Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 241800
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
100 PM CDT SAT SEP 24 2016

.UPDATE...
Issued at 1040 AM CDT Sat Sep 24 2016

Most of the fog lifted across central IL by 10 am and did an
update to the forecast at that time to remove the morning fog
working. Still have lingering stratus clouds below 1k ft along and
north of a Canton to Bloomington/Normal line, but that shallow
cloud layer is starting to dissipate too and should scattered
out by noon. Scattered cumulus clouds should develop by afternoon
across much of CWA with mostly sunny skies overall prevailing.
Another very warm summerlike day expected over central and
southeast IL, with highs ranging from mid 80s from I-74 northeast
to the upper 80s to around 90F sw of I-74.

Latest surface map shows 1029 mb high pressure over central
Ontario province and ridging southward into the Great Lakes and
Ohio river valley. 1005 mb low pressure was along the western
SD/ND border, with IL inbetween these two features. A weak frontal
boundary extended from near Quincy to Taylorville to Robinson.
Models show this frontal boundary lifting back north during the
afternoon especially across western half of IL as weak ENE winds
less than 10 mph veer more southerly. This to keep rather muggy
conditions around with dewpoints of 65-70F. Hi-res models are
keeping much of CWA dry through this evening as strong upper
level ridge (591 dm 500 mb high over mid MS river valley) hold
over IL. HRRR and RAP models do show very isolated convection
along the frontal boundary from mid afternoon into early evening
over IL river valley in nw CWA, but like yesterday feel the upper
level ridge will be strong enough to suppress this convection,
plus forcing/lift along front is quite weak.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 325 AM CDT Sat Sep 24 2016

A weak boundary will located from west central IL into southeast IL
this morning. Most of the CWA is north of this boundary where winds
are primarily out of the east-northeast. Patchy fog has developed
north of this boundary over a good portion of the CWA, as well as in
southeast IL. In addition, stratus is spreading west into northern
parts of the CWA and is forecast to ooze south some early this
morning. Do not expect this area of clouds to remain the whole day,
but could take several hours before it dissipates/burns off/lifts
north out of the CWA. So will have to have some mostly cloudy skies
in the north and northeast this morning, then becoming partly sunny
this afternoon. Temps will be a little cooler as well, probably only
reaching into the lower 80s by this afternoon. Other areas of the
CWA where there will be much more sunshine will see afternoon
highs reaching the mid to upper 80s, and around 90 in some areas.

Late tonight there should be an influx of more moisture and clouds
into the CWA as the next weather system approaches the area. Trend
in the models is for a little slower timing of the onset of precip.
So, any chance of precip will be very late tonight, well after
midnight. Clouds will keep temps up some, but still expecting mid to
upper 60s for overnight lows. In addition, patchy fog should be an
issue across the CWA late tonight.

.LONG TERM...(Sunday through Friday)
ISSUED AT 325 AM CDT Sat Sep 24 2016

Only real precipitation issue in the longer range will be the timing
of the front Sunday afternoon and evening. Most of the model
guidance has it roughly along the I-55 corridor by around 7 pm and
exiting the forecast area toward midnight. While an isolated severe
storm can`t be ruled out, both the GFS and NAM are indicating very
weak bulk shear values where the higher CAPE`s are progged, although
the GFS has the higher CAPE`s more along the front near the edge of
where the shear increases. By evening, the instability quickly
wanes, and any thunderstorms will mainly be east of I-55 and during
the early evening. A few storms may linger past midnight east of I-
57, though.

Welcome shot of more fall-like weather is on tap early next week, as
upper low currently over southwest Wyoming lifts northeast and
reforms near the Minnesota/Ontario border. As the low drifts north
of the Great Lakes, it will draw down a slug of cooler air into the
Midwest, with 850 mb temperatures as low as 3C over central Illinois
by late Monday evening. Temperatures Monday night and Tuesday night
likely to dip into the upper 40s, with daytime highs Monday-Tuesday
in the upper 60s to lower 70s. The strength of the low will also
result in fairly windy conditions on Monday, with Bufkit guidance
indicating some potential for 25-30 mph gusts across the northern
CWA.

The upper low will be a bit slow to depart, with the latest ECMWF
gradually sinking it into the eastern Tennessee Valley late in the
week. That solution would result in a more extended period of cooler
conditions most of the week. This is a fairly substantial change
from the previous run, which was much closer to the evening GFS
solution that builds modest ridging eastward late in the week.
Thus, will follow more of a blend of the current GFS and yesterday
morning`s ECMWF, indicating a gradual warming trend toward the
upper 70s late next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1259 PM CDT Sat Sep 24 2016

Low stratus clouds of 1-2k ft lifted north of PIA by midday while
scattered cumulus clouds with bases of 4.5-6k ft developed by
midday south of I-74. Added tempo broken vfr ceilings along I-74
this afternoon. These diurnally driven cumulus clouds will
disspate around sunset 00Z/7 pm leaving fair skies this evening.
Several models continue to show patchy fog developing overnight
and continued the MVFR vsbys after 06Z and tempo groups down to
1-1.5 miles with scattered clouds below 1k ft. A cold front over
the central plains extending southward from 1005 mb low pressure
in sw ND will track eastward into eastern IA and central MO by
18Z Sunday. Added VCSH at PIA after 15Z Sunday but feel brunt of
convection will hold off until after 18Z sunday afternoon as cold
front moves east into IL. Winds stay fairly light next 24 hours
generally less than 10 kts with lights winds this afternoon and
tonight becoming south 5-10 kts after 15Z Sunday.

&&

.ILX Watches/Warnings/Advisories...
NONE.

&&

$$

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


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