Scientific Forecaster Discussion
000 FXUS63 KLSX 210448 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1148 PM CDT Fri Sep 20 2019 .SHORT TERM... (Through Late Saturday Night) Issued at 253 PM CDT Fri Sep 20 2019 No changes to the Flash Flood Watch. Moisture continues to surge northward into the region, evident in TSRA coverage over southern portions of the CWA. Storms should diminish with sunset, however, expect storms to linger a little longer than over the past couple of days. The focus of precip should shift to western, then northern, portions of the CWA as the LLJ increases. That said, with the vort max over southern MO into AR lifting into the region, going forecast may not have high enough PoPs far enough southeast. Models are also suggesting a band of showers lifting eastward through the central portions of the CWA around and just after sunrise. Some of the later cycles of the RAP have shifted this a little further north. As such, confidence remains on the lower end for timing and placement. Still expect precip to gradually diminish through the morning hours. After a lull in activity through much of the afternoon, expect precip coverage to increase across northern portions of the CWA during the late afternoon and persist through the overnight hours. Tilly .LONG TERM... (Sunday through Next Friday) Issued at 253 PM CDT Fri Sep 20 2019 Main focus continues early in the period. A confluent upper trof approaches the region on Sun with the surface cold front reaching northern portions of the CWA mid to late Sun morning. Moisture advection ahead of this front continues with PWs of 2+ inches. With the LLJ parallel to the front, training storms will be possible. These factors in addition to high freezing level and the high PWs, a threat of flash flooding exists for mainly the northern third or so of the CWA. However, will keep the watch as is due to continued uncertainty. With the available CAPE and deep layer shear ahead of the front on Sun, will need to continue to monitor a severe threat. The cold front is expected to push south through the area Sun night with rain coming to an end. After a dry Mon and most of Tues, the chance for rain increases again mid to late week. With differences among model solns, have kept PoPs low for now. Tilly && .AVIATION... (For the 06z TAFs through 06z Saturday Night) Issued at 1136 PM CDT Fri Sep 20 2019 Isolated to scattered showers and storms are expected to develop in central and NE MO early this morning, pushing east through the morning hours. There is some uncertainty just how far south and east these storms will reach, with UIN being the only terminal where precip is likely this morning. The moisture that will help develop these storms will also result in MVFR cigs in these areas, perhaps falling to low end MVFR for areas directly impacted by any storms. Thinking storm activity will diminish somewhat in the afternoon, though like the last few days, isolated storms will be possible. Also like the last few days, it's difficult to tell if any terminals, will be directly impacted by these afternoon storms. Moisture is a bit richer toward UIN and COU, so have opted to keep a vicinity mention in those TAFs through the afternoon while I've left the STL metro TAFs dry for much of the afternoon. BSH && .PRELIMINARY POINT TEMPS/POPS... Saint Louis 73 85 73 84 / 30 30 30 80 Quincy 70 79 68 73 / 60 60 80 80 Columbia 70 80 69 77 / 50 50 60 80 Jefferson City 71 82 70 79 / 40 40 50 80 Salem 69 83 70 86 / 5 5 5 60 Farmington 68 82 68 85 / 10 20 0 60 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Flash Flood Watch from Saturday evening through late Sunday night for Audrain MO-Boone MO-Callaway MO-Knox MO-Lewis MO- Marion MO-Monroe MO-Montgomery MO-Pike MO-Ralls MO-Shelby MO. IL...Flash Flood Watch from Saturday evening through late Sunday night for Adams IL-Brown IL-Pike IL.