated surface low centered over central
Kentucky and Tennessee. The upper-level system is forecast to
shear east-northeast through the night. The rainfall wrapping
around the north side of the system will start to pull away from
the region overnight, although it should linger into Tuesday
morning south of I-70. Still some question if there will be any
change of precipitation type as colder low-level air wraps in
behind the system. At this point rainfall still appears most
likely until the precipitation departs. Before the precipitation
ends it appears that ice crystals are largely loss, which should
preclude snow occurring. Also, surface temperatures are expected
to stay above freezing until the precipitation ends, which would
eliminate the risk of freezing rain.

Going forecast was in good shape overall, and only made minor
changes to the hourly trend.


.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 00Z TAFS through 00Z Tuesday evening)
Issued at 649 PM CDT Mon Mar 19 2018

Gusty northeast winds are expected across the central Illinois
terminals for much of the 00Z TAF valid time. Light rain is
possible for a few more hours across KSPI & KDEC as a storm system
pulls away from the area, but otherwise dry and VFR conditions are




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