Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 190851

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

.SHORT TERM...(Today and tonight)
ISSUED AT 324 AM CDT Wed Jul 19 2017

Even in the short term, the main story is the heat over the
Midwest for the next few days. Aloft, the deep warm air over the
SW shifts into the Midwest as the upper ridge starts to dominate
the Mid/Lower Mississippi River Valley. Midlevels warm a couple
more degrees temps at the surface will move into the
low to mid 90s. Remnants from last nights convection, however,
will stall the diurnal trend this morning with cloud cover and a
few showers with some isolated thunder, mainly east of Interstate
55. Plenty of moisture in the low levels will keep the dwpts in
the 70s and push the heat indices into the low 100s. The Heat
Warning/Advisories in the area start today and are expected to
last through the end of the work week. Trending the isolated pops
east and south through the morning...and expecting a quick
recovery of the atmosphere...cannot rule out some more quick
convective showers in the east and southeast on the edge of the
older activity. Winds will be light and somewhat variable again
today...but trending more southwesterly as a whole.

Tonight, the activity shifts to northern IL again as another wave
moves into the upper Midwest and spawns more showers and
thunderstorms. Given the models poor performance in handling last
nights convection and/or overestimating the inhibition offered by
the ridge...have brought slight pops down into ILX forecast
area... particularly after 06z...which seems to be in line with
SPC Day One, with the Marginal Risk category dominating the
northern half of the state.


.LONG TERM...(Thursday through Tuesday)
ISSUED AT 324 AM CDT Wed Jul 19 2017

Summary of the rest of the week... hot and humid...with stormy
chances mostly confined to the north...mostly. The waves will
produce nearby convection, leaving much of Central IL subject to
more mesoscale boundary impact from any stronger storms that may
develop...through the end of the week. Best chances to see precip
will remain north of Interstate 74. Guidance is coming
together...resulting in a solution far closer to this weeks ECMWF
solutions with temps on Thu-Fri soaring into the mid to upper 90s.
The low level moisture is not moving in a relatively static
airmass. As a result, heat indices from 100F-110F dominate the
week. Overnight lows will generally not drop below the lower 70s.
Only minor adjustments to the temps through the end of the week
with the blend at this point. Heat headlines in good shape and
changes are not needed.

Central IL remains on the edge of the rising heights over the
southern half of the country...and the slightly cooler air to the
north as a series of waves move through the zonal flow to the
north. The developing boundary is expected to settle into the
region over the weekend, developing a more widespread chance for
showers and thunderstorms...and somewhat cooler max temps. Models,
however, are struggling with the timing of the boundary`s southern
progression...and Saturday looks to remain in the heat threat with
any delay. Heat abates for the first part of next week behind the
boundary...should the boundary actually remain on the move through
the end of the weekend.


.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



AVIATION...HJS is the U.S. government's official web portal to all federal, state and local government web resources and services.