Scientific Forecaster Discussion
fxus63 kilx 250605
Area forecast discussion
National Weather Service Lincoln Illinois
105 am CDT Thu may 25 2017
issued at 917 PM CDT Wed may 24 2017
Showers slowly tapering off this evening and primarily over
eastern half of the forecast area. With a slow eastward movement
of the upper level trough at least isolated showers will be
possible near the Indiana border through the night while showers
taper off slowly from west to east. Otherwise, a steady northwest wind
5-10 mph can be expected through the night. This should keep fog
minimal, but plenty of low level moisture should keep low clouds
from clearing and allow stratus to develop. Lows in the low 50s
expected, slightly cooler than normal. Only minor updates needed
Short term...(this evening through thursday)
issued at 325 PM CDT Wed may 24 2017
Low level cyclonic flow around low pressure in central Kentucky will
keep showers and a few T-storms in eastern Illinois the rest of
the evening. Diurnal showers and isolated thunderstorms in western
and central Illinois will continue early this evening and then dissipate
west of I-55 by 8-9 PM and in the rest of central Illinois after 10 PM.
The latest mid level water vapor loop shows that drying will work
its way very slowly into west central Illinois. This, along with the
loss of diurnal cloudiness may lead to a brief period of partial
clearing later this evening. Any clearing will be short lived
though as plenty of low level/surface moisture should result in a
development of a deck of stratus clouds from east to west across
the forecast area overnight.
Added patchy fog to the forecast tonight into Thursday morning
along and west of the Illinois River valley where the surface wind will
be a bit lighter and allow for fog and stratus to both develop.
Also have fog in much of east central Illinois where it has been raining
much of the afternoon into the evening, which will provide plenty
of low level moisture for fog.
The upper low in central MO and surface low in Kentucky will push off to
the east overnight and early Thursday, resulting in ridging to
move in for Thursday. This will give US drier conditions with more
sunshine and temperatures in the 70-75 range.
Long term...(thursday night through wednesday)
issued at 325 PM CDT Wed may 24 2017
The ridging for Thursday will be progressive, allowing for a west-southwest
upper level flow to develop on Friday. This will allow for
moisture return in west central and central Illinois during the day
Friday. The models are in fairly good agreement that low pressure
will track from the Southern Plains toward eastern MO by Friday
evening. This will spread showers and T-storms into most of the
forecast area Friday afternoon. A southerly surface wind will
allow temperatures to climb into the upper 70s before the
convection moves in/develops Friday.
As the low moves roughly along the I-70 corridor later Friday and
into central in by Saturday morning, the precipitation will
briefly come to an end. However, it appears that an mesoscale convective system may
develop in Kansas/western MO late Friday night, so the remnants of
that system should move along the boundary in southern IL,
resulting in an increase in T-storm potential by late Sat morning
and into Saturday afternoon across central and eastern Illinois.
There is some uncertainty as to the position of the
aforementioned frontal boundary for late Saturday and through
Sunday. Thus, the proximity of a boundary near the forecast area
will result in keeping at least a chance of convection in the
forecast south of a Springfield-Paris line for Saturday
night/Sunday...and into all of the forecast area later Sunday.
We should finally see a break in the precipitation Sunday night
into Monday, before deep cyclonic flow reintroduces the potential
for showers and a few thunderstorms north of I-74 on Monday, and
over the rest of central Illinois Monday night into Tuesday.
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 103 am CDT Thu may 25 2017
Forecast IFR stratus spreading westward from in border this
morning and some patchy fog bringing vis down as well to 2-3sm.
Improving conditions in the morning with the sunshine burning
through and clouds clearing from west to east. Northwest winds
dominate...generally less than 10 kts.