113 
fxus63 klsx 211200 
afdlsx 


Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
700 am CDT sun Mar 21 2010 


Discussion... 
/458 am CDT sun Mar 21 2010/ 


A strong storm system is passing to our S and is gradually 
shifting the precipitation focus from the frontogenetical precipitation that has 
produced 2-4 inch widespread snow accums with some negligible 
sleet accums over the advisory area in northestern/central MO and west-central Illinois 
to the deformation zone that is now pushing northward into southern MO and 
extreme southern Illinois. We expect this transition will take much of the 
morning to fully accomplish...and will linger enough 
frontogenetical precipitation in the advisory area to justify maintaining 
this headline through noon. Plenty of warm air aloft across the forecast area as 
it gets shoved nwwd by wrapped up system to our S and this will 
continue through the day today. Surface temperatures are the key...and with surface 
temperatures at or below 32f over the advisory area...this is creating some light 
freezing rain with light glazing as a result. Farther northwest towards 
Kirk...warm wedge is not as pronounced and is resulting in some 
snow and sleet. As surface temperatures warm up this morning...this will also 
erode the cold layer just above the surface and will ultimately lead 
to all rain by noon...if any precipitation is left. Clouds...pcpn...and northerly 
surface winds will strongly favor going several degrees below MOS temperatures 
once again today. 


By noon...the frontogenetical precipitation should have faded with northward 
approach of deformation rain then to take hold. This precipitation will be 
slow to exit...and have bumped up probability of precipitation for Monday morning in the 
southeastern forecast area including parts of the stl metropolitan area. Heading into Monday 
night...rapid clearing from the northwest with surface ridge sliding through 
will favor the cooler MOS temperatures. Abundant sunshine on Tuesday and 
southwesterly surface winds will lead to large warm up with temperatures possibly 
approaching upper 60s-70f in some spots. 


Another system still on track for late week for rain showers...and 
have maintained chance probability of precipitation for now...but it appears more likely 
these will need to be increased. 


Tes 


&& 


Aviation... 
/641 am CDT sun Mar 21 2010/ 


Precipitation should come to an end over the next couple of hours at uin. 
With temperatures hovering around freezing...freezing rain occur off and on during 
this time capable of producing a light glaze on runways. Area of 
rain across southeastern MO will move north and may affect cou around 15z. Not 
certain that this rain will make it that far north. If it does...precipitation 
type is expected to be rain. Some uncertainty exists as to when 
precipitation will end this morning. Have best estimated times in taf. If 
precipitation continues beyond these times...expect all precipitation to be east/southeast 
of terminals by 18z as system pulls eastward. IFR ceilings should continue 
this morning at cou/uin...with ceilings lifting into low MVFR by noon. 
Ceilings will continue to gradually lift to VFR this evening and 
overnight. For sus...please see discussion for stl below. 


Specifics for kstl...uncertainty exists regarding how long precipitation 
will occur today...but type will remain rain. Rain over southeastern MO will 
reach terminal within a couple of hours and continue through the 
morning. Rain should come to an end briefly late morning/early 
afternoon before beginning again this afternoon and persist into 
the overnight hours. Do not expect rain to reduce visbys...but may 
reach MVFR Cat periodically. Have rain ending around midnight but 
this may be optimistic as metropolitan area will be on northern edge of the 
Pivot Point for this system. Regardless...expect ceilings to improve 
this afternoon and should remain above IFR this evening and 
overnight. 


Tilly 


&& 


Lsx watches/warnings/advisories... 
MO...Winter Weather Advisory until noon CDT today for Audrain MO- 
Boone MO-Callaway MO-Cole MO-Knox MO-Lewis MO-Marion MO- 
Moniteau MO-Monroe MO-Ralls MO-Shelby MO. 


Illinois...Winter Weather Advisory until noon CDT today for Adams Illinois. 


&& 


$$ 


Weather forecast office lsx