Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 222046

Area Forecast Discussion
National Weather Service Des Moines IA
346 PM CDT Mon Aug 22 2016

.DISCUSSION.../Tonight through Monday/
Issued at 346 PM CDT Mon Aug 22 2016

Large area of high pressure across the eastern US to continue to
slide east loosening its grip on the state, while return flow
continues ahead of a deepening upper level trough meandering through
the southern prairie provinces of Canada. Southerly flow to really
pick up ahead of this system into tonight/Tuesday with the theta-e
ridge nosing into ERN NE/WRN IA by Tuesday afternoon. Dewpoints to
climb back into the 70s across the area by Tuesday afternoon, with
strong instability as well. May have a few isolated storms out ahead
of the main cluster of storms in the afternoon, otherwise main area
of convective development should be to the west by 21z Tuesday.
Storms expected to merge into a line/cluster heading into Iowa
during the evening hours. Concerns will center around damaging winds
and heavy rainfall given the mainly unidirectional shear profiles
and amount of moisture available. PWATS close to 1.5 to 2.0 inches
with training of cells and slower storm motions expected. Overall
heavy rain possible with 1-2 inches of rain expected across a large
area, and heavier amounts where storms linger/train.

Storms may linger into Wednesday AM, otherwise cold frontal boundary
to stall across the south with additional storm chances late
Wednesday and again Thursday. Southwest flow pattern develops aloft
into the weekend as an upper trough digs into the western US and
becomes cut off from the main flow across the area into the early
next week. This will set up additional chances for storms into the
weekend and early next week. Therefore a more active pattern
expected for the period, with temps cooling off behind the frontal
boundary for Thursday and Friday and then pushing a few degrees
warmer again for the weekend into next week.


.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1236 PM CDT Mon Aug 22 2016

Expect widespread VFR conditions for the duration of the forecast
period with unrestricted visibilities. Any ceilings will be mid or
high clouds toward the end of the period. Surface winds will be
strong from the south today with gusts approaching 30kts across
the north and west. Winds will decouple and be much lighter
overnight with a much more gradual increase on Tuesday.


Issued at 346 PM CDT Mon Aug 22 2016

Elevated moisture/PWATs and warm cloud depths all still expected
with the storm chances for Tuesday night which could lead to
heavy, efficient rainfall. Storm motions could be parallel to the
front as well increasing the chances for heavy rainfall due to
training storms. Heavy rain is still mentioned in the grids with
confidence increasing in this scenario. A widespread area of 1-2
inches of rainfall is seems likely across portions of the CWA with
more locally heavier amounts of 3 to 4 inches possible. Exact
threat area still being determined, but the trend has been leaning
toward the central/southern half to two-thirds of the CWA at this
time. This situation will continue to be monitored for the
potential of a flash flood watch in the next forecast cycles.





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