Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 290448

Area Forecast Discussion
National Weather Service Lincoln IL
1148 PM CDT THU APR 28 2016

Issued at 910 PM CDT Thu Apr 28 2016

An elongated area of low pressure lingering across central
Illinois, roughly along I-74, will continue to be a focus for
spotty sprinkles or drizzle this evening. Precip should remain
north of I-74, based on radar trends and HRRR output. Some
clearing pushed across southern Illinois, as far north as I-72,
but a return of cloud cover is expected from the west the rest of
the night. As winds shift more northerly north of I-74, low clouds
will begin to advance southward, with some light fog possible as
well. The cloud cover will counteract some of the colder air
pushing into the area, with low temps bottoming out in the low to mid
40s towards Galesburg and Lacon, with low 50s south of I-70.

A few minor updates this evening were done on the weather, sky,
and temp/dewpoint grids. Updated information is already available.


.SHORT TERM...(Tonight)
ISSUED AT 300 PM CDT Thu Apr 28 2016

Mid afternoon surface map shows weakening 1010 mb surface low
pressure over east central Iowa between Cedar Rapids and Iowa City,
with an occluded front lifting slowly ne over central IL/IN near I-
74. Isolated light showers were ne of I-74 isolated showers and
thunderstorms were over central IN around Indianapolis. Broken
cumulus clouds with bases 2.5-6k ft giving mostly cloudy skies over
central IL while partly sunny skies in southeast IL south of I-70.
Temps range from mid 50s from Macomb to Lacon north to the lower 70s
in southeast IL from I-70 south. Aloft a 555 dm 500 mb low was along
the western MN/IA border.

Latest forecast models take 555 dm 500 mb low east into central Lake
MI by Friday morning while weak surface low pressure tracks toward
west central IN by Friday morning. Expect abundant low clouds over
central IL tonight with mostly cloudy to overcast skies especially
from I-72 north with ceilings lowering to around 1k ft or lower
overnight. Will likely see some fog with vsbys 2-4 miles overnight
into early Friday morning. Less cloud cover in southeast IL tonight
with mostly clear to partly cloudy skies south of I-70. Lows
overnight range from lower 40s by Galesburg to lower 50s in
southeast IL from I-70 southeast. Winds to become NW and be fairly
light tonight under 10 mph.

.LONG TERM...(Friday through Thursday)
ISSUED AT 300 PM CDT Thu Apr 28 2016

Another slow moving low pressure area will move out of the plains
and toward the OH valley over the weekend. Pcpn will return to the
area beginning Fri night as the boundary sets up. As the low
pressure area moves along this boundary, south of the CWA, showers
and thunderstorms will dominate for Sat, with chances continuing for
Sat night and Sun. Pcpn will push east of the area on Sun night with
the highest chances of pcpn lingering in the east. Beyond this
system, an upper level cutoff low will sit over the southwest US
while a trough-pattern sets up over eastern Canada and down into
the Great Lakes region. These two things will keep the sfc
boundary south of the area, thereby keeping the CWA relatively dry
during next week.

Clouds and pcpn will keep temps slightly cooler/below normal over
the weekend. Cool/below normal temps will continue next week as well
since the boundary should remain south of the area through the
period and southerly return flow does not look like it returns until
possibly the first full weekend of May.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1148 PM CDT Thu Apr 28 2016

Latest satellite images and observations show a lingering VFR OVC
CU cloud mass covering all but DEC late this evening, with
clearing just south of SPI and DEC. The southern edge of the
clouds has been starting a slow progression northward, in response
to a subtle northward shift in the trough axis. However, the
trough is expected to drift back southward later tonight and
Friday morning, putting the 850mb baroclinic zone directly across
our forecast area. The proximity of cooler air just to our north
and the frontal circulation in the baroclinic zone will help keep
cloud cover in the area more than sunshine. Therefore, we expect
cloud coverage to remain broken to overcast over a majority of
the area during this TAF period. SPI and DEC will have the best
chances at noticeable breaks in the cloud cover on Friday, with
shorter breaks for the northern TAF sites. Any breaks in the
clouds tonight will aid in fog formation, so will continue to
light fog of 3sm br for the northern TAFs. HRRR is not hitting fog
quite that hard at the terminal sites, but winds should become
light toward sunrise, helping tip the scales toward fog as
dewpoints linger in the upper 40s tonight.

Based on forecast soundings and HRRR output, we are still expecting
MVFR ceilings to develop from north to south tonight and linger
into Friday morning. IFR ceilings are projected to develop along
I-74 early Friday morning. Ceilings should improve with turbulent
mixing after sunrise helping lift the LCL. Winds stay fairly
light next 12-18 hours under the weak surface trough. WNW winds 4
to 7 kts will veer NW late tonight and then NE Friday morning and
eventually E during the afternoon. Wind speeds should remain in
the 5-10 kt range on Friday, with speeds increasing to 10-14kt
Friday evening ahead of approaching low pressure from the Plains.
Increasing isentropic lift will aid in mid-level saturation and
spotty showers after 03z Fri eve for SPI and DEC. Better chances
of rain will hold off until after this TAF valid period.


.ILX Watches/Warnings/Advisories...


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