Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271547
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1047 AM CDT FRI MAY 27 2016

.UPDATE...
Issued at 1045 AM CDT Fri May 27 2016

Forecast generally looks on track today and just a few minor
adjustments to a few of the hourly elements today. Mostly cloudy
to overcast skies will occur rest of the day as scattered showers
spread NNE acorss central IL with a few thunderstorms developing
this afternoon. Areas near the Indiana border/Wabash river will
have less of a chance of convection today. Due to more clouds
today, highs a bit cooler than past few days, in the upper 70s and
lower 80s with mildest readings in northern and eastern CWA where
a bit more sunshine seen this morning. Temps at 1030 am range from
upper 60s to near 70F in rain cooled areas of sw CWA, to the mid
70s near the IN border and northeast of I-74. Rather humid again
today with dewpoints in the mid to upper 60s with breezy south
winds 10-15 mph and gusts 20 to 25 mph. Persistant southerly flow
over IL due to 1022 mb high pressure anchored near the southeast
Atlantic coast and 1003 mb low pressure over central KS. A subtle
short wave lifting NNE into central IL late this morning will
continue to bring an area of showers and isolated thunderstorms
(currently form I-74 south) NNE across area into early afternoon.
Another weak short wave to move into sw IL late this afternoon and
bring another area of showers and scattered thunderstorms into
central IL late this afternoon and into this evening. SPC has a
marginal risk of severe storms west of the IL river from mid
afternoon into mid evening.

&&

.SHORT TERM...(Today)
ISSUED AT 301 AM CDT Fri May 27 2016

Broad southwesterly flow will continue to bring warm and unsettled
weather to central Illinois today.  While main synoptic front and
associated strongest forcing will remain well to the west across the
Plains, a series of subtle short-waves embedded within the southwest
flow will serve as triggering mechanisms for scattered showers and
thunderstorms.  08z/3am water vapor imagery shows an MCV over
northeast Missouri/southeast Iowa that is currently responsible for a
cluster of thunderstorms around Galesburg.  This feature will lift
to the north out of the area over the next couple of hours, while a
another wave noted upstream over the Ozarks approaches from the
south.  This wave will provide enough lift within the warm/moist
airmass to trigger a few showers/thunderstorms.  Since there is no
synoptic front in the area today, any convection that develops will
likely form along mesoscale outflow boundaries from previous storms.
With no focused forcing and only weak upper support, have opted to
only carry high chance PoPs today.  Due to extensive cloud cover and
scattered convection, temps will be a bit cooler than they were
yesterday, with most locations remaining in the 70s.  A few lower
80s will be possible along/east of I-57 where areal coverage of
showers will be lowest.

.LONG TERM...(Tonight through Thursday)
ISSUED AT 301 AM CDT Fri May 27 2016

Upper low over Colorado this morning is expected to reach southeast
Nebraska by early Saturday morning, before lifting into the upper
Mississippi Valley. Greatest shower and thunderstorm activity
through Saturday night is expected to be over the western half of
the forecast area, where there will be more lift associated with the
nearby low. Any stronger storms would be most likely on Saturday, as
CAPE values rise to over 2500 J/kg, albeit with some weak bulk shear
of 20-30 knots. Most of this area is covered by a marginal severe
weather risk in the latest SPC Day3 outlook. However, the models
continue to struggle in this particular pattern, as has been the
case the last few days. The latest GFS favors much of Saturday being
dry before a cold front triggers some storms west of I-55 in the
afternoon. The NAM favors more of an evening arrival of the next
wave of storms ahead of the front, offering a dry afternoon, while
the ECMWF almost completely dries things out by late afternoon and
favors mostly dry weather the rest of the weekend. Leaning more
toward a GFS solution with high chance PoP`s Saturday afternoon and
evening for now.

As the upper low degenerates into a broadening trough, rain chances
will decrease the remainder of the weekend, with most of the model
solutions favoring dry weather by Sunday afternoon. Memorial Day
still shaping up to be rather warm, with highs in the mid 80s, but
mostly sunny and less humid than recent days.

Longer range models continue to struggle in depicting a closed upper
low over the northern states next week. The ECMWF favors more of a
clean surface frontal passage around Wednesday with dry weather
after that, while the GFS has a surface cyclone loitering over the
Mississippi Valley through most of Thursday. This latter solution is
reflecting much more of a phasing of the northern and southern jet
streams, while the ECMWF keeps these fairly distinct. The forecast
grids favored more of the ECMWF solution albeit a bit slower,
limiting chance PoP`s by Thursday to areas east of the Illinois
River.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1155 PM CDT Thu May 26 2016

As has been the situation lately, the short range models are
having a hard time with the developing convective situation in
central IL for tonight. The HRRR is the closest, but it has been
all over the place with various timing scenarios for the overnight
hours. The shorter ranges of the TAFs are based on persistence of
a north-northeastward moving shortwave which is combining with the
remnants of a decaying MCS from Missouri. These features will
spread t-storms into the central and eastern IL TAF sites between
06z-09z. Ceilings/visibility may briefly dip into the MVFR
category with the heavier rain, but overall VFR conditions should
prevail overnight.

Lingering showers can be expected, in the wake of the initial
t-storms, into mid-morning. After a brief break in the showers
from mid-morning into early afternoon will re-introduce VCTS in
the TAFs. There is too much uncertainty as to the exact timing and
extent of the convective potential for later Friday, so will stick
with diurnal VCTS with plenty of low level moisture/instability.

&&

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

&&

$$

UPDATE...07
SHORT TERM...Barnes
LONG TERM...Geelhart
AVIATION...Miller



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