Area forecast discussion
National Weather Service Lincoln Illinois
902 PM CDT sun may 19 2013
Discussion...
issued 856 PM CDT sun may 19 2013
forecast is mostly on track this evening...multiple lines of
thunderstorms west of Illinois...bringing a threat for some severe
weather potential later tonight...with some scattered ts to the north
as well. Majority of ts activity from the west not anticipated
until after midnight. Monitoring for any cells that develop ahead
of the advancing line...but otherwise...no updates to the forecast
anticipated at this time.
Hjs
&&
Aviation...
issued 632 PM CDT sun may 19 2013
not much of a shift in the forecast at this point. Best chances
for ts moving into the ilx terminals after midnight...though a
small complex to the northwest is getting close to pia. Thunderstorms in the vicinity for all
after midnight...starting between 07-09z. Most confident in pia and
potentially spi to see some precipitation prior to dawn. May have a break
in activity through the morning hours and a return to ts activity
tomorrow afternoon for most of central Illinois as the storm system
draws closer. Threat remains borderline through the evening hours
and does not warrant a predominate group...nor a tempo...but the
risk will come close to pia with the current complex. Keeping the
gusts in place as they are increasingly influenced by a tightening
pressure gradient.
Hjs
&&
Previous discussion...
issued 300 PM CDT sun may 19 2013
Periodic chances of severe storms will highlight the short term
forecast. The weather pattern will be dominated by a slow moving
low pressure system that will linger in the northern plains until
Tuesday then slide east as the upper wave occlusion opens up.
The models are in general agreement on the progression of the
upper low...but have differences in the development of shortwaves
and surface boundaries through Tuesday night. When the upper low
slides east on Wednesday...the NAM is the quickest with the cold
front...while the GFS/ECMWF/Gem all agree on a slightly slower
solution. Preferred a GFS/European model (ecmwf) blend today.
Short term...tonight through Tuesday night.
A line of convection that approached our western area around
17z/noon dissipated quickly as it moved away from the low level
jet to the west and into a slightly more capped airmass. The cap
over our area is eroding with boundary layer heating this
afternoon...which is evidenced by a few showers that were able to
pop up near Lincoln and Bloomington in the last hour. We may
eventually see some storms from Missouri advance into our western
counties late this afternoon and this evening. Middle level lapse
rates have climbed to 8.5c over much of the area...and MLCAPE
values have climbed near 3.5k j/kg. The models all show some
indication of a middle level short wave moving across northern
Missouri and Iowa tonight...which may trigger strong to severe
storms in western Illinois later tonight. That convection may reach as
far east as I-57 by Monday morning...but better chances for storms
tonight will be west of I-55. Based on the track of the low level
jet maximum and progression of bulk shear values from plains
tonight...we only went with likely probability of precipitation northwest of the Illinois River after
06z/1 am.
Monday may see a break in the storms during the morning...allowing
the atmosphere to recharge for late afternoon convection. A line
of convection is expected to develop in western Illinois and progress
eastward on the nose of a low level jet. Instability...helicity and shear
parameters look favorable for supercells Monday afternoon and
evening...with large hail and damaging winds possible...along with
isolated tornadoes. The degree of boundary layer heating from
sunshine will play a roll into updraft strength initially...but
MLCAPE values above the elevated mixed layer /eml/ will climb over
3k again tomorrow...providing plenty of fuel for strong to severe
storms.
Shear and instability will weaken Tuesday morning...but a few
ongoing severe storms may linger through 12z Tuesday morning in
our northeast counties. A shortwave is forecast to move across c
Illinois on Tuesday afternoon/evening...in concert with a cold front.
Instability will not be as strong as today and Monday...but severe
storms remain a possibility Tuesday afternoon and evening...mainly
southeast of the Illinois River.
Long term...Wednesday through Sunday.
As the upper low finally makes some progress across Minnesota and wis on
Wednesday...the surface cold front will push into Indiana and colder
air will filter into c Illinois. A 500mb shortwave and 300mb jet maximum
will still be affecting eastern Illinois Wednesday morning...so ongoing
showers and storms are likely in the east at sunrise. By
afternoon...middle level lapse rates will become steep and allow for
additional showers and storms to develop behind the front.
An lobe of vorticity will rotate around the back side of the upper
trough and across northern Illinois late Wednesday night and
Thursday...keeping shower chances going. Dry conditions should
finally develop Thursday night and continue Friday under surface
high pressure and rising heights aloft. The coldest day of this
week will be Friday morning and afternoon...with cool northeast
winds prevailing that day.
Southeast flow will develop on Saturday as a shortwave rolls over
the top of the ridge in the plains. A stationary front is expected
to develop across Illinois as well...that will linger into Sunday. So it
appears that rain and storm chances will return to central Illinois for
Memorial Day weekend...with at or below normal temperatures and cooler
northeast flow. Some warming and dry conditions appear in the
offing for Memorial Day at this time. Hopefully that holds true.
&&
Ilx watches/warnings/advisories...
none.
&&
$$
