Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
545 am CDT Tuesday Jul 28 2015
issued at 257 am CDT Tuesday Jul 28 2015
Main concern for today remains with the heat. No changes planned
for the timing or alignment of the heat advisory. Dew points
already in the middle 70s across western Missouri...and this will be
advecting our way the next several hours. Will likely see some
upper 70s dew points by late afternoon...especially across the
southwest County Warning Area. This translates to heat index of 105-110 from about
Galesburg-Effingham westward...with the higher readings toward the
Illinois River valley near Havana and Beardstown.
Still some concern about some thunderstorm development today.
Surface observations showing a weak boundary persisting along the
Ohio Valley northwest near the Illinois/Missouri border. This
would serve as one focus for any isolated development. Of more
concern is the mesoscale convective system currently rolling across eastern South Dakota.
High-resolution models such as the arw...hrrr and hop-WRF are
doing a respectable job with the system thus far...and show some
of the remnants making it as far as Galesburg by early afternoon.
The nmm mostly fizzles it out before reaching US...while the
NAM-12 is casually ignoring its existence altogether. Recent
southward development along the Nebraska/Iowa border would lend
some credence toward the hrrr solution...although there will be
some weak capping to get through first between here and there.
Will stick with isolated storms for now...as early as middle-morning
across the western County Warning Area and across most of the area during the
Long term...(tonight through monday)
issued at 257 am CDT Tuesday Jul 28 2015
Main cold front still scheduled to cross the forecast area
Wednesday morning and afternoon. Main organization to convective
cluster should take place across central/southern Iowa this
afternoon and roll east-southeast. Will focus higher pop's
beginning middle-late evening northwest of the Illinois River...and
shifting it as far as Champaign and Mattoon by late night. Have
kept the southeast County Warning Area largely dry until closer to sunrise... with
the higher pop's in that area later on Wednesday. Significantly
drier air will be pushing in during the afternoon behind the
front...but middle 70s dew points are still likely across the eastern
County Warning Area into the afternoon. May need another heat advisory south of
I-70 on Wednesday...but this is borderline with the increase in
clouds and convection...so will not put an extension there yet.
Remainder of the week looks dry and more comfortable...with a
northwest upper flow as the ridge rebuilds across the West Coast.
GFS shows no significant change in that pattern for several days
and in fact brings a lobe of much cooler air into the Midwest
early next week...while the European model (ecmwf) is warmer as the ridge only
gradually flattens. Have gone the warmer solution although
temperatures will still be near normal...generally highs in the
middle 80s from Thursday Onward. Next concern for rain will be late
weekend...as an upper trough swings through the Great Lakes.
West-east axis of high pressure at the surface will be present
across the Ohio Valley at the time. The European model (ecmwf) keeps it strong
enough to prevent the surface front from making much progress
south of I-80...while the GFS gets the boundary through in a
weakening state. Have capped pop's at slight chances across the
north on Sunday...but brought some 30% chances in for Monday as
another upper trough arrives.
Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 545 am CDT Tuesday Jul 28 2015
Some MVFR visibilities of 2-4sm occurring early this morning in
the humid air mass...but so far lower visibilities have held off
likely due to some high cloud remnants from overnight convection.
Conditions should improve over the next couple hours.
Have some concerns about isolated storms along a weak boundary
that extends from near kmli-kspi-kmvn. Earlier high-resolution
model guidance had been suggesting some storms as early as middle
morning west of the boundary...but have eased off recently. More
concerning is a large thunderstorm complex moving through Iowa...
with an associated Wing of storms from kcid northwest. Overall
weakening of the storms has been seen on infrared satellite
recently...and the leading Wing should track north of the central
Illinois taf sites. So...am planning to keep the taf sites dry
during the day. Thunder chances will be increasing from west to
east tonight as a cold front approaches from the west. The front
should be passing through the taf sites after 12z with a wind
shift to the northwest.
heat advisory from 1 PM this afternoon to 8 PM CDT this evening