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Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
723 am CDT Monday Mar 15 2010 


Discussion... 
/214 am CDT Monday Mar 15 2010/ 


While the light rain and drizzle finally appear to have come to an 
end...the cloud trends are now the tough part of this forecast. 
Ramifications where the clouds persist vs. Not are big...evident in 
the spread of high temperatures recorded yesterday from northern MO 
through eastern Iowa into WI. A sizeable wedge of clearing is currently 
spreading southward across eastern Iowa and northwest Illinois. Current trends would 
suggest this will continue south southwestward into eastern MO this 
morning. However there are also indications that stratrocu will 
redevelop late morning where there is any clearing...and this 
seems reasonable given the weak cyclonic flow present across the 
area. Temperatures will certainly be warmer than yesterday. At this time 
have shaded most of the MO region expect the Eastern Ozarks towards 
the warmer met MOS. I wish I could say the problems with the 
clouds will go away tonight but portions of the region...most 
likely from western Illinois into southeast MO will still have quite a bit of 
cloudiness at sunset and these clouds will gradually clear southward. 
Fewer issues appear on tap for Tuesday. Provided the NAM relative humidity fields 
are correct...which I have followed...partly cloudy skies are 
expected with above average temperatures in the upper 50s and 
maybe even pushing 60. 


The next northwest flow system is still on track to impact the region 
Tuesday night into Wednesday. The models are beginning to come 
into better agreement with an upper low center moving southward somewhere 
from eastern Kansas into western MO late Tuesday night. If the models maintain 
this location and it is indeed correct...then the extent of probability of precipitation 
in the current forecast are probably a bit overdone...as the 
greatest chance would probably be across western and central MO where 
the strongest qg forcing is prognosticated. I'm a bit reluctant to trim 
back the already low probability of precipitation at this time...and will maintain a low chance of 
showers with this forecast. After this system The Heights aloft 
will rise and low level flow will gradually become more southwesterly. In 
response a good warm-up is still on track for the later part of 
the week with highs into the 60s. 


Glass 


&& 


Aviation... 
/559 am CDT Monday Mar 15 2010/ 


Tricky cloud forecast today with north-northeasterly low level winds bringing 
drier air southwestward through portions of northestern MO west central Illinois SW into central 
MO. Fog has developed in uin due to the clear sky early this morning. 
This fog will dissipate later this morning and it appears that most 
of the stratus cloudiness will remain west of uin this morning. Stratus 
clouds have advected into cou but drier air from the NE may erode 
this quickly this morning. Stl/sus is on the western edge of a cloud mass 
over east central Illinois...southern Illinois and southeastern MO but this cloud cover is not 
as low at 2500-4000 feet. Leaned toward the more optimistic NAM 
model relative humidity...cloud forecast later today and tgt. Forecast scattered low level 
clouds in uin and cou this afternoon and tgt...with a broken VFR ceiling 
in stl/sus until 12z Tuesday then scattering out. Should be scattered-broken 
diurnal stratocumulus clouds developing in the clear areas late 
this morning with ample low level moisture present. North-northwesterly surface winds 
will continue this forecast period as the surface ridge over the northern 
rockies and northern plains builds slowly southeastward. 


Specifics for kstl...do not think the lower level stratus clouds 
over portions of northestern and central MO will make it into stl this morning 
but stratocumulus clouds from Illinois may continue to move through the area 
with ceilings around 3000 feet. More diurnal stratocumulus clouds 
should develop late this morning and this afternoon with ceilings around 
3500 feet expected. This cloud deck should scatter out later tgt and 
early Tuesday morning. 


Gks 


&& 


Lsx watches/warnings/advisories... 
MO...none. 
Illinois...none. 
&& 


$$ 


Weather forecast office lsx