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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Wednesday
• 
• High: 84 °
• Low: 68 °
• Chance of a Thunderstorm

• Thursday
• 
• High: 88 °
• Low: 70 °
• Chance of a Thunderstorm

• Friday
• 
• High: 90 °
• Low: 70 °
• Chance of a Thunderstorm

• Saturday
• 
• High: 88 °
• Low: 70 °
• Chance of a Thunderstorm

• Sunday
• 
• High: 90 °
• Low: 72 °
• Clear

Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
505 am CDT Wednesday Jun 19 2013 


Short term...(through late this afternoon) 
issued at 303 am CDT Wednesday Jun 19 2013 


Early this morning...upper level ridge exists over the hi plains 
with northwest flow downstream from it over our region. A ridge-runner 
shortwave is over western Kansas and Nebraska generating clusters of thunderstorms and rain 
with a weaker upper level disturbance over southeastern Kansas helping to 
maintain some thunderstorms and rain activity near ict. At the surface...an ill-defined 
boundary snakes from southern Indiana through southern Illinois and southern MO and curves 
northward near the Kansas-MO border. To the north of this boundary...a light NE 
surface flow has built in. Surface temperatures have fallen into the 60s with a 
few spots threatening to dip into the upper 50s...a real treat for 
late June. 


It seems we cannot escape discussing rain chances each day...and this 
day seems to be no exception. 


Northwest upper level flow is expected to weaken today...flatten overhead 
with rising 500 mb heights. This will tend to not result in much push 
for surface fronts...and so will probably see the weak surface boundary 
linger near its present position through the day...though questionable 
in what shape it will be in by middle-late afternoon. In any event... 
all models show relatively modest sbcapes of 500-1000 j/kg with zero 
cinh during middle-late this afternoon over an area that normally 
inclines towards precipitation more than other areas given its intangibles 
such as topography...in southeastern MO and southern Illinois. GFS overdoes precipitation 
development with surface dewpoints of 70f...but even WRF model and its more 
realistic middle 60s dewpoints should result in isolated shra/tsra. Have 
introduced slight chance probability of precipitation over much of the southern and eastern forecast area...including 
the stl metropolitan area...for middle-late afternoon for what should be 
short-lived single cell convection with the very weak deep layer 
shear and modest Cape. Ridge-runner shortwave is expected to still 
be too far west to have any impact by early this evening. 


H850 temperatures and comparison to persistence support maximum temperatures near or 
just above the warmest MOS values...or middle 80s for most locations 
with upper 80s expected for stl metropolitan. 


Tes 


Long term...(tonight through tuesday) 
issued at 400 am CDT Wednesday Jun 19 2013 


May still have isolated showers and storms into the early evening 
across parts of southeastern MO and southwestern Illinois. A weak shortwave will move eastward 
into Iowa and western MO late tgt. This coupled with a southwesterly low level jet 
bringing low level warm air advection and increasing low level moisture into northwestern 
MO may lead to some convection across parts of northestern and central MO 
late tgt into early Thursday morning. The better threat of convection 
should be on Thursday as low level moisture increases over the entire 
area...although the shortwave should weaken as it gets further east. 
NAM model appears a little deficient in its quantitative precipitation forecast on Thursday. The upper 
level ridge over the Southern Plains will build slowly northeastward into MO Thursday 
night and Friday. The NAM model is a little lower with its middle-upper 
level heights compared to the GFS as it continues to forecast 
shortwaves moving through our area and just north of our area. May 
still have convection across mainly northestern MO and west central Illinois during 
this period. By Friday night and Sat the upper level ridge should build 
over our region with most of the convection remaining north of our forecast 
area. With the upper level ridge over our area...persistent 
S-southwesterly surface/low level winds...and plenty of daytime sunshine a prolonged 
period of above normal temperatures is expected for the weekend 
into next week. The GFS model flattens the upper level ridge on 
Monday and Tuesday which may lead to a better chance of convection... 
especially over the northern portion of our forecast area. 


Gks 


&& 


Aviation...(for the 12z tafs through 12z Thursday morning) 
issued at 505 am CDT Wednesday Jun 19 2013 


VFR conditions and light easterly surface winds will prevail at the taf 
sites through the valid taf period. Isolated rain showers/thunderstorms and rain are possible middle- 
late afternoon over parts of east-central and southeast MO as well as southern Illinois 
but probs too low to mention in tafs at this time. 


Specifics for kstl...VFR conditions and light easterly surface winds 
through the valid period...very low probability of rain showers/thunderstorms and rain middle-late 
afternoon but not enough to mention in forecast at this time. 


Tes 


&& 


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


$$ 


Weather forecast office lsx