Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 ktop 210529 

Area forecast discussion
National Weather Service Topeka Kansas
1129 PM CST Wed Nov 20 2019

..update to aviation forecast discussion...

Short term...(this evening through thursday)
issued at 316 PM CST Wed Nov 20 2019

At 20z, satellite imagery -- along with upper air plots from 12z -- show a
trough-ridge-trough set up across the Continental U.S.. working into the
Central Plains are a pair of lead shortwave troughs ahead of the
main upper low spinning over the Southern California region. At the
surface, stronger dewpoints have advected north with a baroclinic
zone sharpening across western Kansas extending in Nebraska with a
deepening low over southwestern portions of Kansas.

Throughout this afternoon, stronger vorticity advection has allowed
for deeper forcing for ascent through the atmosphere over the
region. This has led to increase isentropic ascent and thicker
cloud cover that previously forecast. As a result high temps didn't
have to be adjusted much due to the overall lack of insolation.
Mixing has been limited enough that the deepest mixing along with
momentum Transfer has allowed winds and wind gusts to remain below
advisory criteria. There could still be a few areas that mix deeper
in or see some stronger winds transported down with precipitation
but overall the spatial coverage and duration would likely be
limited. Therefore, decided not to Post a Wind Advisory. At the
current time, some of the strongest winds observed across the area
has been Emporia Airport reported light rain and a gust up to 36
kts. The first push of moisture over the area is mostly represented
on composite radar with still too much sub-cloud dry air to fall as
precipitation over most of the area -- exception has been Emporia as
of this hour.

This evening into the early portions of the overnight period, will
see the bulk of the sensible weather as the next more intense
shortwave works over the area. Deeper moisture with more widespread
precipitation reports and higher dewpoint air is now over north
central OK working into south central Kansas. This round of
precipitation will begin to work into the area between 6pm to
midnight mostly. Have increased precipitation amounts only
slightly. Still expecting most locations will likely see a quarter
to about a half an inch of all liquid rain. No concern with the
warm airmass in place and depth of warm air in place to see mixed
precip or snow. Additionally, as the cold front comes through low
temperatures probably don't reach much lower than the upper 30s
tonight over north central areas and remain closer to the upper 40s
over east central Kansas with winds veering to the northwest by
early morning. With some areas of showers tonight, can't rule out
there could be some embedded thunderstorms with elevated mu cape
reaching up to 600 j/kg. No severe weather is expected tonight, but
it may be possible some stronger winds mix down with some storms due
to strong 850 mb winds around 45-50kts.

Any lingering showers should end generally by sunrise over eastern
portions of the area. Clouds likely linger over much of the area
however with the main trough still over the Desert Southwest as much
of the day is spent in between storm systems. As a result of less
insolation and some push of dry cooler air from the north, highs
reach only into the upper 40s and low 50s.

Long term...(thursday night through wednesday)
issued at 316 PM CST Wed Nov 20 2019

The Great Basin upper low weakens Thursday night as another pv
anomaly rotates northeast into eastern Colorado causing another low
to form. Modest upper forcing and mid-level frontogenesis develops
across southern and eastern Kansas overnight into Friday afternoon
as this weak low moves east, though both moisture in the ice Crystal
formation zone and over the lower several thousand feet are not
impressive. Will keep some low chances for precipitation in mainly
southern areas Thursday night, pushing northeast during the day
Friday. Temperatures may be near to below freezing for much of this
time and bring some concern for freezing drizzle, though expect any
lift strong enough to form precipitation should saturate the ice
Crystal zone for mainly a snow situation. Any amounts continue to
look very light with the frontogenesis shifting northeast across the
area around the mid/upper circulation during these periods.

A fairly benign period is still anticipated Friday night through
Monday with northwest flow and little appurtenant for moisture
return until at least the end of these periods. A few modified
boundaries could pass from northwest to southeast but should do
little to prevent warming temps. For Monday night into Wednesday,
there continue to be quite large disagreements in how energy along
the strong upper flow from the Bering Sea into the Pacific northwest
develops as it enters the central Continental U.S.. interestingly, the recent
operational GFS runs are quite similar with a quickly-deepening
system (though keeping the bulk of any precipitation in our area in
liquid form), while the last two operational European model (ecmwf) runs are equally
similar with a much weaker system with possibly some cold-season
types. Confidence in any particular solution is quite low and at
this point some chance for rain and snow seems to be the best Route.


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1129 PM CST Wed Nov 20 2019

A line of tsra will move through the terminals to start the
forecast period. Expecting the boundary and storms to move through
mhk around 0630z and top and foe around 08z. Winds will shift to
the northwest around 15 kts with gusts to around 25 kts.
Widespread MVFR cigs will continue for much of the forecast period
with IFR cigs not out of the question through 13z. Cigs gradually
improve after 20z to VFR by 23z. Winds expected to decrease after


Top watches/warnings/advisories...


National Weather Service Glossary of Abbreviations