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afdilx

Area forecast discussion
National Weather Service Lincoln Illinois
854 PM CDT Wed Jun 28 2017

Update...
issued at 854 PM CDT Wed Jun 28 2017

Thunderstorms, several of them severe and tornadic continue from
northern MO to northern Illinois and southern WI this evening. A fairly
pronounced break has developed between activity in northern MO and
northern Illinois 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 Illinois
as it shifts eastward. Hrrr model suggests thunderstorm activity
will generally be weakening is it shifts eastward into central Illinois.
Primary threat should be strong wind gusts by the time it reaches
west central Illinois. 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
accordingly.

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 County Warning Area.
Mid afternoon surface map has 998 mb low pressure over west
central Minnesota with its cold front extending through eastern NE and
western Kansas. This front to push se over Iowa through Thu, getting
closer to central Illinois 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 Illinois River. Currently have scattered
showers and thunderstorms over northwest Illinois moving east-northeast toward Macomb,
Galesburg and Peru. Storm Prediction Center day1 outlook continues slight risk of
severe storms tonight NW of the Illinois 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 mesoscale convective system will weaken later Thu morning.
Then more scattered convection to develop during Thu afternoon and
get further south into central Illinois to about I-70. Breezy south-southwest 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

Storm Prediction Center day2 outlook with slight risk of severe storms north of I-70
Thu night for next mesoscale convective system system, while marginal risk expected about
a County se of I-70. Far southeast County Warning Area will likely stay dry
through Thu night with highest pops shifting into east central and
southeast Illinois on Friday. Storm Prediction Center day3 outlook has marginal risk of
severe storms across County Warning Area for Fri afternoon/evening and believe
highest risk will be se of I-55 in warm sector. Front appears to
push through southeast County Warning Area during Fri evening and toward the Ohio
River overnight Fri night. This could linger small chances of
convection in southeast Illinois 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 Illinois River. Highs in the
lower 80s on Sat over central Illinois and mid 80s in southeast Illinois 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 County Warning Area Sat night and
Sunday as weak high pressure settles into area and frontal
boundary moves into the Tennessee River valley. Seasonable highs on
Sunday in the mid 80s, with dewpoints in the lower 60s.

The 12z GFS and ecwmf 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 Illinois 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 Illinois. Northern Illinois and possibly northern County Warning Area
could see chances of convection as early as Sunday night
especially after midnight, while rest of County Warning Area to see convection
chances return on Monday and continue through Wed as upper level
trof moves into Iowa/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 00z tafs through 00z Thursday evening)
issued at 700 PM CDT Wed Jun 28 2017

Thunderstorms ahead of a cold front in Iowa expected to push
eastward overnight into the central Illinois area. Weakening of
thunderstorms is expected as it approaches I-55 corridor and
certainty of thunderstorms and rain/rain showers diminishes with approach to a kdec-kcmi
line. As eastward movement of developing thunderstorm complex has
yet to become established, timing still remains uncertain but
following model guidance brought thunderstorms in the vicinity into kpia, kspi, and kbmi in
04-06z timeframe. In addition, a southwesterly low level jet of
around 45 kts will bring low level wind shear from around 04z-10z.
Surface winds to remain breezy, south-southwest 14-18 kts with higher gusts
much of the night, potentially diminishing somewhat Thursday
as the surface frontal zone approaches from the northwest.



&&

Ilx watches/warnings/advisories...
none.
&&

$$

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