Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 172356

Area Forecast Discussion
National Weather Service Lincoln IL
656 PM CDT Sat Mar 17 2018

.SHORT TERM...(This evening through Sunday)
ISSUED AT 303 PM CDT Sat Mar 17 2018
Ridging at the surface and aloft over the Plains this afternoon,
keeping a northerly component in the winds over the forecast area.
Cooler air filtering into the region, but the stubborn stratus
associated with the low passing through the Midwest into IN this
afternoon is slow to erode. HRRR slowly progresses this shield of
clouds to the south tonight, eventually moving to mostly clear for
Central IL by morning. Concerned that the dry air is a little
further to the north than prev addition to the fact
that there is not significant llvl flow to change the airmass
quickly. Lighter winds in the overnight combined with llvl
moisture still trapped in the low levels may slow the progression
of the low clouds to the southwest. There is currently a good 30
mile or so lag of the dry air behind the clearing line to the
north/northeast. With that in mind, have put patchy fog in the
forecast after midnight for where the clearing is anticipated.
Should the delay last longer, there is a potential for some of
that fog to become dense...but guidance winds stay up just enough
to drop confidence in that for now. Tomorrow, mild temps with
highs in the 50s. The swath of low clouds holding just to the
southwest with light easterly winds attempting to advect some of
that drier air in at the surface. How far south those clouds get
will greatly impact temperatures particularly SW of a line from
Macomb to Decatur.

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 303 PM CDT Sat Mar 17 2018
Overnight Sunday into Monday...lows drop only to the low to mid
40s as increasing clouds once again inhibit cooling in the
overnight hours. Next system for Monday/Monday night went with a
more southerly solution this run, with the GFS and ECMWF keeping
the associated precip well south of the NAM solution. Given the
erratic nature of the solutions out of the models at this point,
keeping the slight chc/chc pops across the northern tier for now.
Rain for Monday and Monday night is expected, before briefly
changing over to snow on its departure to the east on Tuesday.
Models are relatively consistent in suggesting that this wave will
shift us back to a busier and more progressive northwesterly flow
pattern aloft. Several waves suggested in this pattern, but the
GFS is pretty robust with the development of a surface ridge,
inhibiting precip development (Wed night in particular). Low
confidence dry forecast through the middle of the week once the
northwesterly flow kicks in. The next major storm is taking shape
going into next weekend, with precip starting on Fri.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 653 PM CDT Sat Mar 17 2018

Low-end MVFR CIGS will sink south of central Illinois this
evening, providing a return to VFR conditions. However, expect at
least MVFR fog to develop across the area later tonight. Once the
fog burns off Sunday morning, VFR are expected. Light winds will
prevail through the 00Z TAF valid time.




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