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fxus63 kilx 290014 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
714 PM CDT Thursday Aug 28 2008 


Discussion... 
issued 714 PM CDT Thursday Aug 28 2008 


Did a quick update to the grids for likely storms this evening in 
the SW third of the County Warning Area. Added mention of severe storms with hail 
and winds for the Severe Thunderstorm Watch area as well. Watch is 
in effect until 06z. The strongest portion of the Bow echo appears 
like it may clip Scott County. Farther to the north and east...the 
severe threat will be of a scattered nature and primarily for 
large hail. Less organized downbursts will still be possible in 
that area as well. 


Updated zones and grids are already available. 


Shimon 
&& 


Aviation... 
issued 636 PM CDT Thursday Aug 28 2008...for the 00z tafs 


Storms are developing in our West County warning area...ahead of the main mesoscale convective system in north 
MO. The storm tracks appear to take most of the activity south of 
Lincoln...with spi in the path of the strongest storms. Have hit 
spi the hardest with IFR visible to 1sm...+tsra and gusty winds between 
00z and 03z. Dec may see some of that...but areas north and east of spi 
will see more scattered storms and a bit weaker. May be seeing a 
severe storm watch soon for our SW areas as well. 


Did not extend the thunderstorms in the vicinity in the tafs much beyond 06z...but may need 
to adjust as the line progresses into our County Warning Area. 


Fog is expected to become locally dense in the wake of these 
storms. Cmi will have a chance for vlifr visible again...since the 
lower dewpoint air is lagging well behind this line of storms. 
Dewpoints will likely remain around 70 in much of the area through 
morning. Will keep at least IFR fog in a tempo for all sites. 


Shimon 
&& 


Previous discussion... 
issued 300 PM CDT Thursday Aug 28 2008 


Short term...tonight through Sunday... 
mesoscale convective system that moved across central Illinois earlier today has left a 
modified airmass that should preclude any meaningful convection into 
the early evening hours. The western edge of this bubble of 
relatively stable air is recovering over northeastern Missouri... 
and this process should continue eastward into western Illinois 
through 00z until the sun begins to go down. Upstream airmass over 
northern Missouri and northeast Kansas is quite unstable near the 
cold front that extends from central Iowa to just northwest of 
Topeka. Healthy elevated convection is increasing north of the front 
over southeast Nebraska...and expect further development of a 
surface-based variety across northern Missouri. Some chance that our 
airmass may recover sufficiently to support a hail/wind threat in 
the west as the developing storms move eastward along the southern 
edge of the upper jet. Will hold off on likely probability of precipitation due to questions 
regarding areal coverage...but will still have healthy chance probability of precipitation 
over the west/southwest. 


The cold front should progress toward the Illinois River valley by 
midnight with a reduction in precipitation in its wake. Will 
therefore take probability of precipitation down to slight chance after 06z in the 
northwest. As the front makes it into the southeast by 12z Friday...it 
will become increasingly separated from its associated upper trough 
that will be moving into the eastern Great Lakes. It should 
therefore slow down and pose at least a chance of additional 
precipitation southeast of Interstate 70 for the morning and early 
afternoon hours. Forecast soundings over that area show cape values 
of 2000-2500 j/kg by 18z before the drier air pushes completely 
through...so will maintain chance probability of precipitation down there into early 
afternoon. 


Remainder of short term period Friday night through Sunday should be 
mainly clear and dry as high pressure now over the plains comes east 
and Parks across the Midwest. 


Long term...Monday through Thursday... 
Monday and Tuesday will continue to be dry with a warming trend as 
high pressure remains anchored from the Great Lakes southwestward 
into the Central Plains. The GFS and European model (ecmwf) models both indicate a 
Continental U.S. Upper pattern featuring a trough-West Ridge-east which will 
aid in warming highs into the lower 90s...especially in southeastern 
Illinois. 


By Wednesday...the western trough will begin to move northeast into 
south-central Canada and drive the next cold front into the Midwest. 
By then...the remains of Gustav will also be moving north toward 
Arkansas. Like yesterday...the European model (ecmwf) depiction of the track of 
Gustav fits reasonably well the the latest NHC projected track. In 
any event...a complicated situation will evolve with a possible 
interaction between the cold front and the deep tropical moisture 
from the remains of Gustav. Predictability is still rather poor this 
far in advance...but will raise probability of precipitation into the slight chance to 
chance categories Wednesday and Thursday. 


04 


&& 


Ilx watches/warnings/advisories... 
none. 
&& 


$$