Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 131004

Area Forecast Discussion
National Weather Service Lincoln IL
404 AM CST Wed Dec 13 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 330 AM CST Wed Dec 13 2017

Deep upper low moving into the Upper Midwest this morning on the
surface map. Predominantly northwesterly flow continues aloft as
the wave dives to the southeast. Southwest winds expected
throughout today to bring temps up to the upper 40s/lower 50s with
limited sunshine as mid level clouds stream across the region.
However, will be a very windy and blustery day. Winds are expected
to remain at sub advisory criteria as the storm moves into the
region bringing a much tighter pressure gradient. Winds just off
the surface come to a maximum before expect some of
the higher gusts from mid morning to early afternoon, once the
inversion breaks. A cold front moving through Central IL will
bring a round of sprinkles/flurries today before clearing the area
after sunset. Much colder air moves into the area behind the wave.
Whereas clouds tonight will help to keep the lows in the 20s,
tomorrows high temps will be about a 10-15 degree departure from


.LONG TERM...(Thursday through Tuesday)
ISSUED AT 330 AM CST Wed Dec 13 2017
Cold air in place for Thursday keeps the high temps just below
freezing. North winds will remain relatively light and wind
chills will drop into the 20s in the afternoon. Weak warm air
advection kicks in for Friday with a west wind trying to pull some
of the warmer air into the region, and highs start to move into
the mid to upper 30s as another wave dives into the western
trough, altering the flow pattern aloft. The remainder of the
forecast centers around the interaction between the wave moving
onto the Pac NW coast on Friday, and an upper low over the Baja.
Either way, the westerly flow aloft allows for a slight warm up
and weak ridging over the eastern half of the country as the wave
digs in. The models are trying to resolve the two waves as to
phasing or ejecting the southern wave into more northeasterly
flow. Models are spinning up a sfc low and pushing precip into the
region for Sunday on this most recent run. Given the pattern
shift involved, expect details to start to come out in the next
few runs for the remains of the forecast pd.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1149 PM CST Tue Dec 12 2017

The lighter winds from this evening have already shown an
increasing tendency. A low approaching from the NW will continue
to bring increasing S-SW surface winds and winds aloft by late
tonight into early Wednesday morning. As a result of strong SW
winds aloft, have included low level wind shear at all TAF sites
late tonight and tomorrow morning due to 45 kt flow at 1500 ft
AGL. CMI and DEC will be the latest to see LLWS, but a few hours
from 12z- 15z or so could see those conditions as well. As a cold
front approaches and then passes tomorrow, winds will be shifting
from SW winds to start the day, then become westerly in the
afternoon while continuing at 20G35kt. Winds will eventually
become NW by late afternoon, once FROPA occurs. Winds will remain
brisk even into the evening, but could drop below 10kt at PIA by
the end of the 00z TAF period.

Cloud heights look to approach MVFR by mid to late afternoon
tomorrow, with the TAF sites along the I-74 corridor having the
better chances of dropping down into MVFR levels. No precip of
significance is expected, although some light rain or snow could
develop with the frontal passage.




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