Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 172320

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
620 PM CDT Wed Oct 17 2018

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 341 PM CDT Wed Oct 17 2018

Main concern for tonight will be on overnight low temperatures and
frost potential. As of 2000 UTC, strong area of surface high
pressure was located near across west-central Iowa and will continue
to slide southeastward into central Illinois by early Thursday
morning. Light/variable winds are likely in the vicinity of this
surface anticyclone, and this factor combined with a clear or mostly
clear sky should ideal conditions for radiational cooling. One
caveat is the potential for cirrus across far southern sections of
the forecast area this evening and early overnight. Current
thoughts are that this cirrus should be pretty thin as evidenced
by upstream satellite imagery. In addition, models RH plots at 300
hPa suggest this area of cirrus should move off to the southeast
of the area by 0900 UTC. Because of these factors, no change made
to the frost advisory tonight across far southern sections of the
forecast area. Frost was not mentioned in areas further to the
north because these locations have already observed a widespread
freeze or frost.

A mostly sunny sky is expected on Thursday with high temperatures
forecast to be in the upper 50s to mid 60s. Based on the large
diurnal temperature swing observed today, leaned at or above warmer
MAV guidance in most locations.


.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 341 PM CDT Wed Oct 17 2018

(Thursday Night - Saturday)

Lone rain chances in the extended forecast remain from late Thursday
night through Friday evening. Light rain is expected to focus across
southern sections of the area, with the highest chances on Friday
coincident with period of strongest low-level warm/moist advection
and mid/upper level forcing for ascent.

Temperatures for this period should continue to be below normal,
with the cooler of the two days on Friday due to increased cloud
cover and aforementioned precipitation chances. Highs on Friday
are forecast to be in the mid to upper 50s. Slightly warmer
conditions are expected to start off the weekend as highs reach
into the low 60s across central and southern sections of the area
ahead of a secondary cold front.

(Saturday Night - Next Wednesday)

Much colder air is likely behind this potent secondary cold front
Saturday night into Sunday. Temperatures are likely to be 10-20
degrees below normal night and day. The strength of this upcoming
airmass actually appears to be more impressive than a couple of days
ago, so a hard freeze is on the table for many, including those
locations that did not receive a hard freeze this past Monday.
Lowered minimum temperatures a couple of degrees from the previous
forecast, with most locations bottoming out in the upper 20s to near
the freezing mark.

Temperatures are expected to rebound heading into the next work week
as surface high pressure slides into the Ohio Valley. Some
oscillation in temperatures is likely as another cold front slides
through the mid-Mississippi Valley Monday night. Overall,
temperatures next week are expected to be near to slightly below
normal for mid/late October.



.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 601 PM CDT Wed Oct 17 2018

Steam fog may impact KSUS during the overnight and early morning
hours from 1000-1300z, resulting in MVFR flight conditions/
visibilities. The occurrence is conditional recognizing a light
north-northeast wind could advect the fog from the Missouri River
into the terminal. Otherwise VFR flight conditions are expected
through the forecast period with high clouds across the southern
half of MO and IL tonight, and clear to few high clouds on
Thursday. Surface high pressure will result in predominately light


VFR flight conditions are expected through the forecast period
with periodic high clouds tonight, and mostly clear skies on
Thursday. Surface high pressure will result in predominately light



MO...Frost Advisory from 1 AM to 8 AM CDT Thursday for Crawford MO-
     Iron MO-Madison MO-Reynolds MO-Saint Francois MO-Sainte
     Genevieve MO-Washington MO.

IL...Frost Advisory from 1 AM to 8 AM CDT Thursday for Randolph IL.



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