Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260605
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
105 AM CDT Fri May 26 2017

.UPDATE...
Issued at 902 PM CDT Thu May 25 2017

Mostly clear skies across central IL this evening as a shortwave
ridge crosses the area with the upper level trough of the past few
days moving farther east. Warm advection precipitation over
northern Missouri and Iowa could reach western portions of the
forecast area early in the morning. Timing may need to be moved
up for this feature, but for now no significant updates needed
this evening.

&&

.SHORT TERM...(This evening through Friday)
ISSUED AT 320 PM CDT Thu May 25 2017

19z/2pm surface analysis shows weak ridge of high pressure
extending from the western Great Lakes to the Gulf Coast.  Despite
presence of ridging, clouds associated with a slowly departing low
over eastern Ohio persist across the E/NE KILX CWA this afternoon.
The clouds are most prevalent along/northeast of a Lacon...to
Bloomington...to Mattoon line.  Further west...only scattered
diurnal clouds are noted.  Once the sun sets, skies will become
mostly clear across all but the far NE CWA around Champaign and
Danville where partial cloud cover will continue.  After a brief
period of mostly clear skies this evening, mid/high clouds will
increase from the west in advance of the next approaching system
overnight.  Low temperatures will drop into the middle to upper
50s.

A warm front will lift northward through the area Friday morning,
possibly setting off a few WAA showers across the NW CWA.  A better
chance for showers and thunderstorms will develop later in the day
as a short-wave trough tracking eastward out of the Plains enhances
synoptic lift ahead of an approaching cold front.  Most models have
trended northward with this wave, with the 12z NAM suggesting any
convection associated with this feature will entirely miss central
Illinois to the north.  The GFS takes a similar northern route:
however, its a bit more robust with its QPF further south into
central Illinois.  The airmass in the warm sector will become weakly
capped as 700mb temps are progged to climb into the 8-10C range by
afternoon.  Despite this, think lift ahead of the approaching wave
will be strong enough to overcome the cap and set off a few
thunderstorms across the northern half of the area.  Have therefore
carried 20-30 PoPs everywhere north of the I-70 corridor.  High
temperatures will range from the middle 70s far north around
Lacon...to the lower 80s along/south of I-70.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 320 PM CDT Thu May 25 2017

Scattered showers and thunderstorms will linger into Friday evening
across the northern half of the CWA before exiting the region
overnight.  All models agree that a period of quiet weather will
develop Friday night through Saturday morning before the next round
of potentially strong to severe convection arrives late Saturday.
The 12z NAM/GFS/ECMWF are all in relatively good agreement with the
track of the next short-wave and its associated weak surface low
along a stalled frontal boundary draped across south-central
Illinois Saturday evening.  Differences arise in how far north the
boundary will lift and thus how far north the severe weather threat
will spread.  The NAM is the furthest south...showing a highly
unstable/sheared airmass mainly along/south of I-70. Meanwhile...the
GFS is slightly further north focusing along/south of I-72.  The
exact location of the boundary will determine the main severe
weather corridor, and subsequent model runs will pin this down more
thoroughly by tomorrow.  For now, it seems prudent to focus on the
southern half of the CWA from late Saturday afternoon through
Saturday evening.  Given high degree of instability and moderately
strong shear in the vicinity of the front, threat for damaging
winds, large hail, and perhaps a few tornadoes will exist.  Have
gone with dry conditions across the board Saturday morning...with
high chance PoPs developing across the SW CWA by Saturday afternoon.
Bumped PoPs to likely along/south of I-72 for Saturday evening as
the wave of convection passes through the area.

Once the main wave exits into the Ohio River Valley, it will push
the baroclinic zone further south out of the area on Sunday.  While
a few models linger a few showers across the area, think conditions
will mainly be dry with temperatures cooling into the middle 70s.
After that, cyclonic flow will dominate across the Great
Lakes/Midwest through the middle of next week...resulting in cool
conditions.  Isolated showers/thunder will develop across the
northern half of the CWA Monday afternoon as a weak trough rotates
southward into the area: however, most locations will remain dry.
Cool/dry weather will then prevail into Thursday with daily highs
in the lower to middle 70s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 100 AM CDT Fri May 26 2017

Weak returns on radar scattered may warrant an update for a VCSH
but otherwise VFR with variable/SE winds through the overnight.
More southerly winds tomorrow with some gusts up to 15-20kts.
VCTS as a wave passes to the north with a cu field building in.
Low level moisture gets trapped in the overnight and results in a
bkn stratocu deck with light winds with a sw/se component.
Guidance starting to drop to MVFR for tomorrow night, but that
will be highly dependent on how deep the moisture trapped in the
low levels actually is. Not willing to drop that far as of yet.

&&

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

$$

UPDATE...37
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...HJS


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