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Area forecast discussion 
National Weather Service Lincoln Illinois
1045 am CDT Sat Jul 4 2015

issued at 1045 am CDT Sat Jul 4 2015

A beautiful 4th of July weekend is expected across central/southeast Illinois.
Updated the forecast to remove the patchy fog this morning which
lifted by middle morning. Also updated sky cover with a little more
cumulus clouds developing late this morning southeast of the Illinois River
where mostly sunny skies expected with partly sunny skies south of
I-70. Few to scattered cumulus clouds to dissipate by sunset
though still may have a lingering haze from the smoke from the
Canadian rockies wildfires. Highs 80-85f this afternoon with
light winds with weak surface high pressure over Illinois/MO today.
Dewpoints in the low to middle 60s again today.


Short term...(today)
issued at 326 am CDT Sat Jul 4 2015

07z/2am surface analysis shows frontal boundary south of the Ohio
River...while weak high pressure is centered over eastern Nebraska.
As the high shifts slowly eastward...mostly sunny skies and light
winds will be the rule across central Illinois today. Forecast
soundings indicate mixing up to about 875mb...resulting in afternoon
high temperatures in the lower to middle 80s. Despite the warmer
conditions...dewpoints will remain fairly tolerable in the 60-65
degree range.

Long term...(tonight through friday)
issued at 326 am CDT Sat Jul 4 2015

Once the high shifts further increasing southerly return
flow will bring even warmer and more humid air into the region
Sunday and Monday. High temperatures will reach the middle to upper
80s both days...while dewpoints climb over 70 degrees.

Short-wave trough currently evident on water vapor imagery over
northern British Columbia will drop southeastward over the next
couple of days...triggering surface cyclogenesis in the Lee of The
Rockies across western Kansas on Sunday. The low will then track
into southern Minnesota by 12z Monday then to Lake Superior by 00z
Tuesday. As it will drag a cold front toward central Illinois
by late Monday. Models continue to delay the front...with the 00z
July 4 runs now keeping it west of the Mississippi River until
Monday night. While atmosphere ahead of the boundary will become
highly unstable with SBCAPE values in excess of 3000j/kg Monday
afternoon...synoptic forcing will be absent and 0-6km shear will
remain quite meager at just 15-20kt. Am therefore expecting a
largely hot and dry day...with perhaps a few thunderstorms arriving
in the Illinois River valley ahead of the front by late afternoon.
Have cut back probability of precipitation accordingly. As the front pushes into the
area...showers and thunderstorms will become widespread Monday night
into Tuesday.

As the front becomes parallel to the zonal upper-level
will eventually become stalled across southern Illinois by Tuesday
night. Based on GFS/ECMWF/Gem consensus...think boundary will slip
far enough south to end rain chances along/north of a Canton to
Bloomington line Tuesday night and Wednesday. Further south...will
continue probability of precipitation as a weak wave ripples along the boundary. Once this
feature passes to the east...European model (ecmwf) shows front getting shunted
further southward and short-wave ridging arriving Wednesday night
and Thursday. Will go with a largely dry forecast during that time
accordingly. After that...rain chances will return for the end of
the week as upper heights build and front gets pushed back northward.


Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 646 am CDT Sat Jul 4 2015

Ground fog is affecting all but bmi this morning. Spi has dropped
to vlifr at times, but has returned to IFR and should remain
there or above since sunrise has passed. The fog is shallow and
should burn off quickly, at least by 15z. Scattered cumulus may
redevelop in the heat of the day, but no broken ceilings are
expected. MVFR fog is indicated in the forecast soundings for pia,
bmi, and spi, so have added that to the end of this taf forecast
period. Winds will remain light and variable over the next 18-24
hours under weak high pressure. A southeast direction will begin
to develop after 09z tonight, as the high begins to slide off to
the east.


Ilx watches/warnings/advisories...


short term...Barnes
long term...Barnes

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