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Area forecast discussion 
National Weather Service Topeka Kansas
1143 PM CDT Thursday Jul 2 2015

..update to aviation forecast discussion...

Short term...(this evening through friday)
issued at 329 PM CDT Thursday Jul 2 2015

The afternoon scenario is rather messy with only loosely defined
surface features in the form of a weak surface low over south
central Nebraska and a more organized cold front in northern
Oklahoma. There was also a cold front associated with the NE low and
easterly low level flow to the east of it. Aloft, a series of weak
disturbances was moving through the northerly flow
moving through central Nebraska and another in eastern South Dakota.
Light showers had dissipated across the local area early this
afternoon and allowed for some clearing and warming from north
central Kansas into central Nebraska. This area has seen an increase
in surface based instability and is also a broad zone of weak low
level convergence. Inhibition is weak and the surface warming has
produced modest SBCAPE despite weak middle level lapse rates.
Additionally...low level lapse rates have steepened markedly with a
fair amount of cape in the lower levels. All of this has led to the
development of scattered thunderstorms in south central Nebraska and
north central Kansas this afternoon with weak supercell
characteristics owing to the combination of modest cape and fairly
strong effective shear. There is some potential for an increase in
intensity into early evening and a few of the strongest storms could
produce severe hail or even a localized strong wind gust. Will need
to monitor these storms closely through the evening although
widespread severe storms seem unlikely at this point.

This activity is likely to weaken after sunset although the short
wave over eastern South Dakota will likely track into northeast
Kansas late tonight. Have thus increased probability of precipitation after midnight
especially in the eastern half of the forecast area where the best
lift will focus. Instability will once again be quite weak and
severe storms are unlikely overnight. Overnight activity may be
ongoing near/south of I-70 after sunrise...depending on the speed of
short wave progression...but expect a gradual decrease in convective
activity through the day on Friday from north to south with highs
warming into the lower 80s by late afternoon as clouds decrease.

Long term...(friday night through thursday)
issued at 329 PM CDT Thursday Jul 2 2015

On Friday night the middle level shortwave will continue to dig
eastward into the lower MS valley. In the wake of this system a
surface high pressure will build into the region from the northeast,
while the cold front reaches as far south as Texas. On Saturday another
shortwave will drop down out of the northern plains and over
northeast Kansas during the evening and overnight hours. The NAM is
showing some elevated showers in the morning over central Kansas due to
isentropic lift ahead of the wave, but no other models are
forecasting as of now it appears that the bulk of the convection
associated with this wave will remain out in western and eventually
central Kansas. High based storms will likely form in western Kansas
during peak heating possibly along a moisture gradient within the
return flow regime. This storm cluster is forecast to move east to
southeastward during the evening hours although it is uncertain
how far east, which will be determined by the track of the wave
and initiation. The GFS is further east with this activity and
has decent instability and deep layer shear. Although not sure how
much of that will be effective given the bases will be high. The
wave is forecast to move overhead Saturday evening within a weakly
capped environment, but not focus in the lower levels and over the
surface high. I guess a storm could not be completely ruled out,
but they are fairly low. For now kept slight chances across most
of the forecast area. The chances in southeast Kansas will be more
tied to elevated showers and storms north of the southward moving
cold front during the morning hours.

On Sunday, with the previously mentioned wave still in the vicinity
and any possible remnant outflows this could help initiate more
convection during the daytime hours. As for now those chances will
be highest in southeast Kansas underneath the departing wave. The next
best chance for precipitation will come on Monday as a decent shortwave
tracks across the northern plains and upper Midwest. This will send
a cold front into the forecast area and will be responsible for a
widespread precipitation event. That cold front will eventually stall out
somewhere in the area as the middle level flow becomes more westerly.
There is then a chance for several waves within the western flow to
track over the forecast area although the models are struggling with
this scenario.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1124 PM CDT Thursday Jul 2 2015

Complicated aviation forecast through 12z as a moistening boundary
layer with light winds is beginning to develop low end MVFR to
IFR stratus over terminals at 6z. Similar to the previous
evening, believe the short term guidance is too aggressive on the
stratus deck. Utilizing upstream obs, MVFR to occasional IFR
ceilings are likely through middle morning. While stratus appears
more likely than fog at this time, could have MVFR visibilities near
sunrise. By the afternoon cloud deck is expected to clear to VFR
for remainder of the period.


Top watches/warnings/advisories...


Short term...barjenbrach
long term...Sanders

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