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Area forecast discussion
National Weather Service Topeka Kansas
628 am CDT Thu Sep 19 2019

..update to aviation forecast discussion...

Short term...(today and tonight)
issued at 401 am CDT Thu Sep 19 2019

A unseasonably sticky and humid day has turned into an unseasonably
sultry night. Much the same will likely continue for the short term
forecast period.

Currently, the upper level pattern is mostly meridional across the
Continental U.S. With a strong pronounced ridge generally working into the
eastern Continental U.S.. meanwhile, a deep and slightly positively tilted
trough has worked onshore over the western Continental U.S.. southwest flow
regime is in the transition zone across the center of the country. A
moderately strong low level jet is focused into NE where flooding is ongoing
from training and backbuilding storms. Much of this activity is
progged to begin propagating southeast with time and will likely
miss the area as the better instability remains through portions of
Iowa into northern Missouri. Some short-term hi-res models suggest
that an outflow boundary may be able to make its way into portions
of far east and northeastern Kansas by mid to late morning today.
Therefore, have maintained some slight chance pops in the forecast.
However, confidence in storms is low and may not materialize at all.
High temps today will again rise to around 90 with dewpoints in the
upper 60s.

Thursday night into Friday morning will likely see another low level jet over
western Kansas which will be a focus for storms to develop in the
overnight period. As the western trough begins to translate east a
few ill timed lead waves begin to impact portions of the Central
Plains and into the northern plains. The warm air advection pattern may support
some increasing chances for showers and storms into the late morning
and afternoon on Friday as isentropic ascent increases with deeper
moisture per sounding profiles. As a result instability will also
increase across the region. Therefore, can't rule out at least
slight chance to chance pops generally increasing through the day
into the evening hours. It does look like shear profiles will be
minimal, so organized updrafts don't appear likely.

Long term...(friday through wednesday)
issued at 401 am CDT Thu Sep 19 2019

For the mid to long range forecast the main concern will become the
potential for severe weather into Saturday afternoon and evening as
well as heavy rainfall Saturday night into Sunday.

It does appear that overall better agreement amongst longer range
solutions and ensembles is coming into focus which supports the
thinking of several inches of heavy rainfall into Saturday night and
early Sunday across the area with some of the highest amounts likely
being focused across portions of east central into northeast Kansas as a
slow moving frontal boundary tracks across the area. Saturday
afternoon will likely see the risk for severe storms develop across
the area on the warm side of the southwest to northeast oriented
baroclinic zone. As upper southwest flow associated with the main
trough moves closer to the region, shear profiles could increase to
levels that would be supportive for more organized updrafts which
could give rise to a few supercells. One caveat right now appears
to be that hodograph structures appear to have several inflections
which would make for a challenging environment for more organized
storms to maintain themselves or develop to the most severe limits.

Probably the larger concern comes by late evening and into the
overnight period. As a low level jet develops and focuses strong moisture
flux into already statistically very high precipitable water air into the baroclinic
zone, the expectation is that several inches of rain would be likely
across the area. Right now, overall soil moisture is still high
which may increase some flooding concerns over the area.
Additionally, much of the overall steering flow will be along the
boundary within a deeply saturated environment. Can't rule out that
a Flash Flood Watch may be needed in subsequent forecast periods.
But right now would be premature.

Past Sunday, too much spread in guidance gives rise to lesser
confidence in the overall forecast or environmental setup.
Therefore, keeping off and on rain chances Tuesday through Thursday.
Eventually, with modified Canadian air intrusions, lower overall
dewpoints are expected by the end of next week and lower precipitable water air will
result in much more comfortable conditions.

&&

Aviation...(for the 12z tafs through 12z Friday morning)
issued at 624 am CDT Thu Sep 19 2019

VFR prevails as light southerly winds increase to 10 kts sustained
aft 18z. Consensus guidance dissipates the line of thunderstorms and rain over
southeast Nebraska later this morning with only a few models
suggesting convection could impact terminals by late afternoon.
Confidence is too low for mentioning at this point, however radar
trends will be monitored and amendments made as needed.

&&

Top watches/warnings/advisories...
none.
&&

$$

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