051 FXUS63 KLSX 252058 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 358 PM CDT Thu Apr 25 2019 .SHORT TERM... (Through Late Friday Afternoon) Issued at 358 PM CDT Thu Apr 25 2019 Low pressure over the mid Mississippi Valley will be exiting the region this evening, taking the persistent rain over southeast and east central Missouri and southern Illinois with it. The rain should begin moving a little more quickly over the next few hours as the upper level low trough continues to open up and accelerate to the east-northeast. Meanwhile, a secondary cold front which is currently pushing through south central Iowa and northwest Missouri will continue moving southeast tonight, and sweep through southern Illinois and southeast Missouri by 08Z-10Z. A broken line of showers is already forming just ahead of the front in southeast Iowa and north central Missouri. Short range guidance including all of the convection allowing models continue to develop convection ahead of the front late this afternoon and push the broken line into northeast and central Missouri and west central Illinois...and even into east central Missouri and southwest Illinois by mid-evening. RAP and GFS do show a bit of instability ahead of the front, so have kept isolated thunder mention in the forecast with this convection. Most guidance shows the line weakening between 03-05Z. Cooler and drier air will filter into the mid Mississippi Valley behind the front tonight with lows dropping into the 40s. There will also likely be some gusty winds of 20-30 mph behind the front tonight and Friday. While we'll start Friday on the cool side, it looks like a mostly sunny day, and even with northwest wind temperatures should easily rebound into the mid 60s per guidance...and these temperatures agree well with upstream highs over Nebraska this afternoon. Lows may be tricky on Friday night though as the wind drops off during the evening and then turns back to the south ahead of the next system. With dry air in place and a clear sky temperatures could drop fairly quickly in the evening and then remain nearly steady in the pre-dawn hours of Saturday. Carney .LONG TERM... (Friday Night through Next Thursday) Issued at 358 PM CDT Thu Apr 25 2019 An active pattern is staged to impact the Midwest through the period. The greatest potential for heavier rain comes next week as a boundary becomes nearly stationary and meanders through the Midwest. This will also bring the potential for a north/south spread in temperatures. The first system will come in the form of a surface low passing southeast through the Dakotas, under an upper level shortwave. As it progresses east, it will continue to the place the MO/IL region deeper into warm air advection and associated southwesterly flow. Moisture will continue to increase, along with the presence of isentropic lift over Missouri Saturday morning. Showers are expected to develop over Missouri Saturday morning and toward the MO/IL border around early afternoon. Activity will move into Illinois through mid-afternoon. Showers are likely to be the mode of activity with little/no MLCAPE and early morning clouds should keep temperatures in the 60s/near 70 with little opportunity for diurnal surface heating, despite warm air advection. Behind the first round of showers will likely be somewhat of a lull Saturday afternoon. Overall rain chances will remain limited with hit-or-miss showers until the surface low's trailing cold front approaches from the northwest late Saturday afternoon into Saturday evening. Even this isn't all that impressive with scattered activity confined to a narrow area of convergence along the front. Given marginal convective potential, thunder was kept to slight wording in the going forecast. All should move east with the front by late Saturday evening. Clouds could break late with winds remaining between 5-10 mph, even in the coldest areas of NE Missouri. therefore, frost still looks like a long shot. Sunday currently looks like a dry day between systems with a surface high pushing through the Upper Midwest underneath upper level ridging. There could be some lingering low level moisture through the morning hours, but the loss in moisture depth from late morning into the afternoon will allow for clearing. Temperatures will be held in the 60s as cooler air continues to advect in behind the aforementioned cold front. Upper level flow goes nearly zonal late Sunday into Monday, taking on the slightest tilt out of the southwest. Additional disturbances will begin to push west to east through the zonal flow during this period. As this occurs, the surface boundary stalls through the region, becoming the focus for the storm track from early week through the midweek period. I believe the main feature we will need to watch will be the building ridge over the western Atlantic and southeast CONUS. Should this ridge continue to build westward, it lending to warmer and more moist southwesterly flow over the region. The strength and westward build of this ridge will be a factor in boundary placement, determining the track of additional waves along the boundary, resulting rainfall totals and north/south temperature spread in the Monday through Wednesday timeframe. For now, each of the three days will involve chances for rain with the potential that some rain could be heavy given ample moisture transport out of the gulf. Maples && .AVIATION... (For the 18z TAFs through 18z Friday Afternoon) Issued at 1233 PM CDT Thu Apr 25 2019 Expect rain and IFR flight conditions to continue to prevail along and southeast of a line from KMTO to KVIH this afternoon. Intermittent MVFR/IFR conditions conditions are likely on the northwest edge of the rain...with MVFR ceilings improving to VFR during the afternoon further north and west into central and northeast Missouri and west central Illinois. The rain and lower ceilings should clear from west to east by late this afternoon, but another cold front will move into northeast Missouri by 23-00Z. Scattered showers are likely along the front, and there may be a thunderstorm or two as well. A brief period of MVFR ceilings/visibility will be possible with any of these showers that move through. The showers are expected to weaken significantly as they move into east central Missouri and southwest Illinois late this evening. VFR flight conditions and gusty northwest wind is expected to prevail after the showers move out of the area. SPECIFICS FOR KSTL: Current thinking is that Lambert will be right on the northwest edge of the IFR for a few hours this afternoon...but that the lower clouds and precipitation will move away from the vicinity of the terminal by 22Z-00Z. VFR flight conditions are expected to prevail thereafter...though there may be a brief period of MVFR ceilings/visibility as a cold front with scattered showers moves through the Metro Area. Wind will become gusty from the northwest after the front passes. Carney && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX