742 
FXUS63 KILX 020756
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
256 AM CDT Wed Apr 2 2014

.DISCUSSION...
ISSUED 255 AM CDT Wed Apr 2 2014

A busy period on tap through Friday, with excessive rainfall
amounts and severe weather a concern.


SHORT TERM...Today through Friday:

Large upper low currently located near San Francisco will be
swinging eastward across the Rockies tonight and into the central
Plains on Thursday. Showers and isolated thunderstorms have been
moving through the central third of the CWA over the last several
hours, in the narrow baroclinic zone along the 850 mb warm front.
Dry air sampled by the 00Z upper air sounding was still in place
over the northern CWA and has kept the rain at bay up there, but
this will erode later this morning. Much of the rain will be
across the northern half of the CWA by afternoon, with a period of
more scattered showers/storms south of I-70 where the surface warm
front will be moving in from the south this afternoon.

The front is still progged to lift northward to around I-72 late
tonight, then slowly creep northward Thursday before the surface
and upper low track northeast into eastern Iowa and drag the front
fully through the forecast area. Showers/storms should be on the
increase again tonight as mid level lapse rates steepen.
Precipitable water values increase to 1.4 to 1.5 inches by late
tonight and will remain very high through Thursday evening.
Forecast rainfall for this event through early Friday on the order
of 3 to 4 inches over a large area of central Illinois, with 2 to
3 inches from about Rushville to Bloomington northward. While this
is not expected to fall fast enough to cause flash flooding,
there is still a significant concern for areal and river flooding
to develop, thus a flood watch is being issued for a large part of
central and southeast Illinois. 

Some more sustained breaks in the showers/storms expected for a
time on Thursday as the CWA gets more fully in the warm sector.
Still think that 70-75 degrees will be common from I-72 southward
for highs, which will allow CAPE's to rise to around 1800 J/kg
during the afternoon and evening. Decent 0-6km bulk shear of
around 35-40 knots will contribute to the severe weather
potential, with a large part of the forecast area in the SPC Day2
outlook's 30% "hatched area" which indicates potential for more
significant severe conditions. Main severe weather threat will be
in the evening, perhaps lingering across eastern Illinois after
midnight as a squall line pushes through. 

Much of the precipitation will end on Friday, but some wraparound
showers are possible into the afternoon across the north. Freezing
level dips to around 1500 feet, so cannot rule out a couple of
snowflakes mixing in, but will keep the forecast as all rain for
now.


LONG TERM...Saturday through Tuesday:

Main concern in the long term remains with the storm system that
will form near the Gulf coast late this weekend, as a large upper
trough pushes through the central U.S. The ECMWF has continued its
trend of stronger, faster and further northwest than the GFS. This
solution would spread rain as far northwest as I-55 by early
Monday, while the GFS precipitation shield largely misses us. Have
generally kept PoP's in the 30-40% range due to the potential for
some light showers with the trough itself as it moves through
Illinois. 

Geelhart

&&

.AVIATION...
ISSUED 1115 PM CDT Tue Apr 1 2014

Not much change from previous discussion. The main challenge will
be how far north the rain gets overnight and its affect on cigs 
and vsbys by morning. Band of rain continues to edge slowly north
late this evening and expect this trend to continue overnight with
most areas seeing some light QPF. Showers and TSRA were developing
over parts of NW Missouri late this evening and expect this batch
of precip to make its way into west central Illinois by morning
and encompass most of the area by afternoon, which looks to be
enough to saturate the lower levels of the atmosphere enough to
bring cigs to MVFR category which looks to last thru most of 
tomorrow night with periods of rain and isold TSRA. Surface winds
will be mainly from an east to northeast direction with speeds
ranging from 7 to 12 kts tonight and from 10 to 15 kts on Wed.

Smith

&&

.HYDROLOGY...
ISSUED 255 AM CDT Wed Apr 2 2014

QPF values of 3 to 4 inches forecast for a large part of central
and southeast Illinois through early Friday. While this will be
over an extended period limiting the flash flood potential, there
will still be areas of flooding as the ground becomes very
saturated. Significant river rises will be on tap, with flooding
likely to develop along the Illinois and Sangamon Rivers.
Ensemble hydrographs from NCRFC using 50th percentile
precipitation showing sites reaching minor flood stage by Friday
or Saturday. Similar guidance from OHRFC projecting flooding also
along portions of the Little Wabash, Embarras and Wabash Rivers. 

Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH from this evening through early Friday morning for
ILZ042>057-061>063-066>068-071>073.

&&

$$