Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 262327
AFDTOP

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

...Update to aviation forecast discussion...

.SHORT TERM...(THIS EVENING THROUGH Thursday)
ISSUED AT 251 PM CDT WED AUG 26 2015

On Wednesday afternoon, an upper ridge remainder centered over
eastern New Mexico with weak waves of energy and mid level moisture
running around the ridge. One such piece of energy was supporting
light showers and sprinkles over the Missouri River Valley of
eastern Nebraska but this activity is expected to generally remain
east of the forecast area as it continues to move southeast and
dissipate this afternoon. Should see mainly sunny skies through the
remainder of the day and mostly clear skies through much of the
evening.

Of particular interest in the coming days is a stronger short wave
trough currently over Utah that is forecast to move east and
eventually across Nebraska with some forcing into Kansas. A weak
lead short wave associated with this system will be of interest
between midnight tonight and late Thursday morning as a steep west-
to-east theta-e gradient slowly drifts east across the area.
Condensation pressure gradients are large, but the focused area for
ascent as the low level jet veers into the theta-e axis during the
early morning hours. This will be the main uncertainty regarding
whether lift is strong enough for convection to develop. Parcels
rooted near 700 hPa may be the initial lifted parcels as they have
weaker inhibition but also weaker instability. However, with time,
expect parcels rooted closer to 850 hPa or below to become the
source parcels. If/when this occurs, will have very steep lapse
rates and 2000+ J/kg of CAPE to work with. Effective shear will not
be impressive, but may be sufficient to support large hail, with a
small but non-negligible threat for damaging winds as the cluster of
storms builds/moves south and southeast. As the LLJ continues to
veer with time, may see this cluster of storms build all the way
south from eastern Nebraska across much of eastern Kansas with a
gradual shift toward the east and dissipation by late morning.

Temperatures on Thursday will be largely dependent upon cloud cover
from morning convection. Do expect some destabilization especially
in central KS by mid afternoon in advance of the primary incoming
short wave trough and cold front. Should watch thunderstorms develop
just west of the forecast area and then monitor for eastward
progression, with the main uncertainty being the quality of
available instability in the wake of morning convection. Most of
this activity should hold off until the evening hours in the local
forecast area.

.LONG TERM...(Thursday NIGHT THROUGH Wednesday)
ISSUED AT 251 PM CDT WED AUG 26 2015

Main focus is on storm chcs Thursday night into Friday. Upper wave
will move into the region Thursday evening with an associated
500mb mid lvl speed max of 40-50kts. An elongated sfc low is fcst
to develop across western KS into south central NE by 00Z. Appears
that the most likely scenario to occur is that sct convection
develops within the deep mixed layer across western KS between
21-00z and moves ENE toward north central KS. Fcst soundings show
abundant CAPE AOA 2000 J/KG with 6km shear increasing to 35-40kts
however model fcst soundings from CNK suggest that CIN/capping of
100-150 J/KG may remain in place even at 90/70F so extent that
storms would become sfc based remains uncertain. Most likely
scenario is that sct elevated convection will move across the area
Thursday night into Friday as the front slowly progresses across
the area. The cold front will remain a focus for re-development on
Friday afternoon so will keep storm chcs into Friday night with
ensembles suggesting some low chc into Sat morning.

Beyond Sat morning the upper pattern becomes quite amplified with
ridging fcst to develop across the Midwest with lower hts across
the southern Plains. In a nutshell...warm and increasingly humid
conds with mainly dry weather through that period.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z Thursday EVENING)
ISSUED AT 626 PM CDT WED AUG 26 2015

VFR conditions are expected for the majority of the TAF period for
for all hubs. IFR conditions are possible at all hubs from 8-14z
for lowered visibility due to thunderstorms. However, VCTS
conditions are maintained due to low confidence in location and
timing of thunderstorm development.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...Omitt
AVIATION...Baerg


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