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