Area Forecast Discussion
Issued by NWS Central Illinois

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271
FXUS63 KILX 060435
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1135 PM CDT THU MAY 5 2016

.UPDATE...
Issued at 824 PM CDT Thu May 5 2016

As high pressure remains over the region, fair weather will
continue tonight as skies clear out following afternoon and
evening cumulus cloud cover. Winds will decrease, becoming nearly
calm as weak pressure gradients remain over the area. The only
cloud cover feature of note through tomorrow is a disturbance
moving out of the north which will move into central IL early in
the morning, bringing scattered mid and high level cloud cover.
Lows will reach the mid 40s tonight, only a few degrees warmer
than last night, as a result of good radiational cooling with
clear skies and light winds. The air mass continues to warm aloft,
and will be around 10 degrees F warmer by morning than 24 hours
prior. No significant updates needed tonight, with only a few
tweaks based on short term cloud cover, temperature, and wind
trends.

&&

.SHORT TERM...(Tonight)
ISSUED AT 257 PM CDT Thu May 5 2016

Robust Cu-field across east-central and southeast Illinois this
afternoon will quickly dissipate by sunset, leaving behind clear
skies across the board this evening.  Meanwhile, a weak disturbance
currently over Lake Superior will drop southward, spreading a few
mid clouds into the area toward dawn Friday.  End result will be
mostly clear and cool conditions tonight, with lows dropping into
the lower to middle 40s.

.LONG TERM...(Friday through Thursday)
ISSUED AT 257 PM CDT Thu May 5 2016

The Omega-block pattern across the lower 48 will shift slightly
eastward on Friday. That will lead to a warm and sunny day as
the surface and upper ridges shift east closer to Illinois. Highs
will climb to around 80 west of the Illinois river, with mid to
upper 70s in the remainder of the area. There could even be some
lower 70s along the Indiana border, where cooler air will linger
near the upper low.

The blocking pattern will break down this weekend, as the eastern
trough is lifted toward a lobe of Canadian low pressure advancing
into the Great Lakes. A surface low will progress across southern
Canada, dragging a cold front south into Illinois on Saturday.
Showers and a few storms will remain post-frontal, keeping Saturday
morning primarily dry. A few showers could approach the I-74
corridor before noon, but better chances for precip will come Sat
afternoon and evening as the cold front reaches as far south as I-70
by 00z/7pm Sat eve. The front should drop south of our counties by
Sunday morning, but since the precip triggers will remain post-
frontal, much of central IL will remain under the threat of showers
and storms Sunday morning. Decreasing coverage of precip is
indicated for Sunday afternoon in the 12z versions of the ECMWF,
NAM, GFS and Canadian models, so at least some of Mother`s Day
could end up dry.

Beyond that, model differences develop with respect to when the rain
and storm chances will increase again. The cold front will return
northward as a warm front on Monday with precip primarily initiating
again north of the front. The GFS is showing a sizable break in the
rain from Sunday afternoon through early Monday morning, while the
ECMWF and Canadian activate storms after midnight Sunday
night between I-70 and I-74.

Shower and storm chances will increase to likely from west to east
Monday and Monday evening as our area sees the warm sector arrive.
Although overall severe potential appears to remain low, the main
window of stronger storms based on GFS timing looks to be Monday
evening as the warm front lifts and stalls near I-74. The ECMWF and
Canadian appear to weaken the front and lift it farther north of our
area, which still supports rain/storms, but a lower severe threat.

There is agreement in the farther extended that the upper level
trough over the Plains will eject a surface low east across Illinois
late Tuesday and Tuesday night. That prompted a continuation of
likely PoPs on Tuesday north of Springfield to Mattoon, and
Tuesday night east of I-57 as the low departs and a cold front
progresses to near of I-70 by 12z/7am Wednesday.

In the wake of that low, Wednesday is showing the best potential for
a break in the rain, especially north of I-70 and the cold front.
The GFS actually is now indicating dry conditions continuing through
Thursday as a second wave of low pressure passes just south of our
forecast area. The ECMWF takes that second low toward central IL,
and brings additional rain chances Wed night and Thursday. So chance
PoPs were left in place for the latter extended forecast.

As for temperature trends, Friday will be the warmest day of the
next week, with Saturday still in the mid to upper 70s before rain
develops. Sunday will be cooler in the mid 60s behind the cold
front. Depending on the progression of the warm front northward on
Monday, highs could reach back into the low to mid 70s Monday, with
mid to upper 70s Tuesday. The GFS influence of cooler air arriving
on Wed into Thursday shows highs trending downward, but still in the
70s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1135 PM CDT Thu May 5 2016

VFR conditions will prevail through the 06Z TAF period. Skies will
be mostly clear overnight then scattered cloud cover around 10
kft will spread across the area from the north starting around
10Z. Winds light and variable overnight becoming west 8-12 kts
with gusts 15 to 18 kts by 18Z. Winds and gusts decreasing after
02Z to 5-8 kts.

&&

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

&&

$$

UPDATE...Onton
SHORT TERM...Barnes
LONG TERM...Shimon
AVIATION...Onton



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