Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 290454
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1154 PM CDT THU JUL 28 2016

.UPDATE...
Issued at 906 PM CDT Thu Jul 28 2016

Latest short-range model guidance suggests that the bulk of the
shower/storm threat has ended for the forecast area tonight and
into Friday. Given the fact that diurnal instability is weakening,
the weak wave that boosted chances today is now pushing off to the
east, and radar trends are sharply drier in our vicinity, this
seems reasonable. Have updated forecast to go mostly dry into
midday Friday with this thinking in mind.

Other main concern is how extensive low clouds will be across the
area tonight as well as the fog potential. The former could have a
major impact on the latter. While the forecast area is mostly
clear at the moment, satellite loops suggest some low cloud cover
is beginning to bubble up, and this has shown up in a few local
surface observations. Expect this trend will likely continue,
especially across our north (closer to next wave and more
expansive low clouds), although short-range models are less
bullish now on clouds than they were earlier this evening. So,
expecting at least a fair portion of the night will be mostly
clear, and will keep patchy fog going.

Remainder of forecast is in good shape, with only minor tweaks
needed.

&&

.SHORT TERM...(This evening through Friday)
ISSUED AT 245 PM CDT Thu Jul 28 2016

A cool front moving southeast toward I-55 at mid afternoon will push
into thru eastern IL late today and stall out in southeast IL
tonight. Had a few reports of funnel clouds over central IL since
midday east of the IL river, with the most recent report near
Metamora. Isolated to scattered thunderstorms where over much of IL
in the tropical airmass over IL where dewpoints in the low to mid
70s and temps in the 80s. Most heat index readings were in the
upper 80s and lower 90s, though Springfield had heat index of
98F. LAPS CAPES ranged from 1500-3000 J/kg with highest readings
west of I-57. Isolated to scattered thunderstorms will gradually
diminish from west to east during tonight as instability weakens
and front pushes into southeast IL. Have patchy fog overnight
until mid morning Friday with light winds and moist low levels.
HRRR show more widespread fog over eastern IL with locally dense
fog possible. Lows overnight range from 65-70F with mildest
readings south of I-70. Highs Friday range from upper 70s nw of IL
river, to the mid 80s in southeast IL from I-70 south. Another
frontal boundary and a shortwave trof pushing southeast over
central IL on Friday to develop chances of thunderstorms and
carried 30-40%. SPC day2 outlook has a marginal risk (5%) along
and south of a Canton to Bloomington line on Friday where
instability will be higher.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 245 PM CDT Thu Jul 28 2016

Weak shortwave trof that will affect the area on Friday should start
to shift east of the forecast area Friday night. Still have POPs
going Friday night but it appears that most of any convection that
develops during the day Friday will be diurnal in nature and be out
of the area during the evening. After that, the frontal boundary
should push far enough to the south on Saturday to limit the rain
chances to far southern Illinois as weak high pressure settles in
from the northwest. Latest ECMWF looking drier with this fair
weather system for Saturday and Sunday with the return flow setting
up Sunday night along with POPs over southwest Illinois.

Upper level ridging is forecast to build over the region early next
week as a deep trof shifts eastward over the northern Rockies. This
should start the heat back up over the area with medium range models
showing varying solutions to how strongly the ridge builds north.
Unfortunately, as has been the case most of this Summer, the ridge
is rather flat and convection has no problem riding the northern
periphery of the ridge and then southeast into the Midwest at least
through the middle portion of the week. This will result in daily
chances for thunderstorms starting Sunday night just ahead of the
warm front, and for the remainder of the period as the model
consensus is rather conservative with any amplification of the
central U.S. ridge early next week. After our "cool-down" this
weekend, model guidance has most of the area back to or just above
90 Wednesday and Thursday of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1146 PM CDT Thu Jul 28 2016

Very tricky aviation weather forecast for the next several hours.
Skies across central Illinois are mostly clear at the moment, but
there area some patches of low end VFR and MVFR clouds floating
around. More widespread cloudiness exists upstream, as close as
the WI/IL border area, with VFR, MVFR, and IFR conditions all
represented. These clouds are ahead of an upper-level disturbance
that will help produce scattered thunderstorm across the area
tomorrow. Main concern until the more widespread cloudiness moves
in is if additional cloud cover will develop overhead and/or fog
becomes more widespread.

The short-range model guidance has overdone the low clouds/fog in
this airmass of late, and this may be the case again tonight.
Run-to-run consistency has not been good either tonight, with
guidance becoming cloudier/foggier one run, only to back off the
next hour. For now, have gone more optimistic than the current
guidance based on trends from recent nights. However, have still
carried periods of MVFR CIGS & local IFR VSBYS. Have conditions
improving diurnally tomorrow, with a chance of thunderstorms
developing by afternoon.

&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

UPDATE...Bak
SHORT TERM...07
LONG TERM...Smith
AVIATION...Bak


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