Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
1146 PM CDT Wednesday Sep 2 2015
issued at 858 PM CDT Wednesday Sep 2 2015
A weak upper level shortwave trough crossing central Illinois this
evening provided enough lift to trigger a few weak thunderstorms
around Champaign just after the peak afternoon heating...but
these have since subsided. For the rest of the night...subsidence
behind this feature should bring mostly clear skies. Temperatures
should fall to around 70 degrees with light south winds. Updates
were sent earlier for isolated thunderstorms...but no significant
updates anticipated at this time.
issued at 300 PM CDT Wednesday Sep 2 2015
Earlier shower activity that had been approaching the Mississippi
River has largely faded out as expected...with still a fair amount
of associated cloud cover spreading over areas west of I-55.
Locations east a bit sunnier this afternoon...but with a fair amount
of diurnal cumulus.
The associated upper wave is currently moving across eastern Iowa
and western Wisconsin...and is expected to start digging southeast
tonight as the upper ridge over the plains begins to amplify.
Showers and thunderstorms have been developing over northern
Wisconsin the last few hours...and these will be tracking southeast
as the wave digs. The GFS is the most generous in bringing a
convective cluster all the way down to the I-72 corridor by sunrise.
Am favoring more of a NAM/European model (ecmwf) blend which keeps the overnight
activity closer to northeast Illinois.
Long term...(thursday through wednesday)
issued at 300 PM CDT Wednesday Sep 2 2015
The overall pattern of an upper level trough in the western U.S. And
broad ridging across the central and eastern U.S. Is expected to
remain in place into the upcoming weekend. However...as is often the
case...subtle, mainly sub-synoptic features will play a role in the
weather Thursday into Saturday.
First of all...the upper ridging will keep a large, very warm
airmass over the entire forecast area through the weekend. This
mornings upper air analysis of the lower atmosphere only indicated
pockets of higher moisture instead of a fetch of tropical Gulf air.
In addition, crop moisture has been fairly stunted lately, so really
high dew points into the middle 70s or higher are not expected. This
will keep the daily maximum heat index in the 95-100 range through the
With respect to precipitation potential the next few days...a
shortwave trough crashing through the ridge in Wisconsin this
afternoon will drop southeast into Indiana Thursday. This should be
enough lift to produce isolated showers/T-storms east of a
Bloomington-Tuscola-Paris line late Thursday am into the afternoon...
with a better chance toward late in the afternoon. The anticipated
slow movement of these storms could result in pockets of heavy
rainfall. Much of the same is anticipated Friday in east central Illinois
and Saturday along and north of the I-74 corridor from Peoria-
Danville as weak shortwaves are expected to drop into the area from
In the longer range...the GFS and European models are indicating
some important differences in how fast they break down the central
U.S. Ridge and allow shortwave troughs and an associated frontal
boundary to impact our weather. The European model is much quicker
breaking down the ridge and pushes a cool front into our forecast
area by Monday morning. The GFS keeps the front to the north and
west of our region until Wednesday. Prefer the GFS solution since it
appears that the greatest upper level energy should stay to our
north which would cause the front to become more parallel to the
upper flow and allow for a slower progression toward central/southeast Illinois.
This scenario would favor scattered showers/T-storms Monday into
early Tuesday...with better chances toward mid-week.
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1146 PM CDT Wednesday Sep 2 2015
VFR conditions and south winds up to 6 kts across central Illinois this
evening. Areas of MVFR visibilities possible once again 08-12z in
a warm and humid air mass. Some concern for potential
thunderstorms on Thursday as an upper disturbance drops southeast
across the Great Lakes. At the moment...isolated showers/storms
look like they will remain north of kbmi-kcmi late Thursday
morning through evening. Chances for thunderstorms are too small
to warrant a thunderstorms in the vicinity mention at this point. Winds to continue S-SW up
to 10 kts through the period.