Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 231817

Area Forecast Discussion
National Weather Service Lincoln IL
1217 PM CST Thu Feb 23 2017

Issued at 1038 AM CST Thu Feb 23 2017

Visibilities improving late in the morning for most
locations...although a few spots are having trouble burning off
the fog. Fog/low clouds...impeding the warm up this morning and
have knocked several degrees off of the highs through the center
of the state. Dry air aloft should help to mix out a lot of the
clouds in the south...but not low and early enough ahead of the
front/precip to make a difference in the MaxT. Precip shield
already forming and models keeping much of the precip west of
I-55. Minor updates to the forecast this morning already for max
temps and hourly trend.


.SHORT TERM...(Today and tonight)
ISSUED AT 332 AM CST Thu Feb 23 2017

09z/3am surface analysis shows weak cold front along the I-55
corridor.  With light/variable winds and ample boundary layer
moisture in place, patchy dense fog has developed near the front.
Observations have been showing visibilities varying from 1/4 mile to
1-3 miles at several sites between the Illinois River and I-55.
Since visbys are not consistently remaining at 1/4 mile or less over
a widespread area, have opted not to issue a Dense Fog Advisory at
this time.  Will however continue to monitor trends.  HRRR shows
lowered visbys spreading into portions of east-central Illinois over
the next few hours as the front edges eastward.  Will mention patchy
dense fog this morning from the Jacksonville/Springfield area
northeastward to Champaign/Danville accordingly.  The fog will
dissipate by mid to late morning, followed by mostly cloudy
conditions for the balance of the day.  The front will eventually
stall between I-72 and I-70, and as synoptic lift increases ahead of
a short-wave ejecting out the Rockies, showers will develop
along/north of the boundary this afternoon.  Model consensus
suggests the greatest areal coverage of showers will be focused
along/north of a Macomb to Minonk line, where likely PoPs are
warranted.  Further south rain chances will steadily decrease, with
dry weather expected south of I-70.  With frontal boundary bisecting
the KILX CWA, a tight north-south temperature gradient is expected.
Afternoon highs will range from the middle 50s far north around the lower 70s far south around Flora.  Showers will
become more numerous across north-central Illinois tonight as low
pressure approaches from the west and the boundary begins to lift
back northward as a warm front.  Low temperatures will occur in the
evening...with readings rising through the night.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 332 AM CST Thu Feb 23 2017

00z Feb 23 models are in good agreement with low pressure tracking
from western Kansas this evening to the southern Great Lakes by
Friday evening.  NAM/GFS/ECMWF all show cold front along I-55 by 18z
Fri...while the GEM continues to be the odd model out by holding the
boundary further west near the Mississippi River.  Timing of FROPA
is essentially locked in: however, the main question is how quickly
convection will develop ahead of the front.  The NAM suggests storms
will not fire until late afternoon along the Indiana/Illinois
border...with most of the convection impacting Indiana.
Meanwhile...the other models develop storms a bit further west along
the I-57 corridor.  At this time, prefer to follow the GFS/ECMWF
consensus...therefore am including likely PoPs across the E/SE
Friday afternoon.  With MUCAPE values of around 1000J/kg and 0-6km
bulk shear increasing to between 55-65kt, strong to severe
thunderstorms will be likely.  Latest Day 2 SPC Convective Outlook
shows slight risk for severe across this area, with damaging winds
and a few tornadoes possible.  Once the front pushes into Indiana,
any lingering storms will come to an end across east-central
Illinois by early Friday evening...followed by sharply colder
conditions overnight.  Models continue to suggest wrap-around
moisture will brush the N/NW CWA late Friday night into Saturday
morning.  With temperatures falling into the upper 20s and lower
30s, a period of light snow will be likely.  Given unseasonably warm
ground temperatures and very light nature of the precip...little to
no snow accumulation is expected.

Cool/more typical mid-February weather will prevail over the
weekend...with highs in the 30s on Saturday rising into the 40s by
Sunday.  The return to normal will be short-lived however, as zonal
flow will allow temps to warm significantly by early next week.
Unfortunately the warming trend will also be accompanied by
precipitation.  At this time, it appears a brief period of light
snow will be possible Sunday night into Monday morning before temps
warm sufficiently for all rain Monday afternoon into Tuesday.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1212 PM CST Thu Feb 23 2017

Cloud decks at multiple layers. A broken layer at around 1000 ft
this afternoon with the remnants of the early morning fog...and
10-15000 ft deck almost spread over the region. Cold front
slowly making its way across the state with northeasterly winds
behind it. Front already slowing and expected to stall out
entirely shortly...and lift as a warm front later this evening.
Models have many responses to this system...and moisture low confidence in precip/thunder forecast has
resulted in a very conservative forecaster through the overnight
hours. LLWS representation in the models weakening somewhat, but
not convinced that it isn`t warranted in PIA and BMI as the systemmoves
NE out of the area.




LONG TERM...Barnes
AVIATION...HJS is the U.S. government's official web portal to all federal, state and local government web resources and services.