Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 200601

Area Forecast Discussion
National Weather Service Lincoln IL
101 AM CDT Thu Apr 20 2017

Issued at 855 PM CDT Wed Apr 19 2017

Warm frontal boundary remains draped from near Galesburg to El
Paso this evening and is expected to begin moving northward out of
the area in a few hours as low pressure over central IA continues
moving northeastward toward Wisconsin overnight. Convergence along
the warm front could still result in a few thunderstorms this
evening and have kept slight chances in the forecast nearby,
however the main focus for thunderstorms will be late in the night
as the cold front draped to the south of the low approaches.
Thunderstorms have become active along the cold front from KS into
IA with numerous large hail reports, however with nocturnal
cooling and less favorable lift storms should weaken considerably
as they move into central IL late in the night. Updates this
evening mainly focused on decreased PoPs through a few hours
after midnight. Otherwise, forecast is in good shape as increasing
southerly winds bring very mild temperatures overnight with lows
mostly in the mid 60s while gusty south-southwest winds 15-20 mph
develop ahead of the cold front.


.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 upper 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 into northern Illinois
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 range.

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 06Z TAFS through 06Z Thursday night)
Issued at 1257 AM CDT Thu Apr 20 2017

Cold front currently draped across central Iowa will advance
slowly eastward over the next 12-24 hours. Convection associated
with the boundary has diminished greatly over the past few hours,
so am not expecting much at all to arrive at the central Illinois
terminals early this morning. Have therefore just mentioned VCTS
after 09z at KPIA...and after 12z at both KDEC and KCMI. Once the
front passes, winds will veer to the W/NW and gust to 20-25kt this
afternoon. A brief period of MVFR ceilings will be possible
immediately along/behind the front...with skies clearing by
Thursday evening.




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