Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 231109
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
609 AM CDT Wed Apr 23 2014

...AVIATION UPDATE...

.SHORT TERM...(Today and Tonight)
Issued at 341 AM CDT WED APR 23 2014

08Z water vapor shows a longwave trough moving into the Rockies with
a mid level ridge axis over the Great Plains. At the surface, obs
shows ridging along the upper and middle MS river valley with a lee
trough over WY and CO deepening. Radar shows scattered shower
activity gradually expanding in coverage over the past couple hours.
The RAP and NAM show isentropic upglide on the 305K surface, which
seems to line up with where the elevated showers are developing,
persisting into the early afternoon. With the HRRR, RAP and NAM all
showing this scattered activity going on through the morning, have
increased pops and will include coverage wording in the forecast.
Forecast soundings show little if any instability for this activity
to work with so would anticipate thunder to remain relatively
isolated this morning. Meanwhile the models continue to show some
surface based instability developing this afternoon across north
central KS ahead of a Pacific cold front. As the upper shortwave
moves out across the plains, thunderstorms are expected to develop
along this boundary. This activity is expected to quickly evolve
into a linear system and move across the forecast area overnight.
Initially there may be some hail and damaging wind threat as the
line begins moving into north central KS. And there remains a large
amount of low level bulk shear progged by the NAM. But the NAM also
develops quite a lot of CIN suggesting the line of storms may be
driven more by the front and not necessarily persisting on
instability ahead of the boundary. So the expectation is that storm
intensity will diminish as the storms move into eastern KS. In any
case, good forcing from the shortwave and steep mid level lapse
rates should be good enough for much of not all of the forecast to
see rain overnight and will maintain categorical POPs tonight.

Do not plan to change the wind advisory issued earlier. The latest
RAP continues to show a strengthening pressure gradient over south
central NEB and north central KS that may be strong enough for
sustained winds of 30 mph for a brief period. Otherwise the NAM and
GFS are more marginal with the pressure gradient and do not produce
as strong of winds. For highs today, am a little concerned the
scattered precip and cloud cover could hold temps down especially
over northeast KS where this is likely to hang on longer into the
afternoon. So tweaked temps down a degree or two over northeast
zones. Although there may still be enough mixing and insolation
across north central KS for highs to reach around 80. With rain and
some cold air advection behind the front tonight, trended min temps
Thursday morning down towards the MOS consensus of lower 50s in
north central KS to the mid and upper 50s across eastern KS. If the
front moves through a little quicker, lows in the east are likely to
be to warm.

.LONG TERM...(Thursday through Tuesday)
Issued at 341 AM CDT WED APR 23 2014

Cold front will continue to move southeastward and out of the far
southeast corner by mid morning on Thursday as the upper trough axis
swings through CWA. Will therefore continue a steady decline in
precipitation chances over the eastern CWA through the morning hours
and a dry afternoon forecast. Although the day may start out wet and
cloudy early...decreasing clouds and backing low level winds will aid in
temperatures rising back into the low to mid 70s for highs. Winds
back around to light southwesterly overnight with lows in the 40s
before increasing through the day Friday with mostly sunny skies.
Have therefore edged high temperatures upwards slightly to around 80
in many areas.

Elevated moisture return and weak instability slowly increase late
Friday night/early Saturday morning across the southern CWA and have
maintained low chances for thunderstorms. A better chance for
thunderstorms will exist with the deeper moisture and instability
later in the day into early Sunday as the next strong shortwave
trough digs into the desert southwest and ejects out into the
central high plains. Thunderstorms may remain elevated until
an initial capping inversion is overcome for surface based storms to
develop. Either way...strong to severe thunderstorms will be
possible Saturday into Sunday ahead of an expected dry slot as the
system rotates out into the plains and occludes. It will then slow
and shift east and southeastward into the MS river valley with a
lingering chance for showers in its wake as much cooler air filters
into the area from the north for Monday and especially Tuesday.
Highs in the 70s on Saturday will lower into the low to mid 60s for
Monday...then the 50s for Tuesday. Lows by Wednesday morning could
fall into the mid to upper 30s.

&&

.AVIATION...(For the 12Z TAFs through 12Z Thursday Morning)
Issued at 609 AM CDT WED APR 23 2014

The RAP and NAM show isentropic upglide within the warm air
advection pattern continuing into the early afternoon. Regional
radars are hinting at more elevated showers starting to form over
southwest KS. Therefore will carry -SHRA until 19Z when the
moisture advection and isentropic lift diminish. Low level
moisture advection remains rather modest so even with the -SHRA
expect VFR conditions to prevail until the front moves through
with TSRA. This looks to occur at the terminals after 06Z based on
the RAP and NAM forecasts. Have MVFR CIGS and VSBY as the TSRA
pass through. Confidence in timing the ending and beginning of
precip is average and may need to be adjusted plus or minus a hour
or so. Otherwise expect increasing south and southeasterly winds
through the morning as the pressure gradient strengthens.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY from 10 AM this morning to 6 PM CDT this evening
FOR KSZ008-009-020-021-034-035.

&&

$$

SHORT TERM...Wolters
LONG TERM...63
AVIATION...Wolters





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