Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271033
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
533 AM CDT Thu Apr 27 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 309 AM CDT Thu Apr 27 2017

Cold front continues to push slowly eastward, and was roughly
along a Lacon-Lincoln-Taylorville line at 2 am, with a low
pressure area centered just south of Bloomington. Initial band of
showers/storms has pushed east of the Indiana border, but
widespread showers behind the front were associated with the upper
wave that is lifting northeast toward west central Illinois. The
short-range models are in good agreement that much of this will
lift of the forecast area by 7 am as the low tracks to Lake
Michigan, with some lingering showers northwest of the Illinois
River for a couple hours beyond that. Forecast soundings show
skies remaining rather cloudy through the day, although some
clearing should start moving in from the southwest during the
afternoon as the low pulls away. Once the rain moves out, dry
conditions are expected until late tonight, when the next system
starts spreading a few showers into the far western CWA.

&&

.LONG TERM...(Friday through Wednesday)
ISSUED AT 309 AM CDT Thu Apr 27 2017

Main focus remains with the copious rainfall expected over the
weekend, along with severe weather potential.

Southern branch of the jet stream was focused along the southern
tier of states this morning, but a developing upper low over
Utah/Colorado on Friday will force this northward. Developing
frontal boundary over central Illinois on Friday will result in
light rain showers during the morning, with some thunderstorms
possible by afternoon a frontal boundary drops southward. Latest
SPC Day2 outlook has a slight risk of severe weather from about
Shelbyville-Paris southward, with some enhanced chances near
Lawrenceville. NAM is much more generous with the instability, but
the GFS`s MUCAPEs of up to 1000 J/kg and strong 0-6km shear
support some severe potential during the afternoon and early
evening.

Main show will be Friday night into Sunday evening, though, as a
strong transport of moisture takes place (widespread precipitable
water values of 1.5 to 2 inches much of the period).The front will
become stationary Friday night as it starts to parallel the upper
flow. Exact positioning of this boundary will be critical for the
heavy rain focus, with the southeast CWA favored Friday night and
the central CWA by Saturday afternoon as the front starts to edge
northward. Heaviest rains likely Saturday night with a widespread
1-2 inches in many areas, except the far southeast CWA where some
breaks in the rain will be developing by afternoon. A large
surface cyclone will develop through the weekend as a cutoff low
strengthens over the central Plains, and there is good agreement
among the longer range models of the surface low lifting northeast
into northern Illinois or southern Wisconsin by late Sunday
night. Stronger storms are possible Sunday afternoon as the cold
front pushes eastward, with very good rain chances continuing
Sunday night in the deformation zone behind the low. It will
likely take until Monday night to fully get the showers out of the
area, once the upper low moves to near Lake Superior.

Flood watches will likely be needed at some point, with
indications that totals will likely exceed 3-4 inches over much
of the forecast area. Will hold off on issuing them at the moment,
though, as the current rainfall ended up being less than
initially expected, and the initial wave should be able to absorb
some of the heavier rain.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 528 AM CDT Thu Apr 27 2017

Cold front has passed KCMI recently, and precipitation has largely
lifted north of the TAF sites, so will not include any rain
mention in the upcoming TAF set. MVFR ceilings are widespread over
central Illinois, with a few pockets of ceilings below 1,000 feet
which should not last much longer. Ceilings will be slow to lift,
and it will likely take until mid afternoon for ceilings to rise
above 3,000 feet.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Geelhart


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