Scientific Forecaster Discussion
fxus63 kilx 250209
Area forecast discussion
National Weather Service Lincoln Illinois
909 PM CDT Mon Jun 24 2019
issued at 905 PM CDT Mon Jun 24 2019
The strong west wind gusts have subsided for the most part, but
sustained winds are lingering in the 12-15 mph range for some
locations from Bloomington to Champaign and east. Those winds
should also weaken more the rest of the evening, but remain in the
5-10 mph the rest of the night, driven by sustained pressure rises
in the wake of the cold front.
Clouds will be minimal overnight, and even Tuesday morning in the
relatively dry airmass pushing into central Illinois. The next cold
front will arrive late Tuesday afternoon and evening, triggering
scattered showers and storms. The best instability still looks to
be focused on the Mississippi River valley, with lower MLCAPES the
farther east you go. We have a slight risk tomorrow all the way
to cmi, but best severe potential looks to be west of I-55, if not
west of the Illinois River. Cams are all over the place with coverage of
storms, so we are not overdoing pops into the likely range
(60-70%) and mainly in our far western counties Tue eve.
Main updates this evening were to remove all mention of
showers/storms the rest of the evening, and adjust the pops later
Tue afternoon/eve to match the current thinking. Also bumped up
the southwest wind gusts tomorrow afternoon a few mph, as momentum
Transfer looks to tap into gusts in the mid 20s miles per hour.
Short term...(this evening through Tuesday night)
issued at 250 PM CDT Mon Jun 24 2019
Latest surface map shows the cold front is near the Illinois/Iowa
border southwest into central Missouri. Earlier cloud deck is well
to our east, and we're more in a diurnal type pattern. Scattered
thunderstorms have been developing ahead of the front, where
cape's are 1500-2000 j/kg. Bulk shear remains quite minimal,
though, so any stronger storms are likely to be more of the
pulse-type. Bulk of the rain should be east of the forecast area
by early evening, though with the front near I-57 by 7 PM, some
lower pop's will be kept in that area until near sunset.
Next focus is on Tuesday afternoon and evening, involving the
shortwave currently moving into western North Dakota. Made some
significant changes to the pop's late afternoon into the evening,
going with 60% pop's across the far northwest by evening. Latest
Storm Prediction Center day2 outlook greatly expanded the slight risk, which is now
over the northwest 2/3 of the County Warning Area. Latest NAM and GFS bring
cape's over 3000 j/kg west of the Illinois River by late
afternoon. A number of the high-res models focus more on a line of
storms forming in southern Iowa and dropping through western
Illinois, with a separate segment closer to Lake Michigan. With
shear again nothing to write home about, not expecting a large
outbreak, but potential for stronger wind gusts and hail is there.
Long term...(wednesday through monday)
issued at 250 PM CDT Mon Jun 24 2019
Longer range continues to show a very warm and humid pattern into
next weekend, as upper level ridging amplifies over the plains.
850 mb temperatures rise to around 19c by Friday, and rise a
little more through the weekend. High temperatures will gradually
creep upward and will be near 90 by the weekend, with peak heat
index values in the mid 90s.
This sort of a pattern will keep rain chances lower. The main
concern is with a shortwave riding over top of the ridge Thursday
night and Friday. GFS is quite generous with the rain amounts all
the way down to the Ohio Valley, while the European and Canadian
models keep the activity to our north. Think the drier solution is
more reasonable. A stray storm can't be ruled out, but will only
mention silent 20 pop's across the northern County Warning Area for now. Other
thunderstorm activity across the region will be more in the form
of ridge-riding mesoscale convective system complexes, with the Great Lakes region more
likely to be the recipients.
Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 624 PM CDT Mon Jun 24 2019
A cold front has already progressed past all of the taf sites, as
evidenced by their gusty west winds at 14g24kt. Drier air will
filter into the area, helping to diminish most of the remaining
clouds. There will be a rapid decrease in winds as sunset
approaches, and decoupling takes place in the boundary layer.
Advancing high pressure will provide VFR conditions for a majority
of the day on Tuesday. However, gusty southwest winds will develop
by mid-day. The late afternoon storms that are expected to roll
out of Iowa into our northwest counties could affect pia very late in
this taf period. MVFR conditions would be likely at pia if that
occurs. Better chances of storms will come early Tue evening for
the taf sites.