Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 161738
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1138 AM CST Tue Dec 16 2014

.UPDATE...
ISSUED AT 1021 AM CST TUE DEC 16 2014

Late morning surface map indicated 1005 MB low pressure over
central lower MI. Tight pressure gradient on the back side of the
low was causing blustery W/WNW winds locally, gusting 30-35 mph.
The last batch of scattered showers embedded within deep cyclonic flow
was progressing through the central/northern CWA at 10 AM, and
these will continue to shift east, moving out of the northeast CWA
early/mid afternoon. An expansive area of stratus/stratocu extends
back through the upper Midwest, thus expect cloudy skies to
continue at least through this evening. Brisk winds will continue
to provide cold advection through this afternoon, causing slowly
falling temps.

&&

.SHORT TERM...(Today)
ISSUED AT 312 AM CST TUE DEC 16 2014

The surface and upper level low pressure center of today`s storm
system is crossing northern Illinois early this morning with an
occluded frontal zone wrapping around the low and bringing scattered
showers mainly in the northern half of the state. This system will
accelerate eastward today as a northern stream trough drops out of
Manitoba into the western Great Lakes region. Cold northwesterly
flow will develop across central IL with brisk northwesterly winds
at the surface reaching 15-20 mph from mid-morning on. Forecast
soundings indicate mixed layer winds reaching around 30 mph below an
inversion based around 900 mb, thus we can expect gusts reaching up
to around 30 mph from late morning through afternoon. Temperatures
will hold fairly steady through morning then steadily decline
through afternoon as cold advection takes place. Based on expected
movement of the current storm system, will expect scattered showers
mainly north of Springfield until mid-morning gradually lifting
northeastward late morning/early afternoon. Isolated showers
possible to the south.

&&

.LONG TERM...(Tonight through Monday)
ISSUED AT 312 AM CST TUE DEC 16 2014

Tranquil weather on tap for tonight and Wednesday, as surface high
pressure ridge drifts through the area. NAM forecast soundings
retain a rather stout inversion around 950 mb. The GFS is a little
more optimistic in the inversion breaking, but still shows some
decent mid-level cloud cover, so am reluctant to go any more
optimistic than partly cloudy at this time.

Southern branch of the jet stream to be the most active over the
next several days, with several shortwaves advancing along it.
Wednesday night/Thursday system remains just to our southwest, but a
more prominent trough digs across the Plains on Friday as the next
wave moves into southern Texas. The evening model trends continue to
trend more toward the lower portion of the Mississippi Valley with
the track of the developing storm this weekend, with the surface low
generally along the Gulf Coast. The latest ECMWF bypasses us
completely with any precipitation, with the GFS bringing some light
snow as far north as about I-70 late Friday night. Have kept some of
the GFS solution in mind and focused the precipitation chances
across the southeast CWA Friday night and early Saturday. While the
precipitation fields off these models would keep much of the CWA dry
on Saturday, have kept some slight chances in for now east of I-55,
and 30% chances south of I-70.

Remainder of the current forecast is dry, with the main concern more
late Monday night into Tuesday as an upper low carves a position
into the upper Mississippi Valley. Any associated precipitation
chances for that time frame will be introduced with the afternoon
forecast package.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 1138 AM CST TUE DEC 16 2014

Remnant showers and drizzle with visibility reductions to 2-4 SM will
exit the eastern TAF sites by 20Z. Ceilings have already risen to
MVFR levels at PIA/SPI, and this trend will continue to the east
this afternoon, as low pressure shifts farther away from the
region. Main concern for this forecast is possibility/extent of
scattering out MVFR ceilings tonight into tomorrow morning.
Forecast soundings from higher resolution models point to a
familiar scene from the past few weeks, with a strong subsidence
inversion trapping moisture around 1500 FT. This looks likely to
keep ceilings in place at least through 15Z/Wed, even with
northwest winds bringing in drier air at the surface. Tight
pressure gradient will keep west winds gusting at 25 kts this
afternoon. Gusts will diminish after sunset with speeds tapering
to around 10 kts as the gradient relaxes, and under 10 kts towards
sunrise as surface ridge builds in from the NW.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...25
SHORT TERM...Onton
LONG TERM...Geelhart
AVIATION...25





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