Area Forecast Discussion
Issued by NWS Central Illinois

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396
FXUS63 KILX 251441
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
941 AM 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 12Z TAFS through 12Z Sunday morning)
Issued at 659 AM CDT Sat Mar 25 2017

A stalled frontal boundary remains stretched across central
Illinois early this morning, with CMI and DEC still on the warm
side of the boundary with southeasterly winds, while the remainder
of the sites have northeast winds. The boundary should begin to
shift back to the north this morning. Dry air pushing into central
Illinois should provide a sizable break in the rain this morning
into early afternoon. As the low pressure center pushes toward
eastern Missouri later today, showers and storms should develop
again across southern Illinois and advance northward through the
TAF sites. Showers and isolated thunderstorms will be possible
from mid afternoon through this evening.

The surface low will slowly move into NW Illinois tonight, with a
break in the rain expected later this evening and overnight. An
abundance of surface moisture should allow for low clouds and fog
to form after 06z/1am. Look for cigs and vis to deteriorate to
MVFR and possibly some IFR cigs by Sunday morning.

Southeast surface winds south of the front should become gusty
this morning, increasing to between 12 and 17 kts with a few
gusts up to 25 kts possible into the afternoon hours. PIA has the
better chances of avoiding the stronger winds due to a weaker
pressure gradient extending toward PIA from the approaching low.
Winds this evening should diminish to less than 10kt while
remaining southeast overnight.


&&

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

$$

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



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