Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 192000

Area Forecast Discussion
National Weather Service Lincoln IL
300 PM CDT Wed Apr 19 2017

.SHORT TERM...(This evening through Thursday)
ISSUED AT 256 PM CDT Wed Apr 19 2017

A weak frontal boundary was located just to our north as of 200 pm
this afternoon with widely scattered convection occurring along and
to its north. We even had some isolated cells develop in south
central through southeast Illinois this afternoon in an unstable and
uncapped atmosphere as temperatures in central and southeast
Illinois have warmed into the uppper 70s to lower 80. Latest high
resolution objective analysis across central Illinois indicates
Mixed Layer Capes of around 1500 J/KG, mainly south of the I-74
corridor. 0-3km Helicity values of 200-250 m2/s2 were noted north
of the I-74 corridor closer to the stalled frontal boundary just
to our north.

We will still have some low chance POPs for this evening along the
frontal boundary that is expected to shift well north of our area
as low pressure, currently over northern Kansas moves into Iowa
later this evening. It still appears the better threat for more
organized/severe storms will be tied into the surface low and
cold front well out to our west this evening, with the convection
pushing east late tonight before gradually weakening as it shifts
east of the Mississippi River towards dawn on Thursday. Highest
chances for showers and storms late tonight will be mainly along and
west of the Illinois River valley. Southerly winds and some cloud
cover along with higher dew points tonight point to a rather warm
night with early morning lows generally in the 60 to 65 degree

Most of the high resolution convective allowing models suggest what
is left of the showers and storms over west central Illinois will
track east with the cold front during the morning with redevelopment
expected to take place along and especially east of the I-55 corridor
Thursday afternoon. Mixed Layer Capes in the 1500-1800 J/KG range
tomorrow afternoon just ahead of the cold front with 0-6km shear
values of 40-50 kts so the potential still exists for isolated
strong to severe storms in east central through southeast Illinois
through late afternoon/early evening.


.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 256 PM CDT Wed Apr 19 2017

The cold front and shower threat should shift southeast of our area
Thursday evening with about a 12 to 18 hour period of dry weather
before a more vigorous upper wave and surface low pressure area
starts to affect parts of central and southeast Illinois Friday
afternoon or evening and continuing through at least the first half
of the weekend. Models have shifted the track of the surface wave a
bit further north than the last couple of runs but it still keeps
all of our area on the cool side of the storm with brisk northeast
winds setting in on Saturday along with the best chance for showers
over east central through southeast Illinois. Cloud cover, northeast
winds and the rain all point to a rather chilly day Saturday with
afternoon highs struggling to reach the 50 degree mark across east
central and southeast Illinois. Further north, generally north of
the Interstate 74 corridor, there may be a bit of sunshine which
should help push temperatures into the middle 50s.

The storm system and rain chances will finally push far enough to
our east by Sunday which should allow sunshine to return along with
warming temperatures. Most areas should see the mercury return back
into the 60s on Sunday, around 70 on Monday and well into the 70s
by Tuesday.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 554 AM CDT Wed Apr 19 2017

Clusters of thunderstorms currently ongoing across far southern
Iowa/northern Missouri will continue to track east-northeast into
north-central Illinois early this morning. Based on radar timing
tools and HRRR guidance, have included VCTS at KPIA between 12z
and 16z. Storms will wane/shift north of the area by late
morning...with little or no additional convection expected through
the afternoon. A cold front will approach from the west late
tonight, with a broken line of storms potentially pushing into the
Illinois River Valley toward dawn Thursday. Have therefore
included VCTS at KPIA after 09z. Further east at the remaining
terminals, think scattered convection will not arrive until later
Thursday morning. Winds will initially become light/variable near
a stalled frontal boundary at both KPIA and KBMI early this
morning, then will become S/SE everywhere during the afternoon as
the front lifts toward the I-80 corridor.




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