Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 181734
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1234 PM CDT Mon Sep 18 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 316 AM CDT Mon Sep 18 2017

Convection was occurring across southwest Kansas ahead of a mid
level trough moving out of Colorado. Low level jet was veering to
the southwest across western and central Kansas since 04Z. Band of
showers and thunderstorms had developed over central and north
central Kansas in the nose of the low level jet within an area of
good 850mb moisture transport. The warm front over northern Oklahoma
is forecast to lift northward across Kansas through the day today as
the mid level wave traverses the state. Ascent associated with the
wave and isentropic lift over the frontal boundary should increase
precipitation from mid morning through early afternoon. Moisture
transport increases through the morning focusing on northeast and
east central Kansas where highest QPF is expected to occur. Shear
looks rather weak as do lapse rates along with around 1000 J/kg of
elevated cape. A few of the stronger storms may produce locally
heavy rainfall and small hail. Temperatures will be affected by
clouds and precipitation with north central and parts of northeast
Kansas clearing out in the afternoon will experience the warmer
temperatures.

Tonight shortwave ridging occurs across eastern Kansas behind the
departing wave. Warm advection continues through the night across
eastern Kansas. Convection will be possibly linger across northeast
and east central Kansas tonight. Soundings show elevated instability
around 1000-1500 J/kg remaining in place. Isentropic lift in the
305K-310K layer through the evening hours shifts east into Missouri
after 09Z and have decreased precipitation chances thereafter. Lows
tonight will only cool into the mid 60s.

.LONG TERM...(Tuesday through Sunday)
Issued at 316 AM CDT Mon Sep 18 2017

On Tuesday a strong mid/upper level trough will be moving over the
northern Rockies and lifting out over the northern plains. This will
cause the lee side trough to deepen and the pressure gradient to
become maximized over eastern KS. There could be a stray shower
lingering across east central KS in the late morning, but most
locations are dry through the day. The pressure gradient should
cause winds out of the south 15 to 25 mph with gusts upwards of 35
mph. As that main energy lifts over southern Canada it will drive a
cold front through the area on Wednesday. The convergence along the
front appears to be rather weak and there is a lack of upper level
support. Temperature and moisture from the day prior should set the
stage for decent instability, but there is a lack of deep layer
shear. If the cin can decrease enough through surface heating there
is a chance isolated to scattered storms could develop along the
front in the afternoon and early evening on Wednesday. There is
fairly good model agreement that the front will stretch from far
northeast through east central KS and gradually pushing eastward.
Some of the models keep precipitation through the night although the
apparent forcing is not obvious, and isentropic lift is present, but
weak. For now the slight chances are mainly confined to western MO.

The pattern remains quiet until the longwave trough deepens over the
western US this weekend. The evolution of this system is certainly
complex with several pieces of shortwave energy within the trough
axis. It is difficult to tell if the main energy moves over Canada,
digs over the southwest US, and or gets sheared out while over the
eastern Rockies. Either way an elongated cold front will set up over
the plains and remain rather stationary through the weekend. The
models have trended to keep this boundary west of the area through
the weekend with the exception of portions of central KS.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1232 PM CDT Mon Sep 18 2017

Another short lived batch of showers and scattered low clouds
lingers for the early part of the TAF cycle but clears up over the
next several hours. Main impact for overnight hours would be LLWS
that develops over the inversion tonight before the boundary layer
mixes out tomorrow.

&&

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

$$

SHORT TERM...53
LONG TERM...Sanders
AVIATION...67



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