513 FXUS63 KTOP 140444 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 1144 PM CDT Sat Apr 13 2019 ...Update to aviation forecast discussion... .SHORT TERM...(This evening through Sunday) Issued at 337 PM CDT Sat Apr 13 2019 Mid and high clouds depart from west to east late tonight with the threat for a hard freeze along and west of a line from Council Grove to Seneca. A large, meridional longwave trough dominates the upper-level pattern early this afternoon across the central CONUS, with a negatively-tilted shortwave/PV lobe at the base of the trough in western TX closing off and starting to lift northeastward through the Ozarks this evening--reaching the Ohio River Valley on Sunday. At the surface, a 1000 mb low north of Houston lifts northeastward through the ARK-LA-MIS region late this evening and follow its parent wave up the Ohio River Valley tomorrow. Across Kansas, a broad quasi-zonal surface ridge axis stretches from the Nebraska panhandle towards St. Louis, with the diffluent flow off this ridge axis providing northeasterly flow over the forecast area. As the surface low lifts northeastward, the pressure gradient tightens to some degree in the eastern third of Kansas through the overnight hours, keeping winds sustained in the 10 to 15 kt range in east-central Kansas. The mid-tropospheric deformation zone likewise pivots along a southwest to northeast line through southeastern Kansas and southwestern Missouri. There will likely be a sharp cutoff along the northwestern edge of this precipitation shield as the mid-level precipitation interacts with continued lower-tropospheric negative theta-e advection along the northern periphery of the cyclone. Forecast soundings from the RAP/NAM/GFS, coupled with the 12Z TOP RAOB, depict a stout sub-H700 dry wedge with Td depressions of 20-25 C at H850. Expect that there will be ample virga--maybe even some sprinkles-- southeast of the Kansas Turnpike, with the best chances of any measurable precipitation being along and southeast of the I-35 corridor. Rainfall amounts should be light at best, with the system departing before sunrise on Sunday. The potential for freezing temperatures is the main concern of this forecast, but hinges heavily on how fast the winds and clouds can lessen with the departure of the low. Most CAMs are in good agreement in the mid to high clouds having cleared as far east as Topeka by sunrise. North to northwesterly winds should fall to around 5 kts in north-central Kansas and 10 kts towards the Missouri border. Due to the increased mixing from these winds, only issued a freeze warning for areas along and west of a Dickinson to Nemaha county line, where lows are expected to fall to or below 32 F. A frost advisory was not issued further east as winds should keep the lower BL mixed enough to deter frost development. Later shifts will need to monitor the clearing trends of the clouds to determine if any eastward expansion of the freeze warning is warranted. Sunday should be seasonably cool and clear as the surface ridge axis passes through, with WAA overspreading central Kansas by the afternoon hours on the backside of the ridge axis. Highs should top out around 60 degrees with a light northwesterly wind backing to the southwest in the afternoon/evening. .LONG TERM...(Sunday night through Saturday) Issued at 337 PM CDT Sat Apr 13 2019 A warm-up is in store for early in the week, followed by the chance for showers and storms mid-week. Broad longwave ridging becomes established over the central CONUS for Monday, gradually amplifying Tuesday into Wednesday as a northern stream PV lobe digs southeastward into the Great Basin. Return southerly flow should boost temperatures back into the 70s and even 80s for Monday through Wednesday. A lee cyclone develops along the Front Range by Monday afternoon with a surface baroclinic zone extending along the Kansas/Nebraska border. Medium range solutions depict this low ejecting eastward on Monday night, but with little in the way of deep support, this low rapidly retreats westward with little in the way of sensible impacts on the local weather. The reestablished low ejects again early Wednesday in response to the approaching upper wave, tracking eastward through the state druing the afternoon and evening hours. The 12Z guidance rotates the surface baroclinic zone well north of the forecast area by the arrival of this low, which at the moment appears to minimize the threat for typical supercellular tornadoes. GFS forecast soundings depict 1500-2000 J/kg of MLCAPE and a modest unidirectional shear profile oriented parallel to the advancing boundary, supportive of initially discrete updrafts congealing into a line segment. However, at this range there still exists ample discrepancy in the model mass fields that cast modestly high uncertainty in this forecast. Temperatures cool off on the backside of this system, with the raw GFS/EC guidance struggling to reach 50 degrees for a high late in the week. && .AVIATION...(For the 06Z TAFS through 06Z Sunday night) Issued at 1130 PM CDT Sat Apr 13 2019 VFR prevails at terminals with mid clouds lifting over KTOP/KFOE through sunrise. As the system exits eastward, gusty northeast winds calm and back towards the northwest before increasing close to 10 kts aft 15Z. && .TOP WATCHES/WARNINGS/ADVISORIES... Freeze Warning from 3 AM to 9 AM CDT Sunday for KSZ008>011- 020>023-034>036. && $$ SHORT TERM...Skow LONG TERM...Skow AVIATION...Prieto