Area Forecast Discussion
Issued by NWS Topeka, KS

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000
FXUS63 KTOP 210442
AFDTOP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1142 PM CDT Sun Jul 20 2014

...Update to aviation forecast discussion...

.SHORT TERM...(This Evening through Monday)
Issued at 315 PM CDT SUN JUL 20 2014

Warm and moist advection are in full swing across the central Plains
today with temperatures climbing into the upper 80s to mid 90s
locally and dewpoints into the upper 60s and lower 70s. Surface low
pressure over South Dakota will keep the southerly flow overnight
with a developing LLJ continuing to pump warm and moist air
northward. Surface winds should also remain in the 5 to 15 mph range
overnight and low temperatures should hold in the 70s.

On Saturday, there will be a thermal gradient across the area with
the hottest 850 hPa temps around +30C in north central KS,
decreasing to around +25C in east central KS. South southwest winds
will persist through the day across the forecast area with gusts,
and expect some decent boundary layer mixing by mid afternoon. The
airmass at the top of the mixed layer is not particularly dry
though, and even deep mixing seems unlikely to send dewpoints below
the upper 60s. In areas with deeper mixing, the temperatures will
also be markedly warmer. So, with higher dewpoints east and higher
temperatures north and west, expect the afternoon heat index to be
in the 104 to 109 range roughly anywhere north of a Council Grove to
Lawrence line, with 100 to 104 in the remainder of east central KS.
Will issue a heat advisory accordingly for those areas of 105+ from
noon through 9 PM.

Precipitation appears quite unlikely through Monday, although there
is a very small chance (10% but not negligible) that an isolated
storm or two could develop very late in the day near the
Nebraska/Kansas border in central parts of the state.

.LONG TERM...(Monday Night through Sunday)
Issued at 315 PM CDT SUN JUL 20 2014

By Tuesday morning a shortwave trough will advance through the upper
Midwest and Great Lakes region. This trough will drag a front
through the central plains during the day Tuesday. There is fairly
decent agreement among the models with regards to the track and
speed of the shortwave. In the morning the front passes through
central NE and northwest KS. Both the NAM and GFS show decent mid
level frontogenesis moving into far southern NE during the late
morning hours although soundings show the moisture does not arrive
until the afternoon. If any precip was to form within the mid levels
it would struggle to reach the ground with all the dry air.
Therefore have kept a dry forecast across north central as the front
approaches. The frontal passage will introduce some complications to
the forecast during the afternoon and evening. First, compressional
warming and deep mixing is possible ahead of the front especially
along the interstate 70 corridor. This would lower the dew points
and raise the temps, which would affect the heat indices. While,
across far northern KS the dew points pool behind the front
inhibiting the deeper mixing there. Heat indices around 102-110
are possible on Tuesday, although given the uncertainty with
regards to temps and dew points will have later shifts evaluate the
situation further. The degree of mixing will also ultimately
decide the strength of the cap as the front provides lift. If
storms are able to develop along the front a deeply mixed profile
and low level dry air will enhance the risk for strong downburst
winds. Initially, multi-cell clusters would be expected, but
things may transition to a more organized complex during the
overnight hours further into southern KS.

The front will continue to advance southward overnight Tuesday,
and precip chances could linger into Wednesday morning depending
on fast things clear out. Temperatures cool back to normal into
mid and late week as high pressure builds in from the north. Not
many changes were made to the extended forecast as another front
slowly works into the area by Friday. Towards the weekend another
strong mid/upper level low pressure digs through the Great Lakes,
which ultimately pushes the front through and introduces better
precip chances. The front then moves well south of the area and
ushers in another unseasonably cool air mass.

&&

.AVIATION...(For the 06Z TAFs through 06Z Monday Night)
Issued at 1137 PM CDT SUN JUL 20 2014

Vfr conditions will persist across all terminal sites through the
forecast with only scattered AC around 15 kft. South winds will
increase again aft 14Z with gusts in the 22-25kt range before
decreasing again near 01Z to sustained 8-10 kts.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY from Noon to 9 PM CDT Monday FOR KSZ008>012-
020>024-026-034>040.

&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Sanders
AVIATION...63





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