Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 231744

Area Forecast Discussion
National Weather Service Lincoln IL
1244 PM CDT Wed Aug 23 2017

Issued at 1051 AM CDT Wed Aug 23 2017

High pressure centered on the Iowa/Nebraska border will continue
to slowly build eastward today. A light NW wind will usher in low
dewpoint air, with dewpoints generally in the mid-50s late this
morning. The KILX 12z sounding confirmed the amount of dry air
above the surface, and turbulent mixing will work down some even
lower dewpoints as we near peak heating this afternoon. The
cooler/drier air will help limit high temps today to the mid to
upper 70s. The only clouds expected this afternoon should be fair
weather cumulus across our N counties, mainly N of I-74.
Otherwise, plenty of sunshine is on tap today in central and SE
IL. The current forecast database has a good handle on the trends,
and no formal update will be needed this morning.


.SHORT TERM...(Today and tonight)
ISSUED AT 311 AM CDT Wed Aug 23 2017
Pleasant weather anticipated through the remainder of the week and
into the weekend as high pressure dominates the weather map. This
morning, a surface ridge stretches through the Plains, as
northwesterly flow aloft ushers some mild temperatures into the
region. Dewpoints are also dropping into the low to mid 50s as the
drier air filters in from the NW. A few cu possible across Central
Illinois, diminishing just before sunset. Another clear night
expected, with temps dropping a degree or two lower than this

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 311 AM CDT Wed Aug 23 2017
The quiet weather continues for the Midwest through the end of the
week for the most part. 500 mb map shows a deep trough over the
NE, and weak ridging over the western half of the country. The
northwesterly flow remains anchored over the region through the
end of the week and into the weekend. Currently a wave over
western Canada is expected to top the ridge and dive into the
broader trough, traversing ILX late Wed night/Thu morning.
However, the dry air being advected into the region will keep the
passage of that wave dry in the forecast. The wave itself will
reinforce the trough, and keep northwesterly flow over the region.

Towards the end of the week, the upper low just north of the
Pacific NW will push further inland, effectively narrowing the
upper ridge and starting to kick the low over the NE further
eastward. The high pressure at the surface shifts to the east as
the pattern progresses, with winds coming around to more southerly
just to the west...but flow across the forecast area remains
easterly. Around Sunday/Day 5, the forecast becomes problematic as
another wave dives into the Plains states, moving towards the
Midwest, collapsing the ridge...while the next tropical system
potentially moves into the coast and progresses eastward. Models
vary considerably with the solution. Previous runs brought a trof
early enough to pull that system to the northeast and out of the
region. But the 00Z runs are quicker with the trof, more or less
leaving the system over the Gulf Coast without a prominent
influencing system. Either way, the wave diving into the Midwest
for the end of the weekend/beginning of next week is working with
a questionable moisture profile in the models as they are pulling
most of it out of a system that could remain well to the south at
that point...not to mention a lack of southerly flow ahead of it
advecting any moisture or warmth into the region.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1244 PM CDT Wed Aug 23 2017

Minimal impacts expected in aviation weather over the next 24
hours. High pressure will remain firmly in control of our sensible
weather. Minimal fair weather cumulus this afternoon should not
reach BKN at any location, and will remain at VFR levels. Winds
will remain below 10kt in general, except for CMI during the last
hour. As the surface high axis drifts closer to Illinois later
today and tonight, the pressure gradient will weaken, keeping
winds below 10kt for the remainder of the 18z TAF period. A weak
shortwave in Manitoba is expected to progress into N Illinois late
tonight, but the very dry air in place across C and SE IL will
prevent any precip from reaching the ground. Tomorrow will be
similar to today, with FEW-SCT050 developing late




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