Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 250830

Area Forecast Discussion
National Weather Service Lincoln IL
330 AM CDT TUE OCT 25 2016

.SHORT TERM...(Today and tonight)
ISSUED AT 330 AM CDT Tue Oct 25 2016

The ridge of high pressure that helped provide quiet weather across
central and southeast Illinois yesterday will start to pull away
from the area today. A developing storm system will approach the
area tonight as the ridge continues to pull away. Main forecast
problem in the near term revolves around the risk of showers/storms
tonight as the system approaches.

Southerly return flow will develop today between the departing ridge
and approaching storm system. This will gradually increase moisture
levels across the area, especially in the mid-upper levels of the
atmosphere, but the additional cloud cover should keep today`s highs
pretty similar to yesterday (in the 60s). The local atmosphere will
be too dry and the approaching system too far away to produce
rainfall during the daylight hours today.

The precipitation threat for tonight increases slightly as
WAA/isentropic ascent increases ahead of the approaching
system/upper-level wave. However, it appears that the bulk of the
rainfall threat will remain north & west of the forecast area, in
the vicinity of the system`s warm & cold fronts. Forecast sounding
moisture profiles also stay pretty dry, at least in the low levels,
suggesting not much rainfall reaching the ground. Have confined PoPs
tonight to the far NW portion of the forecast area which will be
closer to the approaching system and also where moisture profiles
moisten most significantly. Removed mention of thunder tonight
considering the very sparse precipitation coverage expected, and
weak lapse rates.


.LONG TERM...(Wednesday through Monday)
ISSUED AT 330 AM CDT Tue Oct 25 2016

00Z forecast models are in fair agreement next few days with a good
shot of showers and a few thunderstorms spreading east across
central and southeast IL on Wed and then diminishing from west to
east during Wed night. A mid level trof will eject east from the
central rockies into IL by sunset Wed while 1013 mb surface low
pressure tracks east into southeast IA by 18Z/Wed, into northern IL
near I-80 early Wed evening and into northern IN by overnight Wed
night. Cold front to pass east across area Wed evening. Models have
continued with quarter to half inch of rain over central IL with one
to two tenths inch of rain in southeast IL before convection
diminishes by overnight Wed night. Highs Wed to range from the lower
60s from I-74 north to the lower 70s south of I-70 where showers and
a few thunderstorms arrive later on Wed. Lows Wed night in the mid
to upper 40s, with lower 50s southeast of I-70.

Clouds to decrease during the day Thu as high pressure settles into
IL Thu afternoon. Cooler highs in the upper 50s and lower 60s on Thu
and mildest over sw CWA. Lows Thu night in the low to mid 40s and
coolest over east central IL.

00Z models have trended warmer and drier from Friday through
Saturday as models are further north with low pressure passing
through the upper Great Lakes region. Now have a dry forecast for
this weekend with milder highs in the upper 60s/lower 70s Fri/Sat,
with mid 70s in southeast IL on Sat. A cool front passes through Sat
night with highs Sunday in the low to mid 60s. Upper level ridge
near IL early next week with dry weather continuing and looks like a
nice Halloween for central and southeast IL with highs 65-70F and
mildest over western CWA. Even warmer on Tue in the low to mid 70s.
GFS shows chances of showers on Tue while Ecmwf models remains
dry. Kept small consensus pops on Tue.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1139 PM CDT Mon Oct 24 2016

Surface high pressure will gradually shift east over the next 24
hours, as a low pressure system approaches from the west. Skies
will remain generally clear through tomorrow morning. High clouds
will increase tomorrow afternoon, with mid-clouds increasing
during the evening as precipitation chances increase NW of the IL
river. Rain will mainly arrive after the end of this TAF period,
but a few showers could approach the PIA terminal site after 03z,
so a VCSH was included after 03z. The dry lower levels will help
to delay the onset of precipitation, and cloud ceilings will
remain VFR through this TAF period.

Light northeast to east winds will continue the rest of tonight.
Directions will become southeast after sunrise tomorrow, as the
pressure gradient begins to tighten ahead of the next low
pressure systems. Wind speeds should remain in the 8-12kt range
tomorrow and tomorrow evening.


.ILX Watches/Warnings/Advisories...


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