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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Thursday
• 
• High: 70 °
• Low: 48 °
• Chance of Rain

• Friday
• 
• High: 70 °
• Low: 52 °
• Clear

• Saturday
• 
• High: 70 °
• Low: 46 °
• Chance of T-Storms

• Sunday
• 
• High: 73 °
• Low: 59 °
• Fog

• Monday
• 
• High: 82 °
• Low: 64 °
• Chance of a Thunderstorm

Area forecast discussion 
National Weather Service St Louis MO 
333 PM CDT Thursday may 23 2013 


Short term...(through late tonight) 
issued at 325 PM CDT Thursday may 23 2013 


Secondary shortwave dropping down back side of Great Lakes trough has 
maintained a few spotty showers over the area this afternoon. Think 
most of this activity will either advect out of our area or 
dissipate by 00z...but will watch radar trends to determine if any 
of this activity will persist into the early evening. If it 
does...it shouldn't last much past sunset. 


Rather extensive and persistent SC deck is also holding tough across 
area. However ceilings have been increasing and visible satellite 
imagery suggests clouds are becoming a bit more cumuliform with 
time....so believe clearing is still in the offing during the early 
evening hours. 


Since we're still leaning towards a decreasing cloud trend 
tonight...i've remained on the cool side of guidance for mins. 
Temperatures will begin the evening on the chilly side...and with 
the southward push of the surface ridge into the area winds should be 
rather light and dewpoints should be fairly low during time of maximum 
radiational cooling. 


Truett 


Long term...(friday through next thursday) 
issued at 325 PM CDT Thursday may 23 2013 


The main forecast issues continue to be temperature trends and precipitation chances. 


A strong surface high will continue building into the western Great Lakes on Friday 
with the ridge axis extending southward into MO/IL. Ely surface flow around 
the high will keep temperatures seasonably cool on Friday/Friday night 
in addition to reinforcing a baroclinic zone across the plains. 
Meanwhile...a developing low pressure system over the plains will 
reorient the aforementioned baroclinic zone and lift it northeastward as a 
warm front. Temperatures will warm up quickly on Sat across central MO 
due to both the warm front and the late may sun angle. The extent of 
warming across western/southwestern Illinois for the weekend is more in question 
because of uncertainties regarding the location of nocturnal 
mesoscale convective systems and the effect of their outflows on 
the position of the effective front. Temperatures across western/southwestern 
Illinois will warm up once the front lifts farther north...but that may 
not happen until Monday. Temperatures across the area will also 
depend on the extent of remnant cloud cover from overnight 
convection that occurs upstream. 


Generally dry conditions are expected through Friday night however 
nocturnal convection driven by the low level jet may reach the northwestern County Warning Area on 
late Friday night/early Sat morning. A few vorticity maxes may try to 
undercut the upper ridge that will be in place over the central 
Continental U.S. Through early next week...and these features may support scattered 
rain showers/thunderstorms and rain at times. Additionally...the forecast weather pattern will be 
conducive for nightly mesoscale convective system development across various parts of the 
central Continental U.S.. some of these thunderstorm complexes may move 
across the lsx County Warning Area depending on the position of the effective 
front each night and its orientation with respect to the low level jet axis. 
Upstream convection could also produce an mesoscale convective vortex which then focuses 
thunderstorms and rain development in our area on the following afternoon. These kinds of 
mesoscale details cannot be forecast very far in advance therefore 
this forecast package maintains chance probability of precipitation /higher values where models 
seem to be in slightly better agreement/ for several days where 
thunderstorms are possible but mesoscale details are unknown at this time. 


A pattern shift will be underway by the middle of next week once a 
closed low pressure system develops over the southwestern Continental U.S. And shifts the 
upper air pattn over MO/Illinois from ridging to SW flow. GFS/European model (ecmwf) depict 
very different scenarios for how the low lifts into the plains 
therefore generally followed the recommended CR initialization for 
Tuesday and beyond. 


Kanofsky 


&& 


Aviation...(for the 18z tafs through 18z Friday afternoon) 
issued at 1225 PM CDT Thursday may 23 2013 


Beginning to see some thin spots in the high end MVFR ceilings that 
blanket area. This should allow for an increase in low level 
mixing that should cause ceiling heights to increase to low end 
MVFR no later than middle afternoon. This trend towards the cloud 
deck becoming more cumuliform should also mean a gradual clearing 
trend during the late afternoon and early evening hours as heating 
ebbs and as cyclonic low level curvature decreases with the southward 
push of the surface ridge. Once clearing occurs...expecting clear 
skies and light NE/east winds for the remainder of the overnight 
hours and into Friday morning. 


Specifics for kstl...ceilings over kstl should increase to 3-4kft by 
middle afternoon with north winds 10-15kts. This VFR cloud deck should 
erode during the evening...leaving clear skies for much of the 
night with NE winds 4-8kts. 


Truett 


&& 


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


$$ 


Weather forecast office lsx