Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 222000
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
300 PM CDT THU SEP 22 2016

.SHORT TERM...(This evening through Friday)
ISSUED AT 259 PM CDT Thu Sep 22 2016

Unseasonably warm conditions will continue in the short term as
upper level ridging holds over much of the Midwest and a nearly
stationary front remains from eastern Nebraska across central Iowa
into southern WI.

Spotty showers across southeast Iowa this afternoon are trying to
work their way into northwest IL, but plenty of mid-level dry air
should result in rapid dissipation. Wouldn`t be surprised to see a
few sprinkles make it through toward Galesburg early this evening,
but not enough for measurable rainfall. Only the GFS and SREF are
allowing for light rainfall overnight, with the other models
continuing dry weather for us and keeping the focus on waterlogged
areas of NE Iowa and SW Wisconsin overnight.

The upper level ridge is expected to strengthen a bit over us on
Friday which will keep the synoptic front to our north. This will
result in another very warm day with highs around 90 in much of
central IL. The exception will be in areas roughly north of I-74
where a few more clouds will keep temps in the mid 80s. With the
front to our north and only a light south wind/very weak convergence
will keep the rain chances out of the forecast through Friday.

&&

.LONG TERM...(Friday night through Thursday)
ISSUED AT 259 PM CDT Thu Sep 22 2016

The 12z models have kept a similar solution for Friday night
through Sunday, with warm and humid conditions in Illinois under
upper level ridging. A long wave trough over the central Rockies on
Friday with lift NE toward Canada this weekend. This will cause a
sharpening of the ridge across Illinois. Southwest flow aloft will
increase as a result, bringing a continued flow of low level warmth
and humidity. Highs will likely maintain in the mid 80s to around 90
Saturday and Sunday, with overnight lows in the mid to upper 60s.
Dewpoints will linger in the mid to upper 60s, creating a muggy
weekend.

Precip chances for the first half of the weekend look to remain
primarily north of Illinois, closer to a warm frontal boundary.
However, there is continued support in the ECMWF, GFS and NAM that a
cold front will push across IL on Sunday or Sunday evening. The NAM
is the fastest, pushing it to the Indiana border by 7 pm
Sunday/00z Mon. The GFS and ECMWF are next in timing, indicating the
front should reach the Indiana border shortly after 06z/1am Monday.
The Canadian Global halts the front near the Mississippi river in
response to cutting off the Plains upper low and drifting it south
toward Oklahoma on Monday. We held with the consensus of a frontal
passage later on Sunday into Sunday evening, with increasing chances
of storms Sunday afternoon west of I-57. Storm chances look to
continue in the post frontal airmass through Monday, as the upper
level trough axis finally progresses across the area.

A cooler and less humid air mass will arrive for Monday, and linger
through Thursday. While we see slight chances of diurnal showers
each day due to steep mid level lapse rates, most areas should
remain dry. High temps from Monday to Thursday should be in the mid
70s, with lows in the mid 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1251 PM CDT Thu Sep 22 2016

Mainly thin cirrus clouds were moving east-southeast into central
and eastern Illinois early this afternoon from the remnants of
early morning thunderstorms back in northern Iowa. At the surface
the main synoptic front extended from the central Plains across
central Iowa into southern WI, with an outflow boundary from
southwest WI into eastern IA. These boundaries are expected to
stay north of the region today so a southwest wind should prevail.
A little more mixing than previously anticipated will allow winds
to stay at or a bit above 10kts in central/eastern IL the rest of
the afternoon.

Weak wind fields and very few clouds this evening should lead to
rapid decoupling of the low levels of the atmosphere and pretty
strong inversion. The RAP and CONSShort point to light fog
developing toward daybreak, so included MVFR visibility for the
TAF sites along the I-74 corridor. A lower crossover temperature
at SPI and DEC should keep light fog from forming.


&&

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

$$

SHORT TERM...Miller
LONG TERM...Shimon
AVIATION...Miller


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