Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 211109

Area Forecast Discussion
National Weather Service Topeka KS
609 AM CDT Mon Aug 21 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 358 AM CDT Mon Aug 21 2017

There are two areas of interest early this morning that may play a
role in our weather later today. One is an expansive MCS moving
southeastward through IA. The resulting outflow is pushing southward
and new development is taking place on the southwest flank. This is
where the 850 moisture transport vectors are maximized and intersect
the outflow. Most of the models take the most intense convection
through southern IA and are not handling this backbuilding very
well, so confidence on how far south this convection and outflow will
push is low. Some of the models actually resolve the outflow and
bring it into northeast KS later this morning and develop isolated
storms which seems reasonable. The other complex of storms is in
south central KS and moving northeastward. The models are also
struggling with this activity likely supported by some weak wave
embedded within the moist southwest flow aloft. The experimental
HRRR is showing these storms reaching portions of northeast KS after
sunrise. Other models are showing development at the same time
likely associated with this cluster and or wave. These storms could
contribute to lower and thicker cloud cover, which could obstruct
the eclipse viewing. If these storms weaken and or dissipate then
thicker clouds might not be an issue. Cirrus clouds are spreading
over the region from the southwest shortwave. Although it appears
that subsidence from the MCS is causing the cirrus to erode. If
that is the case once the MCS weakens the cirrus should begin to
cover northeast KS later this morning.

By eclipse time the aforementioned outflow from the MCS in IA will
be somewhere in the vicinity of the path and may be the focus for
isolated storms. The storms cluster in south central KS looks to be
maintaining strength and is forecasted to reach northeast KS around
mid day. Most of the models increase the coverage of precipitation
across the entire area through the afternoon in response to a
stronger shortwave lifting out of the southwest and providing large
scale lift. Plenty of moisture is already in place and pwat values
are expected to be over 2 inches. This wave will contribute to a
deepening surface trough this afternoon, which will stretch from
southwest KS to northeast KS. This trough will be the focus for
further development and more intense convection. Instability is
expected to be high, but existing cloud cover and precipitation
could be an inhibiting factor. There still may be enough to support
storms capable of hail and strong wind gusts in the late afternoon
into the evening. With increasing lift, low level convergence, and
plenty of existing moisture heavy rainfall will be possible across
the forecast area. As storms form along the surface trough it will
slowly progress to the southeast, which doesn`t exit the area until
late tonight. A majority of the models place the axis of heavy
rainfall along and near the KS turn pike. The highest rainfall
totals from the deterministic and ensemble solutions is around 2.50
inches. Among some of the ensembles is quite the spread of total
amounts, which is somewhat concerning.

.LONG TERM...(Tuesday through Sunday)
Issued at 358 AM CDT Mon Aug 21 2017

The waning of precipitation is the main challenge initially. Outflow
could easily push the effective front south of the area by dawn,
though high amounts of moisture should keep convection going well
behind it. Have kept Likely pops for the southern 1/3 or so with
still chances to along I-70. Still have some risk of heavy rain with
PWs still around 2 inches and under the right-rear quadrant of the
upper jet. Cooler/drier air comes in late in the day but 850mb temps
still fall about 5C from Monday for a cooler day.

Tuesday night through Friday periods remain dry with surface ridge
in place and little significant temperature or moisture advection
under modest northwest flow aloft. Deeper moisture does work its way
northeast into the area with some suggestions of a weak southern
branch wave this coming weekend along with a stronger northern
branch wave passing through the northern Plains, worthy of some
mention of precipitation. Temperatures should be fairly close to
slightly below normal.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 605 AM CDT Mon Aug 21 2017

VFR conditions most likely through the morning. There is a slight
chance for isolated storms late this morning and into this
afternoon although confidence is low at this points. The storms
chances increase during the evening as more widespread
precipitation is expected as a cold front passes through the area.
A few storms may produce hail and gusty winds, but periods of
heavy rainfall is more likely into the late evening and early


Flash Flood Watch from this evening through Tuesday morning for



SHORT TERM...Sanders
AVIATION...Sanders is the U.S. government's official web portal to all federal, state and local government web resources and services.