Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 122341
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
641 PM CDT Sat Jul 12 2014
...Update to aviation forecast discussion...
.SHORT TERM...(This Evening through Sunday)
Issued at 336 PM CDT SAT JUL 12 2014
19Z water vapor imagery shows a broad mid level ridge centered over
northern OK/southern KS while a deep closed low spun over Manitoba
and was beginning to move south. One trough axis appears to have
rotated through NEB with a second shortwave trough digging southeast
through ND. At the surface a cold front stretched from northwest KS
into central IA, and has been slowly moving southeast this afternoon.
For tonight and Sunday, the models continue to show the cold front
moving through the forecast area late tonight. This seems to make
since with the initial mid level trough rotating through IA tonight
and the ridge overhead breaking down. Most of the model guidance
shows a well defined band of frontogenesis within the mid levels of
the atmosphere along with a narrow axis of moisture. This appears to
be the main driver of precip tonight and Sunday as forecast
soundings continue to show limited moisture in the lower atmosphere.
So think there is a good chance for elevated showers and storms to
develop this evening and overnight rather than deep moist convection
from surface parcels. Not sure if the HRRR is handling the
frontogenesis as well as it depicts convection and is the reason it
has been one of the drier solutions. Would not be surprised to see
precip lingering through the morning much like it has over
northeastern NEB and northern IA today. Since I`m expecting precip
to be elevated, chances for severe weather appear to be very limited
due to modest elevated instability from 700-500MB lapse rates only
around 6 C/km.
There does not appear to be a big surge in cold dry air behind the
front tonight. Obs upstream show decent moisture pooling behind the
boundary. With mostly cloudy skies anticipated behind the front and
dewpoints remaining in the mid and upper 60s behind the front, think
lows will once again be mild. Areas along the NEB state line should
see lows in the upper 60s while elsewhere is expected to remain in
the lower 70s. Think highs Sunday will depend on how much insolation
reaches the ground. With skies likely to remain partly to mostly
cloudy across east central KS from the elevated showers, have highs
in the mid 80s across Anderson and Coffey counties. Elsewhere think there
could be enough sunshine for highs to reach the upper 80s to around
90. Considered maybe bumping highs up a degree or two from what I
have now since there isn`t a lot of cold air advection behind the
front, but held off since models show some cooling at 850 and the
thermal ridge setting up further south.
.LONG TERM...(Sunday Night through Saturday)
Issued at 336 PM CDT SAT JUL 12 2014
Will linger a low pop across the far southeast counties of the cwa for
Sunday evening...otherwise will leave the remainder of the forecast dry
overnight except for the far northwest corner with the approach of the
next shortwave trough. As this wave and stronger cold front moves
through...mid level frontogenesis will increase from north to south
through midday with decreasing lift in the mid to late afternoon
across the southern cwa. Will therefore go dry all areas of the
county warning area. Rainfall amounts will generally average a tenth
to a third of an inch during the day.
Much cooler and drier air works southward across the cwa through the
night with 850 temps by sunrise Tuesday falling into the 7 to 10 deg
C range with diminishing winds and mostly clear skies. This will
probably be the coolest morning of the week with lows in the low to
middle 50s all areas which will be near or just above record lows
for July 15th.
By late Tuesday night models try to bring the remnants of an MCS
east and southeast across central Ks which may clip the far
southwest corner of the cwa by sunrise...then the southern half of
the cwa during the day. Have inserted low pops across this
area...and inched low temps up due to more cloudcover...but still
unseasonably cool in the middle to upper 50s and highs in the 70s.
As another northwest flow shortwave moves from the central high
plains into the southern plains...most of the precip through the end
of the week should remain south of the cwa with weak upper ridging
building back into the area by the weekend. Will keep the remainder
of the fcst beyond Wednesday dry with a gradual warming trend. Highs
will warm through the 80s as low temps moderate through the 60s to
around 70 by Saturday night.
.AVIATION...(For the 00Z TAFs through 00Z Sunday Evening)
Issued at 631 PM CDT SAT JUL 12 2014
VFR prevails through forecast as a cold front tracks southeast,
veering south winds to the north aft 07Z at KMHK and 08Z at
KTOP/KFOE. Low level moisture through 9 kft is fairly shallow with
VFR cloud bases expected as light SHRA with possible embedded
thunder impacts sites between 07Z and 13Z. Dependent on coverage
and intensity of showers, there is some indication from guidance
of a SCT MVFR deck forming as showers exit Sunday morning.
Lowered cigs to 3 kft for this issuance and will continue to see
how convection and short term guidance trends.