366 FXUS63 KLSX 122123 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 423 PM CDT Wed Jun 12 2019 .SHORT TERM... (Through Late Thursday Afternoon) Issued at 357 PM CDT Wed Jun 12 2019 The main band of rain/showers has begun to shift east into Illinois late this afternoon in association with the movement of lead short wave rotating east within the amplifying upper trof. This rain shield will continue to move east through the remainder of the afternoon, exiting east of the CWA by early evening. Decreasing clouds in the wake of the main rain shield along with cold air aloft has resulted in weak instability from central into western MO which is fueling scattered showers and thunderstorms. A few of these storms over the next few hours cold produce some small hail and gusty winds in central MO. Otherwise scattered showers and storms will continue to be the threat into the first half of the evening hours. The eastward movement of the large scale upper trof, progress of the cold front across eastern MO into western IL, and loss of heating/instability by 00z should lead to a decrease in coverage of showers and thunderstorms between 00-02z and a total demise of precipitation by 04z or so. Clouds should decrease late evening into overnight. Northwest winds in the wake of the cold front will bringing cooler and drier air into the area through the overnight hours. Lows will be cool by June standards with readings in the upper 40s to middle 50s. The long wave trof centered to our east will slowly progress into the eastern U.S. Thursday into Thursday night, and will result in a short, dry and somewhat cool period. Deep cyclonic flow will help produce some diurnal cu across the region on Thursday, especially from eastern MO into western IL where occasionally gusty northwest winds are expected. Temperatures Thursday/Thursday night will average around 10 degrees below normal with highs in the upper 60s to lower 70s. High clouds will begin to spread into the area late Thursday night as the upper flow begins to back and transition to quasi-zonal. These high clouds however shouldn't prevent another cool night as surface high pressure slides across the area. Lows Thursday night into early Friday morning will range from the upper 40s to lower 50s. Glass .LONG TERM... (Thursday Night through Next Wednesday) Issued at 357 PM CDT Wed Jun 12 2019 An active pattern will settle into the area beginning Friday. Upper level flow will become largely zonal, allowing disturbances to propagate eastward across the Nation's mid-section. These disturbances along with a wavering frontal boundary will result in waves of showers and thunderstorms this weekend and into the first half of next week. Rainfall totals over this extended period are expected to range from 2-4 inches. The impact of this rain on local rivers is most likely to slow or flatten the current fall. By Friday the upper level trough and associated jet will have lifted out of the bi-state area, and flow will become largely zonal for the remainder of the period. As flow at the 300 and 500 mb level is westerly, disturbances will repeatedly move into the area. These disturbances will provide the lift for precipitation throughout the extended period. A shortwave trough will advect through the area on Monday, and then again on Thursday, with precipitation accompanying it. At the 850-925 levels moisture is in ready supply from the Gulf of Mexico and advected into the Mid Mississippi River Valley by southwesterly flow. A moist column throughout the period will provide the necessary moisture for the widespread rain expected. A surface high will persist over the southeast US, producing a southwesterly flow regime over the Mid Mississippi River Valley. A surface cold front, driven by an upper level disturbance, will move to the southeast through the CWA Sunday into Monday, slowing as it nears the edge of our service area. The weekend and early part of next week remain the best time for precipitation with the wavering movement of the cold front through the region, though showery precipitation and scattered thunderstorms cannot be ruled out for the remainder of the period given the plethora of synoptic level moisture and lift. MRM && .AVIATION... (For the 18z TAFs through 18z Thursday Afternoon) Issued at 1243 PM CDT Wed Jun 12 2019 A large swath of rain/showers centered through eastern MO will continue to move eastward this afternoon. Flight conditions with the showers will be largely VFR, however there is the potential for the visibility to briefly lower to MVFR. The whole shield of rain showers should be east of all the terminals by 22z or so. Thus far there has been a lack of any thunderstorms, however as the afternoon progresses I expect to additional isolated to scattered showers and storms develop, mainly in the wake of the current precipitation. Most terminals have only VCTS given the lower coverage and will update if a direct terminal impact is anticipated. The coverage of this additional precipitation should diminish significantly between 00-02z as heating wanes and a cold front moves through the area, with VFR dominating through the remainder of the forecast period. Occasionally gusty northwest winds and diurnal cu are expected on Thursday. SPECIFICS FOR KSTL: Rain/showers will impact the terminal through mid-afternoon. Flight conditions with the showers will be largely VFR, however there is the potential for the visibility to briefly lower to MVFR. The whole shield of rain/showers should be east of the terminal by 21z or so. Thus far there has been a lack of any thunderstorms, however as the afternoon progresses I expect to additional isolated to scattered showers and storms develop, mainly in the wake of the current precipitation. The potential impact at KLSX would be after 21z. I have only VCTS given the lower coverage and will update if a direct terminal impact is anticipated. The coverage of this additional precipitation should diminish significantly between 00-02z as heating wanes and a cold front moves through the area, with VFR dominating through the remainder of the forecast period. Occasionally gusty northwest winds and diurnal cu are expected on Thursday. Glass && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX