833 FXUS63 KLSX 212028 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 328 PM CDT Sun Jul 21 2019 .SHORT TERM... (Through Late Monday Night) Issued at 324 PM CDT Sun Jul 21 2019 Main concern for tonight will be convective trends. The composite outflow boundary from last night's MCS currently arcs from near KOWI>>KLBO>>KPCD>>KSLO. The most likely convective evolution scenario overnight is for convection to develop along the intersection of the western portion of the aforementioned outflow boundary and the intersecting cold front across east/southeast Kansas by early evening. These storms should move east/southeast overnight aided by a shortwave trough moving through and moisture convergence associated with the low-level jet. Our CWA should be on the northern end of this complex of storms, so showers and embedded thunderstorms have the best chance of impacting all or portions of central, east-central, and southeast Missouri as well as far southwest Illinois through Monday morning. Any convection in our area should be elevated due to time of night and the fact that the outflow boundary is well to the southwest. Therefore, do not see much of a severe threat overnight tonight. Rainfall amounts over an inch are possible for central and southeast Missouri by the time the rain ends midday Monday, but storms should progress fast enough and convection and associated higher rainfall rates may subside by Monday morning to preclude any widespread flash flood threat. In addition, many of the areas expected to get rain tonight into the day on Monday received little to no rainfall from the MCS last night. Other storms may try and develop ahead of a remnant MCV currently near the MO/KS/NE border where there is also a weak surface wave and associated low-level convergence. Some of these storms may impact northern sections of the area early tonight, but not certain how much of this activity will survive as surface analysis shows a meso-high near Chillicothe, MO (KCDJ) and SPC mesoanalysis depicts a minima in surface-based instability. The threat for showers and embedded thunderstorms should move off to the south and east by Monday afternoon as the synoptic cold front moves into the mid south. The big change on Monday compared to this weekend will be the sharp temperature change. High temperatures for most areas will only be in the 70s due to lingering (low) cloud cover and strong low-level cold air advection. Compared to yesterday, it will likely feel 30-35 degrees cooler on Monday after humidity is factored into the equation. Decreasing cloudiness is forecast for Monday night. This factor combined with continued low-level cold air advection and light northerly surface flow should combine to yield a chilly night across the bi-state region. Low temperatures are forecast to drop into the mid 50s to near 60 degrees across the area, which would be about 10 degrees below normal for the date. Gosselin .LONG TERM... (Tuesday through Next Sunday) Issued at 324 PM CDT Sun Jul 21 2019 A high amplitude omega block will dominate the weather pattern from Tuesday until at least Thursday this week. This will lock a large and cool surface high over the eastern half of the CONUS through Thursday as well. Medium range guidance shows a shortwave moving across the US/Canada border through Friday evening. This wave will slowly break down the block through the end of the week which will bring a more zonal flow pattern aloft back to the country. However, that cool surface high should continue to influence our weather here in the mid Mississippi Valley at least through Friday and possibly into Saturday as well. Dry weather, low humidity, and relatively cool temperatures with highs in the low to mid 80s and lows mainly in the low to mid 60s look likely through Friday. Saturday and Sunday should warm up a bit as return flow on the western side of the high begins to draw some warmer and more humid air back into the mid Mississippi Valley. Highs should warm back up to the mid 80s to around 90. Certainly warmer than earlier in the week, but not as hot as we saw in this recent heat wave. Carney && .AVIATION... (For the 18z TAFs through 18z Monday Afternoon) Issued at 1229 PM CDT Sun Jul 21 2019 Isolated storms are possible this afternoon and early evening for the terminals, but better chances will be overnight tonight as a complex of storms moves in from western Missouri. These storms are forecast to affect KCOU and the metro terminals late tonight into Monday morning. Reduced visibilities in downpours are likely. Rain chances will leave from west to east Monday morning, but MVFR ceilings will likely remain for approximately three hours afterwards. SPECIFICS FOR KSTL: While an isolated storm cannot be ruled out this afternoon and evening, better chances for showers and storms will be after midnight tonight. This activity should last into the morning hours before moving off to the east. Shortly after the shower activity begins, ceilings should fall below VFR thresholds toward 1500 feet above ground level. MVFR ceilings should then continue until about midday Monday before they lift back to VFR and remain that way for the remainder of the afternoon. Gosselin && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Excessive Heat Warning until 8 PM CDT this evening for Crawford MO-Franklin MO-Jefferson MO-Saint Charles MO-Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO- Washington MO. Heat Advisory until 8 PM CDT this evening for Iron MO-Madison MO- Reynolds MO. IL...Excessive Heat Warning until 8 PM CDT this evening for Bond IL- Clinton IL-Fayette IL-Madison IL-Marion IL-Monroe IL- Montgomery IL-Randolph IL-Saint Clair IL-Washington IL. && $$ WFO LSX