Area Forecast Discussion
Issued by NWS Central Illinois

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755
FXUS63 KILX 301956
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
256 PM CDT SAT APR 30 2016

.SHORT TERM...(Tonight)
ISSUED AT 255 PM CDT Sat Apr 30 2016

19z/2pm surface analysis shows 1004mb low over northern Missouri,
with warm front extending E/SE into southern Illinois.  After being
nearly stationary for much of the day, the front is slowly lifting
northward and should eventually stall between the I-72 and I-70
corridors this evening.  Most of the steady rain from earlier has
pushed into northern Illinois, leaving behind only isolated showers
across the KILX CWA this afternoon.  Will be watching locations near
and south of the warm front where latest LAPS data is showing
SBCAPES of 1000-1500J/kg across Missouri into the Ozarks.  Visible
satellite imagery is beginning to show the first signs of convective
development from just west of St. Louis southward into Arkansas.
HRRR suggests scattered thunderstorms will develop within this
corridor over the next couple of hours, then will spread E/NE into
portions of central Illinois tonight.  Based on expected position of
front and latest HRRR forecast, think the best storm chances will
remain across the southern half of the CWA through the evening
hours, with any convection pushing further east into Indiana by
midnight.  With surface low pressure tracking into the area and
winds becoming light/variable, think fog will become an issue later
tonight within the very moist low-level airmass.  While MET/MAV
guidance only show minor reductions in visby, the HRRR is much more
bullish with the fog, particularly near the expected position of the
front.  Have therefore included areas of fog in the forecast for all
locations north of I-70, with patchy fog further south into the warm
sector.

&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 255 PM CDT Sat Apr 30 2016

Morning upper air and satellite imagery showed spinning upper closed
low over northeast CO-southwest NE. Models in good agreement on
drifting it to the east overnight, which should provide upper
support for instability showers over region on Sunday. For
overnight, best instability in area of MO where CAPE values have
increased due to cloud break up this afternoon. Expect storm
development still possible in along and south of warm frontal zone,
then pcpn moving north into central IL region. Pcpn should remain
elevated, as cold dome north of front has been reinforced by
rainfall today, so only marginal risk of severe, with mainly hail
threat in a few stronger storms.

Upper system drifts through on Sunday, with scattered showers
triggered. Pcpn break Sunday night, then a second upper wave moves
through that will trigger slight chance of showers over parts of
area.

Upper flow becomes northwesterly into midweek, with a minor wave
moving through Tuesday night into Wednesday. Instability showers
again possible with cool air aloft with this wave. Temperatures
through next week with be generally cool and below normal.






Surface low expected to track northeast across the region this
evening, reaching northeast Indiana by midnight, although the GFS is
quite a bit slower with this scenario. General thought is that the
steadier showers will be quickly diminishing this evening, with a
good portion of the overnight hours dry. However, the remnants of
the upper low currently along the Colorado/Kansas border will move
across southern Iowa Sunday morning and across Illinois in the
afternoon, bringing another period of scattered showers to the area
by midday. Have included isolated thunder mention in the afternoon
most areas, as the trough moves overhead. Any lingering showers
should be out of the area around sunset.

Highly amplified pattern expected next week, as upper level ridging
over the western U.S. builds well into British Columbia and Alberta.
Longer range models showing some differences with the extent of the
corresponding upper trough over the eastern half of the CONUS, with
the ECMWF on the deeper side. This would trend toward significantly
cooler conditions over the Midwest during the second half of the
work week. By the end of the week, the upper pattern on both the GFS
and ECMWF models trends toward an omega block type configuration
which would linger the cooler air even longer. Have trended downward
on the temperatures for late in the week, although not as low as the
blended raw model guidance at this point.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 118 PM CDT Sat Apr 30 2016

Area of rain continues to lift steadily northward early this
afternoon, with latest radar imagery now showing it along/north of
the I-74 corridor. Despite an end to the steady rain, IFR ceilings
will persist for the next few hours before ceilings slowly rise
later this afternoon. As winds become more southerly rather than
easterly, HRRR shows ceilings rising into the MVFR category at
KSPI/KDEC/KCMI late this afternoon into the early evening. As low
pressure moves across central Illinois, the IFR ceilings are
expected to advect/develop back southward later this evening
through the overnight hours. In addition, with plenty of low-level
moisture in place and winds becoming light/variable in the
vicinity of the low, fog will be a good bet. Have included visbys
down to around 1/2sm at all sites accordingly. May see scattered
showers/thunder re-develop late this afternoon/evening as per
latest HRRR/NAM guidance, so have included VCTS at all terminals
between 22z and 04z.


&&

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

$$

SHORT TERM...Barnes
LONG TERM...Goetsch
AVIATION...Barnes



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