Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 241958
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
258 PM CDT Fri Mar 24 2017

.SHORT TERM...(This evening through Saturday)
ISSUED AT 257 PM CDT Fri Mar 24 2017

Abundant sunshine and southwest winds gusting 30-40 mph have helped
push temperatures into the mid-upper 70s over most of central
Illinois this afternoon. Southeast CWA has been more affected by the
stratocumulus which spread out of southern Illinois earlier today,
but even those areas have reached the lower 70s. Clouds are steadily
increasing from the west, and the temperature rise there has slowed
a bit as a result.

The frontal boundary is not too far off to the north, with 50s and
40s from south central Iowa to near Milwaukee this afternoon. High-
resolution models sink this down to the extreme northern CWA this
evening, but its southern progression will be slowed as the
prominent stacked low over the Oklahoma/Texas panhandles lifts
northeast and slowly fills. Consequently, temperatures should stay
in the mid-upper 50s over much of the area overnight, but may be
significantly lower across the north if this boundary sinks a bit
further south. With the front pushing back north on Saturday as the
low moves into Missouri, temperatures should be well into the 60s
over the forecast area.

Precipitation-wise, the rain currently over Missouri and Iowa will
slowly push eastward toward the Illinois River through mid-evening,
then reach the eastern parts of the forecast area after midnight.
Latest high-res models suggest the southeast CWA may even stay dry,
but will not go that optimistic and will have at least a 30-40% PoP
there overnight. Periodic showers and scattered thunderstorms will
then continue into Saturday.

&&

.LONG TERM...(Saturday night through Friday)
ISSUED AT 257 PM CDT Fri Mar 24 2017

A 1003 mb low near the Oklahoma panhandle this afternoon will move
slowly eastward and weaken...arriving in west central IL Saturday
night. The cold front will be considerably ahead of the
low...already east of Illinois by Saturday evening. Showers and a
few thunderstorms will continue Saturday night and into Sunday
morning before tapering off as the upper low moves off to the
northeast and an upper ridge builds in for the night. Only a very
marginal instability and shear profile will accompany this period so
thunderstorms should lose intensity and coverage compared with
Saturday afternoon. The next low will be approaching close
behind...passing east through Southern Illinois Monday evening.
Another round of showers and thunderstorms will accompany the second
system Monday morning through evening. Again the better instability
and shear profiles will pass by to the south of the central IL
forecast area...and thunderstorms expected to be confined to around
I-72 southward. Still a ways off and subject to considerable
forecast uncertainty is another potentially stronger system for late
in the week...likely targeting the lower or middle Mississippi
Valley region. Current forecast models and ensembles showing a large
spread in solutions for this later system.

Temperatures should cool off a bit following Saturday`s cold
front...with highs hovering mainly upper 50s to mid 60s for the
upcoming week. Lows will be 40s and lower 50s through Monday
night...then cooling off to upper 30s and lower 40s near I-74 to mid
to upper 40s south of I-70. Main temperature uncertainty looks to be
Thursday/Friday, where the storm system track could play a
significant role in temperatures. ECMWF brings fairly warm
temperatures well into the 60s ahead of the low...while the faster
and more southern track of the GFS pushes cooler northeasterly flow
into central IL...and could result in highs only in the 40s. Have
opted for a compromise at this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1230 PM CDT Fri Mar 24 2017

Concern in the shorter term is with an area of ceilings around
3000 feet streaming northeast out of southern Illinois. Current
trajectories keep the lower ceilings just south of KCMI/KDEC but
these areas will likely see some of the fringes. Ceilings may
briefly drop below 3000 feet there, but cloud heights have been
rising and the probability of this happening that far north is
low. Southerly winds will continue gusting to around 30-35 knots
as good mixing takes place, but will subside toward late afternoon
as the clouds increase over the region.

Longer range, focus remains in the showers and thunderstorms that
will be moving east out of Missouri and Iowa later this evening.
Morning model suite continues to slow the arrival a bit, with
locations around KBMI-KSPI westward seeing some storms arriving
toward 02-03Z and KCMI toward 06Z. Thunderstorms will remain
scattered but not prevailing, so will continue with the VCTS
mention along with prevailing showers. As the rain arrives,
ceilings and visibility will lower to MVFR levels in most areas
after 06Z and continue through the remainder of the forecast
period.

&&

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

&&

$$

SHORT TERM...Geelhart
LONG TERM...37
AVIATION...Geelhart



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