Area forecast discussion...correction long term
National Weather Service Lincoln Illinois
329 am CDT Tuesday may 21 2013
Discussion...
issued 330 am CDT Tuesday may 21 2013
Short term...today through Friday
Mesoscale convective system that brought heavy rains...frequent lightning and several
severe wind damage reports to central/eastern Illinois during Monday
evening has weakened eastward across Indiana with lingering
showers and isolated thunderstorms southeast of a Champaign to
Springfield line and tracking NE. 998 mb low pressure over NE South Dakota
with its warm front over northern WI/lower Michigan and its cold front
over western Iowa...northwest MO...southeast Kansas and central OK. Strong 555 dm 500
mb low was over NE South Dakota and has not moved much past 24 hours. One
more very warm and humid day expected over central and southeast Illinois with
highs in the low to middle 80s as some sunshine returns during the
morning and early afternoon. Showers and isolated thunderstorms to
diminish east of I-55 during the morning and refire up later this
afternoon and evening.
Storm Prediction Center has shifted slight risk of severe storms a bit further east
and generally east of the Illinois River valley late this afternoon and
evening. Per Storm Prediction Center day1 outlook discussion...SW flow will be in
place today from the middle MS valley NE into the Great Lakes region.
Surface low pressure is forecast to move eastward across the upper
MS valley with a corridor of low level moisture extending north-northeast from
the lower Ohio Valley into lower Michigan. Surface dewpoints across
central and eastern Illinois should be in the middle to upper 60s
resulting in moderate destabilization. Model forecasts initiate
storms by middle afternoon along the instability axis with storms
moving northeastward across the region. Forecast soundings along the
instability axis west of Detroit and north of Indianapolis at
21z/4 PM show MLCAPE values in the 1000 to 2000 j/kg range with
steep low-level lapse rates and unidirectional wind profiles. This
environment should be favorable for wind damage as cells increase
in coverage during this afternoon. Several model forecasts show an
enhanced severe threat across Southern Lower Michigan to the southeast
of the surface low and on the nose of the low-level jet. For this
reason...an enhanced wind damage threat (30%) will be possible
with bowing line-segments in lower Michigan late this afternoon. Large
hail and a few tornadoes (5%) may also occur with the more intense
cells. Central and eastern Illinois has 15% risk of damaging wind gusts
and large hail and 2% risk of a tornado late this afternoon and
evening.
Strong cutoff low to move east and be 557 dm 500 low over northwest Iowa by
dawn Wednesday with 1004 mb surface low moving east/weakening into NE Iowa
and northern Illinois. Continue high chances of showers and thunderstorms
through tonight with the slight risk of severe storms east of the Illinois
River valley through the evening. Cold front to move east through Illinois
Wednesday morning as surface low moves into southeast lower Michigan by sunset Wednesday.
This to keep a good chance of showers and a few thunderstorms
around on Wednesday with likely chances over eastern Illinois. Storm Prediction Center has 5% risk
of severe storms near the Wabash River Wednesday while slight chance of
severe storms is from Ohio east. Highs Wednesday in the middle to upper
70s with Lawrenceville near 80f.
562 dm 500 mb low to over into northern Indiana Thursday morning and
continue chances of showers and mostly cloudy skies with cooler
temperatures in the upper 60s and lower 70s for highs Thursday and mildest
from Springfield to Terre Haute south. Upper level low/trough pulls
away from Illinois Thursday night and Friday as 1031 mb Canadian high pressure
settles into the western Great Lakes and Illinois. This to bring more
sunshine but cool temperatures with highs in the upper 60s to around 70f
after lows Thursday night in the middle to upper 40s over central Illinois and
lower 50s southeast Illinois.
Long term...Friday night through Monday
Upper level ridging into the Great Plains late this week and models
still showing a disturbance ridging over the upper level ridge with
quantitative precipitation forecast but differ on timing on position of this disturbance. Have
slight chance of convection over the Illinois River valley after midnight
Friday night. Then 20-40% chance of convection over central Illinois Sat
through Monday while southeast Illinois appears to stay drier Sat and Sat night and
Monday. High pressure over the Great Lakes region Memorial Day
weekend will tend to keep areas NE of central Illinois drier as well.
Temperatures to gradually modify from Sat through Monday with highs in the
middle to upper 70s Memorial Day.
07
&&
Aviation...
issued 109 am CDT Tuesday may 21 2013
Most intense convection along outflow boundary has weakened
considerably as its moved into southeast sections of County Warning Area...and over the
next few hours elevated...and generally light...convection will be
tapering off along and east of a bmi-Dec line. Some lighter
elevated showers working into eastern Missouri should return to the
area during the predawn hours...and will also need to keep an eye on
some elevated convection refiring as low level S flow intensifies
and taps residual instability but for now have held these out of the
tafs. Once the heavier convection exits east tafs by 08z...VFR
conditions should prevail with ceilings at or above 8kft...with perhaps a bit of
St forming during the predawn hours and have hinted at that with scattered
3kft. Not many changes made to forecasts for later today...with scattered
cumulus forming by middle morning. Due to uncertainty of timing/location of
convective initiation...will let next shift monitor trends before
introducing next round of storms.
Truett
&&
Ilx watches/warnings/advisories...
none.
&&
$$
