Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 181730
AREA FORECAST DISCUSSION
National Weather Service Topeka KS
1230 PM CDT THU AUG 18 2016
...Update to aviation forecast discussion...
.SHORT TERM...(Today and Tonight)
Issued at 303 AM CDT THU AUG 18 2016
An upper ridge across the southern and central plains will shift
east across the Great Lakes states and lower MS river valley
Tonight. An intense upper trough across west central Canada will dig
southeast into the northern plains late Tonight.
Early this morning the low-level jet has increased to 30 to 35 KTS
across central and north central KS and may be providing enough
ascent for a few elevated showers and thunderstorms to develop
across central and north central KS this morning. There was also
weak isentropic lift noted at the 310K layer across north central KS
through 15Z. These isolated showers and thunderstorms may persist
into the mid morning hours but should weaken as the boundary layer
deepens, which will result in a decrease in the lift.
The remainder of Thursday looks dry with highs once again reaching
the lower 90s across much of the area. Southerly low level winds
will continue to advect deeper moisture northward across the CWA
during the afternoon hours, thus dewpoints should remain in the mid
to upper 60s. The slightly higher dewpoints will cause the heat
index to once again be slightly warm then the highs with heat
indices reaching the mid to upper 90s during the afternoon hours.
Tonight, The stronger low-level jet develops across southeast NE and
IA, thus I don`t expect any elevated showers or thunderstorms to
develop after midnight across the CWA as the better isentropic lift
will remain north and northeast of the CWA. Weak mid level flow
should keep any high based storms, that develop this afternoon
across the high plains of eastern CO and western KS, well west and
northwest of the CWA. By 12Z the surface cold front will be well
north of the CWA across northern NE, southwest into eastern CO.
Overnight lows will be around 70 degrees.
.LONG TERM...(Friday through Wednesday)
Issued at 303 AM CDT THU AUG 18 2016
On Friday a lead shortwave will kick out over the northern plains
while another wave dives southward out of southern Canada. This will
push a cold front into the forecast area during the afternoon hours.
This front will continue southward overnight and will be the focus
for showers and thunderstorms. Ahead of the front temperatures warm
to near 90 with the dew points in the upper 60s to lower 70s, which
should yield modest instability. Deep layer shear still appears to
be rather weak, which should lessen the overall extent of severe
weather. The shear will be orientated parallel to the boundary and
this along with deep daytime mixing should promote cold pool
development. These cold pools may be capable of producing damaging
wind gusts, and could force further downstream storm development.
Storms are expected to form along the cold front as it reaches south
central NE and north central KS in the late afternoon. These storms
will continue to progress eastward through the overnight hours. The
low level jet is forecast to strengthen out of the southwest, but
the speeds are not particularly strong. Also, the low level shear is
forecasted to be weak, which may lead to a cold pool dominate
environment. This together with the loss of daytime heating might
not favor much of a severe wind threat further downstream into
eastern KS. Some of the high res models depict several bowing
segments that develop in central KS that possibly lose strength
through the evening.
There are some models that show storm develop in the afternoon
across southeast and east central KS. Forecast soundings indicate
the cap will erode during peak heating. Although there is still no
obvious signal for forcing with the exception of possible elevated
convection from the morning that moves out of OK. If surface based
storms can develop then the environment would also support a
localized damaging wind threat through early evening. Widespread
rainfall ranging from 0.25 to 1 inch is expected across the area with
localized amounts up to 3 inches. Therefore localized flash
flooding can not be completely ruled out. Most locations dry out
Saturday as cool dry air filters in behind the front. Temperatures
drop below normal through early week. Conditions remain dry until
return flow increases below west to southwest flow aloft. Several
weak waves may lift out over the plains bringing chances for
precip back to the area.
.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 1229 PM CDT THU AUG 18 2016
VFR conditions are expected. Models indicate a chance for fog
tomorrow morning, but have left this out until there is more