Area Forecast Discussion
Issued by NWS Central Illinois

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609
FXUS63 KILX 180834
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
334 AM CDT Tue Jul 18 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 304 AM CDT Tue Jul 18 2017

High pressure is dominant in the region this morning as the next
warming trend kicks in. Aloft, the deep warm air over the SW
starts to shift into the Midwest as the upper ridge starts to
dominate the Mid/Lower Mississippi River Valley. 850mb temps will
go up a couple of degrees C by the end of the day...as temps at
the surface will move into the upper 80s/low 90s. A wave to the NW
will continue some convection into the early evening in IA. HRRR
is scant with bringing any convection across the Mississippi, but
has been more aggressive with a quick advancement of the resultant
cold pool into the region. With any activity moving into a ridge
axis and the days warming in the midlevels all but neutralizing
any lapse rate...not putting in pops at the moment. Should that
storm prove to be more aggressive and/or quicker...the northwest
may need to be reconsidered with a sct chance for some remnant
showers. Potential blow off sky cover in the west from that
activity may end up keeping the overnight lows a little bit higher
in the western portions of the CWA. Winds will be light and
somewhat variable...but trending more southerly as a whole.

&&

.LONG TERM...(Wednesday through Monday)
ISSUED AT 304 AM CDT Tue Jul 18 2017

Summary of the rest of the week... hot and humid...with stormy
chances shunted to the north providing glancing blows of precip
north of the I-74 corridor through the end of the week. The
forecast for the weekend falls apart with some divergence in model
solutions. In other words...not much has changed in the last
couple of runs. The ECMWF is far warmer than the blended
forecasts...and thinking is that the better forecast may be
somewhere in between. So some minor adjustments to the blends only
to bring up the guidance a degree or two. Dewpoints remain in the
mid 70s through the end of the week, resulting in 100F+ heat
indices, and limiting the overnight lows to the low to mid 70s as
well. Heat Watch is warranted if only for duration, as the heat
will remain Wed thru Sat, although some areas may actually see a
couple days of heat indices over 105F.

The rising heights aloft over the southern half of the country
puts Central IL on the cusp between more progressive flow and a very
weak gradient. Several waves moving through the almost zonal flow
to the north have resulted in a periodic low pops north of I-74
through the end of the week...with the better chances for precip
moving in for the weekend as a front slowly settles into the
region. The warm air out of the SW and the cooling impact of the
showers to the north and northeast will help to further define a
developing boundary at the surface...providing a focus for waves
into the weekend as the front settles into the region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1240 AM CDT Tue Jul 18 2017

VFR in most sites, though HRRR has started to develop some fog for
SPI tonight. With only a 2 degree dewpoint depression and calm
winds...putting a tempo in for the predawn hours down to IFR.
Other than that...CU rule for GFS and NAM both hinting at a gap in
a cu field...so leaving out BMI and DEC for some cu development
everywhere else today. Winds light and variable under the ridge
and cirrus.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Wednesday afternoon through Saturday
evening for ILZ027>031-036>038-040>057-061>063-066>068-071>073.

&&

$$

SHORT TERM...HJS
LONG TERM...HJS
AVIATION...HJS



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