Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 271946
AFDTOP

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

.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
vort max will rotate cyclonically around the western edge 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 18Z TAFs through 18Z Sunday Afternoon)
Issued at 1241 PM CDT SAT SEP 27 2014

All terminals are expected to remain VFR throughout the afternoon
into the early morning hours on Sunday. The shallow fog between
09-14Z Sunday at KTOP and KFOE will be the challenging time frame.
Confidence is higher though due to no major airmass change and
favorable conditions setting up similar to the previous day. The
small possibility of showers could also begin to affect KMHK
between 1200Z and the end of the TAF period but have been left out
for now due to lower confidence.


&&

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

$$

SHORT TERM...Sanders
LONG TERM...Barjenbruch
AVIATION...Drake





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