Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 261726
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1226 PM CDT WED AUG 26 2015

...Update to aviation forecast discussion...

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 308 AM CDT WED AUG 26 2015

08Z water vapor imagery shows the upper ridge centered over northern
NM/southern CO while a longer wavelength trough has set up well off
the west coast. At the surface, a ridge of high pressure stretched
from MN through far eastern KS. A surface moisture axis stretched
from the TX gulf coast northwest into southwestern KS with dewpoints
in the mid and upper 60s.

For today and tonight, a trough of low pressure in the lee of the
central Rockies is progged to deepen while the surface ridge axis
slowly moves east. This should allow for a bit more of a pressure
gradient through the day and a southeasterly wind to develop. This
should also allow for the surface moisture axis to shift more into
central KS through the afternoon. Model forecast soundings show a
good elevated mixed layer maintaining a cap over the boundary layer
through the day. So with no real forcing seen up stream, today
should be dry once again with plenty of sunshine. Warm air is
progged to advect into central KS from the west as the surface ridge
slides off to the east. Because of this highs should be a couple
degrees warmer than yesterday. Areas out around Abilene and
Minneapolis should see highs around 90 this afternoon.

This evening is again expected to be pleasant, but after midnight
all the guidance is pointing to a strong warm air advection pattern
developing over northeast KS. Isentropic surfaces develop some
upglide from 900MB through 750MB while 700-500MB lapse rates steepen
to around 8 C/km. Because of this think there is a chance for some
elevated storms through the early morning hours Thursday. The main
question is whether there is enough moisture for elevated parcels to
become positively buoyant as there looks to be more than enough
lift. The GFS continues to have a drier solution than other models
and still its solution hints at the possibility for elevated storms
in its prog of condensation pressure deficits. Therefore think
chances for precip may be better than a slight chance and have
trended POPs up. If it looks like the moisture will be there, the
potential for storms is probably higher than the forecast shows.
Also if storms are rooted near 850MB, there could be quite a bit of
elevated instability for storms to possibly produce some severe
hail. The NAM solution appears to be the most bullish with the
moisture and develops MUCAPE on the order of 2000 J/kg with
reasonable 0-6km shear. So this will need to be monitored. A little
more of a gradient keeping winds from going calm Thursday morning
and the possibility for AC to develop should help keep lows in the
lower and middle 60s.

.LONG TERM...(Thursday THROUGH Tuesday)
ISSUED AT 308 AM CDT WED AUG 26 2015

Thursday, isentropic lift at the 310K level will continue through the
morning hours across the eastern counties of the CWA. The NAM model
seems to be the most aggressive in breaking out QPF across most of
the CWA during the early morning hours and continuing elevated storm
chances through the late morning hours. The NAM has MUCAPES between
2,000 and 3,000 J/KG but I`M not sure if the parcels will originate
within the deeper 850mb moisture. If they do, then we could see some
of the elevated storms becoming strong to possible severe with penny
to quarter size hail. The WRF solutions hold off on developing
elevated convection until after 12Z across the extreme northeast
counties of the CWA, then builds the elevated storms southward
across the extreme eastern counties of the CWA. I think for now, I
will keep slight chances for thunderstorms across much of the CWA
and place a 30 POP across the extreme northeast counties in the 12Z
to 18Z time period.

The morning elevated storms should end across the eastern counties
during the early afternoon hours as the stronger WAA shifts
northeast of the CWA. An upper level trough will round the upper
ridge axis over the southwestern US and amplify as it move eastward
across WY and northern CO into NE and western KS. Thunderstorms will
develop across western KS along a surface trough due to surface
convergence and increasing ascent ahead of the H5 trough. Highs on
Thursday afternoon will reach the lower 80s across northeast KS with
some upper 80 degree readings across the southwest counties.

Thursday night, the thunderstorms across western KS will congeal
into a line or cluster of thunderstorms. If enough instability
develops across north central KS during the late afternoon and early
evening hours, then some of the storms moving into the western
counties of the CWA may be strong as the SFC to 6 KM effective shear
increases to 40 to 45 KTS. If the storms remain surface based then
the stronger storms may produce damaging wind gusts and large hail.
The storms will most likely become elevated and weaken as they move
east into northeast and east central KS through the night.

Friday, the upper trough will become a closed upper low as it moves
east across NE into IA. The surface cold front will move very slowly
across the eastern counties of the CWA through the day. The
combination of ascent from minor H5 troughs digging southeast on the
back side of the closed low over IA and surface convergence ahead of
the front will provide a chance for showers and thunderstorms. Highs
Friday afternoon will range from near 80 across the northwest
counties on the west side of the surface front to the mid 80s across
east central KS.

Saturday through Tuesday, an upper level ridge across the four
corners region will amplify and expand east across the plains into
the mid MS river valley by Tuesday. Highs on Saturday will only be
in the lower to mid 80s with northwest flow aloft. However, highs
will warm into the mid to upper 80s on Sunday and into the lower 90s
next Monday and Tuesday as the upper ridge axis expands northeast
across the plains and into the central US.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z Thursday AFTERNOON)
ISSUED AT 1215 PM CDT WED AUG 26 2015

VFR conditions expected most, if not all, of the TAF period.
However, there is a small chance for some morning thunderstorms to
work into the terminal sites mainly around KTOP/KFOE. If
thunderstorms do develop, they will likely be high based, so most
likely any restriction would be concerning visibility if a storm
passes over the terminals. KMHK is expected to stay out of the
immediate concern for storm development or at least maintain a smaller
chance. This is the reason no mention of storms as far West as
KMHK at this time. Planners for that area should monitor
subsequent TAFs in case areas of concern do need to be spread
further West.

&&

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

$$

SHORT TERM...Wolters
LONG TERM...Gargan
AVIATION...Drake



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