Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271755
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1255 PM CDT Sat May 27 2017

.UPDATE...
Issued at 1103 AM CDT Sat May 27 2017

Late night fog has lifted into a low overcast across central
Illinois this morning. 15z/10am satellite imagery is showing the
cloud cover beginning to thin...and this trend will continue over
the next couple of hours. Am expecting skies to become partly to
mostly sunny by midday...with afternoon high temperatures ranging
from the middle 70s far north around Galesburg to the middle 80s
south of I-70. Widely scattered thunderstorms may develop across
the far S/SE CWA by late afternoon: however, the bulk of the
convection will hold off until this evening.

&&

.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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1255 PM CDT Sat May 27 2017

Overcast conditions persist at KCMI early this afternoon: however,
skies have become mostly sunny at the remaining terminals. Based
on satellite trends, have lingered MVFR ceilings at KCMI through
20z. After that, attention will turn to developing convection
across Missouri. With synoptic boundary well to the south across
Missouri into southern Illinois, it is becoming apparent that the
bulk of the convection will remain south of central Illinois this
evening. As a result, have removed all mention of thunder at KPIA
and KBMI. Further south at the I-72 terminals, have gone with a
period of VCTS between 01z and 06z at KSPI/KDEC and between 04z
and 10z at KCMI. High-res models are suggesting low clouds/fog
will re-develop late tonight once the convection ends, so have
introduced MVFR ceilings at all sites after 09z through midday
Sunday.

&&

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

$$

UPDATE...Barnes
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Barnes



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