Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 232048

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

.SHORT TERM...(This evening through Friday)
ISSUED AT 247 PM CST Thu Feb 23 2017

This afternoon, looking at the observations across the region...the
front seems to be just north of I-70, with northeasterly winds
behind it...and warm air still to the south of the boundary.  The
short wave riding up the front in this system is spreading
precip...mainly to the north and west of the Illinois River Valley.
The surface low at the next storms center is invof the Oklahoma
panhandle.  This system will continue to move to the northwest,
deepening and sending todays front back to the north as a warm front
as the warmer airmass in the SE pushes back with more significant
warm advection...keeping much of Central IL in the warm sector
overnight. This warmer and minimally higher RH air will be the
instability that will potentially fuel the storms that may develop
tomorrow afternoon after the low passes to the north, dragging the
cold front across eastern Illinois.  The slight risk for eastern
Illinois for tomorrow has lost a little bit of area with the latest
model runs. Seems the surface convergence has become weaker and the
boundary less distinct...but the divergent exit region of the jet
will assist with the vertical lift of the airmass.  1000 J/kg of
MUCAPE available by mid morning and intensifying as the front shifts
eastward out ahead of the system. Storms look to be initiating over
Central Illinois tomorrow...and becoming more organized as they slip
to the east. Damaging winds are the biggest threat with these
storms, with 0-3km and 0-6km bulk shear  35 to 40kts or 60-70 kts


.LONG TERM...(Friday night through Thursday)
ISSUED AT 247 PM CST Thu Feb 23 2017

The low pressure area of the ongoing weather system should be in the
Great Lakes region Friday evening. There remains a possibility that
convection could still be ongoing in the eastern part of the CWA
during the first few hours of the evening. So, will keep likely pops
in the southeast and the chance for thunder east of I-57 til about 9
pm. Beyond that, showers will continue in the east the later part of
the evening in the east. In the northwest, colder air will begin to
wrap around the system and into the northern part of the state. This
will bring rain chances during the evening, but then changing to
snow as colder air advects into the region. This change over to snow
in northern part of the CWA will continue into the overnight hours
and then in extreme northeastern parts of the CWA...northeast of PIA
and BMI...Saturday morning. This system should push well east and
northeast of the CWA Sat morning so that Sat afternoon will be dry.
All models are in good agreement with the movement, location and
timing of this system and expected weather through the weekend.
Cooler high pressure will then bring dry weather to the region Sat
afternoon through Sunday morning.

Beyond Sunday morning, the models have major differences. The GFS
has precip for Sunday afternoon through Monday while the Canadian
and ECMWF are dry. Then the ECMWF and Canadian have precip for
Monday night through Tuesday while the GFS is dry. Even beyond
Tuesday, the models do not agree with timing and location of the
next chances of precip. Though do not like pops in some many
continuous periods of the forecast, will go with a model blend
forecast for most of the extended and have some form of pops for
Sunday afternoon through Wednesday. Hopefully in the next couple of
days the models will come to some agreement.

Cooler temps are in store for the first part of the weekend and with
overnight lows falling to below freezing Fri night, Sat night and
Sun night, any trees or plants that have begun to bud may get bit by
the freezing temps, especially Sat night. Remainder of the extended
forecast, temps will warm back up to above normal levels.


.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 system
moves NE out of the area.




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