Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 220208
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
908 PM CDT Sun May 21 2017

.UPDATE...
Issued at 900 PM CDT Sun May 21 2017

A persistent band of strato-cumulus clouds will continue to erode
from south to north as the upper low in N Minnesota lifts farther
away into Canada. Satellite loops confirm that scenario, as the
back edge of the clouds continues to make progress eastward from
central Iowa and far northeast Missouri. The timing of cloud
dissipation and/or departure look to be close to our forecast
database, so only minor adjustments were needed there.

Once the skies clear out, and winds remain light and variable,
radiational cooling will increase. Another chilly night is on tap
as low temps bottom out in the mid 40s toward Galesburg, with
upper 40s to near 50 toward Lawrenceville.

The next wave of rain chances still looks on track for tomorrow
afternoon and overnight. No changes were needed for that timing
with the evening update.

&&

.SHORT TERM...(This evening through Monday)
ISSUED AT 230 PM CDT Sun May 21 2017

Large area of stratocumulus continues to swing eastward across the
state this afternoon. Skies will clear from south to north this
evening with loss of daytime heating, and the upper low currently
over northern Minnesota edges northward.

A piece of energy from an upper low over northern Saskatchewan
tonight, and will swing southeast around the Minnesota low on
Monday. Showers and a few thunderstorms will begin moving into the
Illinois River valley early in the afternoon and reach the I-55
corridor toward late afternoon. Expect temperatures to reach the
70s with a southwest wind flow in place.

.LONG TERM...(Monday night through Sunday)
ISSUED AT 230 PM CDT Sun May 21 2017

A piece of the Minnesota low will break off and slowly settle into
the the Midwest beginning Monday night, as the main low is
shunted off to the northeast. By late Wednesday afternoon, it is
only expected to be in central Illinois, before getting a stronger
nudge eastward by a wave moving into Montana and Idaho. With steep
lapse rates underneath the low, numerous showers are expected
Tuesday into Wednesday, along with a few thunderstorms. Without a
deep fetch of moisture much of this time, rainfall amounts should
generally be less than half an inch.

Late in the week, the upper flow begins to shift to the southwest,
bringing warmer air back into parts of the region. There still
remains some significant differences between the GFS and ECMWF
models with a series of fast-moving waves beginning on Friday.
While not as glaring of a difference on Friday, the GFS starts to
exhibit some feedback issues Saturday which drifts its solution
off course. Will limit PoP`s to about 30-40% due to the
differences.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 652 PM CDT Sun May 21 2017

An expansive area of strato-cumulus will begin to dissipate with
the passage of sunset this evening. Southern TAF sites will clear
the soonest, with SPI scattering our during the first hour or so of
this TAF period. PIA and BMI will clear out toward midnight/05Z,
with DEC and CMI clearing sometime around mid-evening.

Brisk west winds early this evening will quickly weaken after
sunset. Wind directions will gradually shift to the southwest
later tonight and remain SW tomorrow. Wind speeds will increase to
12-15kt as a frontal boundary approaches western Illinois.

VFR clouds and visibility will prevail throughout this TAF period
as the upper low in the western Great Lakes loses its grip on our
weather.


&&

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

$$

UPDATE...Shimon
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Shimon


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