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Area forecast discussion 
National Weather Service Lincoln Illinois
1108 PM CDT Friday Jul 3 2015

issued at 845 PM CDT Friday Jul 3 2015

Weak upper level wave that produced the light showers over east
central Illinois this afternoon and the widely scattered
thunderstorms...with locally heavy rainfall over southeast
Illinois...has shifted just off to our southeast this evening.
In its place...high pressure will shift slowly across the state
overnight and Saturday bringing quiet weather to central through
southeast Illinois. The combination of light winds...clear sky and
abundant low level moisture will lead to some patchy fog late
tonight into early Saturday...especially over east central and
southeast Illinois. Forecast soundings showing any fog that does
form will be quite shallow and quick to burn off just after
sunrise Saturday morning. After that...a warm day shaping up for
Saturday with afternoon temperatures a bit closer to where they
should be for early July. The current forecast has a good handle
on the evening and overnight a zone forecast product update
will be needed.


Short term...(tonight)
issued at 247 PM CDT Friday Jul 3 2015

Upper level trough (576-578 dm at 500 mb) over northern Indiana and
central Illinois was interacting with daytime heating and modest dewpoints
in the middle 60s generating isolated showers in east central Illinois east
of I-55. Heavier rains with scattered showers and thunderstorms were
along and south of Highway 50 in southeast Illinois and more numerous in
Kentucky and far southern Illinois closer to a frontal boundary tied to a weak
1010 mb surface low pressure in north central Kentucky. Isolated
convection should diminish from northwest to southeast during the evening and
mostly be dry after dark (02z/9 pm).

Weak high pressure 1016 mb over central Nebraska/IA/lower Michigan to
drift southeast into central Illinois overnight into Saturday helping decreasing
clouds with NE winds 5-10 miles per hour this afternoon become light and
variable tonight. Hrrr shows some fog appearing in east central and
southeast Illinois overnight where higher dewpoints currently in middle to upper 60s
and agree fog will form especially with light winds and decreasing
cloud cover. Lows overnight range from 58-64f with mildest readings
in southeast Illinois where higher dewpoints.

Long term...(saturday through friday)
issued at 247 PM CDT Friday Jul 3 2015

Holiday weekend looks to be in good shape for our high
pressure drifts eastward through the Midwest. Have removed any
lingering pop's in the far southern reaches of the forecast area for
Saturday. Warmer conditions return through the weekend...and raised
temperatures on Sunday by a few degrees into the 86-88 degree range
as 925 mb temperatures rise to around 22c.

Main focus remains with precipitation trends for next week. Latest
model guidance has been slowing down the cold front early next week
a bit...which would favor dry conditions continuing over the eastern
third of the forecast area through Monday afternoon. Bulk of the
rain will occur Monday night and Tuesday morning. Precipitable water
values still prognosticated to be around 2.1 inches ahead of the front with
an attendant threat of heavy rain...but most of the guidance
suggests a more progressive front which should hopefully reduce the
excessive rain potential in any given area. The models are fairly
divergent for the second half of the upcoming week...with the
disparities focused on the potential for the front to return
northward as low pressure rides along the boundary. The GFS is most
gung-Ho on this solution and has the boundary all the way into
northern Illinois by Thursday evening...while the European model (ecmwf) keeps the
wave across the Ohio Valley and our area mostly controlled by high
pressure. Have kept probability of precipitation in the 25-35% range over most of the area
for now...but confidence is not especially high at the moment.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1105 PM CDT Friday Jul 3 2015

Little change in thinking from the previous aviation discussion.
The main concern this period will be in the 09z-13z time frame for
the potential for some MVFR visibilities in fog. Otherwise...VFR
conditions are expected through 06z Saturday. Weak high pressure will
drift over the area over the next 12 to 18 hours bringing light
winds to all of the taf sites. Any fog we do see early Saturday
morning will quickly dissipate with some scattered cumulus forming
with bases in the 3000-4000 foot level by early afternoon. Surface
winds are expected to be light and variable through most of this
forecast period.


Ilx watches/warnings/advisories...


short term...07
long term...geelhart

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