663 FXUS63 KTOP 212257 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 457 PM CST Sat Nov 21 2020 ...AVIATION UPDATE... .DISCUSSION... Issued at 246 PM CST Sat Nov 21 2020 An upper level trough was digging southeast across the northern and central Plains early afternoon and will amplify Sunday morning as it moves into the upper and mid MS river valley. Drier low-level air parcels were advecting west around a surface ridge of high pressure located across IA. Much of the radar returns across the CWA this morning were not reaching the surface. Isentropic lift at the 295-290K levels will continue increase across the southern and eastern counties of the CWA through the remainder of the afternoon and into the evening hours. The DCVA ahead of the H5 trough axis will increase across eastern KS as the upper level trough begins to amplify as it digs southeast towards eastern NE later this afternoon and through the evening hours. The dry low-level of the atmosphere will become saturated enough for light rain to reach the surface. The best chance for rain will be generally along and south of I-70 from SLN to TOP, then along and east of US 75. The highest forecast QPF will be located across the southeast counties, around 0.25". QPF across much of east central and northeast KS will range between 0.10" to 0.2". North central KS will only receive a few hundredths of an inch up to 0.1". As the H5 trough axis digs southeast across the CWA, isentropic downglide should bring an end to the the light rain chances. A few showers may linger across the northeast counties into the morning hours of Monday as several CAM models show a weak TROWAL developing on the west side of the upper trough, so I kept some low chance PoPs going for the northeast counties through 12Z SUN. Vertical temperature profiles look warm enough for the precipitation to be in the form of rain. The clouds will decrease from northwest to southeast across the area during the mid and late morning hours of Sunday. Afternoon insolation will help highs to the lower to mid 50s, despite northwest surface winds. Sunday through Tuesday, an upper level trough will move onshore across CA and shift east across the the southwest US and Great basin and begin to amplify as it approaches the central Rockies. Ahead of the trough a lee side surface low will develop in eastern CO, with the lee surface trough extending southward across the southern high Plains. Strong warm advection and deeper moisture transport by 850mb winds and LLJ will cause isentropic lift to develop across western and central KS through the night. If the isentropic lift expands east fast enough into north central KS, precip could start out as light snow but if it does begin as snow, it will quickly change over to rain as the WAA increases and 850mb and surface temperatures warm above freezing. Cloud cover and scattered to numerous showers will keep highs in the mid to upper 40s Monday afternoon. The rain chances will increase through the day Monday across the CWA as the isentropic lift increases. Temperatures Monday night may remain nearly steady in the 40s, as the WAA increases. The upper trough will move east across the Rockies into the high Plains by 18Z Tue. There may be enough instability above the low- level inversion for elevated thunderstorms to develop on Tuesday. It is too early to tell what type of MUCAPE will be realized Tuesday but given the strong dynamics and vertical windshear some of the elevated storms may be strong and have the potential to produce small hail. At this time the surface based storms will remain across OK and north TX, and some of these may be severe as they spread northeast across eastern OK, AR and south central MO. Tuesday night through Wednesday night, as the center of the H5 trough will shift east across KS, as a strong cold front will move east across the CWA during the evening hours. This should bring an end to any elevated storms. Strong CAA on the west side of the H5 trough axis may cool vertical temperature profiles enough that some some of the rain may mix with and change to snow before the stronger isentropic downglide arrives. The ECMWF shows a TROWAL developing along the NE/KS border on the back side of the upper low over northern MO and eastern IA. This may cause some measurable snowfall to occur along the NE and KS border through the morning hours of Wednesday. As the upper low tracks towards the Great Lakes States, skies should begin to clear Wednesday afternoon with highs only reaching the upper 40s to lower 50s. Thursday (Thanksgiving), looks to be dry, as an upper ridge shifts east across the Plains into the east central US. An upper level trough will dig southeast into the southern CA and west-southwest mid-level flow will be noted across the Plains. Partly cloudy skies will allow highs to reach the mid to upper 50s with light southeast winds through the day. Friday through Saturday, the upper trough across the western US will shear apart with the northern stream sections moving east across the northern Plains. The resulting low-level CAA across the northern Plains will bring a surface cold front southward across the CWA early Friday morning. Highs on Friday will only reach the mid to upper 40s with northerly surface winds. The southern stream section of the H5 trough will become a closed upper low and will slowly shift east into the southern high Plains by Saturday. There may be some light rain or even snow showers across the southern counties on Saturday. Highs may only reach the lower 40s. If the ECMWF solution verifies there will be a better chance of the rain changing over to snow Saturday night and into Sunday as the upper low ejects northeast across southern KS and phases with a northern stream H5 trough. The ECMWF shows vertical temperatures profiles below freezing with surface temperatures in the 20s and 30s Saturday night into Sunday. This solution will probably change quite a bit over the next several model runs. && .AVIATION...(For the 00Z TAFS through 00Z Monday) Issued at 457 PM CST Sat Nov 21 2020 Water vapor shows a shortwave at 700MB moving into north central KS, and models dry out mid levels behind this wave. So will precip continue through the night? Forecast soundings keep the low levels saturated until a more amplified 500MB shortwave swings through mid to late morning Sunday with generally weak to neutral isentropic lift. So think some BR or -DZ may linger through the early morning hours with a few hours of IFR CIGS and MVFR visibility generally between 06Z and 12Z. Conditions should rapidly improve after 14Z as dry air advection from the northwest increases. && .TOP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ DISCUSSION...Gargan AVIATION...Wolters