Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 300838
Area Forecast Discussion
National Weather Service Lincoln IL
338 AM CDT TUE AUG 30 2016
.SHORT TERM...(Today and tonight)
ISSUED AT 337 AM CDT Tue Aug 30 2016
Surface high pressure ridge will sit over the northern part of the
state through the day and then slowly slide south. As this occurs, a
weak surface wave will move east into the area. Storms have already
developed in the northwest part of the CWA, but additional storms
are expected to develop in the west and northwest and then move east
and southeast through the afternoon and into the evening. Likely
pops are expected early this afternoon northwest of I-55 to account
for where storms are expected to move into first. Storms will
probably be scattered across the area this afternoon and into this
evening, so will just maintain chances pops over most of the area
east of I-55 this afternoon and through tonight. Temps will be warm
again today, but should be more clouds this afternoon where the rain
is expected to be. Warmest temps will be in the southeast where
should be lots of sun through the day.
.LONG TERM...(Wednesday through Monday)
ISSUED AT 337 AM CDT Tue Aug 30 2016
A 593 dm 500 mb subtropical ridge was over the mid MS river valley
this morning and has been ridging in from the mid Atlantic states
the past few days, providing the tropical summer time heat and
humidity. The upper level pattern will begin to shift as a 563 dm
500 mb low near the Manitoba/Ontario and Hudson Bay border deepens
to around 560 dm as it tracks southeast into western Quebec by Wed
afternoon. This deepens an upper level trof over the Great Lakes
and Ohio valley on Wed and Wed night, and drives a cold front sse
over central IL on Wed, and exiting southeast IL by sunset Wed and
bringing a good chance of showers/thunderstorms on Wed with its
passage. MUCAPES run from 1500-2200 J/KG from IL river southeast on
Wed afternoon while 0-6 km Bulk Shear fairly weak from 20-25 kts
over eastern IL. So SPC does not have a marginal risk on Wed
afternoon, but will continue a threat of locally heavy rain as
Precipitable water values are 1.60-2.10 inches from IL river
southeast through Wed afternoon and into southeast IL early Wed
evening until dusk and lingered isolated convection early Wed
evening in far southeast IL. One more muggy day on Wed with
dewpoints in the upper 60s and lower 70s with highs around 80F from
I-74 north and mid 80s south of I-70.
Big change in airmass on Wed night and Thu as 1029 mb Canadian high
pressure noses southward from Hudson Bay and Ontario into WI with
NNE flow bringing in cooler and less humid air. Lows Wed night will
be in the upper 50s over central IL, and lower 60s from I-70 south.
Mostly sunny skies Thu with highs actually below normal in the upper
70s, with Lawrenceville near 80F. More comfortable dewpoints in the
upper 50s/lower 60s. Similar conditions expected Thu night and
Friday as surface high pressure slowly builds over the western
Great Lakes and upper level ridge shifts eastward toward IL by
Friday afternoon. Fair and less humid weather prevailing with
sunny skies Friday. Lows Thu night in the mid to upper 50s, highs
on Friday in the upper 70s. Dewpoints only 55-60F on Friday.
Another pleasant sunny day expected on Saturday over central and
southeast IL as surface high pressure drifts into the eastern Great
Lakes and upper level ridge expands into the Ohio river valley.
Highs near 80F on Saturday with dewpoints in the upper 50s/lower 60s
with fairly light ESE winds. Temperatures and dewpoints gradually
rise on Sunday and Monday as surface high pressure moves into New
England and the mid Atlantic states and get an increasing southerly
flow. Sunday still looks dry across the CWA with mostly sunny skies.
Highs in the lower 80s Sunday with Lawrenceville near 85F with
dewpoints rising into the mid to upper 60s by Sunday afternoon.
Highs in the mid 80s on Monday (Labor Day) with more muggy dewpoints
in the upper 60s to near 70F.
A weather disturbance ejecting northeast across the upper Midwest on
Sunday night and Monday, to bring a slight chance of showers and
thunderstorms nw of the IL river overnight Sunday night and then a
20-30% of showers/thunderstorms from I-55 northwest on Monday while
eastcentral and southeast IL stays dry on Monday. Have 20-40% chance
of convection nw of I-70 on Monday night into Tue with highest pops
focused over the IL river valley closer to low pressure tracking
northeast across central or nw parts of IA and WI.
A tropical depression with 35 mph winds drifting westward off the
west coast of Cuba is forecast by NHC to become a tropical storm and
turn northeast and move into northeast Florida by sunset Thursday,
and pass southeast of NC on Friday night into Saturday. This
tropical system should keep its rainfall well southeast of IL. But
if traveling to Florida or the southeast Atlantic coastal region,
monitor later forecasts and statements from the National Hurricane
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1100 PM CDT Mon Aug 29 2016
Main concern this forecast period will be with the potential for
some MVFR and possibly brief IFR cigs/vsbys in fog in the 08z-13z
time frame, and then the threat for widely scattered showers and
storms again late tomorrow morning into the afternoon hours. Areas
such as PIA that received some rainfall today would have the
higher probabilities for seeing some fog and lower clouds just
before dawn. Convection that occurred over a small part of our
area this afternoon has dissipated. Short term models have been
consistently showing some redevelopment along the Mississippi
River after 06z and then spreading east into the forecast area.
Will keep an eye on the radar over the next half hour to 45 min
and if we see development start to occur, will add VCTS to our
western TAF sites for the early morning hours.
Any MVFR or lower cigs and vsbys will improve after 14z with VFR
conditions over the entire area by early afternoon Tuesday.
Another threat for widely scattered TSRA after 17z Tuesday but
coverage still appears to be too limited to go much greater than
VCTS, especially this far out in the forecast. Any lingering
TSRA should dissipate again by Tuesday evening. Light and variable
winds tonight should be mostly out of an east to southeast
direction Tuesday with speeds in the 3 to 8 kt range.