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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Tuesday
• 
• High: 86 °
• Low: 64 °
• T-Storms

• Wednesday
• 
• High: 77 °
• Low: 57 °
• Chance of T-Storms

• Thursday
• 
• High: 70 °
• Low: 46 °
• Mostly Cloudy

• Friday
• 
• High: 68 °
• Low: 46 °
• Clear

• Saturday
• 
• High: 68 °
• Low: 59 °
• Partly Cloudy

Area forecast discussion 
National Weather Service St Louis MO 
343 PM CDT Tuesday may 21 2013 


Short term...(through late tonight) 
issued at 314 PM CDT Tuesday may 21 2013 


The overall severe weather threat has diminished significantly 
from earlier thinking owing to a series of mcs's tracking to our 
south from Oklahoma to Arkansas into the Tennessee Valley. These systems 
have produced a good deal of cloud cover which has limited heating 
and that combined with much weaker lapse rates has limited the 
instability. The highest values of SBCAPE presently are from 
1000-2000 j/kg extending from metropolitan St Louis into east central 
Illinois...this half or less the amount of the previous few days. All 
this said the precipitation chances still look pretty high tonight 
across eastern MO into southern Illinois. We might see some isolated storms 
develop in this higher cape air through sunset and we will also see 
the northern portion of the stratiform rain region of the Arkansas mesoscale convective system 
impact southeast MO into southern Illinois. The main threat of precipitation however 
appears to be later this evening into the overnight hours. Water 
vapor imagery and vwp data is showing a powerful short wave across 
extreme western OK and this will eject east-northeastward tonight and be centered 
through eastern MO at daybreak on Wednesday. Deep large scale ascent associated 
with this short wave should lead to an upswing in showers and 
thunderstorms later this evening. I cant rule out an isolated 
severe threat but again the marginal instability would suggest the 
chance is low. Rainfall amounts will be substantially less than 
last night...less than an inch. 


Glass 


Long term...(wednesday through next tuesday) 
issued at 314 PM CDT Tuesday may 21 2013 


The majority of the precipitation should be east of the MS river 
in Illinois or further east at daybreak and continue to move 
eastward as the shortwave trough and attendant cold front move east. 
Cooler and drier air will overspread the region in the wake of the 
front and any additional precipitation threat after middle-morning 
should be from isolated diurnal showers. Another secondary cold 
front will push through the area Wednesday night ushering high pressure 
and even cooler air into the area. This large high will dominate 
the area Thursday into Friday. 


Not much has changed in the extended ranges of the forecast. An 
upper ridge will dominate the central U.S. With the ridge axis 
remaining just west of Missouri Sat-Mon. This will place US just 
downstream of the ridge crest and subject to weak short waves 
topping the ridge. These disturbances combined with return flow 
and low level warm air advection on the backside of the retreating low level high 
pressure system will bring a prolonged threat of showers and 
thunderstorms to primarily the northern half of the County Warning Area from Sat 
through Monday night. Thereafter the upper ridge axis moves to our 
east...precipitation chances diminish and temperatures warm. 


Glass 


&& 


Aviation...(for the 18z tafs through 18z Wednesday afternoon) 
issued at 1243 PM CDT Tuesday may 21 2013 


Diurnal cumulus and cirrus shield to persist over taf sites today ahead 
of cold front. Timing and coverage of storm development is still 
hard to pin down for late this afternoon and tonight as atmosphere 
is struggling to destabilize. Feel that kcou should remain dry. 
Otherwise...some storms possible over metropolitan area after 22z and 
linger over area through daybreak on Wednesday. As for KUIN...they 
will be on northern fringes of activity after 05z...tapering off 
by 10z. Otherwise...southwest winds to diminish towards 
sunset...veering to the west behind the frontal boundary early 
Wednesday. The winds will pickup to near 15kts by middle morning on Wednesday. 


Specifics for kstl...diurnal cumulus and cirrus shield to persist over 
metropolitan sites today ahead of cold front. Timing and coverage of storm 
development is still hard to pin down for late this afternoon and 
tonight as atmosphere is struggling to destabilize. Some storms 
possible over metropolitan area after 22z and linger over area through 
11z Wednesday. Otherwise...southwest winds to diminish towards 
sunset...veering to the west behind the frontal boundary by 11z 
Wednesday. The winds will pickup to near 15kts by 17z Wednesday. 


Byrd 


&& 


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


$$ 


Weather forecast office lsx