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FXUS63 KTOP 231136

636 AM CDT Sat Aug 23 2014

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 337 AM CDT SAT AUG 23 2014

Latest satellite water vapor loop shows drier air moving north
across eastern Kansas while the moisture axis extends from the
Western High Plains into the Dakotas. Shortwave trough was evident
over southwest Colorado into central New Mexico. Another trough was
moving across eastern Idaho at 08Z. Some elevated isolated showers
were developing across the CWA north of Interstate 70 in an area of
isentropic lift and within the low level jet. Expect the isolated
showers and thunderstorms to be possible through sunrise.

For today, the upper trough over Idaho will move across Wyoming
while the southwest trough over southern Colorado and New Mexico
will eject northeast out into the High Plains and western Kansas.
Models bring some energy as far east as central Kansas by 00Z
Sunday, then move it northeast into eastern Nebraska and western
Iowa overnight. Will continue with slight chances of precipitation
for tonight mainly across the western and northeast portions of the
CWA within the moisture axis. Shear is relatively weak and soundings
show relatively small CAPE tonight and not expecting storms to
become severe.

Drier air mixing down from near 750mb today will decrease dew points
into the into the upper 50 to middle 60s this afternoon. Combined
with temperatures in the upper 90s to around 100 will produce heat
indices from 100 to 103 degrees today. Will keep the heat advisory
going through expiration at 8 PM this evening. Lows tonight will
range from the lower to middle 70s.

.LONG TERM...(Sunday through Friday)
Issued at 337 AM CDT SAT AUG 23 2014

Cold front remains on track to nudge southeast into the area Sunday
afternoon as the Pacific Northwest upper trough emerges into the
Northern Plains. Convergence along the boundary is weak at best, but
deep mixing should allow little convective inhibition to be left by
mid afternoon. Have kept small thunder mention going along it for
the afternoon and night. Weak and unidirectional wind fields should
keep any severe weather potential to isolated downburst winds. As
the upper wave continues east, the front could sink farther south
into Kansas late Sunday night into early Monday but limited moisture
should keep elevated convection limited at best and have maintained
only small chances near it. Could see some fog again develop in the
light winds near the boundary. Front should mix back northwest
Monday night into Tuesday as this wave moves off. Have some concern
northern and western locations could be brushed by activity moving
in from the Front Range and will keep small chances again for these
periods. As for temperatures and heat index values, coolest air
temps should be in the north nearer the front and any potential
precip, but with airmass not much cooler even behind the front,
highs should still reach the mid 90s near it and near triple digits
to the south Sunday through Tuesday as 850mb temps remain around
25C. Boundary layer moisture levels improve a bit for Sunday and
Monday and should support apparent temps a few degrees above air
temps, bringing continued concern for low-end Advisory potential.
Given somewhat borderline values today`s heat and the spotty
nature of the higher heat levels in previous days, have left
these periods without an Advisory and will see how conditions and
progs transpire in the next few periods.

A somewhat more organized precipitation potential remains for the
middle of the week, but guidance continues to differ in how it will
play out. The GFS is again more progressive with the next upper
trough`s eastward movement, with the ECMWF and GEM cutting off the
trough and moving it on at various speeds. Have kept the greater
chances in the Tuesday night though Wednesday night periods as
somewhat of a compromise. Temps will back off considerably as the
trough passes, but just when that will occur brings much uncertainty
to Wednesday`s highs in particular.


.AVIATION...(For the 12Z TAFs through 12Z Sunday Morning)
Issued at 636 AM CDT SAT AUG 23 2014

VFR conditions expected to continue through the period. Isolated
TSRA possible after 05Z near the MHK terminal. However will leave
out VCTS for now as probability is to low. South winds will
increase after 14Z to around 14 kts with gusts near 22 kts, then
decrease to less than 10 kts around 01Z Monday.


HEAT ADVISORY from 1 PM this afternoon to 8 PM CDT this evening
FOR KSZ008>012-020>024-026-034>040-054>056-058-059.




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