Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 071740
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1240 PM CDT Fri Aug 7 2020

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 358 AM CDT Fri Aug 7 2020

Heights aloft continue to rise early this morning, as the upper
ridge over the Southern Plains strengthens and begins to shift
northeastward. Atop the ridge and east of a lee trough, several
areas of thunderstorms are still ongoing from Oklahoma up through
the Dakotas, maintained by a southerly LLJ. As the LLJ shifts
eastward through sunrise, clouds should develop over the next few
hours across the forecast area. Increasing WAA on the nose of this
LLJ may allow for a few weak thunderstorms to develop across east-
central Kansas by sunrise. Based on current convective trends
though, the developing convection over northeast Oklahoma could keep
the better thunderstorm chances just to the south, if it can expand
and cut off the stronger WAA into the area. Any convection that does
develop in the next few hours should quickly weaken and move off to
the southeast by mid-morning.

Heading into the afternoon, strengthening lee troughing should
tighten the pressure gradient across eastern Kansas, with southerly
winds increasing as a result. These winds will help to further
advect higher temperatures and dewpoints into the area. Coupled with
partly sunny mid-day skies, this should allow highs to approach 90
for many. Added some light PoPs along I-70 this afternoon, as
forecast soundings show some elevated instability in a region of
isentropic ascent. CAMs also depict some weak showers or
thunderstorms in this area, further supporting the idea. By late
evening and into tonight, the LLJ will strengthen again to around 45-
50 kts. Isentropic ascent on the nose of this LLJ will likely kick
off another round of overnight elevated convection somewhere in east-
central Kansas. While very steep lapse rates aloft will contribute
to moderate elevated instability, effective shear above the boundary
layer will be less than 20 kts. So can`t rule out some small hail,
but the overall severe weather risk appears very low. And while
there are some ingredients for locally heavy rain with these storms,
the overall signal for more widespread heavy rain appears low as
well.

.LONG TERM...(Saturday through Thursday)
Issued at 358 AM CDT Fri Aug 7 2020

Any storms Saturday morning should once again quickly weaken by noon
as the nocturnal LLJ diminishes. As this occurs, the upper ridge
axis will move almost overhead, with H70 temps rising to 25-28C.
Fairly deep mixing should help highs reach the mid 90s for many,
possibly approaching 100 towards central Kansas. Dewpoints in the
low to mid 70s will push heat indices to around 105, so may need to
consider a heat advisory to cover those impacts. Sunday will likely
also be hot, though additional uncertainties exist with the
potential for remnant cloud cover and precipitation from earlier
storms over Nebraska.

Monday through the middle portion of next week, temperatures should
generally return to near average, with highs in the upper 80s. This
will be a result of a strong trough over the Northern Plains, that
while not digging far enough south to bring a true cool shot, will
flatten the ridge and allow zonal flow to become predominant.
Shortwaves embedded in this zonal flow will bring increased
precipitation chances, likely starting around Monday as an initial
front moves through.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1240 PM CDT Fri Aug 7 2020

Areas of MVFR ceilings gradually lift to VFR this afternoon with
gusty SSE winds of 15 to 25 kts during the afternoon today and
Saturday. Surface winds decrease this evening with LLWS during the
overnight and early morning hours. A few showers and thunderstorms
cannot be ruled out in eastern Kansas this afternoon through
tonight.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Reese
LONG TERM...Reese
AVIATION...Skow



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