Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
1143 PM CDT Fri Aug 1 2014
issued 900 PM CDT Fri Aug 1 2014
Much of the convection that formed earlier today has faded with
sunset, but some storms persist from near Beardstown northwest
toward Burlington Iowa. That particular area still has some cape's
around 1500 j/kg per Storm Prediction Center mesoanalysis, which will help sustain them
for another hour or two, although the latest rap model shows the
instability weakening with time.
Large area of mostly clear skies west of the Mississippi River,
and skies should start clearing from west to east in our area,
although clouds will likely hang on near the Indiana border much
of the night. Development of fog is most likely in the areas that
had the most rain earlier today, with nearly calm winds overnight,
with speed of development based on the clearing.
Have sent some updated grids to reflect latest precipitation and
temperature trends. Updated zones to follow shortly.
issued 1143 PM CDT Fri Aug 1 2014
Main concern for the upcoming taf set is with visibilities through
early morning. Although convection has ended, skies still mostly
cloudy as of late evening. Satellite imagery showing this will be
eroding from kbmi/kdec westward over the next few hours, but may
persist at kcmi a good part of the night. Already seeing some
patchy MVFR visibility around 5sm, and am expecting this to become
more widespread. Have introduced a period of lower visibilities of
2 to 3sm from about 10-13z with the winds nearly calm and recent
rainfall. Heaviest rain on Friday occurred near kspi and kdec, and
went with lower visibilities around 2sm there. Rap model soundings
showing the fog should be rather shallow. After that, some
scattered diurnal cumulus expected to develop around 4000 feet,
but the threat of rain should be further east.
issued 325 PM CDT Fri Aug 1 2014
Very little change to our overall weather pattern is expected into
the middle of next week as the upper level northwest flow
continues. This will result in temperatures at or just below
seasonal normals, with shortwave troughs providing a focus for
showers/T-storms Tuesday and Wednesday. Medium range models
showing a shift in our pattern by Thursday, but there are quite a
few differences regarding how this will take place and what the
associated sensible weather will be.
Short term...tonight through Sunday night
Diurnal convection this afternoon has been getting a boost from a
shortwave trough moving into the area. The surface reflection was
only a weak wind shift, but this was enough to combine with the
instability and convective updrafts to produce several funnel
clouds in central and east central Illinois this afternoon. The radar
indicated a myriad of outflow boundaries with scattered
thunderstorms east of the Illinois River and very isolated showers to
the west. Will keep the mention of scattered T-storms in the
forecast for this evening generally along and east of I-55, with a
mention of isolated showers/few T-storms to the west.
The scattered rainfall, some of which was heavy in spots, will
contribute low level moisture to help produce patchy fog overnight
and into Saturday morning. The shortwave moving across the Midwest
tonight could linger just long enough in extreme eastern Illinois to
produce scattered showers/T-storms early Saturday afternoon.
Otherwise, weak high pressure will begin to approach later
Saturday and settle into the area Sunday with mostly sunny
conditions and temperatures in the lower 80s.
Long term...Monday through Friday
A southerly wind will develop Monday ahead of the next approaching
cold front from the northwest. This will give US gradually
increasing humidity and temperatures closer to normal for early
There are some model differences with the speed of the cold front,
with the GFS being quicker and the European and Canadian on the
slower side. The GFS may be a bit too quick with its frontal
depiction, so will keep the chance for thunderstorms north of I-74
for Monday night, and gradually drop them southward with the front
As the models start to depict a breakdown in the northwest flow to
more of a zonal flow, their differences start to show up with the
position of the front Wednesday through Friday. The Canadian model
is farther north while the GFS drops it south toward the Ohio Valley
Wednesday then lift it back north as a warm front by Friday.
Prefer the European solution of settling the front into southern
Illinois then pretty much keeping it there through the end of the week.
This would result in periods of showers and thunderstorms with
high temperatures in the lower to middle 80s.