Area Forecast Discussion
Issued by NWS Topeka, KS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KTOP 020854
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
354 AM CDT Tue Sep 2 2014

.SHORT TERM...(Today and Tonight)
Issued at 312 AM CDT TUE SEP 2 2014

Analysis at 08Z depicts the upper trough axis rotating through Iowa
and Minnesota. Meanwhile the stationary front was positioned from
southwest to northeast over eastern KS. Scattered thunderstorms have
been ongoing for the past several hours as a result of this
boundary. Convection is expected to track south and east away from
the CWA this morning. Clearing skies along and north of the boundary
where dewpoints reside in the upper 60s and low 70s may develop
patchy fog through sunrise. Scattered mid level clouds and surface
winds remaining slightly mixed in some locations should prohibit
widespread development. Areas south of Interstate 70 see the best
chance for patchy fog to form and lift shortly after sunrise.

Light winds and mostly sunny skies reside for much of the afternoon
with highs in the middle to upper 80s. Focus turns to thunderstorm
chances beginning late this afternoon as the aforementioned
stationary front lifts northward as a warm front through east central
KS. Moisture pools along and north of the boundary with dewpoints
progged near 70 degrees. MLCAPE gradient tightens after 21Z with
latest guidance averaging near 3000 J/KG. Main question for this
afternoon is the strength of the capping inversion. Contrary to the
guidance consensus, the past runs of the NAM show a much weaker cap
near the boundary, initiating thunderstorms mainly along and south
of I 70 between 21Z and 03Z. Confidence is marginal on storms
developing during the late afternoon with increased chances this
evening as the veering LLJ transports deeper moisture into the area.
The stronger updrafts will be capable of large hail and isolated
strong wind gusts through early evening. Expect activity to weaken
as it tracks towards western Missouri by Wednesday morning. Cloud
cover within the warm sector tonight should limit lows to the upper
60s.

.LONG TERM...(Wednesday through Monday)
Issued at 312 AM CDT TUE SEP 2 2014

Forecast highlights in the long term include hot temperatures and
heat index on Wednesday and perhaps into Thursday, timing of a
front and associated precipitation chances late Thursday into the
weekend, and a significant cool down behind the front.

Any remnant thunderstorms should be quick to move east of the area
on Wednesday morning. Warm advection through the night and into
the day on Wednesday, along with deep boundary layer mixing,
ample sunshine, and gusty south winds all point to a hot day on
Wednesday. Temperatures are likely to rise well into the 90s, and
while the mixing will be deep the airmass above the mixed layer
will be quite moist and dewpoints may remain in the upper 60s to
lower 70s through the day. This will result in the heat index
ranging from 100 to 105 with some potential to climb into the
105-110 range depending on the eventual dewpoints. A building cap
through the day will prevent any thunderstorm activity through
Thursday morning. Thursday morning lows will be very warm in the
70s, setting the stage for another hot day. A cold front will
approach the area from the northwest by late in the day on
Thursday as a strong trough moves through North Dakota. Current
model timing suggests the front will enter the forecast area by
mid afternoon on Thursday with a thermal ridge immediately in
advance of the front and another well-mixed boundary layer.
Thursday should at least have somewhat drier air available to mix
down to the surface so while temperatures may be a bit warmer, the
dewpoints should be a bit lower. The end result will be a heat
index in the 98-105 range although it seems that Thursday has some
potential to be hotter than the current forecast depending on
frontal timing.

The strongest instability and forcing is expected to be northeast
of the area over Iowa where dewpoints will be higher on Thursday,
but convergence along the front should be sufficient for at least
a chance of thunderstorms by late afternoon into the evening in
northern Kansas. Wind shear will be very weak but with the hot
conditions could see a localized damaging wind threat materialize.
As the low level jet intensifies a bit through the evening, may
see increased thunderstorm coverage despite the LLJ being largely
parallel to the front. Some model guidance is quite aggressive in
producing widespread precip, but with the parallel LLJ and a lack
of strong forcing aloft have trended POPs a bit lower through
Friday morning...although still a fair chance. The front will hang
up over central/southern KS on Friday with faster westerly flow
moving overhead along with embedded weak short wave troughs. This
points to periodic chances for thunderstorms into Friday night,
with chances decreasing during the day on Saturday as the front
continues to push farther south. Then have a dry forecast for
Saturday night into Sunday before troughing builds into the
western CONUS and return flow brings a moisture surge back north
with renewed thunderstorm chances for Monday. Post-frontal
temperatures Friday through Sunday will be much cooler, with highs
likely only in the 70s and lows into the 50s. The main uncertainty
in eventual temperatures will be the density of cloud cover, but
can say with confidence that it will be well below normal this
weekend.

&&

.AVIATION...(For the 06Z TAFs through 06Z Tuesday Night)
Issued at 1149 PM CDT MON SEP 1 2014

Elevated thunderstorms have moved well south and east of the taf
sites. Mid and high level clouds have blanketed the area from the
convection in southern KS, but they are slowly progressing
eastward. Once the clouds clear out there maybe brief periods of
patchy especially during calm winds in the predawn hours. Although the
forecast winds just above the surface may inhibit fog development.
Therefore did not add any tempo for dense fog at this time.


&&

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

$$

SHORT TERM...Bowen
LONG TERM...Barjenbruch
AVIATION...Sanders






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.