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Area forecast discussion 
National Weather Service Lincoln Illinois
1130 PM CDT Friday Apr 24 2015

Update...
issued at 840 PM CDT Friday Apr 24 2015

Band of showers and isolated thunderstorms tracked across the far
northern portion of the forecast area late this afternoon into
early this evening along a weak surface boundary/convergence zone
located from southeast Iowa through northeast Illinois. That area of
rain was moving out of our northern counties and now we wait for
additional showers and isolated storms to develop to our southwest
as the low level jet intensifies to our southwest later this evening.
Most favorable 850 mb Theta-E advection and moisture convergence
is right across the forecast area as we head into the early morning
hours. A warm front on the latest surface analysis was still well
south of our area...from extreme southwest Missouri into northern
Arkansas. This feature will push into extreme southern Illinois
tomorrow and be the focus for scattered strong to severe storms
during the afternoon and early evening hours as the surface low
and warm front move along or just south of Interstate 70.

Have made some adjustments to the hourly temperatures and precipitation
trends for this evening and have already sent out an updated zone forecast product
to reflect the changes...as a result...no additional update will
be needed at this time.

&&

Short term...(tonight)
issued at 308 PM CDT Friday Apr 24 2015

Storm system approaching the Midwest from the west overnight
spreading precipitation ahead of it and setting up a longer duration
rainfall event. Clouds and southeasterly winds keeping the region
considerably warmer than the past couple of nights, but precipitation
accompanying as well. Isolated thunder cannot be ruled out
particularly after midnight as the low center draws nearer. Roughly
a half an inch or so of precipitation possible before 7 am.

Long term...(saturday through friday)
issued at 308 PM CDT Friday Apr 24 2015

Low pressure center associated with the storm system currently
ejecting northeast out of New Mexico will reach near the Illinois/MO
border between St Louis and Quincy around noon Saturday...with a
warm front extending east-southeast from the low to roughly near the I-64
corridor. The low will then track east-southeast across Illinois through Saturday
evening. Roughly 30-45 kts of 0-6 km bulk shear and MUCAPE
instability values around 1500-2000 joules should develop in the
warm sector south of the warm front...with much more modest values
to the north as well as a lack of surface-based instabilty. Values
along/south of the warm front should be enough to support storms
capable of producing hail and severe wind gusts as well as locally
heavy rainfall...potential tornado development as well...while to
the north more of a steady moderate rainfall and cool temperatures
would be expected. Models fairly consistent with the track of the
low at this point...but small errors on exact track still presents
some uncertainty on severe thunderstorm possibilities in the
southern portions of the central/southeast Illinois forecast area. Storm total
precipitation looks to be around 1-1.25 inches across the central/southeast
Illinois forecast area...with locally higher amounts possible. Heavier
areas could initiate some river flood issues.

The low will then move rapidly east Saturday night with showers
coming to an end for central Illinois. Cool and dry northerly flow out of
Canada will follow the system for Sunday and Monday...with highs in
the upper 50s/low 60s and lows dipping into the 30s in some
locations.

A central U.S. High will build toward the end of the week promoting
a warming trend...generally dry conditions...and lighter winds. A
weak trough midweek at this point looks probably too dry for
precipitation as it splits into a stronger low over the deep south
and a separate wave passing far to the north...but at least a slight
chance for precipitation is not out of the question. Highs Tuesday through
Friday should rise from the middle-60s Tuesday to near 70 Friday.

&&

Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1125 PM CDT Friday Apr 24 2015

Showers were starting to redevelop over parts of central Illinois late
this evening and expect this trend to continue into the early
morning hours. As a result...we should see ceilings and visibilities
gradually deteriorate to MVFR and then IFR by morning across
the entire area. The actual surface low is expected to track
south of the taf sites which will keep the MVFR and IFR conditions
going through most of Saturday along with the rain and isolated thunder.
Forecast soundings showing the low level moisture will hold over
most of central Illinois through at least 03z Sunday before we start to
see some drier air advect south into our area which should bring
about an improvement in ceilings and visibilities as the night wears on. Surface
winds will be out of an east to southeast direction tonight at 10
to 15 kts with an occasional gust around 20 kts by morning...then
winds will back into the northeast and eventually the north during
the afternoon and evening hours. Look for wind speeds to average
from 12 to 17 kts with occasional gusts around 20 kts into the
early evening hours.

&&

Ilx watches/warnings/advisories...
none.
&&

$$

Update...Smith
short term...hjs
long term...Onton
aviation...Smith

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