Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 170739
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
239 AM CDT Wed Sep 17 2014

.SHORT TERM...(Today)
ISSUED AT 237 AM CDT WED SEP 17 2014

Recently issued a Dense Fog Advisory across portions of east-central
and southeast Illinois to account for rapidly expanding dense fog.
This dense fog is forming along a northeast-southwest surface ridge
axis, in an area with near zero surface temperature/dew point
spreads and calm winds. It is not entirely clear how far north and
west of the ridge axis a dense fog threat exists, as winds are dead
calm across most of the forecast area. However, a small
temperature/dew point spread exists north/west of the current Dense
Fog Advisory area, and some mid clouds are beginning to spill across
central Illinois from a short wave moving through the plains. These
factors lead me to believe the current advisory should be sufficient.

Aside from the locally dense morning fog, the only forecast problem
for the day revolves around the precipitation threat (if any) from
the wave moving through the Plains. Some of the model guidance is
suggesting the far southern part of the forecast area may be brushed
by light rainfall later today. However, think these precipitation
forecasts are likely too far north. The model consensus has the vort
max with the short wave staying south of the forecast area, along
with the bulk of the isentropic lift ahead of the wave. These
factors, combined with the dry air mass currently in place, support
continuing with our current dry forecast for today. Temperatures
today are likely to be similar to yesterday`s. While weak low
level warm air advection will be taking place, it is likely to be
offset to some degree by additional cloud cover today.


&&

.LONG TERM...(Tonight through Tuesday)
ISSUED AT 237 AM CDT WED SEP 17 2014

High pressure over the Great Lakes to keep us in a dry east to
northeast flow into Thursday evening. After that, incoming shortwave
from the northwest comes into play. As with the daytime models, the
evening runs have continued the trend that the remnant moisture from
Odile will probably make it about as far as Missouri before shunting
southeast, so the incoming wave never really draws from it. This
lessens the threat of widespread heavy rain. The southeast half of
the CWA will likely remain dry through Saturday, while rain chances
increase across the northwest during the afternoon, and the best
chances occur Saturday night.

Sunday may be a bit of a question mark. The GFS and Canadian models
both have a rather clean frontal passage with lingering rain ending
in the morning. However, the latest ECMWF slows the front as a
surface low forms over Kansas, lingering rain across the south half
of the forecast area into Sunday evening. There may be a bit of a
feedback issue with that solution, so will maintain the dry
conditions by Sunday evening.

Rather large surface high will dominate the Midwest early next week,
with dry conditions for a few days.


&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 1130 PM CDT TUE SEP 16 2014

Surface high pressure meandering across the Midwest will bring
light and variable winds for the next 24 hours. A weak mid-level
shortwave trough crossing Illinois will cause some cloud cover
overnight, but no MVFR ceilings. Fog mention in TAFs continues to
be MVFR from 09Z-12Z, however areas mainly KTAZ-KPRG southward
could see lower values due to higher dew points and less cloud
cover expected overnight. Visibility locally down to VLIFR
category is possible. For Wednesday afternoon, scattered cloud
cover expected as daytime heating interacts with low level
moisture, but any local ceilings should remain above MVFR
thresholds.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY until 10 AM CDT this morning FOR ILZ054>057-
061>063-066>068-071>073.

&&

$$

SHORT TERM...BAK
LONG TERM...GEELHART
AVIATION...ONTON





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