000
FXUS63 KTOP 202329
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
629 PM CDT Wed Sep 20 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Thursday)
Issued at 316 PM CDT Wed Sep 20 2017

Front made it about halfway across the forecast area before stalling
out, generally along a line from Hiawatha to Manhattan toward
McPherson.  Temps behind the front are a few degrees cooler, and
dewpoints are only in the 50s, while ahead of the boundary across
eastern counties we have dewpoints in the low 70s and temperatures
in the 80s. Moisture in the boundary layer and good mixing has led
to a layer of thin cumulus at the top of the mixed layer, which may
help keep highs a degree or two cooler for today.

Next fly in the ointment are rain chances, which are not well agreed
upon in guidance. Visually the convergence along the front does not
appear strong enough to erode the cap for today into tonight, and
best chances, which are low at best, will likely have to rely on
something backbuilding from the front in NW MO back into our area.
large scale models giving up some QPF, but convective allowing have
hardly any rain chances. 3KM NAM soundings indicate cap could erode
in the east overnight and allow for a few storms with respectable
elevated CAPE and steep mid level lapse rates, but very little
shear.  Have gone with some low confidence isolated PoPs this
evening and overnight. Boundary quickly becomes oriented in parallel
with the flow aloft and is advected quickly northward for Thursday,
with most of the area in the warm/humid sector.  After lows in the
70s tonight highs rise back into the upper 80s east to mid 90s west.
 Winds from the south are once again breezy, in the 15-20 mph range
and gusts around 30-35mph expected in the afternoon. Despite breezy
conditions and drying grasses, the higher RH should help buffer fire
danger.

.LONG TERM...(Thursday night through Wednesday)
Issued at 316 PM CDT Wed Sep 20 2017

Slow moving upper trough meanders around the western CONUS with the
upper ridge in control across our area, being blocked by the two
tropical systems off the Atlantic. Strong southerly flow each
afternoon through Sunday is aided by a deepening sfc low coming off
the western high plains. Based on trends in guidance and previous
forecast blends, used CONSMOS to increase sustained speeds,
particularly Friday and Saturday afternoons. Fridays heat indices
could once again approach the upper 90s to near 100 degrees with
dewpoints around 70 and highs forecast in the lower 90s.

Overall model trends for the next cold front to sweep through
continue to slow with both the GFS and ECMWF carrying the frontal
boundary through late Sunday night into Monday over much of the CWA.
Timing of the departure of the qpf behind the front still varies
somewhat with the ECMWF slower than the GFS in the Tuesday to late
Tuesday night time frame. A much cooler, Canadian airmass builds
into the region with 70s for highs possible by Tuesday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 627 PM CDT Wed Sep 20 2017

There may be an isolated chance for a shower or thunderstorm this
evening as a weak cold front pushes southeast across the KTOP and
KFOE terminals. Otherwise, expect VFR conditions at all terminals.

&&

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

$$

SHORT TERM...67
LONG TERM...Prieto
AVIATION...Gargan