Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 152003
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
303 PM CDT Tue Apr 15 2014

.DISCUSSION...
ISSUED 300 PM CDT Tue Apr 15 2014

One more night of freezing conditions is on tap, then warmer
conditions will finish out the week. However, very few areas will
see above normal temperatures over the next 7 days. The storm
system that will bring significant snows to NE Minnesota and N
Wisconsin will drag a cold front across IL Thur night into Friday.
We will see a return of colder air Fri/Fri night as a result, but
hopefully not more freezing temps like the 15/06z GFS run indicated.

SHORT TERM...Tonight through Friday.

Scattered flurries developed this afternoon in our NE counties as
the upper trough axis pushed across eastern IL. That precipitation
should come to an end by evening as subsidence prevails in the
wake of the trough. Mostly clear skies are expected overnight with
weakening winds for the balance of the night, setting up favorable
radiational cooling conditions, especially in the east. The
coldest air will be primarily closer to the Indiana border, with
freezing conditions in most of our KILX CWA.

Based on climatological analysis of the current growing season so
far, only out southern third of counties have seen enough growing
degree days to warrant freeze headlines. Given that, and the
expectation for the coldest lows to be in the east, we decided to
issue a Freeze Warning only for 11 of our SE counties. Basically
SE of a line from Christian to Coles counties. We are expecting
southerly winds to begin to develop from west to east late
tonight, which will work to keep western areas warmer, or have
their low temps occur earlier in the night. The winds should even
develop in the east shortly after sunrise on Wed, helping push
temps above freezing by 9 am.

The south winds will increase quickly on Wed, in response to low
pressure to the NW of IL. Momentum transfer plots show mixing
heights will tap into wind speeds of 40-45 mph. We should see
sustained south winds climb into the 20-30 mph range, with some
gusts to 40 mph. The peak winds look to be for 4 hours between 11
am and 3 pm, but gusts will continue into early evening. We are
close to wind advisory criteria, or 30-39 mph sustained winds for an
hour or more. Areas west of I-55 will have the stronger winds, so
closer analysis may be needed from tonight`s models to see if an
advisory is warranted.

As the cold front arrives later Thursday, we will see increasing
mid level moisture, and probably some virga on radar later in the
afternoon. Cold rain showers may develop Thur night as colder air
begins to filter into IL behind the cold front. We can not
completely rule out some snow flakes reaching the ground late Thur
night into Friday morning, but air temps from 850mb to the surface
do not see supportive of snow reaching the ground, so we will keep
all precipitation chances as rain for now Thur night into Fri morn.

By Friday afternoon, a dry punch behind the front will help to
shut down precip from west to east. The pocket of cold air will be
brief, but we may see enough clearing for a few spots in the north
to approach the mid 30s for low temps. No freezing conditions are
forecast at this time Friday night.

LONG TERM...Saturday through Tuesday.

A warming trend will establish next weekend ahead of the next
weather system. Highs should reach the low 60s on Sat and mid to
upper 60s on Sunday, which will be close to normal highs. Rain
chances will begin again Saturday night NW of the IL river, then
expand eastward on Sunday as the lower troposphere saturates
closer to the ground. Our highest PoPs in the extended are Sunday
night, with 40-50 Pct chances across the board, in response to the
upper trough axis and shortwave pushing across IL.

Monday and Tuesday will see a return of high pressure with dry and
relatively mild conditions.

Shimon
&&

.AVIATION...
ISSUED 1255 PM CDT Tue Apr 15 2014

Scattered to broken cumulus cloud field with VFR bases of 4-6k ft
over central IL airports early this afternoon to gradually
decrease from west to east later this afternoon and dissipate by
sunset as upper level trof over MI/IN pulls eastward across the
ohio river valley during this afternoon. Breezy nw winds 10-15 kts
and gusts near 20 kts to diminish light and variable after sunset
as weak high pressure ridge drifts east over IL. 1001 mb low
pressure over central MT to track to the western MN/IA border by
18Z/1 pm Wed. This to increase mid/high clouds from the west later
tonight into Wed morning. Also increasing pressure gradient Wed
morning to increase sse winds 15-20 kts with gusts 25-30 kts
after 14Z/9 am Wed.

07
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FREEZE WARNING from 1 AM to 8 AM CDT Wednesday FOR ILZ054-056-
061>063-066>068-071>073.

&&

$$







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