Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 211752
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1252 PM CDT THU JUL 21 2016

.UPDATE...
Issued at 1045 AM CDT Thu Jul 21 2016

Updated the forecast to remove the patchy fog early this morning.
Otherwise rest of forecast looks on track with main weather story
being the excessive heat warning across CWA through 7 pm Saturday
and extended through 7 pm Sunday southeast of the IL river.
Updated NPW product to continue the excessive heat warning. Mostly
sunny, hot and humid this afternoon with highs 90-95F with
dewpoints in the mid to upper 70s giving peak heat indices of
105-110F by mid afternoon (lowest near the IL/IN border). Ample
sunshine this morning already heating temps up to 82-88F while
dewpoints were 75-81F giving heat indices of 92-104F by 10 am. A
strong to severe MCS over east central WI into northern Lake MI
and heading ESE into nw lower MI will mostly pass by north and
northeast of ILX`s CWA. However an outflow boundary from this MCS
will push from southern WI into northern IL this afternoon and
could develop isolated showers/thunderstorms north of I-74. NAM is
dry south of I-74 today, though HRRR and RAP model also shows some
spotty convection appearing over sw CWA during this afternoon and
will need to watch for this possible development. Kept areas sw of
I-74 dry rest of today for now due to strong cap in place from 595
dm 500 mb heights over central IL and 700 mb temps of 10-13C.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 237 AM CDT Thu Jul 21 2016

Initial concern in the short term is around fog for early this
morning. Winds are light and variable, with skies remaining mostly
clear. Locally dense fog has formed in our eastern areas near
Danville and Paris already, with another area of less dense fog
farther south from Flora to Robinson and Lawrenceville. Dewpoints
depressions range from 0 to 3 degrees across the board. See enough
support to continue mention of fog through just after sunrise, but
confidence not high on how much dense fog will occur.

Next concern surrounds thunderstorm chances over the next 24 hours.
The latest Day 1 QPF forecast from WPC expanded rainfall amounts
from northern IL into central IL, with 1.20" of rain as far south as
Peoria for the time frame between 7 am today and 7 am Friday. Radar
analysis shows an active MCS in MN progressing to the E-SE, and most
high resolution models progress that toward our forecast area later
today. Some dissipate the line more than others, but it appears
there is enough support for some storm activity to make it all the
way to central IL either late this morning or early afternoon.
Therefore, we added some precip chances to today`s forecast. Most
coverage today should be isolated in nature.

However, another complex of storms is projected to develop north of
our area tonight and progress southward into our CWA. Current model
trends show the higher potential being after 08z/3am tonight, and
have expanded and increase PoPs after midnight into the chance
category from Peoria and northward.

The other concern today is how much any convection and cloud cover
will hold down high temperatures. Guidance numbers were going about3-
4 degrees less hot than our previous forecast. Have not cut our
forecast quite that drastically, but did lower todays highs a degree
or two across the north and east where storm potential appears
higher. Expect that even filtered sunshine under this strong of an
upper ridge and warm low-mid layers should be enough to push highs
into the low 90s.

Lows tonight should be held up in the mid 70s by the very moist
boundary layer, with patchy fog possible again.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 237 AM CDT Thu Jul 21 2016

Primary concern remains the intense heat. Will extend the Excessive
Heat Warning into Sunday for areas from about Rushville-Danville
southward, as the front continues to slow down a bit and is more
likely to pass through Sunday evening. A little more in the way of
clouds and scattered storms, which will keep the heat index more in
the 105-110 range vs. the 109-112 on Friday and Saturday, but 850 mb
temperatures are still around 24C at that range, and lesser clouds
than expected could easily bump the heat index up a few notches.

That being said, Friday could be a bit tricky with the heat,
primarily over the northern CWA. Most of the model guidance
continues to favor an MCS track over the central and northern Great
Lakes, with some westward development/retrograding along a frontal
boundary or leftover convective boundaries. The Canadian and ECMWF
are more in line with that philosophy, along with the NAM to a
lesser extent. The GFS is much further southeast and aggressive,
given its CAPE`s in the vicinity of 6000 J/kg on the Peoria forecast
sounding, but 700 mb temps near 12C suggest a significant cap. Have
added some 30% PoP`s along and north of I-74 during the day, with
mainly isolated storms at best elsewhere. Should the clouds be more
widespread, highs in the mid 90s would be tough to attain, but the
tropical dew points would still be present unless a cold pool from
the northern storms tracks into the area.

As the weekend begins, the upper flow becomes more west-east and
subtle ripples may serve as a focus for some convection, addressed
with the previous scattered PoP`s around 30% Saturday. The incoming
front on Sunday may prove to be more of a catalyst with the rain
chances, though.

Much quieter as the new work week begins, and temperatures return
closer to normal as high pressure drifts through the region.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1250 PM CDT Thu Jul 21 2016

VFR conditions generally expected across the central IL airports
next 24 hours. The exception will be isolated convection possible
near BMI and CMI this afternoon. Some models show more convection
developing and tracking se into northeast IL and central IN late
tonight into friday morning and close to I-74. If slight chance
of convection occurring then could get brief MVFR
ceilings/visibilites with the rain. Also MVFR visibilities of 4-5
miles possible with light fog/haze from 09-14Z Friday similar to
early this morning due to very moist tropical airmass in place
with dewpoints in upper 70s to around 80F. Winds remain fairly
light next 24 hours. SSW winds of 6-10 kts this afternoon to
become south 3-6 kts after sunset and sw 7-10 kts after 14Z
Friday.


&&

.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
SHORT TERM...Shimon
LONG TERM...Geelhart
AVIATION...07



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