Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 290603

Area Forecast Discussion
National Weather Service Lincoln IL
103 AM CDT Thu Jun 29 2017

Issued at 854 PM CDT Wed Jun 28 2017

Thunderstorms, several of them severe and tornadic continue from
northern MO to northern IL and southern WI this evening. A fairly
pronounced break has developed between activity in northern MO and
northern IL where analyses suggest instability has diminished,
while activity to the north continues in the vicinity of a surface
warm front and upper shortwave. In northern MO, stronger
instability characterized by CAPE around 2000 J/KG continues to
fuel a slow moving cluster of strong to severe thunderstorms. This
latter cluster should be the primary concern for west central IL
as it shifts eastward. HRRR model suggests thunderstorm activity
will generally be weakening is it shifts eastward into central IL.
Primary threat should be strong wind gusts by the time it reaches
west central IL. Timing of scattered showers/thunderstorms looks
to be reaching Galesburg by 10 p.m., Illinois River
11p.m.-midnight, I-55 2 a.m. according to latest HRRR and have
made adjustments to forecast to slow down onset of precipitation

Otherwise, warm and somewhat humid conditions on track tonight
with lows reaching about 70 degrees following mid-evening
temperatures in the mid 70s to low 80s. Breezy south winds 10 to
15 mph with higher gusts expected through the night.


.SHORT TERM...(This evening through Thursday)
ISSUED AT 300 PM CDT Wed Jun 28 2017

Not too many changes with the forecast through tonight over CWA.
Mid afternoon surface map has 998 mb low pressure over west
central MN with its cold front extending through eastern NE and
western KS. This front to push se over IA through Thu, getting
closer to central IL and increasing chances of convection with
time. Continued increasing chances of showers and thunderstorms
along and north of I-72 during tonight with best chances (likely
pops) along and nw of the IL river. Currently have scattered
showers and thunderstorms over NW IL moving ENE toward Macomb,
Galesburg and Peru. SPC day1 outlook continues slight risk of
severe storms tonight nw of the IL river while enhanced risk just
nw of Knox county. A marginal risk remains as far se as I-55 for
tonight. This convection enhanced by strong sw low level jet
tonight and developing into an MCS will weaken later Thu morning.
Then more scattered convection to develop during Thu afternoon and
get further south into central IL to about I-70. Breezy SSW winds
have brought in higher dewpoints in the low to mid 60s and will
rise into the upper 60s/lower 70s for Thu. Milder lows tonight in
the upper 60s to around 70F. A very warm and humid day Thu with
highs in the upper 80s (mid 80s by Knox and Stark counties).

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 300 PM CDT Wed Jun 28 2017

SPC day2 outlook with slight risk of severe storms north of I-70
Thu night for next MCS system, while marginal risk expected about
a county se of I-70. Far southeast CWA will likely stay dry
through Thu night with highest pops shifting into east central and
southeast IL on Friday. SPC day3 outlook has marginal risk of
severe storms across CWA for Fri afternoon/evening and believe
highest risk will be se of I-55 in warm sector. Front appears to
push through southeast CWA during Fri evening and toward the Ohio
river overnight Fri night. This could linger small chances of
convection in southeast IL on Sat, mainly southeast of
Charleston/Mattoon. Humid still on Friday with highs in the mid
80s, except lower 80s along and nw of the IL river. Highs in the
lower 80s on Sat over central IL and mid 80s in southeast IL and
starting to get less humid behind the front as dewpoints slip into
the low to mid 60s Sat afternoon.

A brief period of quiet wx expected across CWA Sat night and
Sunday as weak high pressure settles into area and frontal
boundary moves into the TN river valley. Seasonable highs on
Sunday in the mid 80s, with dewpoints in the lower 60s.

The 12Z GFS and ECMWF models differ with handling wx system early
next work week going into the 4th of July period. Weak surface
high pressure will shift east of IL Sunday night and Monday
allowing more humid tropical air to return to area. The frontal
boundary lifting ne over MO valley on Monday to likely develop
more convection. But models differ on how quickly this convection
gets into central/se IL. Northern IL and possibly northern CWA
could see chances of convection as early as Sunday night
especially after midnight, while rest of CWA to see convection
chances return on Monday and continue through Wed as upper level
trof moves into IA/MO on Tue and into the Ohio river valley next
Wed. Seasonable highs in the low to mid 80s Mon-Wed and humid
conditions expected to prevail.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1254 AM CDT Thu Jun 29 2017

Thunderstorms to the west slowly working into Central IL. Winds
with even the weaker returns on radar gusting in excess of 40 kts
at times as the higher winds aloft come down. Very blustery night.
Not the classic definition of LLWS as some of the winds are
gusting down to the surface...but definitely expect higher gusts
tonight with the -ra and -dz as well as the ts. Will send updates
as the eastward progression becomes more well defined. A break in
the storms later today, only to bring another round of showers and
thunderstorms in the afternoon. Generally south/southwesterly flow
throughout...becoming more southeasterly at the end of the pd.




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