Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 200726
Area Forecast Discussion
National Weather Service Lincoln IL
226 AM CDT Sun Jul 20 2014
ISSUED 225 AM CDT Sun Jul 20 2014
Stagnant weather pattern resulting in another quiet early morning
across the forecast area. Have been seeing some locally dense fog
mainly along the Wabash River in the far southeast CWA, although
local visibilities are down to 1/2 mile as far west as Flora at 2
am. Latest upper air analysis showing zonal 500 mb flow along much
of the U.S./Canadian border to the northern Plains, then opening
up into a broad upper trough across the Midwest.
The main forecast challenge remains with rain chances from late
Tuesday through Wednesday afternoon, as a cold front pushes
through the area.
SHORT TERM...Today through Wednesday:
Not much change in the forecast through Tuesday. Large 500 mb high
over New Mexico will continue to build to around 600 dm by late
Tuesday evening, resulting in a gradual expansion of hot and humid
conditions eastward into the Midwest. The hottest day will be
Tuesday, with highs in the lower 90s widespread, with heat index
values near or just above 100 across the Illinois River Valley.
Upper trough riding along the top of the ridge will drop southeast
later Tuesday, dragging a surface cold front through the Midwest.
The NAM tries to make the front stationary Tuesday night over the
area, while the remaining model suite is more progressive with the
front generally moving through Wednesday morning. Highest PoP`s
will be west of I-55 Tuesday night and have increased them to
around 60% there. The southeast CWA should remain dry until
Wednesday morning as the front approaches. Not expecting a
significant severe threat given the arrival time. Some lingering
showers/storms will continue through Wednesday across the
southeast CWA, but areas I-72 north should be dry by midday as
high pressure begins to build from the north.
LONG TERM...Thursday through Saturday:
Brief shot of cooler conditions on tap Thursday and Friday, with
temperatures and humidity similar to what we have seen over the
last day or two. High pressure over the Great Lakes will keep us
dry through Friday. Past there, focus shifts to potential MCS
activity Friday night sliding down the upper ridge, which will be
re-establishing itself along and west of the Rockies. Latest ECMWF
has shifted a bit further west with the track of the MCS and
largely misses us, but the GFS has kept it over us the last couple
runs. Have kept the trends essentially in place for now.
ISSUED 1105 PM CDT Sat Jul 19 2014
The main forecast issue remains the potential for a brief period
of MVFR or lower vsbys in fog from 09z-12z, otherwise, we are
expecting VFR conditions to dominate thru the remainder of the
TAF period (06z Mon). The higher probability for more widespread
fog and lower vsbys still appears to be along and east of I-57
which would include CMI with progressively higher vsbys as you
head west. What fog that does form early Sunday morning should
be gone by 13z with some more cumulus forming around 16z. Surface
winds will be light and variable tonight and light southerly on
Sunday with speeds less than 10 kts.