542 FXUS63 KLSX 150850 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 350 AM CDT Sun Sep 15 2019 .SHORT TERM... (Through Late Monday Afternoon) Issued at 350 AM CDT Sun Sep 15 2019 Elevated convection across northwest MO and southeast IA will move through northeast MO and west central IL early this morning. This convection is in a region of low-mid level warm air advection ahead of a weak shortwave over eastern Nebraska and western IA. This convection is also in a region of low level moisture convergence on the nose of a 40-45 knot southwesterly low level jet. This convection should weaken and shift east of our forecast area by late morning. Warmer and more humid conditions can be expected today as an upper level ridge builds over the central US, along with southwesterly surface winds. Highs today will be about 10 degrees above normal. A very weak cold front will sag southward into northeast MO and west central IL by this evening, and then drop into east central MO and southern IL Monday morning as surface ridging builds over the Great Lakes region. At this time it appears that the atmosphere will be too capped for any convection to develop along this weak front tonight. Unseasonably warm conditions will continue on Monday with afternoon heat indices approaching 100 across parts of the forecast area. GKS .LONG TERM... (Monday Night through Saturday) Issued at 350 AM CDT Sun Sep 15 2019 On Tuesday, an upper level RIDGE will continue to dominate our region. A large area of high pressure at the surface will be centered over the eastern Great Lakes and northeast CONUS but its influence will extend all the way westward into our region, resulting in a light east or southeast surface wind for most locales. Despite the E-SE wind direction, the influence from the airmass to our east is only expected to have a slight impact, with forecast max temps a couple degrees cooler for most areas, or from the mid 80s to near 90. While rain chances look minimal on Tuesday, they are not nil, as there is a weak signal for an isolated shower or thunderstorm from the interface of the high pressure area centered to our northeast with the warmer airmass to our west, and this could create enough weak convergence in a weakly capped environment for these isolated cells. Most model guidance then weakens the grip of the upper RIDGE on our area--only slightly--heading into Wednesday with this setup carrying through to Saturday. At the same time, the influence of the cooler airmass to our east should fade, with southerly flow kicking back in. Max temperatures for most of these days should return to much above normal (10-15 degrees higher than mid-late September values), ranging from the mid 80s to the lower 90s, with the highest readings tending to congregate in the STL metro area. Fortunately, another weak area of high pressure to our south will prevent a direct flow from the Gulf of Mexico, and dewpoints should struggle in getting much above 70-72F. This stands to translate into afternoon peak heat index values mainly in the 90s, and approaching but probably falling just short of 100 in the STL metro area. A result of the slightly weakening upper RIDGE would be to steer upper level disturbances from the monsoonal flow to our west into our region, increasing rain chances at least into mentionable range (20%+) for a chunk of this period primarily for areas to the north of Interstate 70. The main surface frontal boundary appears likely not to be a factor in aiding convective development, however, with a stout SW flow aloft remaining in place during this period and will probably limit PoPs to low chance values at best. Another contingency for late week will also depend on convection realized-- and could take a cut at temps ultimately with additional clouds coming into play. TES && .AVIATION... (For the 06z TAFs through 06z Sunday Night) Issued at 1142 PM CDT Sat Sep 14 2019 Dry and VFR flight conditions expected through the forecast period with light south winds veering to the southwest during the morning on Sunday and picking up a bit, especially at KUIN and KCOU. Otherwise, weak upper level shortwave will continue to slide eastward along the IA/MO border late tonight with increasing clouds and a slight chance of showers/storms near KUIN through mid morning on Sunday, but confidence remains low, so kept TAF dry for now. SPECIFICS FOR KSTL: Dry and VFR flight conditions expected through the forecast period with light south winds veering to the southwest by 15z Sunday. Byrd && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX