Area Forecast Discussion
Issued by NWS Central Illinois

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139
FXUS63 KILX 211100
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
600 AM CDT Mon Aug 21 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 230 AM CDT Mon Aug 21 2017

Will be watching current MCS over Iowa closely this morning as it
moves east toward forecast area. Orientation of LLJ feeding the
complex suggests that convection may fire along the NW-SE boundary
in place near I-74 toward sunrise this morning. Unlike the past
two mornings, RAP is forecasting around 2000 J/kg of elevated
CAPE will still be available to tap near the boundary at 12z,
wouldn`t be surprised to see the boundary remain active at least
through the morning with a general trend of redevelopment east and
southeast. Blow-off cloudiness will likely be somewhat of an
issue for eclipse viewing.

A break is possible once the storms move through as a brief
period of shortwave ridging moves across Illinois during the
middle afternoon and evening ahead of a stronger wave plunging
into the Midwest as the overall flow amplifies. In addition a wave
currently over southern high plains is forecast to phase with the
northern stream wave in the Missouri Valley providing additional
dynamics. Winds from 950mb on up increase to over 30 kts by 09z
suggesting that there is potential for significant winds with some
of the stronger storms late tonight.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 230 AM CDT Mon Aug 21 2017

As the wave amplifies the eastern U.S. trough, Its associated cold
front should move quickly through the forecast area. Some of the
storms Tuesday morning through midday ahead of the front may be
strong southeast of I-70 with again wind being the primary threat.
Front clears the forecast area by 00z bringing in drier and cooler
weather into next weekend. Differences in model evolution with a
potential cutoff system over the upper Mississippi Valley/Great
Lakes early next week are too significant to include in this
package.

temperatures behind the front should be mostly 5-10 degrees below
normal with a warming trend toward normal by next weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 600 AM CDT Mon Aug 21 2017

Thunderstorm Complex over Iowa continues to progress toward
Illinois. CAMs this morning seem to be handling the overall
evolution reasonable but a bit slow on the development east and
southeast. Convection will likely form southeast along a boundary
in place near I-74 this morning. SPC mesosnalysis indicates CAPE
gradient evident along boundary and will probably focus new
development. 08z HRRR shows convection impacting all central
Illinois terminals except possibly KSPI between 15z and 19z as it
travels southeast. Will follow this general trend with a
correction of timing.

Should be a lull between this initial convection and development
along and ahead of cold front expected to approach the area
tonight. Strong dynamics and deep moisture will likely lead to
widespread convection after 06z. Model are in pretty good
agreement on timing precip. Since the impact will be mostly in the
outlook period and some uncertainty exists will keep CIGS and
VSBYS VFR but would be surprised to see some MVFR CIGS and VSBYS
at times.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barker
LONG TERM...Barker
AVIATION...Barker



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