Area Forecast Discussion
Issued by NWS Topeka, KS
FXUS63 KTOP 201721
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1221 PM CDT Sun Jul 20 2014
...Update to aviation forecast discussion...
.SHORT TERM...(Today and Tonight)
Issued at 340 AM CDT SUN JUL 20 2014
This morning water vapor satellite shows a weak wave moving across
north central Kansas at 08Z. A band of clouds developed across
Dickinson, Clay and Washington Counties in area of isentropic lift
in the 305K-310K layer and on the nose of moisture advection in the
850mb-700mb layer. Stratus further west across northwest Kansas and
south central and western Nebraska low stratus clouds continued to
expand, mainly across Nebraska, as the low level jet veers to the
Today and tonight will see a transition from northwest flow aloft as
a ridge builds in from the west. The wave is not expected to develop
showers as it moves east as atmosphere is dry.
Expect the clouds to expand some and spread east through sunrise.
Forecast soundings from the RAP indicates that the clouds should
breakup/dissipate during the mid to late morning hours. Temperatures
will be on the rise today as 850mb temperatures increase into the
lower to middle 20s Celsius. Forecast soundings show that these
temperatures should mix down from around 850 mb yielding highs in
the upper 80s east to the middle 90s north central. South winds
today will increase into the 10 to 20 mph range by afternoon with
gusts of 20 to 25mph.
Tonight, moisture will continue to increase across north central and
northeast Kansas. Soundings show that winds should stay up overnight
keeping the lower boundary layer mixed. Have maintained mild
overnight temperatures in the lower to middle 70s. With the upper
ridge building over Kansas this will keep any precipitation to the
north of the forecast area.
.LONG TERM...(Monday through Saturday)
Issued at 340 AM CDT SUN JUL 20 2014
Monday and Tuesday periods still looking quite warm as the upper
ridge continues to build north and east into the central portions of
the CONUS and south to southwest winds persist ahead of a cold
front. Specifics of just how warm and humid surface conditions will
be remain somewhat uncertain with models differing on low level
thermal profiles in terms of how deep mixing will be and how warm
the above-surface airmass will be to mix into. Other complicating
factors include well-agreed upon cirrus in Mexico coming northeast
and into the area Monday and still small chances for elevated
convection to develop ahead of the front in increasingly moist
though still not very saturated mid level parcels. Even if precip
fails to develop, could at least see some mid cloud into much of
Tuesday before the front arrives in the afternoon. At this point,
have leaned closer to the GFS soundings with mixing not as deep as
the NAM suggests and 850-925mb temp fields warmer than then ECMWF.
Dewpoints still support heat index values several degrees above air
temps for steadily increasing likelihood of Heat Advisory levels
being reached for mainly northern and central sections.
Better and more significant thunderstorm chances come with the
front`s passage late Tuesday afternoon and evening. CAPE near the
boundary likely to be around 2000 J/kg but limited shear and high
cloud bases should limit severe potential to mainly
multicell-produced downburst winds. Boundary exits Wednesday
morning for a somewhat cooler though higher relatively humid airmass
as moisture pools behind the front, though Thursday looking a bit
more comfortable as northeast winds persist. Still appears to be at
least minor convective chances as the front pushes back northeast
Thursday night into Friday, with another cold front likely moving
south into Kansas around Saturday. Models vary with just how this
may happen, but the upper ridge appears to again break down with
shortwaves dropping southeast from central Canada. Highs Friday
could again near triple digits.
.AVIATION...(For the 18Z TAFs through 18Z Monday Afternoon)
Issued at 1219 PM CDT SUN JUL 20 2014
Expect VFR conditions and south winds through the TAF period.
Gusts 20-25 kts possible this afternoon and again late Monday
morning. Will have a LLJ around 35 kts at 2000 ft AGL tonight, but
winds around 10 kts at surface suggest that LLWS group will not be