Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 291757

Area Forecast Discussion
National Weather Service Lincoln IL
1257 PM CDT Wed Mar 29 2017

Issued at 1102 AM CDT Wed Mar 29 2017

Showers and isolated thunderstorms associated with warm advection
on the back side of departing high pressure are spreading into
the Illinois River Valley late this morning. The precipitation is
moving to the N/NE and is expected to remain primarily along and
west of the I-55 corridor through early afternoon. Based on radar
trends and high-res model data, it appears the bulk of the rain
will lift into northern Illinois by mid-afternoon...resulting in a
lull in rain chances across the KILX CWA later today. Have
updated PoPs to go categorical and include isolated thunder west
of the Illinois River. Have also adjusted afternoon highs by a
couple of degrees, mainly to drop readings into the upper 40s
across the NW where clouds, showers, and persistent easterly flow
will keep things slightly cooler than previously forecast.


.SHORT TERM...(Today and tonight)
ISSUED AT 329 AM CDT Wed Mar 29 2017

A low pressure area in central OK will slowly lift northeast, only
reaching as far as eastern KS by 00z this evening. The ongoing
precip ahead of the system will continue to move northeast into MO
early this morning. HiRes models have a decent handle on this and
show the associated showers moving into the CWA late this morning
and then moving northeast across the area, reaching north of I-74 by
00z this evening. By the time the precip arrives later this morning,
the best support will have returned west and the instability
parameters will be west of the state. So, will just have showers in
the forecast for today, mainly west of I-57. By this evening,
convection should have refired along and just ahead of the front
back in MO. This area/line of showers and storms will move into
western IL this evening and then progress across the state the
remainder of the night. Thunder chances will have increased for
tonight as better low level instability and wind parameters will be
over the area. Agree with SPC outlook for Day 1 and believe Marginal
Risk for severe weather will mainly be after midnight. Winds will be
easterly through tonight and as the system gets closer,
breeziness/gustiness will increase to where gusts of 25 to 30 will
be possible this evening.

Wide range of temps for today with around 50 in the northwest to the
middle 60s in the southeast. Clouds, winds, and precip tonight will
keep temps from falling too much, so still remaining in the 40s and
50s across the area.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 329 AM CDT Wed Mar 29 2017

The active weather pattern of the past several days shows no signs
of ending through the end of the forecast period. There have been a
couple notable trends in the past 24 hours. The first trend is a
slight northward shift in the storm track for Thursday, which allows
warmer temperatures, higher instability, and a better risk of a few
severe storms over much of the forecast area. The second trend is
better model clustering for the system early next week, with
Monday/Monday night now looking like the most preferred time for

Showers and a few thunderstorms will likely be ongoing at the start
of the period in a strong warm advection regime ahead of a slow
moving storm system lifting northeast from the southern Plains. A
lull in the precipitation risk is likely around midday, but chances
will ramp up again Thursday afternoon/evening as the system tracks
across the state. The northward shift in the storm track now
supports areas along/south of a Jacksonville to Danville line
becoming quite warm and moderately unstable (CAPE values peaking
near 1500 j/kg). Shear profiles to the south of the storm track are
also decent, with bulk shear values of 40 kts or better. Not
surprisingly, the latest SPC Day2 Outlook has pulled the Slight Risk
into this area.

A quieter weather period moves into the area Friday into Sunday as
the lead system pulls away, and upper/surface ridging build across
the area. The next in our recent series of slow moving weather
systems should cross the area Monday into Monday night. This system
has a further south track at this point which would be less
supportive of thunderstorms with its passage.

Temperatures through the period will average at or above normal. The
warmest readings will be seen Thursday and again on Sunday in
advance of the two main storm systems.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1256 PM CDT Wed Mar 29 2017

Band of showers continues to work its way across central Illinois
early this afternoon...with latest radar imagery showing it
generally along and just west of I-55. The showers will lift
northeastward out of the area over the next couple of hours, with
Rapid Refresh forecast soundings showing any residual MVFR
ceilings rising to VFR by mid to late afternoon. After a lull in
the precip chances, the next more significant wave of showers will
arrive late this evening through the overnight hours. Based on NAM
data, have introduced predominant rain at KPIA by 03z...then
further east to KCMI by around 07z. Ceilings will initially lower
to MVFR, but some high-res models are suggesting IFR ceilings will
develop late tonight into Thursday morning. Winds will be
strong/gusty from the E/SE this afternoon through tonight, then
will slowly decrease toward midday Thursday.




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