Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 051155

Area Forecast Discussion
National Weather Service Lincoln IL
555 AM CST Mon Dec 5 2016

.SHORT TERM...(Today and tonight)
ISSUED AT 402 AM CST Mon Dec 5 2016

High pressure ridge is over southeast IL/southwest IN early this
morning and this will continue to move east through the day. Clouds
have been decreasing from the west and ti appears the clearing line
has gotten to Jacksonville, resulting in dense fog developing. Very
low clouds remain over other areas. As the morning progresses, more
clearing from the west is possible, which could result in more fog
developing; but unsure has to how low visibilities will get. So for
now, will have dense fog for 4 counties in west central IL til 18z.
If more develops, then will have to update accordingly. Remainder of
the afternoon will dry with maybe some sun, but only in the
southwest parts of the CWA. Appears the north/northeast and eastern
areas of the CWA will stay cloudy next 24hrs. This will keep temps
down from what first thoughts were. So, upper 30s along I-74 with
lower to middle 40s elsewhere. For tonight, models drying things out
in the northwest and north. So, most of precip will be in the
southern and southeastern part of the CWA. Precip will not reach the
CWA until around 03z and then slowly spread north during the night.
Precip should be primarily rain, but as surface temps decrease to
near freezing in the north, rain or freezing rain will be possible.
Based on temps and forecast soundings, the freezing rain chances,
though in the 20pct category, will be mainly in areas east and
northeast of I-74. Overnight lows in the north will be at or just
below freezing, while central and southeast areas will be warmer, in
the middle to upper 30s.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 402 AM CST Mon Dec 5 2016

Forecast has a lot more variability in the last few synoptic runs
as the operational models are having a hard time handling the
interaction/division between two waves over the weekend.  Other than
that...a cold surge of Arctic air dropping the temps even further at
the end of the week.

Rain will continue through the morning in far eastern and
southeastern IL.  On the retreating back edge of the precip, some
mix of frozen precip possible briefly before becoming all rain by
mid morning.  The surge of colder Arctic air makes its way into the
region and by Wednesday, most areas north of Interstate 70 have high
temperatures at or below freezing...everywhere on Thursday.
Overnight lows dropping each day until widespread teens Thu
night/Friday morning.  Winds Friday morning will be up a bit,
dropping wind chills to single digits.

24 hours ago, two waves were moving through the across
the northern tier of the CONUS, and another out of the Southern
Plains.  Previous runs had brought the two into the Midwest for a
snowy weekend.  However, the latest runs have all but eliminated the
widespread snow.  One wave still moving across the north may bring
some snow to the northern half of the state.  However, the southerly
system is suppressed well to the south, without having much of an
impact for Central Illinois.  With a major shift over the country
from a deep wave over the eastern half of the country to a more
zonal flow by the weekend...again...confidence in the models
in handling the weekend forecast is minimal.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 555 AM CST Mon Dec 5 2016

High pressure ridge will be moving east out of the area during the
day. This will allow southerly winds to return to the area, which
has already begun in western IL, and has begun to push the lower
clouds to the east and northeast. This clearing line is difficult
to pick out on satellite, thereby making it hard to see the low
clouds from the dense fog, which has become more widespread across
west central IL early this morning. So question is how far east
will it reach this morning. Dense fog has reach SPI and is just
east of PIA. Other sites will not see dense fog but still will
have some light fog as southerly winds brings warm air into the
area over the snow cover. So, lots of moisture will evaporate into
the lower levels, continuing the fog and even low stratus clouds.
PIA/SPI/BMI will be LIFR or less for several hours this morning
and then slowly improve to IFR and then VFR late this afternoon
into this evening. DEC and CMI will likely remain at IFR, but also
improve to VFR late this afternoon. Models not handling this lower
clouds and fog very well, so low confidence beyond this afternoon.
As the lower clouds leave this evening, high cirrus will spread
over the sites for this evening. But then as winds lighten later
tonight, expecting fog to develop again at all sites, likely going
down to IFR overnight.


Dense Fog Advisory until noon CST today for ILZ040-047-049-050.



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