Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 290900

Area Forecast Discussion
300 AM CST Sat Nov 29 2014

.SHORT TERM...(Today)

Southerly winds have prevailed through the night bringing mild
conditions, at least compared to what occurred the past few
mornings across central through southeast Illinois. The persistent
southerly flow has resulted in a marked increase in the low level
cloud cover over parts of Arkansas this morning with a north-
northeast trajectory. Forecast soundings have indicated an
increase in low level moisture for the past several runs which
is being validated now over the lower Mississippi Valley. The
last several runs of the HRRR model has brought the clouds
northeast into about the eastern half of the forecast area by
early this afternoon. Surface dew points over extreme southwest
Missouri have risen into the mid and upper 40s early this morning
and expect the persistent 1000-850 mb theta-e advection and
moisture transport to bring the higher dew points and clouds
northeast into our area later today. Despite the increase in
clouds, temperatures are expected to warm into the low to mid
50s north to the upper 50s, possibly 60 degrees over parts
of southwest Illinois this afternoon.

Models for the past several days have hinted at some light QPF
over parts of southeast Illinois with the significant moisture
transport into our area. However, not seeing much in the way
of lift with forecast soundings showing only the low level
moisture trapped beneath a strengthening inversion today and
tonight. Seems to be more of a setup for very light rain or
drizzle over parts of southeast and east central Illinois and
later this afternoon and tonight.


.LONG TERM...(Tonight through Friday)

One more mild day across our area on Sunday before a strong
cold front and associated 1047 mb high settles across the
lower Great Lakes Sunday night and spends a few days early
next week, before slight warmer weather returns for the balance
of the forecast period.

The strong Polar cold front looks on track for mainly Sunday
afternoon along with light rain or drizzle chances just ahead
and behind the frontal boundary. Best chances appear to be over
the eastern half of the forecast area, mainly east of I-55, Sunday
afternoon. Other than the low level moisture trapped beneath the
rather strong inversion, not much moisture above, so looking more
for drizzle or some very light rain Sunday afternoon into Sunday
night. As the colder air settles south, there may be a brief period
of some very light freezing rain or drizzle mainly over the I-70
corridor late Sunday night into the Monday morning commute. There
may be some very light ice accumulations over extreme southeast
Illinois just in time for the return to work and school Monday

Cold and dry conditions expected to settle over our area for
Monday through Wednesday. We may see some lingering light
precip Monday morning over the far southeast counties, but the
front should get shunted well south of our area by Monday
afternoon and evening ushering in some rather chilly temperatures
again across the entire area Monday night. Lows will dip into the
10 to 15 degree range over the north half of the forecast area
Tuesday morning with low to mid 20s common south. Quiet but chilly
temperatures will be the story through Wednesday morning before
we see a gradual moderating trend starting Wednesday afternoon as
the upper flow becomes more zonal over the lower 48. Southerly
return flow develops ahead of the next shortwave on Thursday
bringing in warming temperatures but also chances for
precipitation mainly from Wednesday night through Friday as a
series of weak impulse translate east in the zonal flow across the
center of the country.

With the flow deamplifying during this period, we are seeing some
timing differences with respect to the sensible weather associated
with these fast moving and relatively weak waves, especially
towards the end of the week. However, with a zonal flow pattern
seen over western Canada and medium range models not showing much
in the way of downstream blocking or buckling of the Polar jet, we
should average out above normal on temperatures in the Wednesday
through Friday forecast period.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)

VFR conditions across central/SE IL expected to deteriorate early
Saturday morning as low level moisture overruns a warm frontal
zone. Model forecast soundings indicate saturation down to surface
in this scenario, but based TAFs more on typical MOS guidance
values which look more likely. Went with MVFR cigs/vsby by 14Z
with cloud cover becoming scattered after 19Z. Winds generally
S10-15 kts. Gusts 20-25 kts during afternoon hours. Took low level
wind shear out of TAFs for this update as winds sampled by area
soundings have been a bit slower than previous model forecasts,
meaning total wind shear below 2 kft AGL will struggle to reach
30 kts.




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