Area Forecast Discussion
Issued by NWS Topeka, KS

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442
FXUS63 KTOP 171140
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
640 AM CDT Sun Sep 17 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 348 AM CDT Sun Sep 17 2017

Latest surface analysis at 08Z showed the cold front generally along
Interstate 35 with surface high pressure in southwest South Dakota.
Showers and thunderstorms continued to develop along the cold front
and move northeast into Missouri. Additional showers and storms were
occurring over northeast Kansas ahead of the 850 mb front. Short
term high resolution models linger the convection across east
central Kansas through the morning hours. Additional thunderstorms
over southwest Kansas may move northeast and reach north central
Kansas this morning. The frontal boundary is forecast to stall over
far southeast Kansas and southwest Missouri this afternoon. Small
chances of showers and thunderstorms are possible again this
afternoon as perturbations move northeast in the southwesterly mid
level flow across the area. Forecast soundings Clouds and cold
advection with northerly winds will keep temperatures much cooler
than yesterday with highs in the lower to mid 70s expected.

Tonight the front begins to lift north during the evening and
overnight as a warm front. Isentropic lift over the frontal boundary
occurs tonight with elevated showers and thunderstorms becoming
widespread after midnight. Additional shortwave energy in the mid
levels is forecast to move northeast across the area later tonight.
Also upper level difluence associated with the exit region of the
southern stream jet and the entrance region of the northern stream
jet max will enhance the upward vertical motion across north central
and northeast Kansas later tonight. Therefore have increased
precipitation chances along with forecast QPF. Could see some
locations receive close to an inch of rain in northern Kansas after
midnight. Lows tonight will range from the lower to mid 60s.

.LONG TERM...(Monday through Saturday)
Issued at 348 AM CDT Sun Sep 17 2017

On Monday morning it appears there is some spread among the models
as to how much precipitation will linger in portions of eastern KS.
The ECMWF and GFS are much wetter than the NAM, which could likely
be contributed to the speed and location of the shortwave activity.
Most of the models show a decent low level jet that continues
through a good portion of the day, which keeps moisture and lift in
place. The is some weak lift indicated on the 310-315 K theta
surfaces that persists into the afternoon and is reflected in the
model QPF. A closer examination into that afternoon shows that if
the clouds break up it will allow surface heating therefore cape
values could approach 3,000 j/kg in some spots. The deep layer shear
is forecasted to be 30 kt across the entire area. Weak cin on during
the afternoon could lead to storm development. A lack of obvious
focus for lift especially at the surface makes it difficult to pin
point any specific locations, and there might not be much
organization to the convection due to the lack of forcing.

On Monday night another shortwave trough could track over the
central plains causing additional lift and a strengthening low level
jet. It is difficult to determine if the waves indicated by the
models are convectively driven or actual waves in the southwest flow
aloft. If so another round of showers and storms could occur late
Monday evening and Tuesday morning. The operational GFS seems to be
most aggressive with this overnight precipitation, while the other
deterministic models are indicating much less QPF. Only half of the
GEFS members indicate any accumulation over eastern KS during that
time frame. Things should quiet down until late this week and next
weekend. A longwave trough deepens over the western US with several
stronger embedded shortwaves. A frontal boundary will begin moving
across the central US as a result. Depending on the duration of
longwave trough over the western US that front may be slow to move
eastward so it could make for a prolonged period of rainfall. Too
many uncertainties at this point, but something to watch.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 640 AM CDT Sun Sep 17 2017

MVFR, IFR and LIFR cigs are expected through 17Z this morning at
the terminals. MVFR cigs are then expected along with occasional
VFR cigs as well through the rest of the period. Scattered SHRA
and TSRA are possible around 17Z through 22Z, then increase after
06Z when both vsbys and cigs will likely be mvfr to ifr with the
convective activity. Winds northeast near 10 kts becoming east
then east southeast less than 10 kts after 18Z.

&&

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

$$

SHORT TERM...53
LONG TERM...Sanders
AVIATION...53



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