Area Forecast Discussion
Issued by NWS Central Illinois

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587
FXUS63 KILX 221758
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1258 PM CDT FRI JUL 22 2016

.UPDATE...
Issued at 1045 AM CDT Fri Jul 22 2016

Updating the forecast to lower the high temperatures a degree or
two this afternooon, with eastern IL around 90 and lower 90s from
I-57 west. Dewpoints around 70F over central IL and mid 70s in
southeast IL south of I-70 still expected to rise back into the
upper 70s during the afternoon as the sun appears. Clouds have
been already breaking up over northeast CWA and expect this trend
to continue this afternoon. A few showers lingering south of I-70
and expected to dissipate and move south of CWA by noon. Most
forecast models keep our CWA dry this afternoon and evening with
only a few models like NAM showing some QFP late this afternoon
over western/NW CWA where instability increases more late today.
SPC has shifted marginal risk south and sw of CWA rest of today as
airmass has become stable over area this morning from MCS
overnight. Will continue the excessive heat warning next few days,
though heat indices may be a bit shy of 105F over eastern IL, east
of I-57 due to a bit cooler highs, but still expect heat indices
of 105-110F west of I-57 by late afternoon into early evening
until 7 pm.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 252 AM CDT Fri Jul 22 2016

Last evening, storms blasted their way southward through a +14C 700mb
cap, taking advantage of around 6000 J/kg MUCAPE. Although the
remaining CIN did keep the strength of the storms in check once they
reached central IL. The now dying MCS across central Illinois will
start out the day, with precip eventually coming to an end as the
system loses lift and upper support and drifts south.

A couple versions of the HRRR are showing dry conditions for a
majority of the day today, with a small cluster of storms developing
after 20z in our northern counties. The storms are projected to
progress slowly south into the evening, oriented in a NW to SE line
across central IL. The other operational models have differing
solutions on timing and coverage, but will stick closer to the HRRR-
CR for this short-term forecast update.

Temperatures plummeted about 10-15 degrees with the MCS arrival last
evening. However, still expect clouds to dissipate by mid to late
morning, allowing for plenty of time for sunshine to produce high
temps in the low to mid 90s again today. Due to the additional
moisture from last nights convection, dewpoints should have no
problem climbing back in the mid to upper 70s, with a few low 80s
possible. Those numbers should support peak heat index values in the
107 to 112 range this afternoon. Low temps will remain very mild
again tonight, with some cooler locations where any evening storms
develop. Overall, temps should bottom out in the low to mid 70s again
tonight.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 252 AM CDT Fri Jul 22 2016

A couple more days of heat and humidity expected, before some relief
arrives in the form of a cold front Sunday night. Main challenge
before that will be with any convection and its impacts on the
temperatures. With the main synoptic boundary still off to the
northwest until late in the weekend, the primary focus for
convection will be with mesoscale boundaries which are not handled
very well in the larger scale models. Have not changed PoP`s much
from the previous forecast, mainly 30-40% range this weekend during
the daytime hours. Still keeping the heat indices in the 105-110
range, but the convection could thwart those plans. No changes
planned to the headlines at this time due to the uncertainty.

Moving on to early next week, the movement of the front slows some
as it gets caught in the west-east high pressure axis aloft. Have
updated the PoP`s on Monday to linger about 30% chances as far north
as I-72, until the passage of an upper wave across the mid-
Mississippi Valley. As another trough moves through the Plains mid
week, it will sharpen and provide more of a focus for showers and
thunderstorms. While the GFS and ECMWF are not too different in the
upper level features, the synoptic boundaries are much more
uncertain, as well as the precipitation chances. Thus, will not go
any higher than 40% at the end of the current forecast period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1255 PM CDT Fri Jul 22 2016

Kept VFR conditions over the central IL airports next 24 hours
aside from possible MVFR visibilities of 3-5 miles with light
fog/haze from 09-14Z. Have scattered cumulus clouds 3-4k ft with
broken cirrus clouds 25k ft this afternoon and again on Saturday.
Carried vcsh along I-74 TAF sites later tonight until mid morning
Saturday. Though forecast models have trended drier over central
IL next 24 hours, keeping MCS activity with thunderstorms north of
our area. Winds generally stay below 10 kts next 24 hours out of
the sw this afternoon and more southerly thereafter.

&&

.ILX Watches/Warnings/Advisories...
Excessive Heat Warning until 7 PM CDT Sunday for ILZ040>057-
061>063-066>068-071>073.

Excessive Heat Warning until 7 PM CDT Saturday for ILZ027>031-
036>038.

&&

$$

UPDATE...07/VIECK
SHORT TERM...Shimon
LONG TERM...Geelhart
AVIATION...07/VIECK



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