Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 292003
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
303 PM CDT Fri Aug 29 2014

.SHORT TERM...(This evening through Saturday)
ISSUED AT 302 PM CDT FRI AUG 29 2014

19z/2pm surface analysis shows warm front extending from southern
Minnesota to southern Indiana, generally along the I-74 corridor
across central Illinois.  Widely scattered showers and thunderstorms
have developed along the front and will continue to do so for the
balance of the afternoon.  Meanwhile further upstream, a trough of
low pressure is evident across central Missouri where thunderstorms
are becoming more numerous.  As this trough shifts northeastward,
storm chances will begin to increase across southwest Illinois early
this evening, then across the entire KILX CWA by mid to late
evening.  May see a gradual decrease in areal coverage as daytime
instability is lost, so will keep PoPs in the 50-60 range tonight.
As has been the case for the past several days, any storms that
occur will be capable of frequent lightning and very high rainfall
rates of 1.5 to 2 inches per hour.

The trough axis will lift northeast of the area late tonight into
Saturday morning, with only scattered showers/storms lingering early
in the day.  As a cold front currently across the Plains pushes
eastward and interacts with the very moist airmass in place across
the region, a renewed round of convection will be likely Saturday
afternoon/evening.  Will carry high chance PoPs in the Illinois
River Valley and likely further east across the remainder of the CWA
accordingly.


&&

.LONG TERM...(Saturday night through Friday)
ISSUED AT 302 PM CDT FRI AUG 29 2014

In the wake of Saturdays precip, the boundary at the sfc slows and
becomes a bit more diffuse overall and models are starting to speed
up the clearing as the boundary slips to the southeast into the Ohio
River Valley.  Though precip chances linger in southern and east
central Illinois on Saturday night, Sunday may be a break in the
widespread chances for rain.  Next wave slowing in the 12z runs of
the ECMWF and the NAM...though the wave aloft is slowing, the GFS
qpf is slower to respond.  Postponing the pops resulting in a dry
Sunday evening for the eastern half of the state with pops
increasing in the overnight hours along and west of Interstate 55,
with precip spreading and dominating much of the day on Monday.
Given the high PW values in the atmosphere, heavy rains will remain
a threat for the forecast pd.  Delaying the onset of precip from
Sunday night into Monday also resulting in a prolonging into Monday
night. Question for the models beyond Monday night really revolving
around the boundary stalling in quasi zonal flow aloft not really
supporting any major progression of the sfc boundary and yet another
pd of being just on the edge of the unsettled weather with a signif
lack of 500mb height gradient over the southern half of the CONUS.
Whereas the GFS is pushing a series of MCSs on the edge of the weak
flow, the ECMWF is far more conservative...though both models are
tempering the amplification significantly over the latter half of
the work week.  Thermal ridging in the south keeps above normal
temps over the region.


&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1250 PM CDT FRI AUG 29 2014

Widely scattered thunderstorms will continue to develop across
central Illinois over the next couple of hours as a warm front
lifts north of the area. Will carry VCTS at all terminals
accordingly. Meanwhile further upstream, regional radar mosaic is
showing a band of showers/thunder developing across western
Missouri into northern Arkansas. HRRR is showing this band lifting
N/NE this afternoon, eventually arriving in west-central Illinois
early this evening. Have therefore opted to carry predominant
light rain with VCTS for a 6-hour period at all sites this evening
into the overnight hours. Based on HRRR and observed trends, have
brought precip into KSPI after 02z, then further east to KCMI
after 05z. After this initial band lifts through the area, only
widely scattered showers will be noted Saturday morning.


&&

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

$$

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





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