Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 190531

Area Forecast Discussion
National Weather Service Lincoln IL
1231 AM CDT Wed Jul 19 2017

Issued at 902 PM CDT Tue Jul 18 2017

Will be making some adjustments to current forecast to accommodate
the ongoing convection in the northern part of the CWA. Expecting
this to wane this evening so not sure how far east it will get.
POPs/Wx will be adjusted to account for this uncertainty. Update
will be out soon.


.SHORT TERM...(This evening through Wednesday)
ISSUED AT 315 PM CDT Tue Jul 18 2017

Will convert the excessive heat watch from Wednesday afternoon
through early Saturday evening, into an excessive heat warning for
SW half of CWA and a heat advisory for ne half of CWA. Afternoon
heat indices to peak from 100-105F Wed afternoon, 103-110 Thu and
Fri afternoons and 100-108F Sat afternoon with highest readings in
sw CWA.

596 dm 500 mb subtropical ridge over southern KS and ridging into
central IL at mid afternoon with 594 dm 500 mb height nearing
Lincoln, IL. This ridge combined with nearby weak 1020 mb surface
high pressure should keep CWA generally dry through Wed. MCS
activity should pass north of central IL tonight and Wed, and just
have slight chance of showers and thunderstorms late Wed
afternoon ne of I-74 with any outflow boundary from MCS that get
this far south during day tomorrow. Dewpoints have climbed into
the upper 60s and lower 70s this afternoon and this is where lows
will be overnight with mildest readings in western CWA. Have
patchy fog overnight into early Thu morning in southeast IL again.

850 mb temps of 20-21C on Wed to support highs of 90-95F on Wed
with warmest readings from Springfield sw combined with dewpoints
in the low to mid 70s, to give afternoon heat indices of 100-105F
(highest in sw CWA). This will be the start of a four day heat
wave over central IL.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 315 PM CDT Tue Jul 18 2017

The hottest days still appear to be on Thu and Friday as 850 mb
temps rise a bit more to 21-24C. This supports highs in the 90s
(upper 90s possible from Springfield sw) and dewpoints in the low
to mid 70s to give afternoon heat indices of 103-110F and warmest
from Macomb to Lincoln to Robinson sw.

Models are keeping convection
north of central IL through midday Wed. Winds to stay light next
24 hours, primarily out of the south to southwest. Most of CWA
will continue to be dry through at least Fri morning with MCS
activity mainly passing north/ne of CWA. Have 20-30% pops over ne
CWA mainly from I-74 ne from later Fri afternoon through Friday
night from more outflow boundaries getting closer to central IL.

Another hot and humid day on Saturday with highs in the low to mid
90s and dewpoints in the 70s giving afternoon heat indices of
100-108, highest over sw CWA. Convection chances get a bit higher
and further south on Saturday and Saturday night as upper level
ridge is being suppressed southward as 500 mb heights lower to
588-590 dm over central IL by sunset Sat. This will allow upper
level disturbances/MCS riding over top of flat ridge to get
further south into central IL.

ECMWF model is quickly with pushing a cold front south through
central IL Sat night into Sunday while GFS is Sunday night into
Monday morning. Previous model solutions were slower with front so
skeptical about faster ECMWF model pushing cold front into strong
upper level ridge over the southern states. Will continue chance
of showers and thunderstorms over much of area Sat night and
Sunday, then diminish chances from nw to se during Sunday night
and lingering 20-40% pops just in southeast IL on Monday. Highs
Sunday in the upper 80s and lower 90s (warmest in southern CWA)
while afternoon heat indices in the 90s over central IL north of
I-70 and 100-105F south of I-70. Cooler highs of 82-88F on Monday
and warmest by Lawrenceville and dewpoints slipping into the 60s.

Models differ with wx on Tue with GEM model wetter and cooler with
cutoff upper level low over southern lower MI while ECMWF has
upper level ridging into IL and GFS has IL in a nw upper level
flow and weak surface high pressure settling se over the Midwest.
Stayed close to consensus of models with 20-30% pops on Tue with
highest pops in southeast IL, and cooler highs in the lower 80s.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1226 AM CDT Wed Jul 19 2017

Convection across the Miss River Valley held together and moved
into Central IL tonight...resulting in a couple differences in the
forecast. First, some mid level clouds remain in the region as the
showers and storms continue to dissipate. Second, the llvl
moisture from the showers has increased...with dwpts in PIA and
SPI responding accordingly. Model data has not yet responded to
the influence of the showers. As the clouds break up...any
clearing may result in some radiational cooling in the absence of
wind at the surface under the ridge. Have dropped visbys to 1sm
for both terminals as a start.


Excessive Heat Warning from noon today to 8 PM CDT Saturday for

Heat Advisory from noon today to 8 PM CDT Saturday for



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