Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260351
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1051 PM CDT Sat Mar 25 2017

.UPDATE...
Issued at 842 PM CDT Sat Mar 25 2017

IR and Water Vapor loops indicate the weakening upper low was
edging into northeast Missouri early this evening with the bands
of showers rotating cyclonically around the upper system. This
upper wave will continue to slide east-northeast across central
Illinois late tonight and Sunday morning before shifting off to
our east later Sunday afternoon as the next upstream storm system,
currently over the southern Rockies, shifts east across the
Southern Plains on Sunday. Our shower chances will continue until
the upper low pushes out of the state Sunday evening with forecast
soundings continuing to suggest quite a bit of residual cloud
cover in its wake across the area over the next 24 to 36 hours.

With the cloud cover over the forecast area tonight and a southeast
component to the wind, temperatures are not expected to drop off
very quickly during the overnight hours. Temperatures behind the
system on Sunday not much different behind the weak cool front
that will push through the area later tonight with highs expected
to rise back to between 60 and 65 degrees despite the extensive
cloud cover and scattered shower threat. Current forecast has a
good handle on the trends this evening and into the overnight
hours, as a result, no ZFP update will be needed at this time.

&&

.SHORT TERM...(This evening through Sunday)
ISSUED AT 241 PM CDT Sat Mar 25 2017

Nearly vertically stacked low was edging into central Missouri this
afternoon. The front has finally lifted north of the entire forecast
area, and most areas are now in the 60s, locally cooler where rain
is falling, and a few 70 degree readings were even seen along the
Indiana border. Showers have begun to increase from the south once
again and are becoming more numerous across the forecast area.
Lightning is been fairly sparse in the vicinity of the low so far,
although surface based CAPE`s in that area are currently around 500
J/kg and a few hundred J/kg will be present into the first part of
the evening this far northeast, so will continue some mention of
thunder through the evening. Severe weather threat not especially
robust, but appear more likely in the areas closer to the track of
the low where lapse rates are steepest. In our area, this would be
more in areas west of Springfield.

As the low lifts northward, the initial bands of showers and
isolated storms will track north through the area. Most of the high-
resolution guidance continues to indicate some drying wrapping
around the low with time, suggesting the western parts of the CWA
seeing only isolated showers after midnight. However, moisture being
drawn northward on the fringes of the system will result in more
numerous showers continuing closer to the Indiana border much of the
night. By late Sunday morning, the low is progged to be centered
along the Illinois/Iowa border, and the showers will continue to
diminish through the afternoon as the low lifts toward southern
Wisconsin. Will continue to mention 30-40% rain chances into the
afternoon across the areas north of I-74 and east of I-57, due to
the slow movement of the system.

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 241 PM CDT Sat Mar 25 2017

Weak high pressure...specifically a col or saddle point between the
outgoing low pressure system from Sunday and an approaching system
for Monday...will cross central IL Sunday night. As a result central
IL can expect a break in precipitation chances...light and variable
winds...but not much break in low cloud cover. Moist warm advection
will then promote showers developing Monday morning as the next
weakening low pressure system approaches from the southern Plains.
Model consensus tracks this low through southern IL Monday evening
although some differences exist between various 12Z forecast models
indicating some continuing track/timing uncertainty. A few hundred
to 1000 J/KG MUCAPE look to target areas from around I-72 southward
for the afternoon and evening Monday suggesting thunderstorms for
this area. Current models suggest stronger shear will be primarily
south of the central IL forecast area...although a marginal risk for
severe thunderstorms is forecast as far north as the I-70 corridor
at this time. Showers tapering off overnight Monday night as a high
pressure ridge approaches from the west. The next storm system looks
to develop in the southern Plains midweek...then large track
uncertainties are apparent in the 12Z model runs...with the low
tracking anywhere from northwest IL to northern AL by Friday. As a
result...large uncertainties in the specific timing and impacts of
the late week system continue.

Temperatures Monday through Saturday look to be a few to several
degrees above normal with forecast highs ranging from upper 50s in
Galesburg to mid and upper 60s in Lawrenceville...and featuring
little day-to-day change. Lows upper 30s to lower 40s in Galesburg
ranging up to mid 40s to lower 50s in Lawrenceville.
Nevertheless...weather pattern uncertainty toward the end of the
work week could result in subsequent changes to the forecast
temperatures as current forecast reflects a consensus of solutions.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1045 PM CDT Sat Mar 25 2017

Cigs through the mid evening hours have ranged from MVFR across
the west at PIA and at times SPI, to VFR over our eastern TAF
sites, including BMI. We expect all sites to see MVFR to locally
IFR cigs later tonight as an area of low pressure just off to our
west shifts northeast across north central IL on Sunday. Widespread
MVFR and IFR cigs were noted to the west of the low so its just a
matter of time before MVFR and IFR cigs move into our area as the
low progresses off to our east by Sunday morning. Forecast soundings
not offering much hope for any significant improvement in the lower
cigs on Sunday with a continued threat for scattered showers, at
least over our eastern TAF sites into the early evening hours.
Surface winds will be southeast tonight at 6 to 12 kts with winds
veering more into a south to southwest direction on Sunday with
speeds averaging from 8 to 13 kts.

&&

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

$$

UPDATE...Smith
SHORT TERM...Geelhart
LONG TERM...37
AVIATION...Smith


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