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Area forecast discussion 
National Weather Service Topeka Kansas
1227 PM CDT Thursday Aug 27 2015

..update to aviation forecast discussion...

Short term...(today and tonight)
issued at 331 am CDT Thursday Aug 27 2015

08z water vapor imagery shows an upper level shortwave over Wyoming with
possible a vort Max lifting through eastern Colorado. The center of the
upper ridge has been pushed south towards the Texas Big Bend. At the
surface, an area of low pressure has remained nearly stationary
across the Nebraska Panhandle for the last several hours while the
surface ridge axis slowly moves east. An axis of dewpoints in the
mid to upper 60s stretched from OK into central South Dakota. And area
profilers show a decent warm air advection pattern over central and
eastern Kansas. Satellite is showing a narrow band of ac setting up just
west of the MO river.

For the early morning, models continue to suggest isolated to
scattered elevated storms should develop over far eastern Kansas.
Therefore have continued with some low chance pops over the eastern
portions of the forecast area. Once the low level jet diminishes
later this morning, this elevated convection should also fall apart
with the lift weakening.

Then attention turns to the upper shortwave to the northwest. There
seems to be a trend in the models to lift the vort Max over eastern
Colorado mainly north of the forecast area through Nebraska. Meanwhile the
surface wave is progged to move into southeastern South Dakota overnight. So
the stronger large scale forcing is expected to pass mainly to the
north of the forecast area. Ahead of the front, an elevated mixed
layer is progged to keep the boundary layer capped for much of the
day. A trailing cold front may be the necessary lift for storms to
move into the area, mainly during the late evening and overnight
hours. By this time instability could be waning with the loss of
heating. Additionally deep layer shear is progged to only be around
25 kts through the night on account of rather weak mid and upper
level winds. It appears as though the main severe weather concern
will be if storms are able to develop out ahead of the front across
north central Kansas during the heat of the day. Given the marginal deep
layer shear, think clusters of storms are the would be the more
likely Mode leading to a hail and wind concern if storms are able to
develop. Otherwise think scattered to possibly a broken line of
storms could move through the area with the front.

Think there should be reasonable insolation today with models
showing 850mb temps a couple degrees warmer than yesterday. Mixing
850mb temps to the surface would suggest highs in the upper 80s to
mid 90s. Have not gone quite that warm as the NAM forecast soundings
don't quite mix the boundary layer to 850. Cloud cover and a
southerly wind through the night with not much in the way of cold
air advection behind the front should keep lows Friday morning
around 70.

Long term...(friday through wednesday)
issued at 331 am CDT Thursday Aug 27 2015

Friday, the amplifying upper level trough across southwest
Minnesota/northwest Iowa at 12z will be shifting east through the day. The
upper trough will be slightly positive tilt, thus there may be some
stronger ascent ahead of the upper trough axis across eastern Kansas
during the day. The surface cold front will slowly push eastward
across northeast and east central Kansas during the afternoon hours.
After some scattered showers and thunderstorms in the morning, there
may be a break in the rainfall through he late morning and early
afternoon hours. The timing of the front is still in question. The
European model (ecmwf) has the slowest solution with the arw having the fastest
solution...pushing the front through the County Warning Area by 00z Sat. If the the
front remains across the eastern counties of the County Warning Area then scattered
showers and thunderstorms will redevelop during the late afternoon
and continue into the evening hours. If the the slower 12z European model (ecmwf)
verifies then much of the County Warning Area may see scattered to numerous showers
and thunderstorms redevelop during the afternoon hours and extending
into the evening hours.

Even though the 850 mb and surface winds
will veer through the day the flow at the mid and upper levels of
the atmosphere will become more northwesterly, thus the surface to 6km
effective shear will be 40 to 50 kts ahead of the surface front. The
question will be to what degree the atmosphere will destabilize. The
00z NAM shows MLCAPE around 1500 j/kg which may cause some of the
storms to be strong to severe. However, if the faster WRF model is
correct the storms may initiate along the front over the extreme
southeast counties of the County Warning Area and shift east of the area during the
late afternoon and evening hours. Friday's highs will be dependent
on where the front is located and also cloud cover. At this time
much of the County Warning Area will have highs in the mid 80s.

Saturday, a weak surface ridge will shift southeast across Iowa into
northern MO. Light and variable winds will gradually become
southeast by the late afternoon hours. Highs will be in the lower to
mid 80s.

Sunday through Wednesday, a broad upper level ridge across the west
central US will shift east across the plains and will then slowly
move eastward across the MS River Valley. A longer wave length upper
level trough will develop across the extreme western US and the mid
and upper level jet will remain well north of the cwa, from California
northeast into central Canada. Highs will warm into the upper 80s to
lower 90s on Sunday with lower to mid 90s for highs Monday through
Wednesday. There will be near zero precip chances through the period
even though southerly low-level winds may advect deeper Gulf
moisture northward across the area Monday through Wednesday. So the
apparent temperatures may be slightly higher than the dry bulb
temperatures.

&&

Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1223 PM CDT Thursday Aug 27 2015

Somewhat tricky forecast with convection the primary concern.
Vc activity continues for another hour or so before an
afternoon/evening break. Brought thunderstorms in the vicinity back after midnight with
best chance for a line in the 09-14 time range. Some models break
out showers and ts sooner than this, will need to watch for
updates.

&&

Top watches/warnings/advisories...
none.
&&

$$

Short term...wolters
long term...gargan
aviation...67

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