000
FXUS63 KTOP 221711
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1211 PM CDT Sat Jul 22 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 303 AM CDT Sat Jul 22 2017

07Z water vapor imagery shows the weakening upper ridge over
southern MO while the mean westerlies remained to the north along
the U.S./Canadian boarder. A subtropical plum of moisture was noted
from northern Mexico through the four corners region. At the
surface, an area of low pressure had moved into southwest IA with a
trough axis extending into northwest KS and southeast CO. Surface
obs show low level moisture already pooled to the north of the
surface low and back to the west along and north of the trough axis.

For today and tonight, the atmosphere is expected to become
moderately unstable by the early afternoon with little inhibition to
convection due to strong day time heating. Although there is not
much in the way of obvious forcing progged by the models to impact
the area through the afternoon. Nevertheless there should be some
low level convergence along the surface trough axis that gradually
shifts south through the day. With many of the convective allowing
models developing scattered storms by the late afternoon, think the
convergence should be enough for storms to develop along the trough
axis. Forecast soundings show a deep inverted soundings ahead of the
trough axis and PWs are progged to increase to near 2 inches as the
subtropical plum to the west and north moves into the area. So the
main concerns with the storms will be for the possibility of
downburst winds and locally heavy rainfall. Deep layer shear of only
10 to 25 KT suggests there will not be much organization to the
storms and that they could pulse in strength. Overnight, models show
a modest shortwave moving through the flow and clipping northeast
KS. This wave could act to maintain scattered showers and
thunderstorms into the early morning hours Sunday.

As for temps, models show the thermal ridge breaking down a little
from yesterday. Though forecast soundings once again mix very deeply
ahead of the surface trough. Think the main change in temps from
yesterday will be slightly cooler reading across the north where
winds should shift to the north once the trough axis passes through.
This should limit the mixing. Unfortunately it may not feel any
better with models pooling dewpoints in the mid 70s just behind the
front. So have highs from the upper 90s along the state line to the
105 range just ahead of the surface trough along the KS river. Heat
indices are forecast to once again range from 103 to 112 so will
maintain the excessive heat warning for the entire forecast area.
Lows tonight should be cooler. Although I did not go as cool as some
of the MOS guidance thinking cloud cover and low level moisture may
limit radiational cooling. So have lows in the lower to middle 70s.

.LONG TERM...(Sunday through Friday)
Issued at 303 AM CDT Sat Jul 22 2017

Sunday, the surface front will move south of the CWA and the chances
for showers and thunderstorms across east central KS will decrease
into the afternoon hours as the front shifts southward into northern
OK. Most numerical models have the line of elevated showers and
storms passing south of the CWA after 18Z SUN. It will feel a bit
cooler on Sunday with highs mainly in the lower 90s, though, the
southwest counties may reach the mid 90s. Surface dewpoints will be
in the mid 60s to lower 70s, thus heat indices across east central
KS may reach around 100 degrees.

Sunday night through Tuesday night, The center of the upper level
ridge will amplify across the central Rockies and high plains of NM
and CO. Eastern KS will be under northwesterly flow at the mid and
upper levels of the atmosphere. There may be some weak upper level
troughs that may move southeast across the plains. A lee surface
trough will deepen across eastern CO and will cause the low-level
winds across eastern KS to become southerly. The moisture advection
along with any ascent ahead of the minor H5 troughs may provide
enough lift for isolated to scattered thunderstorms. The vertical
windshear looks weak, so no severe weather is expected. Highs on
Monday and Tuesday will reach the lower to mid 90s. The dewpoints
will continue to be in the upper 60s to lower 70s, thus the heat
indices once again may reach to around 100 degrees.

Wednesday through Thursday, The upper ridge across the southern high
plains will expand east across the southern plains and KS. Highs on
Wednesday and Thursday will warm back into the mid 90s to around 100
degrees. Heat indices will increase to around 105 degrees, thus a
heat advisory may needed for both afternoons. The thunderstorm
chances should remain west and north of the CWA.

Thursday night through Saturday, An upper level trough will round
the H5 ridge axis across the northern plains and dig southeast into
the Midwest. This will cause a surface front to move southward
across the CWA Friday afternoon. There will be a chance for showers
and thunderstorms Thursday night through Friday night as the surface
front moves southward across the region. Highs Friday and Saturday
will cool down into the lower to mid 90s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1210 PM CDT Sat Jul 22 2017

VFR will prevail through the period, although TS development is
expected after 23Z near terminals which could lead to brief
restricted conditions depending where storms develop.  Have included
the best timing for storms over terminals through use of the TEMPO
group.  Some hi-res guidance have been developing TS activity
predominantly south of terminals which is also a possibility.
Precipitation is expected to move south of all terminals between 07-
08Z with light and variable winds continuing through the end of the
period.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM CDT this evening for
KSZ008>012-020>024-026-034>040-054>056-058-059.

&&

$$

SHORT TERM...Wolters
LONG TERM...Gargan
AVIATION...Heller