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343
FXUS63 KTOP 151701 AAA
AFDTOP

Area Forecast Discussion...UPDATED
National Weather Service Topeka KS
1201 PM CDT Tue Aug 15 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 344 AM CDT Tue Aug 15 2017

This morning a mid level ridge resided over the region which will
work eastward ahead of the next shortwave trough tracking over the
northern and central Rockies. As a result a weak surface boundary
was located in far southwest NE and is forecasted to lift northward
today. The models have backed off on the potential for precipitation
along this boundary therefore have lowered the pops. Weak surface
winds have allowed near saturation, but partial mixing in the
boundary layer has been limiting the development of fog, and high
clouds spreading over the area may inhibit additional cooling. The
favorable low lying areas in far eastern KS have the best shot at
seeing a brief period of ground fog around sunrise. Although not
expecting widespread dense fog at this point. The models seem to be
struggling with the possibility of a subtle wave moving over
southern KS later today. This wave may be a result of the MCS moving
through the panhandle since it is not really apparent in the water
vapor imagery as of now. If these models are correct then some
precipitation may move close to the area, and clouds could inhibit
surface heating at some locations. If the skies remain mostly sunny
then temperatures are expected to warm into the upper 80s and lower
90s.

Later tonight the northern shortwave troughs will begin to lift out
of the Rockies. This afternoon peak heating should allow storms to
form along a dry line and cold front, which will stretch from
northwest KS to north central NE. Upscale growth into a fairly
unstable air mass could result in an MCS to move towards north
central KS in the late evening hours. If this were the case mucape
around 1,000 to 1,500 j/kg could support convection strong enough
for small hail and gusty winds. Some of the models are suggesting
the storms stay relatively tied to the advancing cold front. Ahead
of the approaching shortwave troughs the low level jet is expected
to strengthen later this evening. The models are showing some
isentropic lift that could result in additional showers and storms
to develop across the area later tonight. These storms could be
marginally severe given the environment. It appears that the better
chances for any precipitation will be in north central KS. The WRF
and HRRR time lagged ensembles are highlighting the highest QPF
across NE and portions of far northern KS. How far east this
isentropic lift can extend is the biggest uncertainty. Also, some
guidance is showing another area for possible isentropic lift
development in southeast KS where the better 850 mb moisture is
foretasted to reside. Towards the end of the period the veering low
level jet noses over eastern KS, which could focus more development
as the moisture spreads northward.

.LONG TERM...(Wednesday through Monday)
Issued at 344 AM CDT Tue Aug 15 2017

On Wednesday convection may be ongoing in the morning as energy
ejects out of the base of the upper trough over the Rockies. Good
deep layer moisture transport is forecast into the Plains which will
help maintain convection through the morning hours. With the
eastward progression of the upper trough out into the Plains on
Wednesday a frontal boundary will move eastward and into north
central Kansas then bisect the cwa in the late afternoon hours.
Moisture transport will continue into northeast Kansas through the
day with precipitable water values increasing to near 2 inches.
Instability and shear will be favorable for a few strong to severe
storms, but lingering precipitation and clouds may be limiting
factors for destabilization in the afternoon hours. The upper trough
progresses eastward across the Plains Wednesday night with the
trough axis moving through eastern Kansas by 12Z Thursday. The front
will progress eastward Wednesday night through northeast and east
central Kansas. Again given high precipitable water, large scale
ascent and good moisture transport through the evening hours will
keep the threat for locally heavy rainfall before shifting focus
east into the Mid Mississippi Valley after 06Z Thursday. A dry
period is expected Thursday through much of Friday with
precipitation chances increasing Friday evening with the passage of
another upper trough and front through the area. Much of the weekend
looking dry with precipitation chances returning Sunday night and
Monday with another wave moving through the Plains. Though there is
some differences in model guidance with the with the timing and
somewhat with how much the upper ridge is suppressed over the
southern and central Plains. For the eclipse viewing on Monday it
looks like there may be clouds and some precipitation early with
cloudiness decreasing in the afternoon hours.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1158 AM CDT Tue Aug 15 2017

Expect VFR conds through 06z before scattered t-storms develop
across southern KS and move NE toward the TAF sites. Scattered
t-storms appear possible in the 6z to 12z time frame with the
better chances toward or after 12z Weds. Given lack of confidence
in coverage and timing of onset at sites will continue the mention
of VCTS with MVFR CIGS after 06z. Would expect at least a period
of IFR conds due to convection at some point toward or after the
12z time frame however confidence remains low as to where/when.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Sanders
LONG TERM...53
AVIATION...Omitt