Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 291133

633 AM CDT Fri Aug 29 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 359 AM CDT FRI AUG 29 2014

Early this morning, the upper level trough axis was slowly pushing
east into central Kansas. There were several smaller disturbances
within the larger trough as well, one of which has brought enhanced
thunderstorm coverage to north central KS early this morning. In the
near term, expect scattered thunderstorms to persist across the area
through at least mid-morning, with the band of greatest thunderstorm
coverage making gradual progression west-to-east across the forecast
area. This should result in some rain for most or all of the
forecast area through this morning, but to be honest the overall
coverage so far tonight has been less than expected, and saying that
the entire area will certainly see rain today is an uncomfortable
statement at the moment. The impressive nature of the trough at
least lends to the forecast for fairly widespread precip through

By this afternoon, forecast details get a bit fuzzier. Temperatures
will be dependent upon cloud cover and precipitation, and while the
morning storms seem likely to shift east by late morning/early
afternoon, there will still be forcing for ascent across eastern KS
and could see continued development. Whatever happens around mid
day, by late afternoon expect increased coverage of showers and
storms as the upper trough brings one last bit of focused forcing
into northeast KS in the form of an embedded vorticity max with good
model agreement on timing and location. Instability and shear this
afternoon and early evening will be on the low end as has been the
case for several days, and severe storms are unlikely, but pockets
of heavy rain will be possible given the very moist airmass. Rain
chances decrease west-to-east during the evening as the trough axis
moves east of the area and general subsidence overtakes eastern KS.
Clouds will decrease and temperatures should fall into the 60s by
morning. Surface moisture will linger in the area and could see some
potential for fog development especially in areas that get a decent
shot of rain today. For now have not included fog in the forecast as
light northwest winds may keep the boundary layer mixed enough to
prevent it...but any near-calm winds over moist ground could allow
locally dense fog to develop.

.LONG TERM...(Saturday through Thursday)
Issued at 359 AM CDT FRI AUG 29 2014

By Saturday morning, the mid-level trough that is currently
positioned just west of the forecast area will have progressed
eastward over the region, with the main trough expected to lift
northeastward toward the Great Lakes region. The cold front
associated with this system may still be lingering across far east
central Kansas Saturday morning before finally exiting the area. As
a result, have a slight chance for some lingering morning
precipitation over far east central Kansas, but otherwise expect dry
conditions for the remainder of the day across the entire forecast
area. Surface high pressure will build in behind this exiting
system, resulting in mostly sunny skies and southeasterly winds by
the afternoon which should boost high temperatures up into the mid
80s to near 90 degrees. These dry conditions will be short-lived
though as models show another mid-level trough moving into the
northwestern U.S. this weekend, deepening across the northern
Rockies on Sunday. This deepening trough will help to push another
area of surface low pressure (and its associated cold front)
eastward into the region. Models have been trending a bit slower
with this next system, with the cold front not expected to move into
north central Kansas until Sunday evening. As a result, have trimmed
back PoPs for Sunday to mostly slight chances across north central
Kansas. With this delay in precipitation and a strong southerly flow
ahead of this system supporting warm air advection into the region,
have trended temperatures a bit warmer with highs in the upper 80s
to mid 90s. As the cold front slowly tracks eastward across the
forecast area Sunday night through Monday, expect more widespread
shower and thunderstorm activity with the best potential for
precipitation looking to be focused generally along and north of
I-70 as stronger frontogenetical forcing and isentropic lift should
be located over that region. This region also will be favorable for
the development of some strong to severe thunderstorms as a 40-50kt
low-level jet sets up over the region with CAPE values reaching
upwards of 1500-2500J/kg and 0-6km bulk shear values increasing to
around 35-40kts. The primary concerns from these storms will be
large hail and damaging winds. An additional concern though will be
for the potential of heavy rain as PWAT values rise into the 1.7-2.0
inch range. While some locations across the forecast area are fairly
dry and are in need of precipitation, other locations have received
modest rainfall amounts over the last 1-2 weeks from the isolated to
scattered thunderstorms, so those locations will be more sensitive
to possible localized flooding concerns.

Models show the main trough axis shifting east of the area Monday
morning, however more of a broad trough is expected to remain in
place across much of the northern U.S.  With this flattening trough
axis, this cold front may get hung up across southern or central
Kansas and become fairly stationary through mid-week. However, there
is still a great deal of uncertainty with regards to the location of
this boundary and how far north it may lift into the forecast area.
With this weak boundary near the area and with weak embedded
shortwaves likely developing along the southern edge of the trough
axis, both the GFS/ECMWF are hinting at the possibility of some
scattered precipitation chances, but they vary greatly in when and
where it occurs. Have PoPs mentioned for Monday night through Tuesday
night but have gone dry through the remainder of the forecast due to
too much model uncertainty. Temperatures should cool down a few
degrees behind this system with highs in the mid/upper 80s and lows
in the 60s Monday and Tuesday, but may warm back up a few degrees by


.AVIATION...(For the 12Z TAFs through 12Z Saturday Morning)
Issued at 626 AM CDT FRI AUG 29 2014

Scattered thunderstorms will be common today, especially through
mid morning. Ceilings even with TS are expected to be above 4000
feet, and while a few brief vis restrictions are possible, the
vast majority of the morning should be 6SM or better. Could see a
relative break in precipitation between 16Z and 20Z, with
additional development likely during the afternoon and evening.
Precip at TAF sites should end by around 03Z. There is a small
chance for fog to develop by 12Z if winds can turn calm, but have
not included at this time.




SHORT TERM...Barjenbruch
LONG TERM...Hennecke
AVIATION...Barjenbruch is the U.S. government's official web portal to all federal, state and local government web resources and services.