Area Forecast Discussion
Issued by NWS Central Illinois

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602
FXUS63 KILX 251740
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1240 PM CDT Sat Mar 25 2017

.UPDATE...
Issued at 940 AM CDT Sat Mar 25 2017

Latest surface analysis shows the frontal boundary roughly just
south of a Macomb-Hoopeston line, and has started to drift back
north again. Widespread mid-upper 40s were occurring north of the
front, with upper 50s to mid 60s south. Initial band of rain has
largely lifted out of the forecast area, with some more scattered
showers along and east of I-57.

Water vapor imagery shows the upper low has moved into the
southwest corner of Missouri, and this will slowly lift northeast
across the state. The breaks that are occurring with the rain --
complete with a few peeks of sunshine -- should erode as another
wave of rain lifts northeast into the forecast area by early
afternoon. Currently thinking the thunder chances will be with
this secondary surge of showers, and have pulled the thunder
mention for the remainder of the morning. The front itself should
continue to lift north and allow for the northern CWA to reach
into the upper 50s/lower 60s by midday. Some adjustments were made
to the temperatures, specifically in regarding to the location of
the front over the next few hours.

Updated zones/grids have been sent.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 339 AM CDT Sat Mar 25 2017

The 08z surface analysis shows a stalled frontal boundary extending
across central Illinois with low 50s N of the front and low 60s to
the south. The front is oriented roughly just north of I-72. It is
expected to lift slowly north today, as a dry band aloft rotates
into central Illinois this morning into early afternoon. That should
cause a break in the rain to develop during that time, or at least
reduce the coverage of showers for several hours. The latest HRRR
and RAP output indicate a redevelopment of showers and storms
surging north after 20z. Instability and shear parameters appear
favorable for storms early this morning, as well as this afternoon
during the redevelopment. SPC has marginal risk as far north as I-
74, with some hail and gusty winds possible from the stronger storms.

Adjustments to the PoPs/Wx have been to keep categorical PoPs into
early morning with the current bands of showers/storms, then will
lower PoPs back to chance later this morning and increase back to
likely/categorical for mid afternoon.

The surface low is expected to advance from eastern Oklahoma at
08z/3am to eastern Missouri by 00z/7pm this evening. The low
will continue a slow drift to the northeast into W-NW Illinois
overnight. Shower chances will decrease west of I-55 later this
evening, with likely PoPs lingering east of I-57 the rest of the
night. There should be a reduction in coverage tonight in general
due to lower instability and drier air in the 800mb and 600mb layer
advancing eastward across Illinois.

High temps today will be tied to the northward advance of the
frontal boundary, with lower 70s possible in our southern counties,
and mid to upper 60s north to Peoria and Bloomington. The Galesburg
to Lacon areas could remain colder in the lower 60s depending on how
quickly the front pushes north of that area. Lows tonight will be
held warmer by clouds and periodic showers, and little overall
change in air mass. Low temps should bottom out in the upper 40s to
mid 50s, with the warmest readings along the Indiana border,
farthest from the arriving cooler air west of the low.

.LONG TERM...(Sunday through Friday)
ISSUED AT 339 AM CDT Sat Mar 25 2017

As the low moves out of the region Sunday...and weakens...the
precip will slow and stop in the late morning and afternoon.
Overnight Sunday should remain dry in the brief break between the
exiting low and the next low that is developing over the Southern
Plains tomorrow night.  Monday will be more warm air advection
showers in an attempt at the formation of a front...but the sfc
convergence is poorly represented at this time.  The track of the
low in both the ECMWF and the GFS is similar... as well as the NAM.
However, the NAM is considerably drier through Monday morning...and
all day for the northern half of the state.  The NAM is far more
discrete with the precip associated with the two lows than either
the ECMWF and the GFS. So far the forecast looks more like a
GFS/ECMWF solution with more widespread pops and less time without
any rain.  Either way, Monday afternoon and into the overnight hours
looks to bring precip through the state.

A brief break in the precip ends on Thursday as the next deep low
moves out of the desert SW and into the Midwest.  However,
divergence in the ECMWF and GFS solutions after 120 hrs, leaves low
confidence in the details.  Temperatures throughout the forecast are
running a few degrees above normal and well within end of March
expectations.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1240 PM CDT Sat Mar 25 2017

Scattered showers are moving back north into central Illinois at
midday, and will increase as reinforcements arrive from Missouri.
Thunder chances will likely hold off for a couple hours until this
latter area arrives. The rain will linger longest at KCMI as a
weakening storm system slowly lifts northward through Missouri,
but much of the remainder of central Illinois will see the rain
diminish to scattered showers once again after 06Z. Ceilings had
earlier risen to VFR levels but were coming down again, as
stratocumulus around 1500-2000 feet lifts northeast from Missouri.
Expect a gradual lowering of cloud heights through the next
several hours, with MVFR conditions widespread by early evening
and IFR ceilings below 1,000 feet after 06Z.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Geelhart
SHORT TERM...Shimon
LONG TERM...HJS
AVIATION...Geelhart



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