Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 222341
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
641 PM CDT MON AUG 22 2016

.SHORT TERM...(This evening through Tuesday)
ISSUED AT 314 PM CDT Mon Aug 22 2016

The high pressure ridge axis is slipping further to the east and the
surface winds will become increasingly more southerly as the evening
progresses and through tomorrow. Tonights temperatures will be in
the upper 50s and near 60. With the southerly flow, moisture return
also increases, and the threat for some patchy fog is still possible
in low lying areas...particularly in the east, closer to the ridge
axis and the lighter winds. The moisture will also add to the
potential of some cumulus development again tomorrow.

.LONG TERM...(Tuesday night through Monday)
ISSUED AT 314 PM CDT Mon Aug 22 2016

The overall weather pattern shows an upper low in eastern British
Columbia progressing eastward, with a strong upper ridge in the east-
southeastern U.S. The Canadian low will progress to western Ontario
by Wednesday afternoon, while a surface cold front approaches
western Illinois. The 12z models continue to advertise an MCS
developing in eastern Nebraska/western Iowa Tuesday night, and
progressing into W-NW Illinois by 12z Wed. Rain chances were
increase west of Peoria to the 70-80% range to account for the
better agreement in the long range models. The northern periphery of
surface high pressure to the southeast of Illinois will still
influence our eastern and southeastern counties for this initial
wave of precip, with storms struggling to overcome the drier/more
stable air south of I-70 late Tues night/Wed morning.

As surface low pressure develops along the front Tuesday night and
progresses into the central Great Lakes on Wednesday, the low will
drag a cold front toward our NW counties. The front will slow down
as it becomes parallel to the upper flow, and will be the source for
50-70% rain chances in our forecast area from Wednesday and Wed
night. Timing of the waves of storms is not in agreement in the
Aug22/12z models, but the northern half of central Illinois appears
to have better chances throughout that period. Instability remains
moderately high in the 2500-3000 J/kg range, but shear values still
look marginal in the 20-30kt range. Therefore, widespread severe
weather is not expected Wed/Wed eve. Heavy rain will be a concern,
as PWAT values climb to around 2.0 to 2.2 inches.

Rain chances finally increase into southeast IL Thursday afternoon,
as the cold front finally advances through that area. Instability
params remain in the marginal levels, with PWAT values of 1.5 to
1.75 inches.

High pressure arriving for Friday is expected to primarily influence
the northern half of IL on Friday and eastern half Friday night,
with dry conditions. Unstable conditions persisting south and west
of Illinois along the stalled boundary will keep slight chances of
showers in our W and S counties Friday and Fri night. An advancing
warm front from SW to NE across IL on Saturday will increase
rain/storm chances through the weekend into Sunday. We will remain
in the warm sector of the next system through Monday, so typical
summer-time thunderstorm development will be possible in the heat of
the day throughout the weekend and into next week.

Looking at temperatures this week, we expect warmer and more humid
conditions to develop for Wednesday, with heat indices back into the
low to mid 90s. The cold frontal passage on thursday will bring some
relief from the humidity into friday, but the warm front on Saturday
will increase heat and humidity once again.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 641 PM CDT Mon Aug 22 2016

High pressure will shift eastward over the upcoming day allowing
southerly winds to slowly increase. Mostly clear skies expected
overnight. Increasing cloud cover around 5000 ft AGL expected
Tuesday after 17Z as moisture returns in southerly low level flow.
Winds S4-8 kts overnight increasing to 8-12 kts with gusts 15-18
kts by afternoon.

&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...HJS
LONG TERM...Shimon
AVIATION...Onton



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