Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 241757
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1257 PM CDT Fri Oct 24 2014

.UPDATE...
ISSUED AT 1043 AM CDT FRI OCT 24 2014

Low clouds and fog continue to blanket west-central Illinois this
morning, mainly along/west of a Peoria to Taylorville line. A
Dense Fog Advisory remains in effect for this area through noon.
So far, very little erosion of the low cloud cover has been noted
on visible satellite imagery, although the process will likely
begin within the next hour or two, as it did yesterday across
Iowa. HRRR shows this as well, with skies becoming partly sunny
across all but the far northwest KILX CWA by mid-afternoon. If
trends continue, eastern Iowa/northwest Illinois may remain cloudy
for the entire day. Further east, southerly winds and at least
partial sunshine will help boost afternoon highs into the middle
to upper 60s across central Illinois. Forecast update has already
been issued.

&&

.SHORT TERM...(Today)
ISSUED AT 235 AM CDT FRI OCT 24 2014

A weak short wave continues to move through the eastern parts of the
CWA this morning, but this should be out of the state by time the
new forecast is issued, or shortly after. The main concern this
morning is the development and advection of stratus clouds and fog
early this morning. Dense fog is present across most of eastern Iowa
this morning and the HRRR model advects this into the area for this
morning. This will keep lots of clouds in the area for this morning,
and could affect max temps for this afternoon, depending on how
quickly the clouds dissipate. Models have it diminishing during
the late morning hours. And with winds becoming southerly by
afternoon, believe some dissipation of the clouds will happen. So
will have less clouds during the afternoon. However, afternoon
high temps may not be as high as first forecast, so have decreased
max temps 1-2 degrees from previous forecast. MAV guidance is
higher than MET by several degrees, so took a compromise between
the two due to cloud cover issues.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 235 AM CDT FRI OCT 24 2014

Main forecast issue this weekend and into Monday involves
temperatures. Latest model runs for Saturday have been warmer, as
main core of cooler air associated with a frontal boundary track
more across the Great Lakes region. Have bumped up Saturday highs by
a couple degrees. 850 mb warm front progged to lift through the area
late Saturday night and early Sunday, with +16C temperatures
spreading across central Illinois Sunday afternoon, lingering into
Monday. Have also raised highs several degrees both Sunday and
Monday, with a few 80 degree readings possible on Monday across
southwest and southeast portions of the forecast area. Record highs
for Monday are in the mid 80s and currently appear safe.

Split upper flow early next week focuses the deeper part of the next
wave along the northern stream. Model guidance is fairly uniform
with rain chances Monday night through about midday Tuesday, and
pretty much has the forecast area dry by sunset as a high pressure
ridge quickly builds into the mid-Mississippi Valley. However, the
guidance diverges later in the week. The ECMWF persists in a rather
broad trough along the Mississippi River midday Thursday, but now
significantly ramps up rain chances along the associated surface
front. The GFS has a weaker, more progressive wave with little
precipitation. Have leaned more toward the progressive solution for
now. The ECMWF also persists in developing a large closed low over
the Great Lakes late week, which would pump significantly cooler air
into Illinois. Meanwhile, the GFS builds a ridge eastward, with much
warmer air (850 mb temperatures range from -5C to +8C between the
two models). However, this particular aspect is just beyond the
current forecast range, but will need to be addressed with the
afternoon forecast issuance.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1257 PM CDT FRI OCT 24 2014

Low clouds are rapidly dissipating across the area early this
afternoon, with 1730z visible satellite imagery showing one
persistent band from KGBG to KTAZ. Based on satellite trends,
will hold on to IFR ceilings at KSPI for one more hour before
clearing things out by 19z. Once these clouds dissipate, only
FEW-SCT diurnal Cu and high/thin cirrus will be noted for the
balance of the day. Main aviation question will be how low
ceilings will go tonight as trough axis approaches from the
northwest. NAM forecast soundings and latest HRRR both suggest at
least MVFR ceilings spreading in from the NW between 02z and 05z.
This band of low clouds will begin clearing out after midnight,
which will likely lead to fog development toward dawn. Given a
similar airmass to last night and winds expected to become
light/variable in the vicinity of the trough, have reduced visbys
to between 1 and 3 miles at the terminals. Once the trough passes,
winds will veer to the W/NW and any low clouds/fog will clear out
by Saturday morning.

&&

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

$$

UPDATE...Barnes
SHORT TERM...Auten
LONG TERM...Geelhart
AVIATION...Barnes






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