Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 270745
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
245 AM CDT Sat May 27 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 245 AM CDT Sat May 27 2017

Complicated forecast scenario in the short term, mainly involving
potential bow echo/MCS tonight.

2 am surface map showing low pressure centered just north of
Indianapolis, with a trailing frontal boundary extending southwest
roughly along I-70 and linking to another low over southeast
Colorado. Cold-air advection behind the system is weak, and dew
points are still in the upper 50s over the northwest CWA with mid
60s to the south. The front should settle toward the Ohio River
this morning, before pulling back north as the Colorado low moves
into eastern Kansas. Meanwhile, an MCS currently over
Nebraska/northern Kansas will be marching eastward. Much of the
model guidance keeps this MCS intact and west of the forecast area
through this afternoon. However, several of the higher-resolution
models project it to start taking a more southeast track by late
afternoon, either completely missing the CWA or having only part
of the forecast area clipped by the northern end of the bow this
evening. It should be noted that only the HRRR has the current MCS
in the correct position, with the others showing a more northern
bias. Although the highest CAPE`s will be south of I-70, both the
NAM and GFS show CAPE`s up to around 1500 J/kg by late afternoon
over even the northern CWA.

SPC Day1 outlook remains similar to the old Day2, basically
featuring an enhanced risk of severe weather I-72 south and a
slight risk as far north as I-74. Timing-wise, the severe weather
threat would mainly be during the evening hours. That far into the
bow echo`s life cycle, stronger winds would be our main concern,
but large hail and isolated tornadoes would also be possible.


&&

.LONG TERM...(Sunday through Friday)
ISSUED AT 245 AM CDT Sat May 27 2017

Upper level pattern over the coming week is generally one with a
predominant broad trough/closed low covering the Great Lakes into
the northern Plains. This will keep temperatures fairly uniform,
mainly mid-upper 70s through the week. Periodic waves will rotate
around the upper low, producing a few showers at times. Best
chances will be Sunday, as the weekend storm system finally moves
through, and toward Friday, although model agreement is less than
stellar in this regard. Most of the period between, PoP`s are
generally limited to slight chances.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1225 AM CDT Sat May 27 2017

Main challenge in the short term will be coverage of IFR
ceilings/visibilities. Area of stratus below 1,000 feet currently
extends from about KGBG-KDNV and is settling southward. HRRR
guidance suggests this should cover most of central Illinois by
about 09-10Z, with visibilities down to around a mile or two.
Improvement is expected from the northeast early Saturday morning.
Later in the period, focus shifts to a large area of
showers/storms that will be approaching from the west. Some
uncertainty with the exact track, with some of the higher-
resolution guidance suggesting a track that would bypass central
Illinois. As such, will limit convective mention to VCTS for now.


&&

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

$$

SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Geelhart



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