Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 201742
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1242 PM CDT Sun Oct 20 2019

.SYNOPSIS...
Issued at 255 AM CDT Sun Oct 20 2019

Another day of mild temperatures is expected across central and
southeast Illinois today. The next storm system will bring showers
and isolated thunderstorms to the area tonight and Monday. A
cold front sweeping east across the state on Monday will end the
unsettled weather, but blustery southwest winds will follow the
frontal passage.

&&

.UPDATE...
Issued at 1054 AM CDT Sun Oct 20 2019
A narrow high pressure ridge is building into the region briefly
ahead of the next system. Low level moisture resulted in some
patchy morning fog and low clouds, but those clouds are slowly
clearing on sat imagery. As a result, the temperatures are
rebounding quickly with the sunshine. Not going to change much in
the forecast overall...just updating for hourly trends.

&&

.SHORT TERM...(Today)
ISSUED AT 255 AM CDT Sun Oct 20 2019

Abundant low to mid level clouds have lingered overnight, but
clearing has slowly been inching towards the far western CWA.
Dense fog has developed behind the clearing line in SE IA to NE
MO, where dew point depressions go to 0 and light winds prevail.
Areas of dense fog are possible through 8-9 am where skies can
clear out, west of the IL River. Hi-res guidance suggests the more
widespread dense fog limited to the far western fringe of the
CWA, near a Galesburg to Rushville line. Will monitor trends for
need for dense fog advisory early this morning.

Otherwise weather looks quiet today while we are between systems.
Expect some thinning cloud cover and enough sunshine for another
seasonably mild day in the mid 60s to lower 70s.

.LONG TERM...(Tonight through Saturday)
ISSUED AT 255 AM CDT Sun Oct 20 2019

Tonight and Monday...a vertically stacked low pressure system
tracks into the upper Midwest, with a southward extending cold
front pushing towards the Mississippi River by 12z/Mon. As opposed
to our last few systems, a good fetch of Gulf moisture will
return northward, with isentropic lift generating a band of
widespread rain east across the area after midnight and through
Monday morning. Sufficient instability along and ahead of the
front (CAPEs <500 J/kg) for isolated thunder mention. Seasonably
strong 150+ kt upper level jet streak associated with the dry slot
punches into the area midday, and should quickly shut down precip
from the west. With the system trending quicker models have
trended towards lower QPF which is now under one inch. Several
ingredients coming together for possibly near advisory level post-
frontal southwest winds Monday afternoon/evening especially
across the north, including tight MSLP gradient, strong pressure
rises, and a deep mixed layer in strong CAA. Bufkit momentum
transfer showing 40 kt gusts possible through mid evening.

Tuesday...quiet and seasonably cool as the deep low spins over
Lake Superior. Any wrap-around moisture in strong cyclonic flow is
expected to remain to our north. West winds still quite brisk in
tight gradient for some gust over 30 MPH.

On Wednesday we get into return flow ahead of the next front, and
this should push highs back up to near normal.

Thursday...a northern stream wave crossing the Great Lakes drags
a front into the area for our next rain chance. There is a decent
push of cold air behind this front which could place a tight
temperature gradient across the CWA, with highs near 50 northwest,
to mid 60s southeast. Brief surface ridging builds in on Friday,
bringing dry and cool conditions.

Next weekend there is considerable uncertainty as model solutions
diverge in handling a strong southern stream wave. EC/GEM suggest
the wave to lift far enough north to impact the area, however
GFS/ensemble mean and overall blended forecast show a
weaker/farther south solution. So the weekend remains dry but
needs to be monitored.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1232 PM CDT Sun Oct 20 2019

Though there is clearing for SPI PIA and BMI, both CMI and DEC are
still seeing impacts from a narrow swath of higher RH in the
boundary layer. Have MVFR cig for both CMI and DEC up to this
point... but sat imagery is starting to show signs of clearing,
and let the cigs improve going deeper into the afternoon hours.
GFS showing potential for a SCT/BKN cu deck along and east of the
Illinois River Vally and have attempted to account for that as
well, though expect to lose it after sunset. Overnight, a
deepening low pressure system moves in. Winds ramp up much
earlier, getting gusty in the NW before sunrise. There is a hint
of LLWS starting to show up in the model runs... but generally
scattered and less than an hour, so will leave it out for now.
Rain should start in the early hours of the morning, likely all
terminals before sunrise as well. Thunder threat is a little
inconsistent... but anticipated to be relatively isolated.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...HJS
SYNOPSIS...25
SHORT TERM...25
LONG TERM...25
AVIATION...HJS


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