Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271757

Area Forecast Discussion
National Weather Service Lincoln IL
1257 PM CDT WED APR 27 2016

Issued at 1045 AM CDT Wed Apr 27 2016

Just a few adjustments needed to todays forecast with tightening
the temperature gradient from NNE to SSW today and some tweaks to
weather elements today. An expanding band of showers was spreading
ne toward I-74 late this morning with a few thunderstorms south of
I-70 especially near Lawrenceville. Strong 995 mb surface low
pressure over eastern Nebraska had a warm front over ne MO into
far SW IL and northern KY, south of I-64. Dewpoints range from
lower 60s from I-70 south to the mid 40s from Galesburg and Lacon
north. Temps ragne from upper 40s from Galesburg and Lacon north
to the lower 60s in southeast IL. HRRR model doing better with
handling convection today and leaned on this model for forecast
update today. Should continue to see showers become more
widespread with a few thunderstorms developing during mid day and
then diminish from sw to ne during mid/late afternoon. But
isolated to scattered thunderstorms to develop later this
afternoon and into this evening with approaching warm front. SPC
day1 outlook has slight risk of severe storms sw of a Macomb to
Lincoln to Terre Haute line from mainly late afternoon into mid
evening as warm front slowly pushes into sw IL with increasing
instability in our SW counties as MUCapes elevate to 1-2k J/kg.
Highs today will struggle to reach 60F over northern CWA from
Peoria and Bloomington north, to lower 70s in southeast IL south
of I-70.


.SHORT TERM...(Today)
ISSUED AT 322 AM CDT Wed Apr 27 2016

The cold front that pushed across the area yesterday was located
over central Missouri east through extreme southern Illinois
early this morning. To the north of the front, temperatures
have dropped into the mid and upper 40s with a chilly northeast
wind, while over southern Illinois, temperatures were still in
the low to mid 60s. Main question for today will be just how
far north the warm front will be able to move as a wave of
low pressure approaches from the west this afternoon and
evening, which will dictate how far north the severe threat
will be in our area. 06z NAM-WRF continues to show the more
favorable MUCAPE instability axis will be roughly along and
especially south of the I-70 corridor this afternoon and
evening with the HRRR model suggesting the warm frontal
boundary may edge into southeast Illinois late today.

The first wave of showers and isolated storms is expected to
develop along and just north of the boundary over southern
Illinois this morning and arc northwest through our southwest
counties. Just how far north and east the rain will be able
to push into the drier air mass to our north this morning is
a challenge as we have already delayed the onset from previous
forecasts and really not confident that is slow enough. However,
models have been more consistent with the timing north this morning
with the first wave of rain, with even a hint of a break before the
main band of showers and storms tracks northeast into our area this
afternoon and evening. If there is going to be a severe weather
threat, this afternoon and evening would be the primary time frame
and especially along and south of the I-72 corridor. 0-6km shear
values around 45 kts could help to produce some wind and hail threat
in this area from mid afternoon through the mid evening hours before
the main area of forcing shifts off to our north and east.

Quite a range in temperatures across the forecast area today with
areas to our north having a tough time getting to 60, while over
far southeast Illinois, afternoon temperatures should climb into
the middle 70s. Have trended a bit cooler than guidance north of
the frontal boundary due to the extensive cloud cover, expected
rainfall and a cool easterly flow today, while guidance looked
reasonable over our southeast counties which had a decent chance
of seeing the warm front edge just to their north this afternoon.

.LONG TERM...(Tonight through Tuesday)
ISSUED AT 322 AM CDT Wed Apr 27 2016

Another similar round of models overall.  Deep low over the Plains
states this morning will not only drive the weather today, but into
the overnight and tomorrow as well. Showers and thunderstorms
continue through the overnight and begin clearing from SW to N/NE
tomorrow in the first half of the day as the upper low starts to
make its way through the region.  Should the low slow any more than
is currently forecast...the chances for precip could be a little
low...but for now the track of the upper low is further to the
north, allowing the southern tier of the state to be mostly dry on
Thursday. Showers come to an end briefly with a break Thur night and
into Friday before the next wave ejects out of the SW across the
Midwest for the weekend later Friday night.

Rain chances return for Friday night through the weekend with a
similar setup happening again with another slow moving storm system
out of the SW.  Warm sector showers and thunderstorms dominate the
weekend, with some clearing of the precip on Monday with drier air
wrapping around the system. Ultimately, will be interesting to see
how the current slow moving low is handled.  Models beginning to
show some wavering with the solutions as the low for the weekend no
longer looks like it clears the trof completely out of the SW.
Should that trof remain...shortwaves ejecting out over the Midwest
Mon-Tue could change up the forecast again.  For now, the models
shear out that energy in the wake of the main low...leaving the
first part of the work week with little threat.  Slight pops in for
now.  Expect some variability in the forecasts to come. Temperatures
throughout the forecast are in line with some expected seasonal
variance with rain/clouds/sun mix.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1255 PM CDT Wed Apr 27 2016

A fairly large band of showers and a few thunderstorms over
central IL early this afternoon will gradually lift ne and become
more widely scattered from sw to ne during mid/late afternoon.
More isolated to scattered showers and thunderstorms will likely
develop behind this band during late afternoon and into the
evening as a warm front pushes ne into sw IL. Strong 995 mb
surface low pressure over eastern Nebraska will weaken to 1006 mb
as it moves into southern IA Thu morning. This will push a warm
front from northeast MO and far SW IL into central IL by Thu
morning as it occludes. IFR to MVFR ceilings to prevail through
next 24 hours with IFR to MVFR vsbys prevailing as well, though
will be up to VFR at times. Models show a dry slot working ne into
central IL Thu morning especially by SPI and DEC where ceilings
could lift up to VFR or even scatter out. Breezy east winds around
15 kts with gusts 18-24 kts this afternoon to diminish to around
10 kts by overnight and veer more west along I-74 while staying
ENE at PIA and BMI.


.ILX Watches/Warnings/Advisories...


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