613 
FXUS63 KLSX 160859
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
359 AM CDT Tue May 16 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 358 AM CDT Tue May 16 2017

An upper level RIDGE axis is now to our east, resulting in SW flow 
aloft for our region.  A pair of strong storm systems are well to 
our west, with one near Las Vegas and the other just coming onshore 
near British Columbia.  At the surface, our region was in the warm 
sector with a light southerly flow, with a frontal boundary to our 
north extending across far northern IA.  Temperatures were in the 
60s with some thin high cirrus clouds approaching from the west. 

SW flow aloft will continue thru tonight with the strong storm 
system over the southwestern CONUS ejecting out into the central 
Plains by late tonight while the second strong storm system from 
British Columbia settling into southern Idaho.  The warm sector 
setup at the surface will continue thru late tonight with southerly 
flow and the absence of any fronts nearby.  While convective 
development should be very limited at best thru early this evening 
in our region, the approach of the strong storm system from the 
southwestern CONUS and its assocated broadscale lift ahead of it 
should initiate convection well to our west during the evening hours 
with this then propagating northeast and weakening overnight.  Low 
PoPs were maintained for areas north and west of STL metro but even 
this looks to not be too concerning until after 09z tonight with a 
dry forecast elsewhere. 

Thin cirrus and scattered cumulus clouds will be the main cloud 
cover into the evening, and should still result in decent sunshine 
across the region.  With similar temps aloft to mix down from 
persistence, the main variables in play are a bit better mixed lower 
atmosphere and somewhat more cloud cover, but we will be starting a 
few degrees warmer as well.  All of this should largely cancel out 
with a persistence forecast looking awfully hard to beat today, 
which is a couple degs higher than MOS:  from 85-90.  MOS min temps 
used for tonight, with readings expected to drop into the 60s most 
places with around 70 in STL metro. 

TES

.LONG TERM...  (Wednesday through Monday)
Issued at 358 AM CDT Tue May 16 2017

Showers and storms will spread into our forecast area on 
Wednesday, particularly across northeast MO and west central IL 
ahead of a negatively tilted upper level trough moving through 
northwest MO.  The models depict relatively strong upper level 
divergence across this area ahead of this upper level trough.  A few 
strong to severe storms are possible due to strong 0-6 mb deep layer 
shear mainly Wednesday afternoon as a strong mid level wind max 
moves through our area ahead of the upper level trough.  Daytime 
highs on Wednesday will not be as warm as the past couple of days 
due to cloud cover and scattered convection, albeit still above 
normal.  A cold front will sag southward into our forecast area 
Thursday afternoon and night. This boundary will be the focus for 
convection late Thursday night and Friday as low-mid level warm air 
advection increases over this front, well ahead of an upper level 
low moving into the Plains. This upper level trough/low will move 
into the northern Plains and an associated surface low and trailing 
cold front will move through our forecast area Saturday and Saturday 
night. The operational GFS and ECMWF models have come into better 
agreement with the timing of this cold front, although the GFS is 
still a little quicker.  Convection is expected along and ahead of 
this front.  Most of the showers and storms should shift southeast 
of our forecast area by Sunday afternoon or evening, depending on 
the exact timing and strength of the upper level trough moving 
through the northern Plains and the progression of the cold front. 
Cooler temperatures can be expected Saturday night and Sunday after 
the passage of the cold front. Temperatures Sunday and Sunday night 
should be slightly below normal.

GKS

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1138 PM CDT Mon May 15 2017

Dry and VFR conditions are expected through the period. Southerly
winds will turn gusty by mid morning on Tuesday.

SPECIFICS FOR KSTL: 

Dry and VFR conditions are expected through the period. Southerly
winds will turn gusty by 15Z.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX