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000
FXUS63 KTOP 251109
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
609 AM CDT Tue Jul 25 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 314 AM CDT Tue Jul 25 2017

In the mid-levels, the upper ridge continues to build over the
central US through the day keeping dry conditions and hot
temperatures this afternoon. With mostly clear skies leading to
strong diurnal heating, plus deep boundary layer mixing,
temperatures this afternoon will rise into the mid- 90s. Dewpoints
range from the mid-60s near central Kansas to the lower 70s in
far eastern Kansas leading to heat indices ranging from 98-106
degrees across the area, with the hottest indices in far eastern
Kansas. Went with a Heat Advisory for portions of the area this
afternoon where the highest indicies are seen.

The ridge begins to flatten through the evening bringing more zonal
flow across northern Kansas by early tomorrow morning.  At the
surface, low pressure deepens near the Rockies through the evening
and a wave kicks this feature westward into western Kansas during
the overnight hours.  The NAM/GFS bring in precipitation early
morning to north central Kansas, while the ECMWF keeps chances north
of the area.  Went with small POPs in north central Kansas after
midnight to account for this possibility. Shear looks weak during
these hours and severe weather is not expected. Low temperatures
tonight remain warm with mid to upper 70s seen across northeast
Kansas.

.LONG TERM...(Wednesday through Monday)
Issued at 314 AM CDT Tue Jul 25 2017

For Wednesday through Thursday, the big question is timing the
boundary through the forecast area. The NAM is quite a bit faster in
bringing the boundary into the forecast area around mid day
Wednesday while other solutions wait until late in the day or
through the overnight hours. The main impact, aside from precip
chances, would be on temps and the heat index. For now have kept
with the consensus with regard to the timing, bringing the boundary
into north central KS late in the day. This would support hot
weather for another day with heat indices easily into the 103 to 107
degree range. However the ARW/NMM/Experimental HRRR have scattered
convection by the early afternoon as far south as the KS river which
could cause the temp forecast to be to warm. Given this uncertainty
in the precip timing, have opted to not issue a heat advisory at
this time in hopes the solutions converge on a common idea in later
runs. As for potential for severe thunderstorms with the boundary,
deep layer shear remains weak with 0-6KM shear values around 25KT.
But some moderate instability is progged to develop so some pulse
severe storms are not out of the question. Obviously timing of the
storms will also impact severe potential since instability should
wane with the lose of daytime heating. Chances for showers and
thunderstorms will linger into Thursday with the potential for the
front to slowly clear out. Although by Thursday evening, the
boundary should be to the south of the forecast area and have
lowered POPs for Thursday night and Friday.

The synoptic pattern is forecast to amplify through the weekend and
into next week with a longwave trough developing over the Great
Lakes and eastern U.S. while the upper ridge retrogrades to the
inter-mountain west. These leaves northwest flow over the central
plains with transient perturbations noted in the model progs. Since
confidence in any forcing in this pattern is rather low, have a dry
forecast going for Friday through Monday. The good news is the
pattern will favor more comfortable temps as surface ridging sets up
over the upper Midwest and keeps an easterly low level flow across
eastern and central KS. So the forecast has lows in the 60s with
highs in the mid and upper 80s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 608 AM CDT Tue Jul 25 2017

VFR conditions are expected throughout the period.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 8 PM CDT this evening for
KSZ011-012-021>024-026-035-036-038>040-055-056-058-059.

&&

$$

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