Area Forecast Discussion
Issued by NWS Central Illinois

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865
FXUS63 KILX 260400
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1100 PM CDT THU AUG 25 2016

.UPDATE...
Issued at 822 PM CDT Thu Aug 25 2016

Very persistent storm that pushed across northeast Missouri late
this afternoon has shifted into Scott county early this evening
and has progressed into extreme western Morgan county. This storm
has exhibited some mid level rotation at times with even a report
of 40 mph wind gusts in western Scott county as the storm moved
in. Further north, closer to the actual cool front, which has just
shifted south of Bloomington and Peoria, a few showers have
developed and will maintain low chance POPs this evening along and
south of this boundary thru the rest of this evening. Otherwise,
trimmed down the POPS across the north where the front has shifted
away from and adjusted some early evening temperatures. Otherwise,
no additional changes were needed to the ZFP. Should have the
update out by 845 pm.

&&

.SHORT TERM...(This evening through Friday)
ISSUED AT 252 PM CDT Thu Aug 25 2016

Mesoscale Convective Vortex(MCV) associated with large cluster of
storms over the Plains last night continues to track E/NE early this
afternoon, with 19z/2pm obs/satellite data suggesting it is now
located over northeast Missouri/southeast Iowa.  Latest radar mosaic
is still not showing much activity with this feature, although some
new convective development is trying to occur across west-central
Illinois.  Most model guidance has handled this system poorly today,
with the WRF-NMM seemingly doing the best job overall.  It shows
scattered storms developing ahead of the wave over the next few
hours, primarily impacting locations along/north of I-72 between now
and 8pm.  While severe weather will be a possibility, think
widespread severe is unlikely due to strongest instability/shear not
being co-located.  SPC mesoscale analysis continues to show highest
CAPES of around 4000J/kg focused across the far SE CWA south of the
I-70 corridor and the strongest 0-6km bulk shear of 50kt setting up
further north along/north of a Jacksonville to Bloomington line.
Think the strong shear will be great enough to overcome the lack of
instability to produce scattered strong to severe thunderstorms with
damaging wind gusts across the northern half of the CWA late this
afternoon into the early evening.  Once this early convection pushes
further east, a lull in the precip chances will occur for much of
the night, with another round of showers/storms possibly approaching
from the west well after midnight.  Will therefore focus high chance
to likely PoPs along/north of I-72 into the early evening, with only
slight chances lingering after that.  Synoptic cold front will sag a
bit further southward before becoming stationary across south-
central Illinois late tonight into Friday.  With the boundary still
in the vicinity, will continue low chance PoPs across the W/SW CWA
through Friday.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 252 PM CDT Thu Aug 25 2016

The cold front currently positioned from west central to northeast
Illinois looks to slowly edge southward into southern Illinois
through Friday morning then move slowly back northward as a warm
front through Saturday. This will provide a focus for an MCS
developing Friday night over northern Missouri or Iowa...potentially
crossing portions of central IL late Friday night. The highest
probability track looks to be toward northern IL so included a
period of 60% PoP`s from around the Illinois River northward late
Friday night and Saturday morning...and chance (30-40%) elsewhere.

Later in the weekend into early next week models advertise a series
of disturbances on the northern periphery of upper level high
pressure over the SE U.S. which should keep periodic chances for
thunderstorms in central IL. For the most part...the pattern looks
to be moist and unstable through the extended with little in the way
of large air mass changes. Will primarily carry chance PoPs(30-40%)
in the Sunday-Wednesday daytime periods and slight chances (20%) for
the night time periods. Most of the CWA should see highs in the 80s
for the next week, lows in the mid 60s to lower 70s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1100 PM CDT Thu Aug 25 2016

Little overall change in thinking from previous discussion. The
main concern overnight will be with the threat for fog and MVFR/
local IFR vsbys and cigs. Satellite data continues to show quite
a bit of mid and high level clouds across the forecast area
which may tend to limit the fog coverage overnight. Another wave
of showers and storms was located north of STL and was tracking
northeast and may affect the SPI and DEC terminals during the
early morning hours. The low levels of the atmosphere are
saturated and despite a weak cool frontal passage across the TAF
sites this evening, little in the way of drying is expected.
This will bring parts of the area the threat for fog and lower
cigs into the mid morning hours before VFR conditions return for
the afternoon hours. Winds will continue to be a non-factor thru
this forecast period with a light northerly flow tonight of 5kts
or less, and a easterly flow at 5 to 10 kts on Friday.

&&

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

$$

UPDATE...Smith
SHORT TERM...Barnes
LONG TERM...Onton
AVIATION...Smith



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