Area Forecast Discussion
Issued by NWS Central Illinois

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575
FXUS63 KILX 220404
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1104 PM CDT Tue Mar 21 2017

.UPDATE...
Issued at 840 PM CDT Tue Mar 21 2017

Latest surface analysis indicates a weak cold front stretching
from southern Lake Michigan west through northwest Illinois.
Quite a bit of dry air located north of this boundary with
readings as of 800 pm in the 10 to 15 degree range, while to
the south of the boundary, dew points were analyzed in the low
to mid 30s. Winds should shift into the north and northeast
and increase a bit behind the cool front later tonight and
we will be watching a band of lake clouds over southeast
Wisconsin and extreme northeast Illinois shift south and
southwest which may affect our northern counties later tonight.
However, as Canadian high pressure builds south into the Midwest
by Wednesday morning, it appears any of the lower clouds that may
sneak into our north will dissipate as they continue to spread
south.

A rather cold night in store for the forecast area as the large
fair weather system to our north builds south with early morning
lows dipping into the mid 20s north to the lower 30s south where
the current Freeze Warning will remain in place over extreme
southeast Illinois. The updated ZFP should be out by 900 pm.

&&

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 303 PM CDT Tue Mar 21 2017

High pressure continues to build into the Midwest, but a persistent
slow wave of light precipitation with the mid level winds.  Radar
returns relatively high, but most of the clouds are between 7000 and
8000 ft, expect a lot of virga...precip is running into a dry layer
that is evaporating much of the rain.  Echos have been weakening
with eastward progression.  NWerly winds becoming more northerly
this evening... and more northeasterly after midnight.  Easterly
component will continue to dry out the cloud levels through the
overnight and erode the ceilings. A lack of cloud cover throughout
most of the night will assist in providing effective radiational
cooling and temperatures will drop below the freezing mark.  As a
result, a freeze warning is in effect for southeastern IL. New
and/or sensitive vegetation will be impacted. Mostly sunny skies
will prevail tomorrow morning...with clouds slowly moving into the
region later in the afternoon as a quick wave rounds over the mid
level ridge to the west and dives into the mid Mississippi Valley.
Northeasterly winds, however, will keep the temperatures cooler
tomorrow...in the 40s.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 303 PM CDT Tue Mar 21 2017

A progressive upper level pattern will be in store for the Midwest
the next few days resulting in a return to warmer temperatures.
Upper level ridging is then expected to maintain a position to our
east for the weekend, resulting in several upper level shortwave
trofs moving across the area. This will give us a period of
unsettled weather into early next week.

Surface high pressure moving toward the eastern Great Lakes
Wednesday night will give us one more chilly night with temperatures
at or below freezing. Upper level ridging and a southerly wind flow
will allow temperatures to climb closer to seasonal normals
Thursday, although quite a few clouds should keep readings mainly in
the 50-55 range. Previous model runs indicated some light mixed
precipitation toward daybreak Thursday in west central IL as low
level overrunning sets up. However, the latest runs have backed off
on this, so will go with all rain - mainly along the IL River
Thursday morning, and along and north of I-74 in the afternoon-early
evening with the lifting warm front.

The GFS and NAM are trying to develop some spotty showers in the
warm sector on Friday, but a decent cap should keep most areas rain-
free, with a partly sunny sky and windy, warm weather. Temperatures
should climb into the lower to middle 70s, except in extreme eastern
IL where a few more clouds may be present. Shower and isolated
thunderstorm potential will increase rapidly Friday night west of
I-55 and across the whole forecast area Saturday as a stacked,
closed low slowly approaches the MS Valley. The European is a
quicker outlier with this solution, with the slower GFS/GEM
preferred in this situation.

The slow moving nature of this system will keep the likelihood of
showers and t-storms going through Saturday and into Sunday morning.
Widespread 0.75-1.50 inch rainfall amounts are expected Saturday
into Sunday afternoon, with locally higher totals in t-storms, due
to the prolonged nature of this system.

The upper level low will continue to weaken and eventually get
kicked out toward the eastern Great Lakes later Sunday giving us a
brief break in the precipitation. The upstream kicker/shortwave
trough, however, will approach Sunday night and into Monday giving
us the likelihood of more showers and a few t-storms into early
Tuesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1100 PM CDT Tue Mar 21 2017

Watching a band of MVFR cigs coming off Lake Michigan into
northeast Illinois late this evening. Based on its present
movement, the leading edge of the lower cloud deck will
reach BMI and PIA between 07z-10z. Will handle with a tempo
group in those time frames for both BMI and PIA, and keep
mainly VFR conditions for our other TAF sites. Any lower
clouds should dissipate by mid morning on Wednesday as
high pressure builds in from the northwest with VFR conditions
prevailing at all sites for the remainder of the forecast
period. Surface flow will be northeast at 10 to 15 kts for
the rest of the night with gusts around 20 kts at times.
Winds should veer more into an easterly direction on Wed.
with speeds continuing at 10 to 15 kts.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Freeze Warning from 4 AM to 9 AM CDT Wednesday for ILZ066>068-
071>073.

&&

$$

UPDATE...Smith
SHORT TERM...HJS
LONG TERM...Miller
AVIATION...Smith



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