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FXUS63 KTOP 230536 AFDTOP

Area Forecast Discussion National Weather Service Topeka KS 1236 AM CDT Sat Sep 23 2023

Update to aviation forecast discussion

DISCUSSION
Issued at 234 PM CDT Fri Sep 22 2023

Key Points:

- Severe thunderstorm risk Saturday, mainly for northeast and east- central Kansas.

- Quieter weather returns for next week, with temperatures near average.

Currently a break in the action across the area, as this morning's thunderstorms have exited to the south and east. Continued southeasterly surface flow is keeping low-level moisture in place, helping lower stratus persist into the afternoon. Still, breaks in the clouds have helped temperatures approach 80 in spots. The strong upper low we've been watching for the last few days is currently over the Great Basin region and beginning to move east towards the Plains. Initially, this will build shortwave ridging over eastern Kansas. As a result precipitation chances will stay low this evening and overnight, though a brief shower or storm can't be ruled out across far northern Kansas.

As the upper low makes its way onto the Plains tomorrow, it will push a surface cold front eastward, extending southward from a surface low over South Dakota. Guidance is in good agreement that the front will be around Manhattan by early/mid afternoon, keeping the greater severe storm threat across northeast and east-central Kansas. There is still some potential for somewhat elevated storms to develop earlier across east-central Kansas, generally late morning to early afternoon. Some hail and gusty winds could occur with these storms, but more importantly they would reduce the instability for mid/late afternoon storms along the cold front. If this occurred, there would likely be a longer total period of storms, but the overall severe threat would be less. If the early storms are weak or don't occur, diurnal heating, rich low-level moisture, and steep mid-level lapse rates would result in 2500-3000 J/kg of ML CAPE developing ahead of the cold front.
Guidance has narrowed in on effective shear being in the 30-35 kt range, which while not great should be enough for some initial supercells eventually growing upscale along the front. A veering low-level jet looks to limit the overall tornado threat, though one or two can not be ruled out. Instead, damaging winds and large hail should be the main severe weather threats. Analogs to forecast soundings suggest some significant (2"+) hail would even be possible with initial supercells. Damaging winds will increase in potential as the initial cells grow upscale, particularly southeast of I-35 closer to the SPC's enhanced risk. Lastly, some storms could produce locally rainfall, especially if some training of storms can occur across far eastern Kansas.

By Sunday morning, the cold front will have pushed through the entire area, helping clear out any lingering overnight showers and storms. Drier air will filter in behind the front as surface high pressure moves in. Northwest flow will be in place aloft, with ridging to our west and our old upper low slowly moving over the Midwest. Given this pattern, clouds and precipitation will remain limited through the middle of next week. Temperatures stay near to slightly above average, with low/mid 80s for highs and mid/upper 50s for lows.

AVIATION
(For the 06Z TAFS through 06Z Saturday night)
Issued at 1235 AM CDT Sat Sep 23 2023

MVFR stratus moving up from central Kansas could begin to impact the KMHK terminal soon with persistent sub-IFR conditions through the morning hours. The other main concern this TAF period will be afternoon and evening thunderstorms impacting KTOP and KFOE. Moved back timing of VCTS to 3 PM with storms continuing into the evening hours. VFR conditions will be expected as storms move east overnight.

TOP WATCHES/WARNINGS/ADVISORIES
NONE.

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