Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 250840
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
340 AM CDT Sat Mar 25 2017

.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 06Z TAFS through 06Z Saturday night)
Issued at 1040 PM CDT Fri Mar 24 2017

A frontal boundary stretched across the TAF sites late this
evening with CMI and DEC still on the warm side of the boundary
with southerly winds, while the remainder of the sites saw their
winds switch into a light northeasterly direction. The boundary
may slip a bit further south late tonight before become stationary
and then shifting back to the north on Saturday. The combination
of the frontal boundary and a disturbance coming out of the
Southern Plains will keep the threat for showers and isolated
thunderstorms across the area into tomorrow night. With the
increase in low level moisture forecast ahead of the storm system,
we look for cigs to deteriorate to MVFR and possibly some brief
IFR cigs by morning. Cigs will improve to low VFR tomorrow
afternoon as the front shifts north, but may go back to MVFR again
tomorrow night. SPI and PIA will be first to see the cigs go down
followed by BMI and finally DEC and CMI the last to get to MVFR
Saturday morning.

The best threat for more widespread showers will be with the band
now coming out of Missouri into our western areas after midnight
and finally over to the east after 09z. There may be a break in
the rain later Saturday morning before daytime heating aids in
scattered showers and storms in the afternoon. Surface winds
should become southeasterly at all sites later tonight and then
increase by morning to between 12 and 17 kts with a few gusts up
to 23 kts possible into the afternoon hours before winds
gradually diminish after 00z tomorrow evening.


&&

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

$$

SHORT TERM...Shimon
LONG TERM...HJS
AVIATION...Smith



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