Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 250345

Area Forecast Discussion
National Weather Service Lincoln IL
1045 PM CDT Fri Mar 24 2017

Issued at 830 PM CDT Fri Mar 24 2017

The latest surface analysis showing a cold front edging its way
southeast across central Illinois this evening. The front
stretched from weak low pressure over southern Lower Michigan
southwest to roughly the I-55 corridor. Had some weak convection
develop along the boundary over our far northern counties late
this afternoon that has shifted well to our northeast this
evening. May see some additional development along the boundary
although convergence is quite weak with our local objective
analysis indicating MUCAPEs around 200 J/KG. Further to our
southwest, a larger area of showers and isolated thunderstorms was
tracking across southwest through central Missouri and should
push into west central Illinois late tonight. If we don`t see any
activity develop along the weak cool front across the east, they
may have to wait a while before the rain moves in there as most of
the activity was moving more north than east across Missouri this

As the upper low tracks slowly into Missouri tomorrow, scattered
showers will be the rule across the area as the weakening surface
low moves through central Illinois by later in the day. Have made
some adjustments to the precip wording overnight and with early
morning lows across the north where the push of the cooler air
mass to our north will be more noticeable in that area late
tonight and early Saturday morning. We should have the updated
zones out by 900 pm.


.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 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 afernoon hours before winds gradually
diminish after 00z tomorrow evening.




SHORT TERM...Geelhart
AVIATION...Smith is the U.S. government's official web portal to all federal, state and local government web resources and services.