Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 280409
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1109 PM CDT Sat Sep 27 2014

...AVIATION UPDATE...

.SHORT TERM...(This Evening through Sunday)
Issued at 236 PM CDT SAT SEP 27 2014

Quiet weather for the remainder of the afternoon and evening with
partly to mostly sunny skies and highs in the low to mid 80s. An
elevated mix layer currently in place will persist through the
evening hours suppressing any activity. The mid/upper level low
that has be spinning over the region will make a final pass late
tonight and during the day tomorrow. Within the low this evening a
cyclonic rotating vort max could move over over eastern NE and
eventually northeast KS. After midnight weak isentropic lift is
forecast to develop in central KS as the low level jet increases
out west, which will coincide with persistent moisture around 800
MB. It appears as the low approaches mid level temps cool enough
to erode the cap associated with the EML. Limited instability
above this lift will support a slight chance for isolated showers
and thunderstorms through tomorrow afternoon. The cap is forecast
to weaken over north central KS then across eastern KS during the
morning as the low tracks southeastward. The latest NAM and WRF
runs are simulating this activity during the morning hours
therefore kept slight chances in the forecast for now. Not
completely confident that cap will complete erode as the GFS is
suggesting it will not and keeps the area dry. The better chances
for the cap to weaken will be over northern KS through the morning
and far northeast KS around mid day. Otherwise there really is not
any obvious focus for development later in the day other than the
low as it passes overhead.

Clouds overnight in central KS should keep low temperatures in
the low 60s. Across eastern KS the skies will be less cloudy
allowing for decent cooling and lows to reach the upper 50s. It is
in these areas where ground fog is possible again around sunrise
especially near valleys, lakes, and rivers. Clouds and precip
chances should be on the decrease tomorrow afternoon behind the
departing low with high temperatures in the low to mid 80s.

.LONG TERM...(Sunday Night through Saturday)
Issued at 236 PM CDT SAT SEP 27 2014

Sunday night through Monday evening will be dry and rather pleasant
as an upper ridge and surface ridge drift across the forecast area.
Highs will remain in the low/mid 80s and lows around 60.

The upper ridge will move well east of the forecast area by Monday
night into Tuesday while a long wave trough over the western CONUS
drifts closer to the local area. Within this long wave trough, a
rather strong (and deepening) short wave trough will move from the
four corners region into eastern Colorado and eventually central
South Dakota by late Tuesday. Model trends have been stronger and
slightly farther east with this strong energy. Given this trend,
expect some morning and early afternoon thunderstorms across the
western half of the forecast area. This will be southeast of the
trough and early instability will be lacking so strong storms early
on Tuesday are doubtful. The scenario becomes more interesting by
Tuesday afternoon into the evening though as the right entrance
region of a jet streak moves overhead while a Pacific front/dryline
pushes east into central KS. Winds throughout the column are not
particularly strong but shear profiles are likely sufficient to
support supercell structures especially in north central KS. Mid
level lapse rates are modest and MLCAPE is forecast to be in the
1000-2000 J/kg range. If supercell structures develop, will see a
decent potential for hail and perhaps strong winds...while a lack of
supercell structures would point more toward marginally severe hail.
Again, if supercells develop and remain relatively isolated (a
decent possibility), there may be a small threat for a tornado
mainly during the evening when low level shear increases with the
relatively low LCLs. Instability decreases after dark but modest
MUCAPE remains in place through the night and expect scattered
storms to continue midnight through Wed morning...likely non-severe.

Morning storms will probably persist for a while on Wednesday and
could even see sporadic development throughout the day as a series
of weak short wave impulses and height falls move across the area.
Timing of these individual waves will play a significant role in how
the convective threats play out through the day. Current models
suggest one such wave crossing the area by mid day with subsidence
in the wake leading to increased instability during the afternoon.
Another wave then moves into the region by late afternoon into
Wednesday evening. Expect deep layer shear in the 35 to 50 kt range
and instability in the 1000-2000 J/kg range (locally more if clouds
break in the afternoon). This suggests the potential for scattered
strong to severe storms once again during the afternoon and evening
across much of the area. Low level shear again increases during the
evening with low LCLs, and while some signals for severe weather are
present it`s not a cut-and-dried scenario. Another very strong short
wave will finally pull the front through the forecast area by
Thursday morning. At this time, it appears that the front will move
through early enough that instability will be meager while over the
local forecast area.

Friday into Saturday is still looking cooler and quiet as the long
wave trough gradually shifts east and brings northwest flow over the
forecast area. There is still some indication of a secondary vort
max moving down the back side of the trough and perhaps bringing
some lift to the area late Friday or Saturday. If this occurs, would
probably see scattered shower activity. Will be looking at highs
around in the 60s (less if more widespread cloud cover materializes)
and lows in the 40s.

&&

.AVIATION...(For the 06Z TAFs through 06Z Sunday Night)
Issued at 1109 PM CDT SAT SEP 27 2014

Setup this morning with clear skies and calm winds continue to
look favorable for patchy ground fog and will not make any changes
to the forecast in this regard. Dewpoints at TOP have remained
higher this evening so think reduced VSBY is most likely here. As
for elevated precip, models continue to back off on precip over
north central KS due to a mid level inversion above the weak
isentropic lift. At this point think it is more likely to remain
dry then for a -SHRA to impact MHK.

&&

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

&&

$$

SHORT TERM...Sanders
LONG TERM...Barjenbruch
AVIATION...Wolters





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