687 
fxus63 kilx 220501 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
1201 am CDT Monday Mar 22 2010 


Discussion... 
issued 830 PM CDT sun Mar 21 2010 


Light rain has pretty much halted its northwestward progress along a 
line Pittsfield-Lincoln-north of Rantoul. Cloud tops are warming 
over central Illinois accompanied by rising ceilings and decreasing 
reflectivities on radar. A significant shortwave rotating around the 
deep closed low over Mississippi is pushing northward into the lower 
Ohio Valley...and this feature is expected to cause another upswing 
in precipitation in southeastern Illinois mainly to the southeast of 
Interstate 70 later tonight. Further north...precipitation from 
Springfield/Taylorville toward Danville should continue to shrink. 
Although temperatures in the northwest have a ways to go to hit the 
forecast mins...clouds are thinning and dewpoints immediately 
upstream are in the upper 20s/lower 30s. So lower 30s mins still 
look attainable. All of the above is captured well in the current 
forecast and do not anticipate any major changes. 


04 
&& 


Aviation... 
issued 1201 am CDT Monday Mar 22 2010 


Upper low now on MS/Alabama line and moving eastward. Sig shtwv has rotated 
cyclonically around its northern quadrant and is resulting in an area of 
significantly cooling cloud tops on infrared imagery...with an accompanying 
upswing in precipitation over portions of southern/southeastern Illinois. Expect this activity 
to remain just S of the cntl Illinois taf site...but its northern fringe may 
push another rain area westward toward cmi around sunrise as suggested by 
the latest NAM/RUC models. After the current showers/sprinkles die out 
at spi/Dec/cmi by 08z...will bring in another batch of -ra for cmi in 
the 10z-14z timeframe. As steady northerly/northwesterly winds continue to funnel in dry 
low level air...expct ceilings to remain above 3k feet. The same general conds 
will then continue through Monday with northerly surface winds 12-18 knots plus gusts and a 
general clearing trend NW-se. The surface pressure gradient will be relaxing around 
00z as the weak hi pressure ridge moves through. 


04 
&& 


Previous discussion... 
issued 150 PM CDT sun Mar 21 2010 


Nearly vertically stacked low centered over Arkansas early this 
afternoon...with warm front extending northeast along the Ohio 
River. Widespread showers continue to pinwheel around the 
periphery...currently covering about the southeast third of 
Illinois...although a dry slot was working its way through the 
southeast County Warning Area. A raw northeast wind was gusting to over 30 miles per hour in a 
few areas...with a weak area of high pressure from Omaha northeast 
to northern lower Michigan helping to tighten the pressure gradient. 


The short term forecast concern involves the continued effects of 
this system through Monday. In the longer term...rain chances 
Thursday night and next weekend are the challenges. 


Short term...tonight through Wednesday... 
models in good agreement with the Arkansas low moving northeast into 
the Appalachians through Monday. There will be a fairly sharp cutoff 
in the northwest extent of the rain shield during this period...with 
areas northwest of I-55 expected to remain mostly dry. Will continue 
with categorical probability of precipitation across the southeast County Warning Area tonight...and likely 
probability of precipitation in a smaller portion of the area on Monday. A fairly decent 
clearing trend is expected in the meantime across the northwest County Warning Area. 


Narrow axis of high pressure to push across the state on Tuesday...as a 
shortwave zips along the Canadian border. Associated frontal 
boundary is expected to push through the area Tuesday night...although 
moisture will be meager and the frontal passage should largely be 
dry. Overall...dry weather is expected for the middle of the week. 


Long term...Thursday through Sunday... 
a couple of storm systems of interest in the extended period. The 
first one is a shortwave/weak closed low which will push across the 
southern rockies early this week...phasing with the northern stream 
flow across the Midwest Thursday night and Friday. Main storm track 
is expected to remain south of Illinois...but as with the current 
system...should spread some rain north of the low track along a warm 
frontal boundary. Currently have only slight chances on Thursday 
across the southern County Warning Area...but will need to watch trends for rain 
potentially moving into the area during the afternoon. Main chances 
expected Thursday night...and may linger into early Friday if the 
GFS has its way. 


The second shortwave will be digging across the central and northern 
rockies early in the weekend...swinging east into the Mississippi 
Valley on Sunday. The GFS and European model (ecmwf) are in reasonable agreement with 
the upper features...although the GFS is a bit stronger. 
Consequently...it is also more aggressive with intensifying the 
surface cyclone. Meanwhile...the European model (ecmwf) has more of a straight 
frontal passage. Similar discrepancies were noted with the current 
system when it was still at this longer range in the forecast. Will 
begin to spread chance probability of precipitation into the western County Warning Area Saturday 
night...and across the entire area on Sunday. Will carry only slight 
chances Sunday night...although a GFS solution would end up 
requiring an increase in probability of precipitation. 


Geelhart 
&& 


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


$$