Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 012000

Area Forecast Discussion
300 PM CDT Wed Apr 1 2015

.SHORT TERM...(Tonight)

A tight pressure gradient between a large high over the eastern
Great Lakes and a cold front across the Northern Plains will
continue to create strong southerly winds across central Illinois
tonight. Forecast soundings and numeric guidance suggest sustained
winds of 10 to 15mph will prevail throughout the night.  These
southerly winds combined with increasing cloud cover will produce a
much warmer night than has recently been seen, with overnight low
temperatures remaining in the 50s.  The cold front will slowly
approach from the west, but is expected to remain west of the
Mississippi River until Thursday morning.  Meanwhile, a short-wave
trough evident on 18z/1pm water vapor imagery over eastern Oklahoma
will track northeastward into Illinois tonight.  Showers and
thunderstorms currently ongoing with this feature across the Ozarks
will lift/spread northeastward as well.  GFS/NAM/Rapid Refresh all
indicate scattered showers/thunder arriving in central Illinois from
late evening into the overnight hours.  With an initially very dry
airmass in place, think a slower arrival of precip is likely.  Have
therefore kept the evening mostly dry, with chance PoPs coming into
the picture after midnight.


.LONG TERM...(Thursday through Wednesday)

Unsettled weather pattern over IL Thu through Friday. SPC has areas
along and south of a Shelbyville to Paris line in a slight risk of
severe thunderstorms Thu afternoon after 18Z/1 pm into early Thu
evening until dusk. Short wave lifts ne of central IL Thu morning
while cold front pushes se toward the IL river valley by 18Z/1 pm
Thu and south of I-72 by 00Z/7 pm Thu. Increasing moisture/dewpoints
into 55-60F range Thu and CAPES peaking from 1000-1800 j/kg Thu
afternoon and early evening south of I-72 supports a marginal to
slight risk of severe storms for gusty winds and possible large hail
with a few storms. Last time we had severe storms in our CWA was Oct
13th and our ne counties have not had thunderstorms since Veterans
Day morning Nov 11th. Another mild day Thu with highs in the upper
60s to near 70F over central IL and lower 70s in southeast IL.

Cold front to push se across southeast IL during Thu night keeping
high chances of showers and chances of thunderstorms going from I-72
south with lower chances of showers north of I-72. Surface low
deepening along the front near the Ohio river Friday to keep high
chances of showers and few thunderstorms in southeast IL with good
chances of showers over the IL river valley and showers chances
increase northward with passing surface low to our south/se. SPC has
slight chance of severe storms in far southeast IL Friday south of
I-64. Have slight chances of showers Friday evening in eastern IL
with perhaps a chance of light snow mixed in with the light rain in
east central IL but no accumulations. Cooler highs Friday around 50F
northern counties and 55-60F in southeast IL with temps slipping
during the afternoon with breezy nnw winds. Between 1.5-2 inches of
rain expected over southeast IL with locally higher amounts south of
highway 50, but these amounts are below Flash flood guidance values
around 2 inches per hour, so holding off on issuing any flood

Quiet weather still expected Saturday and Sunday with more sunshine
as high pressure settles into TN by sunset Saturday. Lows Fri night
in the lower 30s. Highs Sat in the 50s with mildest readings in
western IL. Breezy south winds Sunday warms highs into the low to
mid 60s as high pressure slips off the Carolina coast by Sunday

Unsettled weather pattern returns Monday-Wednesday with daily
chances of showers and thunderstorms with sw upper level flow over
IL. ECMWF model is much wetter Tue night through Wed night while GFS
model is dry so some differences here to resolve and stuck close to
blended guidance pops. Highs in the low to mid 60s again on Monday
and upper 60s and lower 70s Tue. Then cold front pushes se through
IL Tue night and Wed with cooler highs Wed of 55-65F and mildest in
southeast IL.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)

Southerly winds will gust to between 20 and 25kt through the
afternoon and evening before decreasing to around 15kt tonight.
Despite the slight decrease in surface winds, a strong low-level
jet is expected to develop, leading to 45-50kt of wind-shear in
the SFC-2000ft layer. Skies will initially be mostly clear, but
high/thin clouds will be on the increase later today in advance of
an upper-level disturbance currently over eastern Oklahoma. As
this feature tracks northeastward, scattered showers/thunder will
spread into central Illinois tonight. Models are in good agreement
on the timing: however, exact areal coverage of convection remains
in question. Have therefore opted to include VCTS at the TAF sites
after the 05-07z time frame. Once this initial wave passes, a cold
front will approach from the west by Thursday morning. This
boundary will be interacting with an increasingly warm/moist
airmass, so rain chances will be much higher at that time. Have
introduced predominant showers after 13z at KPIA, then after 16z
further east at KCMI.




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