Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
619 PM CDT Friday Oct 28 2016
Short term...(this evening through saturday)
issued at 249 PM CDT Fri Oct 28 2016
Warm and windy for tonight and into tomorrow morning as the Midwest
is between an exiting high pressure, and a developing storm system
well to the northwest. The increasing gradient and winds just off
the surface to 40 kts later tonight...will result in gusts this
afternoon and evening with some turbulent mixing, and potentially
into the overnight. The gusts may calm a bit after midnight...but
the winds will still stay up in the 10-15kt range out of the south-southwest.
The intense southerly flow will keep the overnight lows up a bit,
mainly in the upper 50s/lower 60s...which is 15-20 degrees f over
last nights lows. Tomorrow the winds veer to more southwesterly
flow...continuing to advect plenty of warm air into the region and
highs tomorrow will soar into the upper 70s/lower 80s.
Long term...(saturday night through friday)
issued at 249 PM CDT Fri Oct 28 2016
Above normal temperatures will highlight the extended forecast, as
relatively zonal flow in the upper levels prevents any deep pushes
of cold air into Illinois.
Saturday night will see low pressure advancing across Illinois which
will help pull a cold front south into central Illinois. The better
forcing for precip will remain north of the low across northern IL,
therefore only expecting spotty showers north of a line from Canton
to Champaign after midnight Saturday night through sunrise Sunday.
Low temps Saturday night will remain quite mild, with readings
ranging from around 55 near Galesburg to around 60 south of Lincoln.
The cold frontal passage Sat night will keep Sunday a little cooler
than Saturday, but highs should remain above normal ranging from the
low 60s north of I-74 to the mid to upper 70s south of I-70.
The cooler temps will be short-lived, as southerly warm air
advection flows crank up by sunrise on Monday. 850mb temps are
projected to climb into the 17 to 19c range by 00z/7pm Monday. Gusty
southwest winds mixing those temps to the surface would support high
temps in the low 70s north of I-74 and the upper 70s S of Springfield to
Mattoon. Very similar temperatures will linger into Tuesday as a
cold front approaches western Illinois, and central Illinois remains
in the warm sector of the nearby frontal system.
There are model differences in how that front progresses on Tuesday
night and Wednesday. Overall consensus is that low pressure will
drift toward or into northwest Illinois, lifting the front northward as a
warm front on Wednesday. That would provide yet another day of very
mild temperatures in the 70s, but would also bring increasing clouds
and chances of rain. We have slight /20%/ chances west of I-55 after
midnight tues night and Wed morning, with chance /30-40%/ pops Wed
afternoon northwest of the Illinois River. Rain chances climb to high chance and
low likely /50-60%/ Wed night through Thursday morning as the front
is pulled across Illinois by low pressure departing into the Great
Lakes. Instability looks weak in general, but isolated thunderstorms
could develop during that time, with help from marginal bulk wind
Model differences become more pronounced for thurs night and Friday,
as the European model (ecmwf) slowly pushes low pressure across Illinois in contrast
to the GFS solution of advancing the cold front southeast of
Illinois under advancing high pressure. For this update, the
extended blend leaned toward the dry GFS, which seems more
reasonable in the zonal flow pattern.
Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 618 PM CDT Fri Oct 28 2016
Low level S-SW flow developing as a result of pressure gradients
between high pressure over the East Coast states and low pressure
over the northern plains will result in breezy conditions over the
next day and low level wind shear overnight. Otherwise...VFR
conditions with relatively thick high cloudiness prevalent over
the next 24 hours. Winds south-southwest 10-15 kts through the period. Gusts
20-22 kts after 14z Saturday. Winds at 2000 ft above ground level SW to around 45
kts from 04-14z resulting in low level wind shear criteria.