Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271139
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
539 AM CST Mon Feb 27 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 227 AM CST Mon Feb 27 2017

Generally neutral flow will be in place across central and southeast
Illinois today, both at the surface and aloft. This scenario is
supportive of quiet weather. Southerly low-level flow will continue
to push warmer air into the area, with most locations expected to
top out in the 50s.

Things start to turn more active by tonight. A vigorous upper-level
trof is currently digging down the west coast of the lower 48, and a
lead piece of energy will eject toward the Midwest from this trof by
tonight. Much of the evening is likely to be dry, as the local
airmass will take some time to moisten. Strong isentropic ascent, a
40-50 kt low-level jet, and at least a few hundred j/kg of elevated
CAPE will begin overspreading the area by midnight. This should
result in the development of numerous showers and scattered
thunderstorms for the overnight hours. The continued southerly winds
and expanding cloud cover will help keep overnight lows in the 40s,
which is about what high temperatures should be this time of year.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 227 AM CST Mon Feb 27 2017

Digging longwave trough west of the Rockies late tonight will reach
the Plains Tuesday evening, and will cross the Mississippi Valley
Wednesday afternoon. Emergence of this feature in New Mexico will
help develop a surface low near the Oklahoma Panhandle Tuesday
morning, which will ride northeast along the frontal boundary from
today`s system. This will help drag the front through the area late
Tuesday night or early Wednesday morning. The GFS is on the faster
end of the model guidance with this feature and has the front
through the southeast CWA by 6 am Wednesday, with the remaining
model consensus exiting the CWA a bit later Wednesday morning.
Favored more of a NAM/ECMWF blend with the speed of this system.

Latest SPC outlook for Tuesday/Tuesday night has expanded the slight
risk of severe weather over nearly all the forecast area. The NAM
and the tail end of the high-res ARW/NMM suggest convection
developing along the front just northwest of the Illinois River by
very late Tuesday afternoon, pushing southeast during the evening,
when CAPE`s should be around 1000 J/kg or so. Bulk shear values
remain very high (60-80 knots from 0-6km) and storm relative
helicity values reach 300-400 m2/s2 at times into the evening.
Threat for strong/severe storms will shift southeast overnight, and
areas from about I-55 west will likely only see light showers after
midnight.

Later in the week, a clipper system is still progged to track
southeast into the Midwest Thursday afternoon. The GFS is farthest
north with this feature, but low chances of light rain remain
warranted across primarily the northern and eastern CWA, mixing with
some light snow east of I-57 before ending in the evening.

Temperature-wise, warmest day of the week will be tomorrow, with
some lower 70s possible over the southwest CWA and mid-upper 60s
elsewhere. The colder weather accompanying the longwave trough
Thursday night and Friday still appears to be short lived, as the
upper flow quickly becomes zonal during the weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 535 AM CST Mon Feb 27 2017

Will have to watch for some brief reductions in vsbys in fog over
the next several hours, otherwise, VFR conditions are expected
into this evening. Forecast soundings do indicate some moisture
around 3000 to 3500 feet lingers into this afternoon so will
continue to carry a scattered group from 3500 to 4000 feet
during this time frame. Later tonight, a weather system will
bring the threat for showers into the region along with a
deterioration in cigs and vsbys to MVFR/IFR after 03z. Models
indicating some rather steep mid level lapse rates in place
across the area after 04z, as a result, we may see some isold
TSRA during the early morning hours, so will include a VCTS group
late tonight. Surface winds will be light southerly this morning
at less than 10 kts and then begin to back into a southeasterly
direction this afternoon with speeds around 10kts. Southeast
winds at 10 to 15 kts can be expected tonight.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Bak
LONG TERM...Geelhart
AVIATION...Smith


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