Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 100128
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
828 PM CDT FRI OCT 9 2015
ISSUED AT 828 PM CDT FRI OCT 9 2015
An elongated surface high pressure ridge axis will move across
central IL from the northwest overnight. This will bring a
continued decrease in the northerly winds across the area...as
well as clearing of the persistent low cloud deck that lingered
across the area through the day. Low temperatures will reach into
the 40s overnight...ranging from around 43 in Galesburg to 49 in
Lawrenceville. Current forecasts are on track with these
features...so no updates are planned this evening aside from
minor updates for hourly temperature/dewpoint/wind trends.
ISSUED AT 253 PM CDT FRI OCT 9 2015
Cooler air filtering into the region and persistent cloud cover
blocking the sun, are both keeping the temperatures down in Central
Illinois this afternoon. Northerly winds are expected to weaken
somewhat after sunset, as the high pressure ridge axis drifts closer
to the forecast area. Models do not have a good handle on the low
clouds that are out there, and concern is that the clearing may be
too quick. Have hung onto the clouds a little bit longer, but
eventual clearing after midnight should allow the temps to drop to
forecast lows, particularly west of I-55.
.LONG TERM...(Saturday through Friday)
ISSUED AT 253 PM CDT FRI OCT 9 2015
Expansive high pressure will be in control of the weather through
the weekend. The surface ridge axis will pass southeast of our
counties by late afternoon, allowing the southwest winds to increase
during the afternoon. Forecast soundings show plenty of dry air by
12z/7am Saturday, so we expect full sun and SW winds to help high
reach into the upper 60s. Gusty SW flow on Sunday will continue the
warming trend, with 850mb temps climbing into the 16-18C range.
Mixing those temps to the surface should yield highs in the upper
70s to low 80s.
There remains consistent agreement among the 12z models about the
next cold FROPA late Sunday night and Monday morning. Despite a 3-5
hour period of focused lift with the front, evident in the omega
time height analysis, very limited moisture will be present for
precip generation during the fronts time in Illinois. There
appears to be increasing support for rain showers Monday afternoon
once the front reaches Indiana and eastward, as the front taps
into moisture from over the southeast states. We will continue a
dry forecast in our counties for Monday afternoon, but showers
could be close by across the Indiana border. The cold air will lag
enough behind the front for high temps to reach the mid to upper
70s early Mon afternoon.
A brief shot of slightly cooler air will arrive behind that front,
keeping high temps on Tuesday in the upper 60s.
Northwest flow aloft will set up a series of fast moving shortwaves
for the rest of the week, with rapid periods of warming and cooling
ahead of and behind the waves. The next one is projected for Tuesday
night and another on Thursday morning. Neither of them are
expected to have sufficient moisture and dynamics to produce any
precipitation in our forecast area. The fast progression of the
systems will limit the affects of potential airmass changes, so
highs Wed and Thur should generally remain in the low 70s.
Slightly cooler air behind the Thursday wave will limit highs on
Friday to the upper 60s, which is normal for this time of year.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
ISSUED AT 648 PM CDT FRI OCT 9 2015
Widespread cloud cover across central IL this evening, based
around 3500 feet AGL, occasionally dipping below MVFR height
threshold of 3000 feet the past few hours. Back edge of this cloud
deck approaching through northern IL, and expected to move across
central IL terminals 02Z-05Z for SKC-SCT035 conditions overnight.
Clearing should be most pronounced at northern sites KPIA-KBMI-
KCMI which should allow at least some thin fog to form by morning
and have tempo MVFR visibilities in TAFS 10Z-13Z. VFR conditions
after 13Z. Winds N up to 10 kts overnight...diminishing through
morning...becoming SW up to 8 kts after 15Z.