Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 202345
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
645 PM CDT Sun Apr 20 2014
.SHORT TERM...(This Evening through Monday)
Issued at 326 PM CDT SUN APR 20 2014
This afternoon the center of an upper level trough was located
across the northern TX panhandle and will fill as it slowly lifts
east-northeast across south central and southeast KS. Stronger
ascent combined with weak isentropic lift was casing a band of
showers and isolated thunderstorms to develop across north
central...south central and southeast KS. This band of showers was
rotating north-northeastward across the western counties of the CWA
and will enter the southern and southeast counties during the next
couple hours. Hopefully this band of showers will hold together as
it rotates northeast across the CWA this evening. Though, the 18Z
HRRR model shows these showers dissipating across east central and
northeast KS during the evening hours.
The 12Z NAM...GFS and ECMWF all show numerous showers and isolated
thunderstorms redeveloping across the CWA during the late evening
hours and continuing into the early morning hours of Thursday. There
should be broad ascent across eastern KS as H5 trough will move east
across KS Thursday morning and a surface cold front will pass
southeast across the CWA during the mid morning hours into the mid
afternoon hours. A line of showers and thunderstorms may redevelop
along the front across the southeast counties of the CWA during the
early and mid afternoon hours but should push southeast of the CWA
by late afternoon.
Even though PW`s on the forecasted soundings are
about 1.25 inches the lack of instability, MUCAPES of 200 to 500
J/KG, deep effective vertical wind shear and deep moisture will
probably only allow for weak thunderstorms updrafts, keeping QPF
through Monday at or below 0.25 inches.
Temperatures Tonight will only drop down into the upper 50s to
around 60 with southerly winds, cloud cover and periods of showers
and isolated thunderstorms. Highs on Thursday will reach the lower
to mid 70s due to cloud cover and periods of showers. The north
central counties may begin to clear during the afternoon hours and
the insolation may allow temperatures to warm into the mid 70s
behind the surface front.
.LONG TERM...(Monday Night through Sunday)
Issued at 326 PM CDT SUN APR 20 2014
On Tuesday high pressure builds across the forecast area only to
quickly retreat eastward and set up the return flow during the
evening hours. Within the return flow Tuesday night a low jet
develops over most of the plains. Moisture convergence on the
eastern edge of the low level jet along with weak elevated
instability may be enough for scattered showers and thunderstorms
especially in north central KS early Wednesday morning.
The main mid level low pressure is forecast to move across the
northern Rockies with a broad mid/upper level jet extending into the
central and northern plains on Wednesday. At the surface a cold
front will advance through NE and NW KS during the day Wednesday. It
is this front that will be the focus for convection Wednesday
evening and overnight. Ahead of the front return flow may struggle
to get the high dewpoints to spread northward from eastern TX in
time. If so modest CAPE could reach north central KS ahead of the
cold front, while mid level height falls and surface heating erode
the capping inversion. There will also be modest shear sufficient
enough to support strong to severe thunderstorms. Depending on the
position of this front during the afternoon this convection could be
surface based across portions of the northwest forecast area.
Overnight Wednesday the mid level trough axis moves overhead causing
more widespread elevated thunderstorms along the frontal boundary.
Furthermore a developing low level jets could also enhance the lift
over the area it intersects the boundary. Therefore have kept the
likely pops during that period. As the mid level trough progresses
into the upper Midwest the front and associated precip pushes east
of the area with the exception of far eastern KS where slight pops
are kept until mid day Thursday. Beyond that the models agree on a
less amplified mid/upper level trough digging into the eastern US.
This keeps the surface boundary not far south of the area just in
time another shortwave trough to move through the central Rockies.
It appears another round of thunderstorms will be possible next
weekend as surface fronts lift into eastern KS.
.AVIATION...(For the 18Z TAFs through 18Z Monday Afternoon)
Issued at 645 PM CDT SUN APR 20 2014
Initial area of light precip weakening, and additional precip
unlikely until the main upper wave nears around 06Z. At this point
will keep VFR going to start, but weakening winds and increasing
low level moisture may lead to MVFR visibilities and ceilings near
sunrise. Front still on track for around 15Z with decreasing
confidence in precip coverage as it passes. Still some concern for
MVFR ceilings to continue along/behind front and will need to
watch this as this time approaches.