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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Saturday
• 
• High: 75 °
• Low: 55 °
• Chance of T-Storms

• Sunday
• 
• High: 79 °
• Low: 63 °
• Chance of T-Storms

• Monday
• 
• High: 79 °
• Low: 63 °
• Chance of T-Storms

• Tuesday
• 
• High: 86 °
• Low: 63 °
• Partly Cloudy

• Wednesday
• 
• High: 84 °
• Low: 68 °
• Mostly Cloudy

Area forecast discussion...updated 
National Weather Service St Louis MO 
756 am CDT Sat may 25 2013 


Update... 
issued at 755 am CDT Sat may 25 2013 


Updated grids/zones for activity that has fired up south of main 
mesoscale convective system...extending from near irk to szl to sgf. So raised probability of precipitation across 
portions of forecast area this morning as this line moves east. 


Byrd 
&& 


Short term...(through late this afternoon) 
issued at 316 am CDT Sat may 25 2013 


Complex forecast for today. A broad low level warm air advection zone spanning from 
north central Illinois westward into Nebraska is responsible for an 
increasing amount of showers and thunderstorms this morning...including 
across northern MO. The most concentrated zone is from western 
Iowa into Nebraska where an elongated mesoscale convective system is occurring at the nose 
of the 40-50 knots southwesterly low level jet...where elevated instability is present 
with MUCAPE above 1000 j/kg and just ahead of a weak short wave 
moving through the upper ridge crest. There is general agreement 
that the short wave will track eastward today with a position in 
northern Illinois by 00z and in association the low level jet will veer providing 
continued warm air advection and transporting moisture back into the region. 
These elements alone favor a forward propagating mesoscale convective system and corfidi 
vectors and thickness fields would suggest a east-southeastward mesoscale convective system motion. 
Several convection allowing runs of the ncar 3km WRF suggest the 
mesoscale convective system will in fact track east-southeastward with the southern periphery...which will 
also consist of new development...moving through or just north of St 
Louis. I have trended the new forecast in this direction with the 
probability of precipitation ramping up this morning...with isolated to scattered 
activity due to warm air advection through 15z or so and then the mesoscale convective system will impact 
the area from late morning into middle afternoon...specially NE MO 
into west central Illinois. 


Glass 


Long term...(tonight through friday) 
issued at 316 am CDT Sat may 25 2013 


The remainder of the forecast is tough trying to give specifics. 
The aforementioned upper ridge axis will basically be located 
through the middle/upper MS valley while a series of weak short waves 
continue to move through it tonight through Monday. The models have 
widely varying solutions on the timing and location of these 
features leading to greater than normal uncertainty. The lower 
tropopause will continue to feature a prominent warm air advection regime and moisture 
and instability will continue to improve with time. Overall the 
pattern is supportive of bouts of organized convection associated 
with the short waves and low level jet. The most favored zone appears to be 
the northern third the County Warning Area with lesser chances with southward 
extent. By late Memorial Day and into Tuesday the warm front will 
lift northward and the upper ridge axis will shift east and build 
through the eastern US resulting in a diminished threat of showers and 
thunderstorms and temperatures well into the 80s. These above 
normal readings should persist into the later part of next week. 


Glass 
&& 


Aviation...(for the 12z tafs through 12z Sunday morning) 
issued at 755 am CDT Sat may 25 2013 


Best chances of storms will be over northern portions of forecast 
area...though north/south line of storms has developed over 
western MO and is making its way towards kcou. So have tempo 
groups of MVFR visibilities with these storms for a few hours...before 
tapering off. As for metropolitan area...not sure if any of it will hold 
together before getting here...so just kept vcsh mention for now. 
Otherwise...will see a break in activity for this afternoon and 
early tonight before next complex develops. Still hard to pin down 
exact timing and coverage of this...so just kept thunderstorms in the vicinity mention at 
this time. 


Specifics for kstl...best chances of storms will be over northern 
portions of forecast area...though north/south line of storms has 
developed over western MO and is making its way east this morning. 
Not sure if any of it will hold together before getting to the stl 
metropolitan area...so just kept vcsh mention for now. Otherwise...will 
see a break in activity for this afternoon and early tonight 
before next complex develops. Still hard to pin down exact timing 
and coverage of this...so just kept thunderstorms in the vicinity mention at this time 
beginning around 08z Sunday. 


Byrd 
&& 


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


$$ 
Weather forecast office lsx