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Area forecast discussion 
National Weather Service Lincoln Illinois
1153 PM CDT Monday Aug 31 2015

Update...
issued at 900 PM CDT Monday Aug 31 2015

Showers have ended this evening, with lingering patches of clouds.
Forecast soundings are pointing toward a residual layer of
moisture overnight could lead to scattered clouds from time to
time, but nothing significant. Of more concern will be the
potential for localized dense fog overnight. Dewpoints remain
quite high, in the upper 60s to low 70s. With mostly clear skies
and light south winds over night, radiational cooling will help
dewpoint spreads decrease to 0-2 degrees after midnight. We
continued with fog in the grids for later tonight into tomorrow
morning. Overall, the current forecast has the expected trends
covered well. No formal update will be needed this evening.

&&

Short term...(tonight)
issued at 249 PM CDT Monday Aug 31 2015

Weak remnants of a boundary draped over the south and a small surface
low over Indiana are dominating the weather this afternoon for
central Illinois. Yesterday the 70 degree dewpoints were confined
to right along the surface boundary. Today, they are a little more
widespread, even this late in the day as mixing out has been limited
in the almost stagnant airmass. Some observation in the southeast are
actually dropping into the upper 60s after some weak convective
storms this morning. However, quite likely going to see those
dewpoints rebound quickly due to a lot of quantitative precipitation forecast/moisture in the soil.
With light southerly winds and very little in the way of cloud cover
expected tonight, fog is once again the biggest concern. With some
mixing still to come, have left the forecast as patchy for the
entire County Warning Area tonight.

Long term...(tuesday through monday)
issued at 249 PM CDT Monday Aug 31 2015

Main weather story through the extended remains the very warm and
humid conditions that are expected to persist through the week and
into the weekend. High temperatures on Tuesday will reach the upper
80s to around 90 degrees...then readings will climb into the lower
90s for the remainder of the period. Dry weather will generally be
the rule...however isolated convection cannot be ruled
out...especially Tuesday afternoon as a weakness in the mean 500mb
ridge axis remains in the vicinity. Models continue to show some
convection across the eastern parts of the County Warning Area as this feature
gradually shifts into the Great Lakes by Wednesday.

The next significant chance for rain will not arrive until early
next week...when a strong short-wave flattens the upper ridge and
pushes a cold front into the region. Models are in disagreement
concerning the front...with the GFS now trending slower with the
cold front passing through central Illinois late Monday night into
Tuesday...while the European model (ecmwf)/Gem does not bring the cold through the
County Warning Area at all and keeps the ridge strong over the area. Given
persistent and highly amplified ridge positioned across the
Midwest...think a slower break down to the pattern is still best
solution. Have therefore trended slower. As a result...am
expecting dry conditions through Sunday night...with rain chances
arriving in the northwest Monday.

&&

Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1153 PM CDT Monday Aug 31 2015

Cloud cover has nearly completely dissipated toward 05z, with no
appreciable fog of note in any local observations, other than cmi
showing 7sm and Danville 5sm br. Dewpoint depressions are ranging
from 8 degree at spi to 2 at bmi, with dnv at 1. Areas of MVFR fog
still appear possible, but hrrr has reduced the areal coverage of
IFR fog to just patchy areas in east central Illinois. Have altered the
tempo groups later tonight to bump up visible from 1 to the 3sm-4sm
range. Forecast soundings are not supportive of significant fog
later tonight. There is more support for areas of low clouds to
bubble up and drift around under weak steering winds.

An upper low spinning over Indiana will once be a focus for spotty
showers and isolated thunderstorms tomorrow, mainly southeast of
cmi to Dec. The potential for precipitation at our eastern terminals is
low enough to not include any thunderstorms in the vicinity with this taf issuance. Will
increase VFR cloud cover to bkn040 at cmi and Dec.

Winds will continue out of the south the rest of the night, with
speeds in the 5-7kt range. As weak high pressure slides farther
east of Illinois tomorrow, winds will become more southwest at 10kt or
less.

&&

Ilx watches/warnings/advisories...
none.
&&

$$

Update...shimon
short term...hjs
long term...auten
aviation...shimon

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