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Area forecast discussion 
National Weather Service Lincoln Illinois
1148 PM CDT Monday Aug 3 2015

issued at 859 PM CDT Monday Aug 3 2015

A cold front has moved southward into southern portions of
Illinois...limiting all thunderstorm out of the central Illinois
forecast area this evening...while bringing cooler and drier air
from the northwest into central Illinois. Mostly clear conditions are in
place this evening...while high cloudiness begins to spread
northeast into the area. A disturbance along/NE of the frontal
boundary lingering from northwest to southeast Missouri will develop
thunderstorm activity overnight...with at least a slight chance
spreading as far northeast as Springfield-Effingham-Lawrenceville.
Lows expected to reach from around 60 in Galesburg-Champaign to
around 65 from Jacksonville-Lawrenceville in the cooler air mass
over the area. Current forecast is on track with these
trends...and no significant updates are needed this evening.


Short term...(tonight)
issued at 241 PM CDT Monday Aug 3 2015

Weak cold front currently extending from central Indiana to northern
Missouri will continue to sag southward this afternoon and
evening...eventually stalling near the Ohio River. Clusters of
thunderstorms have been ongoing for much of the day along the
boundary across northern Missouri...however these cells are
generally tracking southeastward and will remain west/SW of the kilx
County Warning Area. Meanwhile...a cumulus-field is beginning to develop further east
along the front across Indiana where the hrrr/rapid refresh suggest
scattered thunderstorm development over the next couple of hours.
In between these two areas...models are mostly dry across south-
central Illinois. Will hold on to just a slight chance pop south of
I-70 late this afternoon in case a storm fires ahead of the
front...but do not see much evidence of that happening yet. Models
are then showing renewed convective development along/north of the
boundary across northern Missouri later tonight...with scattered
storms then tracking east/southeast into south-central Illinois. Exactly how
far north into the slightly cooler/drier airmass the precipitation will
develop remains in question...with the most recent runs of the rapid
refresh showing it generally just S/SW of the County Warning Area. Have included a
slight chance pop along/south of a
Robinson line after midnight...but think most areas will remain dry.

Long term...(tuesday through monday)
issued at 241 PM CDT Monday Aug 3 2015

Main forecast concern for this part of the forecast will be with
rain trends for the middle of the week.

Latest water vapor imagery and upper air analysis shows a small
upper low over northern Utah...trying to punch through the ridge
that is otherwise prevailing along The Rockies. Most of the models
manage to slip a piece of this energy through the ridge and into the
plains on Tuesday. This is expected to interact with the cold front
currently sinking southward across southern Missouri into the
Ohio Valley. The NAM and GFS models also eject some energy into
the Dakotas...however the GFS is alone in making that the
dominant feature and pulling the front back north across most of
Illinois by midday Wednesday. Most of the guidance focuses the
energy near the existing frontal boundary position...lifting the
boundary northward to just south of I-72 by Wednesday
evening...before an area of low pressure forms in Missouri and
tracks across southern Illinois. Discounting the GFS...will
continue to focus the higher pop's across the southern half of the
forecast area...with likely pop's edging in from the southwest
Wednesday and across a good portion of central and southeast
Illinois by Wednesday night. Heaviest rains will be concentrated
near the low track...which has slipped a bit further south from
earlier forecasts...and have confined the 1 to 2 inch rainfall
projections to areas south of I-70. The rain will be tapering off
from west to east Thursday the low moves into
southern Indiana.

The upper pattern late in the week continues to flatten the ridge
some...allowing for a series of waves to be tracking across the
upper Mississippi Valley. Longer range guidance is in poor agreement
regarding the strength of these waves...leading to lower than normal
confidence in this part of the forecast. Some evidence of the riding
starting to build again late in the weekend across the plains...
setting up some potential for mesoscale convective system will include some
mentionable rain chances Sunday night.

Temperatures expected to be below normal much of the period...with
highs in the 80 degree vicinity...and even cooler than that
Thursday/Friday behind the upcoming storm system.


Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 1148 PM CDT Monday Aug 3 2015

VFR conditions are expected until 00z at all central Illinois
terminals. Skies will be mostly clear initially...with high cloud
cover spreading slowly northeastward across the area starting
overnight. Scattered showers and thunderstorms are expected to
develop along/north of a frontal boundary over Missouri into
southern Illinois overnight...but this will likely remain south of the
central Illinois terminals. However...this feature will likely bring
middle-level cloud cover to kspi and perhaps kdec after 09z. After
00z Wednesday...the frontal boundary lifting northward with an
approaching low pressure system will begin to increase
precipitation chances from the southwest. Included thunderstorms in the vicinity at kspi to
reflect this scenario...but probability of occurrance remains
low through 06z Wednesday. Winds light and variable
overnight...becoming west 6-8 kts around 18z. Winds decreasing and
becoming variable after 00z Wednesday.


Ilx watches/warnings/advisories...


short term...Barnes
long term...geelhart

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