Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 170929

Area Forecast Discussion
National Weather Service Lincoln IL
329 AM CST Tue Jan 17 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 329 AM CST Tue Jan 17 2017

08z/2am surface analysis shows 1008mb low near Chicago, with cold
front extending southward along the I-57 corridor.  A few showers
are ongoing ahead of the front near the Indiana border: however,
most of the precipitation has come to an end across central
Illinois.  The widespread dense fog from last evening has also
mostly dissipated, except for locations along/north of a Canton to
Bloomington line where visibilities are 1 mile or less.  HRRR has
been consistently showing dense fog over eastern Iowa spilling E/SE
along the I-74 corridor this morning: however, based on prevailing
W/SW boundary layer flow, think its forecast takes the fog a bit too
far south.  Based on current upstream obs over northern Missouri,
have decided to trim the southern row of counties from the Dense Fog
Advisory to only include Knox, Stark, Marshall, Peoria, and
Woodford.  Still some question as to how quickly the fog will
dissipate later this morning, with the Rapid Refresh showing it
clearing the area as soon as 15z, while the HRRR lingers it until
closer to 18z.  Given lack of strong dry advection in the wake of
the departing low, have opted to go more pessimistic and have
therefore lingered areas of fog across the north through midday.
Once the fog dissipates, overcast conditions will prevail for the
balance of the day and through tonight as well.  Highs today will
range from the upper 30s around the lower 50s near
the Indiana border.  Lows tonight will generally be in the lower to
middle 30s.


.LONG TERM...(Wednesday through Monday)
ISSUED AT 329 AM CST Tue Jan 17 2017

A weak area of high pressure will build into the Midwest on
Wednesday, leading to a gradual clearing trend.  NAM forecast
soundings show a shallow layer of moisture remaining trapped beneath
a strengthening subsidence inversion, which would lead to continued
cloudy skies through Wednesday.  The GFS on the other hand shows the
moisture mixing out and skies clearing.  Think the NAM may be
suffering from its usual low-level moisture bias, so have decided to
go with skies becoming mostly sunny on Wednesday with highs in the
lower to middle 40s.

NAM/GFS/ECMWF are all in relatively good agreement with the next
system approaching from the southwest on Thursday.  Long-wave trough
currently over northwest Mexico will lift northeastward into the
Plains on Thursday, with a slug of deep-layer moisture pushing
northward ahead of the system into the Ohio River Valley.  As
forcing increases upon approach of the wave, showers will become
likely from Thursday afternoon through Friday morning.  Rainfall
amounts will range from around one tenth of an inch near as much as three quarters of an inch in the Wabash
River Valley.

Once the wave lifts into the Great Lakes, warm and dry weather will
be on tap for Friday and Saturday.  Thanks to building upper heights
and strong southerly flow, temperatures will climb well into the 50s
by Saturday.  In fact, both the GFS and ECMWF numeric guidance
suggests temps could potentially climb into the 60s on Saturday.
After that, another strong wave will approach from the southwest
early next week...bringing a round of rain from Sunday into Monday.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1045 PM CST Mon Jan 16 2017

Warm front continues to edge slowly north late this evening and
its along and south of the boundary where we see a marked
improvement in cigs (MVFR) and vsbys (VFR). However, short term
models continue to suggest any improvement in cigs and vsbys
overnight north of I-72 may be short lived, especially along and
north of I-74 where we will see another band of VLIFR vsbys in fog
track over the area tomorrow morning. Finally, as drier air slowly
works its way east across the area late Tuesday morning into the
afternoon hours, we should see an improvement in vsbys across the
board. However, the forecast soundings continue to indicate LIFR
cigs into the afternoon with little hope for any improvement at
least through Tuesday evening. Surface winds will gradually become
south to southwest as the low passes to our northwest later tonight
and then into a westerly direction in the 08z-12z time frame, which
should continue thru the day on Tuesday with speeds in the 10 to
15 kt range.


Dense Fog Advisory until 10 AM CST this morning for ILZ027>031.



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