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Area forecast discussion 
National Weather Service Lincoln Illinois
1042 am CDT Friday Sep 4 2015

issued at 1035 am CDT Friday Sep 4 2015

Water vapor loop indicating a slow moving upper wave over Southern
Lower Michigan with a secondary circulation noted over southeast
Wisconsin this morning. the surface...high pressure
was located to our southeast while a weak frontal boundary/wind
shift line was analyzed over far northern Illinois. Another hot
afternoon in store for the area with temperatures soaring into
the low to middle 90s and heat index values of 95 to 100. The
aforementioned secondary wave to our north combined with some
cool air aloft...500 mb temperatures were around -10 degrees c...and
mixed layer convective available potential energy of around 2500 j/kg could lead to some isolated
showers and thunderstorms this afternoon...especially across the
north and east. Current forecast has this well handled at the
moment so other than some minor changes to the morning temperature
trends...the rest of the forecast looks fine. Will send out an
updated zone forecast product to remove the mention of morning fog in parts of our


Short term...(today)
issued at 303 am CDT Friday Sep 4 2015

Sprawling upper-level ridge extending from the Southern Plains into
the western Great Lakes will continue to dominate the weather across
central Illinois today...leading to mostly sunny skies with high
temperatures once again topping out in the lower to middle 90s. The
only potential fly-in-the-ointment will be an upper low spinning
over Michigan. 08z/3am water vapor imagery shows the main low over
Lake Huron...however a well-defined circulation is noted rotating
around the low across eastern Wisconsin. Models take this feature
on a southeasterly trajectory across Southern Lake Michigan into
far northern Indiana...with most of its associated convection
remaining north/NE of the kilx County Warning Area. However this wave will pass close
enough to the area to warrant a slight chance pop along/northeast
of a Lacon to Paris line during the afternoon.

Long term...(tonight through thursday)
issued at 303 am CDT Friday Sep 4 2015

Upper low will remain in place over Michigan through Saturday...with
the GFS developing precipitation well to the south into portions of north-
central Illinois. Think this may be a bit too aggressive given the
weakening trend of the system and the fact that both the NAM and
European model (ecmwf) show dry conditions across the area. Will maintain just a
slight chance pop northeast of the I-74 corridor...but if current
trends continue this may be removed by later shifts. Aside from
this very slim chance for rain across the far NE County Warning and dry
weather will prevail both Saturday and Sunday with high temperatures
reaching the lower to middle 90s.

After that...things get a little more interesting as major pattern
change occurs next week. Models are beginning to come into better
agreement concerning the timing of this process...with consensus
bringing the initial weakening cold front into central Illinois on
Monday. As is typically the case with a pattern change of this
magnitude...models have been too fast with the front. As a
result...have trimmed probability of precipitation Sunday night to feature just low chance
across the Illinois River valley late. Have also slowed the
eastward progression of precipitation on Monday...with areas east of I-57
remaining dry through the entire day. The frontal boundary will
become parallel to the upper flow and will stall across the
area...keeping chance probability of precipitation in the forecast Monday night through
Tuesday night. As a more significant upper wave dives southeastward
out of will push a stronger cold front into Illinois on
Wednesday. Given ample low-level moisture...strong upper
dynamics...and adequate convergence along the boundary...have opted
to carry likely probability of precipitation on Wednesday. Front will drop southward into
the Ohio River valley by Thursday...resulting in cooler and drier
conditions with high temperatures dropping into the middle to upper


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 625 am CDT Friday Sep 4 2015

VFR conditions will prevail at all sites next 24hrs. With
dewpoints being close to temperatures this morning...some light fog is
possible this morning for about an hour at only cmi and bmi. Not
expecting any light fog at any of the other sites. Scattered cumulus
will develop across the area later this morning...effecting all
taf sites...but then dissipate early this evening. Light fog
possible again late tonight...but will not place in tafs yet and
let later shifts get better look at conditions. Winds will be
light this morning and again tonight. Winds during the day will be
southwesterly as axis of surface ridge remains southeast of the area.


Ilx watches/warnings/advisories...


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

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