Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 011119

619 AM CDT Mon Sep 1 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 342 AM CDT MON SEP 1 2014

Water vapor imagery showed a broad mid-level trough in place
across the northern U.S. with the shortwave trough that has helped
to support the overnight shower and thunderstorm activity early
this morning centered over the forecast area and shifting
eastward. The cold front associated with this storm system has
been lagging behind the precipitation, with it stretched across
north central Kansas as of 08z. Models still seem to be a bit fast
with the tracking of this frontal passage, but in general expect
it to slowly progress eastward through the day before getting hung
up across east central and southeastern Kansas as the southern
edge of the mid-level trough flattens but continues to dig a bit
further south over the region. With this eastward progression of
the front, will continue to see the widespread showers and
thunderstorms diminish from west to east this morning, with
possibly a few lingering showers over far east central Kansas by
mid-morning. Several short-range models suggest that areas in east
central Kansas may continue to see some isolated showers and
thunderstorms throughout the day as the front stalls over that
area. With this lingering boundary, expect to see a spread in high
temperatures from the low/mid 80s north to the upper 80s/near 90
degrees over east central Kansas where a southerly flow should
prevail for much of the day. This better diurnal heating over east
central Kansas should aid in modest instability developing across
the area this afternoon, which should support additional
thunderstorm development. This initial scattered activity should
become a bit more widespread along the boundary by mid to late
afternoon and into this evening, primarily along and south of I-35
but may extend as far north as around I-70. Severe thunderstorms
will be possible with this activity as MLCAPE values reach upwards
of 2000-3000J/kg with strong 0-6km bulk shear values of 45-55kts.
The primary concerns with these storms will be large hail and
damaging winds, but cannot rule out an isolated tornado threat.
Additionally, there is the potential for localized flooding as
additional moderate to heavy rain is possible over locations that
have already received a few inches of rain from this morning`s
thunderstorms. These storms should diminish during the late
evening hours and shift southward as the cold front gets pushed
south of the forecast area. With light northerly winds and
clearing skies behind this front, expect cooler conditions
overnight with lows dropping into the upper 50s north to mid/upper
60s south.

.LONG TERM...(Tuesday through Sunday)
Issued at 342 AM CDT MON SEP 1 2014

The frontal boundary will remain hung up just south of the area on
Tuesday, and model guidance hints at a weak trough moving across
southern KS late in the day. Expect strong instability in east
central and southeast KS with little to no inhibition and 25 to 35
kts of 0-6 km shear. Low-level convergence will be very weak
however, and any thunderstorm development will have to rely on
lift from any weak mid level troughs. Currently have rather low
POPs focused in the far southern portions of the forecast area for
Tuesday afternoon, but if a slightly stronger disturbance can
bring some vertical motion into the area around peak heating,
could see scattered severe storms south of I-70. A strong trough
will move into Montana on Tuesday night with the low level jet
increasing a bit locally overnight. Expect impressive theta-e
advection and moisture transport into east central Kansas and
eventually northeast Kansas overnight. Steep mid-level lapse rates
will be in place with MUCAPE around 2000 J/kg and effective shear
of 30-40 kts. This should result in scattered to widespread
thunderstorms with large hail possible. Could also see a heavy
rain threat materialize.

Warm advection and ample sunshine by Wednesday point to a hot day
with heat index values possibly topping 100. The warm advection
aloft should also cap surface parcels and expect dry conditions
through Thursday. However, by late in the day on Thursday, a cold
front associated with the northern CONUS trough will approach the
area. Expect strong forcing along the front to result in
widespread thunderstorm development with the main uncertainty
still being the timing of the frontal progression across the
forecast area. The frontal zone seems likely to linger in the area
into the weekend as the main forcing will pass well north. This
will likely be impacted by any organized thunderstorm outflow
though. Elevated instability will remain in place north of the
front although it should diminish over time. Have gradually
decreased precip chances north to south through the weekend as the
surface high should build in stronger with time. Have not made
major changes to temperatures from the prior forecast, and we
still look to be on track for highs in the 70s for next weekend.


.AVIATION...(For the 12Z TAFs through 12Z Tuesday Morning)
Issued at 618 AM CDT MON SEP 1 2014

For the 12z TAFs, some scattered IFR/MVFR cigs have developed behind
the precipitation and should persist through the morning before
lifting to low-end VFR by this afternoon. As the cold front slowly
tracks through the region, winds will be veering to the northwest
and north-northeast through the period. There is the potential for
thunderstorms to redevelop by late afternoon near the lingering
boundary, however there is still some uncertainty as to whether or
not this activity will impact KTOP/KFOE so only have a mention of
VCTS at this time. Any storms that do develop should move further
south of the TAF sites through the evening. Models are starting to
suggest the possibility of some patchy fog developing Tuesday
morning due to the light winds, clearing skies, and low-level
moisture present. Mentioned a scattered MVFR cloud deck at this
time, but too much uncertainty still to add any further details in
the TAF.




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