Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 010806

Area Forecast Discussion
National Weather Service Lincoln IL
306 AM CDT SUN MAY 1 2016

.SHORT TERM...(Today)
ISSUED AT 305 AM CDT Sun May 1 2016

A rather complex forecast exists across central and southeast
Illinois today, with many factors to consider. A nearly stationary
surface front cuts across the forecast area generally a little south
of, and nearly parallel to, the I-72 corridor. To the south of the
boundary, partly cloudy skies exist, with scattered convection to
the south of I-70. To the north of the boundary, extensive
fog/stratus exists, with visibilities significantly reduced in some
areas. The fog is most dense near the edge of the stratus, and
surface obs suggest a Dense Fog Advisory should be considered.
However, the cloud edge is slowly sinking to the south and this
would suggest that dense fog will not remain in any one location for
a significant period of time. Plan to hold off on Dense Fog Advisory
for now with this in mind, but will continue to monitor visibility
trends closely through sunrise.

Other main concern is the expected precipitation coverage today. A
broad northeast to southwest oriented upper-level trof stretches
across the lower 48 states, with several smaller scale upper lows
embedded within it. The feature we need to key in on today is the
upper low spinning over the central Plains. This feature is expected
to shear northeast into the Great Lakes region today. The forcing
associated with this weakening feature, and associated wave on the
surface front, will be our primary precipitation trigger. There is
currently very little on radar upstream, and expect the bulk of our
precipitation will occur through a combination of diurnal heating
and mid-level cooling with the approach of the upper low remnants.
This thinking supports scattered showers across the area by
afternoon, with a few thunderstorms also possible. The thunderstorms
should mostly occur along/south of the surface front. A few of the
storms along/south of I-70 may be strong given the modest
instability (CAPEs from 1000-2000 j/kg) and shear profiles (bulk
shear to 45 kts) anticipated by afternoon.

A significant N-S temperatures gradient is likely across the area
today with the surface front in the area. Daytime highs should range
from the mid 50s NW around Galesburg to mid 70s SE around


.LONG TERM...(Tonight through Saturday)
ISSUED AT 305 AM CDT Sun May 1 2016

Persistent upper troughing pattern expected over the eastern U.S.
much of the upcoming week, as a significant ridge builds west of the
Rockies. This will send lobes of cooler air southward into the Great
Lakes region, with 850 mb temperatures over our area dipping to
around zero Celsius on Tuesday, and Wednesday night through
Thursday. This should result in highs several degrees below normal
for early May. Late in the week, an omega blocking pattern will
evolve, although the latest runs of the ECMWF and GFS do show the
ridge edging eastward, bringing a significant warming trend for next

Remnants of current upper low over Nebraska will drift eastward
early this week, and stretch out into a trough which will drop
toward the Ohio Valley on Tuesday. With these features around, it
will be difficult to eliminate mention of PoP`s. Have increased rain
chances to around 30% on Monday over the southeast CWA and went with
slight chances as far north as Bloomington and Havana, with the
threat diminishing with loss of daytime heating. With the trough
further south on Tuesday, slight chance PoP`s were kept over the
areas south of I-70. A more significant rain chance is expected late
Tuesday night into Wednesday, as a large upper low drops southward
into the Great Lakes. Have increased PoP`s to around 35-40% over the
eastern CWA on Wednesday. Rather significant cold pocket at 500 mb
will accompany this low, and would not be surprised to see some
isolated thunder. However, the coldest part of this will be tracking
into Indiana, so will hold off on any thunder mention for now. Dry
weather is expected late in the week, as high pressure dominates the
Mississippi Valley as the upper ridge arrives.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1150 PM CDT Sat Apr 30 2016

A region of predominantly LIFR ceilings and areas of fog is
currently settling slowly southward across central IL according to
surface observations and satellite imagery. Low pressure
translating eastward across southern IL will continue to draw the
region southward through the night. Some improvement expected by
late morning as daytime heating occurs. An upper low off to the
west will cross over the area late in the afternoon developing
scattered showers and perhaps an isolated thunderstorm as well.
Included VCTS at KPIA-KBMI closer to the upper level cold pool of
this feature, but otherwise probabilities appear to low to
include at this point.


.ILX Watches/Warnings/Advisories...


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