Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 122356
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
656 PM CDT Sat Apr 12 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Sunday)
Issued at 342 PM CDT SAT APR 12 2014

20Z water vapor imagery and profiler data shows a weak wave moving
through the central plains while a shortwave over the southwest
moves into AZ and a second shortwave digs southeast through the
Pacific northwest. Surface obs show an inverted trough just to the
west of the forecast area across central and southwest KS. Strong
southerly winds continue to bring dewpoints in the upper 50s and
lower 60s north into eastern KS. A dryline was noted from western OK
into central KS near Kingman up to near Elsworth.

The main question for this evening is whether a surface parcel will
be able to break through an impressive elevated mixed layer (EML)
that the 18Z NAM shows is still providing 60 to 100 J/kg of CIN just
east of the dryline. The latest high resolution models are still
trying to generate an isolated storm of two off the dryline during
the next hour or two and lift it into northeast KS. Shear profiles
continue to look unimpressive, but with CAPE values on the order of
2500 J/kg, there would be a hail risk if an updraft were able to get
going. At this point am thinking the cap may end up being to strong
since convergence along the dryline is minor and a weak shortwave is
the only real forcing to break the cap. Even at 20Z there is not
much of a CU field along the dryline to speak of either. So
attention turns to the inverted trough to the north and whether
storms can back build into northeast KS. The surface boundary across
IA is further north than previous models had progged with the best
low level convergence across northeast IA. So in general precip
chances look highly dependent on whether a storm or two forms off
the dryline. Because of this have trended POPs lower for tonight.
Lows will be mild for much of the area as southerly winds continue
to bring warm air into the forecast area. The exception may be over
Far north central KS where the trough/front could slip south
shifting the winds to the northeast and allow temps to fall into the
mid 50s.

For Sunday, there should be much better lift and forcing for precip
as the shortwave over the southwest is kicked east and the frontal
boundary pushes southeast. Increasing clouds suggest the
destabilization could be limited ahead of the front and the models
show less instability with the cold front. Additionally deep layer
shear continues to look marginal. Think there will be a broken line
of showers and storms with the front and have continued with
categorical wording in eastern KS through the afternoon. There may
also be enough instability for some of the stronger storms to produce
hail. There should be a modest warm up of 5 or 10 degrees Sunday
before strong cold air advection kicks in and causes temps to fall
behind the front. There may also be a brief period where winds could
reach advisory levels across north central KS late in the afternoon.
Some of the models are showing the potential for gusts up to 40KT.
Opted to hold off on any advisory at this time since it appears to
be a small window where winds would exceed advisory levels and
confidence in the overall model performance is only average.

.LONG TERM...(Sunday Night through Saturday)
Issued at 342 PM CDT SAT APR 12 2014

Several challenges Sunday night into Monday night, including
precipitation chances and types, temperatures, and wind speeds.

Initial upper wave and cold front should exit the east and
southeast early in the evening with next surge of upper forcing
via the next wave aloft coming into the western and central
portions overnight. The NAM continues to be a rather slow and also
deeper solution with the secondary wave, with colder air
throughout the column keeping saturation deeper and heavier/longer
duration precipitation chances. With the split flow continuing and
energy bifurcating along it to the northwest, nailing down
specifics of the forcing and vertical profiles is difficult, but
still believe the NAM is hard to swallow and will rely on the
larger domain solutions again. In this scenario, low and mid
levels dry out Sunday night into Monday morning, keeping amounts
light and highs still reaching the mid and upper 40s Monday.
Although ice crystal formation could still be difficult, with
soundings falling below freezing through the column, still looks
to be a several hour window of light snowfall potential. Given the
warmth of recent days and likely wet ground, any accumulations
should be limited to grassy surfaces. Stout pressure gradient and
diurnally high mixing heights could present a wind advisory
concern Sunday night and perhaps into early Monday, but given this
rare occurrence frequency and aforementioned uncertainty, will
hold off on any headlines at this point. Freezing temperatures
look to impact western and northern locations briefly Sunday night
and the entire area for many hours Monday night as the surface
ridge passes under clear skies.

Zonal flow brings south winds back rather quickly Tuesday and
Wednesday with limited initial moisture return behind the early week
anticyclone. Could see some fire weather concerns here. Next
precipitation chance still on track for the late week, but
considerable uncertainty here too with split flow persisting. Some
consistency in Thursday and Thursday night for chance PoPs here. How
much cold air comes in then for Friday is tricky, but should see
some moderation for Saturday.

&&

.AVIATION...(For the 00Z TAFs through 00Z Sunday Evening)
Issued at 640 PM CDT SAT APR 12 2014

Thunderstorms have developed along a dry in central KS and are
forecast to move eastward through the evening hours. Not confident
on the storm coverage therefore have went with a tempo group for
now. If a thunderstorm were to move over the taf site brief severe
wind gusts could be possible. Things get rather complex as a cold
front sags into the area causing winds the to back more easterly
and eventually northerly. When the front passes through tomorrow
there is increasing chances for showers and thunderstorms to develop
along and behind the front. Winds will increase behind the front
out of the north and northwest.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Wolters
LONG TERM...65
AVIATION...Sanders





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