539 FXUS63 KTOP 230448 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 1048 PM CST Fri Feb 22 2019 ...AVIATION UPDATE... .SHORT TERM...(This evening through Saturday) Issued at 345 PM CST Fri Feb 22 2019 While the main focus for the upcoming forecast will be on Saturday's winter storm, there will be plenty to talk about weather-wise tonight. Low stratus overspread the forecast area by midday as H850 return moisture streamed northward ahead of a digging upper tropospheric trough centered just west of the Four Corners. This trough takes on a negative tilt and lifts northeastward tonight, with the associated PV lobe centered near the Texas Panhandle region by 12Z Saturday. Increasing isentropic and kinematic lift should lead to the formation of widespread drizzle throughout the forecast area by this evening. The combination of increasing H850 WAA and an EML lifting northward from TX/OK leads to the realization of 200-500 J/kg of MUCAPE overnight--producing elevated showers over the drizzle with even the possibility of a few thunderstorms. The biggest question for the short-term revolves around the potential for freezing drizzle formation later tonight along the Nebraska border. While surface temperatures have risen above freezing throughout the entire forecast area, surface wet-bulb values are hovering around 30-32 degrees along the Nebraska border. With dewpoints expected to only gradually rise into the low 30s tonight, there is a concern that precipitation loading will cool the air temperature to the 31 to 32 degree mark along and north of a line from Concordia to Marysville. Confidence in the occurrence of the freezing drizzle is low at best, with even a 1 to 2 degree positive difference in the surface thermal profile negating the freezing drizzle threat entirely. Did issue a winter weather advisory for freezing drizzle, but it will take just the right alignment of ingredients for this threat to be realized. Fog will also be common throughout the area tonight with dewpoints of 30-35 degrees working over what remains of our snowpack and cool ground. .LONG TERM...(Saturday night through Friday) Issued at 345 PM CST Fri Feb 22 2019 Upper trough quickly moves northeast across Kansas Saturday. 100 knot 500mb jet streak rotates south to east around the system with deep cyclogenesis resulting in very potent system. Some track and timing differences persist though the bulk of the guidance is in a slower/farther south track compared to the GFS and FV3. Fog and drizzle transition to more of a rain through the day as deep lift moves in. Expect enough low-level theta-e advection to bring freezing drizzle concerns to an end early in the day with increasing surface winds allow for decreasing fog potential as well. Elevated CAPE values remain limited but such strong forcing could still bring at least isolated convection and contribute to previous light to moderate amounts to raise minor concerns for elevated river levels. Main focus is on the cold sector building in for the afternoon and evening. Strong TROWAL characterized by fairly deep negative EPV including through the dendritic growth zone wraps into northern and western areas, though having large snowflake structures reach the ground will be difficult in the very strong winds, with 925 mb winds still in the 35-45 knot range. Confidence on amounts remains lower than expected at this time range given relatively narrow band and the heavier precip, but at least several inches of snow are expected for much of north central Kansas with amounts quickly dropping off to the southeast. With the very strong pressure gradient immediately following the surface low and potential for at least a few hours of at least moderate to potentially heavy snow rates, went ahead with a Blizzard Warning for locations most likely to see greatly reduced visibilities and an Advisory just to its south. Northwest winds slowly diminish Saturday night and some drifting could persist toward dawn. Shortwave in the northwest flow over the northwest states brings a reinforcing cold airmass southeast into the Central Plains Sunday into Sunday night. Lee cyclogenesis via increasing westerly flow aloft ensues Monday, and where this focuses will be will play a large role in temperatures Monday and Tuesday, with guidance showing a rather wide spread. A weak wave in the southern branch brings small chances for light precipitation to southern areas Tuesday night into Wednesday. Confidence in the large-scale pattern falls in the later periods but the overall flow regime again supports below normal temperatures. && .AVIATION...(For the 06Z TAFS through 06Z Sunday) Issued at 1047 PM CST Fri Feb 22 2019 00Z models support the current forecast thinking, so there isn't a lot of change to the prev forecast other than to fine tune timing of the category changes. Instability is still progged across eastern KS so will keep a mention of VCTS in for TOP and FOE through the afternoon. A change over to snow for MHK looks to be around 20Z while a mix can not be ruled out for TOP and FOE as the precip comes to an end Saturday evening. Dry air on the back side of the system is expected to scourer out the low level moisture pretty rapidly bringing VFR conditions back into the terminals by 06Z. && .TOP WATCHES/WARNINGS/ADVISORIES... Blizzard Warning from noon Saturday to midnight CST Saturday night for KSZ008-009-020-021-034. Winter Weather Advisory from 3 PM Saturday to midnight CST Saturday night for KSZ022>024-035-036. Winter Weather Advisory until 9 AM CST Saturday for KSZ008>011- 020. Blizzard Warning from 3 PM Saturday to midnight CST Saturday night for KSZ010>012. && $$ SHORT TERM...Skow LONG TERM...65 AVIATION...Wolters