Area Forecast Discussion
Issued by NWS Central Illinois

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335
FXUS63 KILX 211544
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1044 AM CDT Tue Mar 21 2017

.UPDATE...
Issued at 1041 AM CDT Tue Mar 21 2017

High pressure ridge stretching south through the Plains from
Canada...and building into the Midwest today. However, a weak wave
will ripple through the flow aloft and bring some very light/weak
showers to scattered locations throughout the day. Keeping the
probability for measurable precipitation low...but trace
amounts and/or sprinkles possible for a large portion of Central
Illinois. Have made minor adjustments to the forecast throughout
the morning.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 338 AM CDT Tue Mar 21 2017

Surface high pressure ridge will remain west of the area over the
plains. However, a weak impulse is forecast to move southeast
through the mid level flow into western Illinois today. There is no
surface reflection of this impulse so models differ on strength,
resulting in differences on qpf associated with it. Trend has been
to decrease pops over the last several forecast packages, and this
mornings package will be no different. Currently, GFS is the only
model to have precip in the CWA this morning and afternoon, while
the ECMWF only has it for this afternoon. QPF is forecast to be less
than one tenth of an inches well. Both models do have the impulse
weakening as it moves east into and through the area so agree with
the trend of highest pops in the west and diminishing pops in the
afternoon. Have decided to keep chance pops in the west/northwest
this morning and then a narrow band/area of slight chance pops
across the northern third of the CWA. Will have just slight chance
in the afternoon. So, the central and southern parts of the CWA will
be dry today.

Will be clouds today but these will get pushed to the south this
evening, leaving a mostly clear to partly cloudy sky. winds should
remain north to northeasterly today and through this evening but
then become northeasterly after midnight. Highs today will not be as
warm as Monday, but still above normal for March. Overnight lows
tonight should drop to just below freezing across the whole area.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 338 AM CDT Tue Mar 21 2017

1039 mb Canadian high pressure over eastern Saskatchewan and
ridging SSe into the upper Midwest, will drift southeast into
northeast MI by sunset Wed and bring dry and chilly wx to area on
Wed and Wed night. Mostly sunny skies to start the day Wed
morning, with increasing clouds from the west during Wed afternoon
with mostly cloudy skies by days end and into Wed night.
Temperatures briefly cool below normal on Wed across central and
southeast IL with highs in the low to mid 40s, similar to this
past Saturdays highs. Another freeze expected Wed night with lows
27-32F. Not quite a hard freeze in southern 6 counties where the
growing season has started, with lows there near 30F.

Temps climb about 10 degrees and getting closer to normal on Thu
with highs in the lower 50s in central IL and mid 50s in southeast
IL. High pressure settles over the mid Atlantic coast on Thu
afternoon while upper level ridge builds east into the MS river
valley. Some warm air advection driven light/spotty precipitation
develops over the IL river valley Thu especially Thu afternoon with
20-30% pops. Could be a light mix of precipitation over west central
IL if it moves in early Thu morning. Have just slight chance of
light rain showers from I-74 north on Thu evening before dry
conditions return overnight Thu night into Friday. Breezy and mild
Friday with highs in the upper 60s and lower 70s with southerly
winds 15-20 mph and gusts 25-30 mph.

00Z Mar 21 models shows a strong storms system emerging over eastern
CO Thu night with cutoff low and surface low moving into central MO
and sw IL by sunset Sat. Showers and thunderstorms to spread into
western IL during Friday evening and into eastern IL too
overnight Friday night. Widespread showers and a few thunderstorms
expected on Sat. Highs Sat range from lower 60s northern CWA and
upper 60s in southeast IL. Good chance of showers Sat night with
isolated thunderstorms in southeast IL Sat evening. Still have a
chance of showers lingering on Sunday especially over central and
eastern parts of IL Sunday morning as cutoff low moves into the
southern Great Lakes by sunset Sunday. A bit cooler highs Sunday
in the mid to upper 50s, with lower 60s southeast of I-70.

Another low pressure system/upper level trof moves into MO/IL by Mon
afternoon and Monday night returning chances of showers, with
thunderstorms possible in southern IL. Highs Mon back up into the
60s. CPC`s 8-14 day outlook for Mar 28-Apr 3 has 60-70% chance of
above normal temperatures and 50-55% chance of above normal
precipitation. So a mild and wet pattern looks to continue into
early April.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 637 AM CDT Tue Mar 21 2017

VFR conditions should prevail at all TAF sites next 24hrs. Light
fog is present at SPI and DEC and am expecting that to continue
for another couple of hours. CMI is close, but is just reporting
HZ. So will have a TEMPO group for 2 hrs for all three sites to
accommodate the fog. Then mid clouds around 12--15kft will move
into SPI/DEC/CMI from late morning thru afternoon. Mid clouds will
be lower at PIA and BMI since they will be closer to the
weakening impulse moving into the area for this afternoon. At all
sites cigs will lower during the afternoon with PIA/BMI being
around 4.5kft and the other three sites being 6-7kft. Once the
weak impulse moves out, clouds will scatter out and all that will
be left is cirrus, which will occur during the evening hours.
Winds will be northerly through most of the period and then become
northeasterly during the evening behind the impulse.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...HJS
SHORT TERM...Auten
LONG TERM...07
AVIATION...Auten



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