Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 121751

Area Forecast Discussion
National Weather Service Topeka KS
1251 PM CDT Wed Aug 12 2020

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 309 AM CDT Wed Aug 12 2020

Thunderstorm activity is again impacting portions of northwest
Kansas early this morning, reinvigorated on a moderate low-level
jet and 850 mb moisture axis. Other MCSs were in northeastern
Nebraska and northern South Dakota where stronger westerlies aloft
lie. Water vapor suggests a modest shortwave moving west into the
Great Basin. Locally, skies have been mostly clear with light
winds though dewpoint depressions of a few to several degrees
persist. Will need to watch trends but at this point a fog mention
does not seem in order. Scattered areas of low cloud were also
depicted from southwest and south central Kansas to northeast

North to northwest upper flow to the west should keep convection
to the west out of the area and expect fairly quiet conditions
today. Will include some small precip chances in northern areas
this afternoon where a consistent model signal exists for modest
upglide on the 320 K surface with weak instability above this
level. Any precip should be light. With somewhat backed winds and
no change in airmass, kept high temps close to Tuesday`s.
Attention will turn to the northwest tonight as the Great Basin
wave enters the Plains with another convective complex possibly
forming. Mid/upper flow would favor this activity moving toward
central Kansas during the night. At least some uncertainty exists
with this scenario with storms continuing in western Nebraska at
this hour, which could impact afternoon instability. The 850 mb
moisture gradient pushes east into central Kansas overnight as
well with a 35 knot low-level jet giving rise to decent moisture
convergence. As seen in several CAMs and conditions to the west
early this morning, storms could form by this means as well.
Enough confidence exists for an increase in PoPs for especially
western areas. MUCAPE around 1500 J/kg and some effective shear
could bring some strong storms and locally heavy rains with any
training storms, though PW values are only around 1.5 inches --
not much above normal.

.LONG TERM...(Thursday through Tuesday)
Issued at 309 AM CDT Wed Aug 12 2020

Overnight convection may persist into much of the day as modest
mid-level isentropic lift continues but should wane as mid/upper
heights rise. With afternoon clearing expected, will keep highs in
the mid 80s northeast to lower 90s southwest though this could on
the high side if precip lingers longer. Some chance for convection
returns in eastern areas Thursday night as 315 K upglide
re-intensifies develops but large-scale subsidence should
moderate this activity. Friday may be the warmest day of this
forecast ahead of a weak cold front sinking southeast toward the
central Plains, and likely brings the greatest, though still
modest, Heat Advisory potential. Depending on its speed, Saturday
could still be quite warm south of I-70. Enough of a cap looks to
be in place in concert with very weak convergence to keep daytime
storms in check, but some chance for overnight storms exists from
convective remnants advecting southeast in a more northwest flow
Saturday night. This flow brings a Canadian-sourced airmass south
into the region early next week for below normal temps.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1240 PM CDT Wed Aug 12 2020

Low clouds finally scattered out late this morning with high
clouds expected to move across the area this afternoon. Main
impacts to aviation will be the potential for storms overnight
into early tomorrow morning. Models still vary on exact timing and
eastward extent of development, so for now have gone with VCTS
during the most likely window. Adjustments will probably be needed
in future updates. VFR conditions prevail overall, but could see
reduced vsby with heavier rainfall and possibly lower cigs with
storms. Winds remain out of the SSE at 5-10 kts.




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