Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 101130
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
630 AM CDT Thu Aug 10 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 302 AM CDT Thu Aug 10 2017

Early this morning the region was wedged between surface high
pressure to the east and low pressure to the northwest.  However,
the pressure gradient was very weak over the area, resulting in
light or calm winds.  These light winds combined with dewpoint
depressions of 2 degrees or less will result in areas of fog
developing across much of the forecast area through just after
sunrise.  Some locations may see areas of dense fog develop with
visibilities possibly dropping to around one-quarter mile at times.

The region was still under northwesterly flow aloft this morning as
a shortwave trough was in place over the Dakotas before progressing
eastward toward the Great Lakes region.  Within this northwesterly
flow, models continue to show several weak disturbances developing
across the region, which may contribute to some of the precipitation
chances today through tonight.  For early this morning, some short-
range models show the potential for some isolated showers and storms
to develop over east central KS as a result of some weak isentropic
lift, so have kept some slight chance PoPs in the forecast.  With
one of those weak disturbances over eastern KS this morning, some
isolated showers and storms may continue to develop through the
morning hours across east central KS.  However, better precipitation
chances will come with the approaching front.  Early this morning
this front was stretched from southwest to northeast NE, with models
showing the front advancing into north central KS by late
morning/early afternoon.  Much of the region should see temperatures
rising into the low 80s ahead of this frontal passage, allowing for
modest destabilization to occur across the forecast area. As the
front tracks southeastward across the CWA this afternoon into early
this evening, short-range models show post-frontal showers and
thunderstorms developing and becoming more widespread across the
forecast area during the afternoon and early evening hours. However,
there are model discrepancies in the coverage of these thunderstorms
across the forecast area and where there may be better chances for
more organized clusters of storms and, thus, higher rainfall
amounts.  As a result of these uncertainties, just have chance PoPs
in the forecast for this afternoon into this evening.  There is the
potential for some strong to severe thunderstorms as CAPE values may
approach ~2000 J/kg by late morning/early afternoon, with 40+ kts of
0-6km shear possible. The main hazards with any strong storms that
develop will be large hail and damaging winds.  Locally heavy
rainfall will also be possible as PWAT values rise into the 1.5 to
2.0 range.  The next area of uncertainty comes with how quickly this
precipitation will start shifting south of the CWA and, thus, when
conditions start drying out across northern KS.  At this time, have
showers and storms shifting to along and south of I-70 by the
overnight hours with conditions clearing out across far north
central to far northeast KS.  As a result, low temperatures tonight
will likely range from the upper 50s to mid 60s from north to south,
with some patchy fog possible for locations where the precipitation
has ended.

.LONG TERM...(Friday through Wednesday)
Issued at 302 AM CDT Thu Aug 10 2017

Showers and thunder Friday morning should be on their way to the
southeast and out of most of the forecast area by around the noon
hour, leaving another day under the influence of cooler surface
high pressure, with highs in the lower 80s and light northeast
winds. Western periphery of that high parks itself over the high
plains just to our west and makes for on again off again chances
for precipitation through the weekend. Chances are a little higher
in the west and south counties overall, which are closer to the
front and storm track. This pattern remains generally entrenched
through the remainder of the extended, as weak shortwaves roll
through the northwesterly flow aloft and trigger rounds of showers
and storms that may or may not make it this far eastward. Chances
could be a little higher on Sunday for the eastern counties if
wave dropping southeastward out of the northern plains clips the
area in the afternoon.

The upper pattern flattens out mid week and may bring a chance
for some warmer temperatures to advect back eastward along with
some rain chances, but is still a week out and timing could
change. Highs by mid week may start to reach middle to upper 80s,
more toward normal for mid August.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 627 AM CDT Thu Aug 10 2017

For the 12z TAFs, some patchy fog will persist near the TAF sites
into mid-morning, with LIFR visibilities reported at KMHK. Once
the fog dissipates, VFR conditions are expected for the remainder
of the period. As a front moves into the region late this
afternoon into this evening, scattered showers and thunderstorms
are possible near the TAF sites. However, due to uncertainty still
in the coverage of these thunderstorms, have just a mention of
VCTS at this time. Light southerly winds will shift to the north-
northeast overnight behind the frontal passage.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CDT this morning for KSZ008-020-
021-034-035.

&&

$$

SHORT TERM...Hennecke
LONG TERM...67
AVIATION...Hennecke



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