Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 200550
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1250 AM CDT Sat May 20 2017

.UPDATE...
Issued at 859 PM CDT Fri May 19 2017

An MCV and line of storms will progress east-northeast across our
forecast area over the next 3-5 hours. Instability and shear
parameters continue to point toward low potential for severe wind
and/or hail from the storms in our area. The latest HRRR indicates
a break will develop behind this line, but another wave will
arrive across our SE counties later tonight. Those storms also
should be sub-severe. The better chances for severe weather now
look to be focused later Saturday afternoon for areas along and
east of I-57, when damaging wind, large hail and even a few
tornadoes could develop.

The main updates for the rest of tonight were to the timing and
coverage of expected showers/storms. Thunder potential will be
higher south of I-72/74, but a few strikes will be possible in our
entire forecast area overnight. A blanket of low clouds will keep
our low temps closer to current readings, with little change in
airmass expected through sunrise.

Updated forecast info is already available.

&&

.SHORT TERM...(This evening through Saturday)
ISSUED AT 253 PM CDT Fri May 19 2017

Frontal boundary is currently located just north of the I-70
corridor this afternoon, with an extremely sharp temperature range
over the forecast area. 2 pm readings ranging from the mid 40s
north of Peoria, to the mid 80s from Flora to Lawrenceville. A
surface low which has moved into southwest Indiana should start
to drag this boundary a bit southward through the evening hours,
although the significantly colder conditions should stay north of
I-72.

Large convective complex over Kansas and eastern Oklahoma this
afternoon is now edging into western Missouri, and should start
moving into western Illinois after midnight. The area immediately
south of the I-72 corridor received 2 to 5 inches of rain last
night. This would be the area most subject to any flash flooding.
However, right now the system looks to be progressive enough, and
more in a north-south axis, to mitigate the threat of additional
flooding. This will be something we will watch closely over the
next several hours.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 253 PM CDT Fri May 19 2017

Large upper low currently over Colorado will shift into the
central Plains by early Saturday, then lift northeast to near the
Iowa/Minnesota border by mid evening. The frontal boundary will
surge northward and place all of the forecast area in the warm
sector by around midday. Have not changed forecast high
temperatures much, mainly low-mid 80s except for some 70s
northwest of I-55. The GFS brings CAPE values over 1200 J/kg over
all of the forecast area by early afternoon, while the NAM limits
the higher values mainly across eastern Illinois. Main threat for
any severe weather would mainly be over the eastern CWA, where
0-6km bulk shear values reach 40-45 knots during the afternoon. By
early evening, the trailing cold front will be pushing into the
western CWA, and should largely be out of the forecast area by
sunrise Sunday.

The upper low will not be breaking any speed records early next
week, mainly loitering just northwest of Lake Superior through
Monday. By Monday night, a secondary lobe of energy will break
free, and swing southeast into the Midwest, where it will slowly
edge eastward through Thursday. In this particular pattern,
temperatures will be relatively cool during mid week, with highs
down into the 60s Tuesday and Wednesday, before starting to
recover on Thursday. Rain chances will increase quite a bit Monday
night into Tuesday as this low starts to move through, with some
wraparound showers lingering into Wednesday. May be enough
instability for a few thunderstorms on Tuesday, mainly over the
eastern CWA.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1246 AM CDT Sat May 20 2017

A brief break in the TS for the short term until around 09-10Z
when another round of showers and thunderstorms moves into Central
Illinois. Models differ on the solutions beyond 12-15Z or so with
how long the breaks will be in the precip today...if appreciable
at all. IFR to MVFR clouds to be the rule with the
overnight...more MVFR in the late morning hours associated with
breaks in the precip. Winds moving from ENE this evening to more
southeasterly tomorrow...becoming southerly by sunset as the
precip finally lifts to the NE and mid level clouds move in.

&&

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

$$

UPDATE...Shimon
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...HJS



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