Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 232357
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
657 PM CDT MON MAY 23 2016

.SHORT TERM...(Tonight)
ISSUED AT 245 PM CDT Mon May 23 2016

A weak but persistent frontal boundary to the west of the
Mississippi River Valley will be driving the weather through the end
of the week. Currently caught between an upper low in the northern
high plains along the Canadian border...and another over the mid
Atlantic Coast...it is expected to slowly advance eastward
overnight.  As it approaches, the region will see increasing cloud
cover with southerly winds.  Precip chances will also increase
slightly before dawn NW of the Illinois River Valley.

.LONG TERM...(Tuesday through Monday)
ISSUED AT 245 PM CDT Mon May 23 2016

The upper level ridge that brought the very pleasant weather to our
area over the past several days will begin to deamplify as it shifts
off to our east later tonight into Tuesday, allowing a moist
southwest flow to set up over the region and hold through this
forecast period. What makes the forecast tough is the fact that
any frontal boundary that would enhance the shower and thunderstorm
chances in our area is forecast to remain well out to our west and
northwest thru the period as it becomes parallel to the upper level
flow. Meanwhile, models suggest upper level ridging builds over the
eastern U.S. later in the week which will continue to funnel deep
tropical moisture northeast into the Midwest. So it comes down to
timing of individual low amplitude shortwaves ejecting out of the
mean longwave trof over the western U.S. during the next 5 days and
then trying to time thunderstorms into our forecast area.

We may see a remnant MCS track into our western areas tomorrow
morning but the further east it goes during the day, the less
support it will have to maintain itself. It still appears the better
instability and shear will be to our west tomorrow with mainly
scattered coverage expected in our area during the day. The setup
appears to become more favorable for nocturnal convection later
tomorrow night into Wednesday morning as some decent 850 mb theta-e
advection sets up just to our southwest as the low level jet veers
more into a southwest to west direction after 06z creating some
favorable moisture convergence over central Illinois. Those storms
should affect a good portion of the forecast area by dawn Wednesday
with steep 700-500 mb lapse rates but marginal, at best, deep
layer shear with values around 20 kts suggesting more of a threat
from hail and heavy rainfall as PWAT values increase to between
1.25 to 1.50 inches Wednesday morning.

After that, confidence will be rather low for timing and coverage of
additional storms on Wednesday, even though there is a distinct
shortwave that is forecast to track across the area by later in the
day Wednesday. Will the atmosphere be worked over enough from the
morning convection to prevent any redevelopment in the afternoon?
What may occur would be a situation where convection redevelops over
our area Wednesday night/Thursday morning as a 40-45 kt LLJ sets up
over central Illinois, and brings another round of storms into our
area late at night or just before dawn Thursday. Unfortunately, we
do not see any significant break in the pattern that would allow
a period or two without the chance for precip, so there will be POPs
through the upcoming holiday weekend. It certainly not a situation
that produces all day rainfall, but the potential is there for
scattered storms, some of which could be strong-severe and definitely
bring the threat for some heavy rainfall to parts of our area thru
the period. Temperatures will remain above normal through the rest
of the week and into the weekend as daytime highs should climb into
the 80s with even some early morning lows that may have a tough time
dropping below the upper 60s later this week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 653 PM CDT Mon May 23 2016

Another mostly quiet 00Z aviation weather period across the
central Illinois terminals. Southerly winds will persist through
the period. A stray shower or thunderstorm can`t be ruled out
during the day Tuesday, especially west toward KPIA & KSPI, but
the probability is too low to carry in the TAFs at this time.
Assuming no rainfall occurs, VFR conditions will persist.

&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...HJS
LONG TERM...Smith
AVIATION...BAK



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