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Area forecast discussion 
National Weather Service Lincoln Illinois
900 PM CDT Tuesday Apr 21 2015

issued at 855 PM CDT Tuesday Apr 21 2015

Latest surface analysis indicating a weak cold front making its
way southeast across the forecast area this evening. Air mass
ahead of and behind the boundary was quite dry with only some
light showers being reported over parts of extreme east central
Iowa into far western Illinois. Weak shortwave noted on the water vapor
loop will streak across the area tonight bringing a limited amount
of lift and just enough moisture to produce some widely scattered
showers. Any threat of rain over far east central and southeast
Illinois should shift off to our east by morning with another
chilly air mass spilling southeast into our area accompanied by
gusty northwest winds...although the winds tomorrow are not
expected to be as gusty as today as a few sites over our northern
counties topped out around 45 miles per hour at times late this morning into
the afternoon hours. Have made some adjustments to the grids with
respect to precipitation wording and temperatures for the overnight
hours. The updated zone forecast product should be out by 915 PM.


Short term...(tonight)
issued at 300 PM CDT Tuesday Apr 21 2015

Cold front extending from Northern Lake Michigan to just north of
Kansas City early this afternoon. Quite a bit of dry air mixing down
to the surface...resulting in dew points in the lower 20s and even
some upper teens across the north half of the County Warning Area...where winds have
also been gusting 35-45 miles per hour. Frontal passage is expected in our area
during the evening...with a few showers possible associated with an
upper disturbance streaming southeast out of South Dakota/Iowa. With
the amount of dry air at the lower levels...there will be some
struggle to moisten the atmosphere enough...with forecast soundings
remaining rather dry below about 3000 feet. Have continued to
mention pop's of around 30% mainly in the central and southern
County Warning Area...with some minor refinements to the hourly values. Skies should
quickly clear once the showers move out...but remain mostly cloudy
across the southeast much of the night. Although lows in the far
northern County Warning Area expected to dip into the middle 30s in some not
expecting frost tonight as winds should generally stay up around 10
miles per hour overnight.

Long term...(wednesday through tuesday)
issued at 300 PM CDT Tuesday Apr 21 2015

A breezy and cool day ahead Wednesday despite more sunshine as
clouds decrease Wednesday morning over southeast Illinois. Highs in the middle 50s
central Illinois and upper 50s in southeast Illinois from I-70 southeast. These
temperatures are about 10 degrees below normal for late April.

Forecast concern is possiblity of frost Wednesday and thurday night
especially north of I-70 as growing season has begun across
Illinois. Strong cutoff low near Eastern Lake Superior slowly pivots
eastward into eastern Ontario and western Quebec Wednesday night and
Thursday. Meanwhile Canadian high pressure ridge to nose into the
middle MS River Valley diminishing winds and clouds. With dry airmass
in place, this will allow a couple of cool nights ahead. Wednesday
night appears to be the coolest night across the area with lows in
the low to middle 30s (near freezing temperatures from I-74 north) and frost
likely overnight into early Thursday morning. Frost and freeze headlines
may eventually be needed overnight Wednesday night. Surface Canadian ridge
only slowly shifts east of Illinois by Friday morning so think frost will
again be possible over eastern Illinois overnight Thursday night into early Friday
morning with lows in the middle 30s after highs reach upper 50s and
lower 60s on Thursday (mildest in SW cwa).

12z medium range models eject a surface and cutoff low from Colorado to MO
by Saturday morning. Think most areas will still stay dry on Friday
and only have slight chances of light showers far western/SW areas
later Friday afternoon with clouds increasing during the day Friday
from the west-southwest. Highs Friday in the lower 60s across most of the
region. Have likely chances of showers Friday night into Saturday
with highest chances southern areas where isolated thunderstorms
possible. Just slight chances of light rain showers in southeast Illinois
Saturday evening then dry rest of the weekend. Cooler highs Sat in
the 50s while more sunshine Sunday returns highs back into the lower

The 12z extended forecast models have another weather system
ejecting out of the Southern Plains on Monday into Tuesday. This
brings next chance of rain showers and rainfall amounts fairly light
due to Gulf of Mexico being cutoff.


Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 602 PM CDT Tuesday Apr 21 2015

VFR conditions are expected through this taf period. A weak cold
front located over parts of east central Iowa will track across
the area tonight bringing some scattered light showers with it
with broken-overcast ceilings between 3500 and 4500 feet. Latest rap forecast
soundings backing off a bit with the precipitation over the past few
runs but still holding with a brief period of low VFR ceilings along
the cold front. The gusty west to northwest winds will diminish
rather quickly after sunset with a light west to northwest wind
expected overnight with speeds of 7 to 12 kts. Those winds will
become northwest and increase in speed on Wednesday to between
15 and 25 kts with a few gusts up to 30 kts at times before
diminishing quickly towards sunset.


Ilx watches/warnings/advisories...


short term...geelhart
long term...07

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