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Area forecast discussion
National Weather Service Lincoln Illinois
854 PM CDT Fri Apr 28 2017

Update...
issued at 846 PM CDT Fri Apr 28 2017

Upper wave that produced the showers and thunderstorms this
afternoon, with most of the storms along and south of a Paris
to Shelbyville line, has shifted off to our east early this
evening with most of the stronger convection that occurred
over southeast Illinois just south and east of our area.
The synoptic cool front was given a bit of a nudge to the
south of our area thanks to the strong convection that pushed
across the I-70 corridor. Convection continues to fire just south
of the boundary this evening and expect that area to start to
shift slowly back north tonight along with the warm front. This
will produce another round of locally heavy rainfall over
southeast Illinois along with the possibility for some large hail
with some of the stronger cores that develop north. Further north,
low clouds, some patchy fog and drizzle will develop overnight
with the shower threat slowly advancing up into central Illinois
as the warm front gradually edges north as well.



With the frontal boundary expected to shift ever so slowly north
on Saturday, look for periods of showers and storms with heavy
rainfall likely, especially in areas that see the thunderstorms
track over the same areas during the day. Have made some minor
adjustments to the overnight portion of the forecast but overall,
the changes were not significant enough to warrant an update at
this time.

&&

Short term...(this evening through saturday)
issued at 309 PM CDT Fri Apr 28 2017

Have expanded the Flash Flood Watch northwest to the Illinois River for
this weekend, from tonight through Sunday night. Widespread 3-5 inch
rain expected over County Warning Area this weekend, with locally up to 6 inch
amounts se of I-55 and west of I-57. 12z forecast models have
continued NW trend of heavier rain axis over central Illinois this
weekend. In addition to heavy rain threat, Storm Prediction Center day1 outlook
continues a slight risk of severe thunderstorms late this afternoon
into mid evening south of a Paris to Shelbyville line with enhanced
risk south of a Robinson to Flora line where 2 inch or larger hail
possible. Storm Prediction Center day2 outlook has slight risk from I-72 south on Sat
afternoon/evening as frontal boundary lifts further north. The warm
front is currently over the southern tip of IL, north of Paducah, Kentucky
and over northern Kentucky and southern MO. Models lift warm front
northward toward I-70 early this evening and then appears to slip
back south for a time overnight before lifting back north toward I-
72 on Sat afternoon. 1st wave of showers and developing
thunderstorms was se of the Illinois River and lifting NE. This will
diminish over central Illinois by early evening, but continue over
southeast Illinois closer to the front. 2nd area of convection to spread
NE into central Illinois later tonight into Saturday.
Temperatures will be tricky depending on placement of frontal
boundary especially on Saturday. Warmer 70s and lower 80s will occur
south of the front in southeast Illinois on Sat while much cooler
upper 40s and lower 50s in NW IL, along and NW of the Illinois River.

Long term...(saturday night through friday)
issued at 309 PM CDT Fri Apr 28 2017

The heaviest rains still appears to be later Saturday afternoon and
Saturday night as precipitable water values are 1.5-2 inches with 50-60 southerly
850 mb winds advecting in deep moisture. Models continue to show
heaviest rain axis between the Illinois River and I-57 during that time
and where the 4-5 inch band and locally 6 inches expected. Frontal
boundary over central Illinois Sat night should lift north of County Warning Area during
Sunday before cold front swings east across central/southeast Illinois
Sunday evening. This will keep high chances of showers and
thunderstorms around especially Sunday afternoon/evening. Storm Prediction Center day3
outlook has marginal risk of severe storms across area during that
time and would not be surprised if slight risk south of I-64 in
southern Illinois works its way further northward with future updates.
Sunday should be the warmest day of the next 7, with area getting
into the warm sector. Highs range from 65-70f from Peoria north to
the upper 70s/lower 80s over east central and southeast Illinois.

Strong cutoff upper level low ejecting NE over Iowa/WI on Monday to
keep a fair amount of low clouds around over Illinois along with chances
of showers especially north of I-70. Much cooler highs in the 50s
with breezy west-southwest winds gusting 25-35 mph. Strong upper level low/trof
pulls away from central Illinois on Tue afternoon with dry wx returning
and partly to mostly sunny skies. Highs Tue in the low to mid 60s,
mildest over SW County Warning Area.

Chance of showers spreads into southern half of County Warning Area overnight Tue
night and Wed and continues into Wed night and Thu as low pressure
passes south of Illinois where better chances of thunderstorms will be.
Below normal highs mostly in the lower 60s during middle of next
week with lows mostly in the 40s.

&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 604 PM CDT Fri Apr 28 2017

VFR cigs are expected to gradually deteriorate to MVFR and IFR
later tonight as moisture streams north of a warm front over
southern Illinois. The most concentrated area of showers and
thunderstorms will be along and south of I-70 this evening
with a gradual shift north of the precipitation as we head
into the early morning hours, roughly in the 07z-11z time
frame. As the warm front shifts north on Saturday, a large
area of showers and storms will affect the taf sites
accompanied by MVFR and local IFR cigs and vsbys, especially
in and near any thunderstorm. Surface winds tonight will be
backing more into an east to northeast direction and should
hold from an easterly direction on Saturday. Speeds will be
rather light tonight, generally from 7 to 12 kts, and then
pick up in speed to between 12 to 17 kts Saturday morning.



&&

Ilx watches/warnings/advisories...
Flash Flood Watch through Monday morning for ilz031-037-038-
041>057-061>063-066>068-071>073.

&&

$$

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