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Area forecast discussion 
National Weather Service Des Moines Iowa
631 am CDT Sat Sep 5 2015

Short term /today/...
issued at 356 am CDT Sat Sep 5 2015

Ongoing precipitation across western County Warning Area will persist through the
early morning hours as forcing remains maximized. Forcing will begin
to lift north and diminish after sunrise with decreasing support
from low level jet...and expect precipitation to begin to diminish as well.
High res models keep precipitation across northern County Warning Area through about
18z...and have held onto chance probability of precipitation across the area a bit longer.
Otherwise...expect precipitation chances to remain west of County Warning Area...and
have left forecast dry through the afternoon.

Will see another hot and humid day across the area. Temperatures
will be similar to yesterday...with slightly cooler temperatures in the
north and northeast where clouds will help keep temperatures down.
However...with humidity will see heat index values once again in the
90s...with warmer readings in the south.

Long term /tonight through Friday/...
issued at 356 am CDT Sat Sep 5 2015

Thunderstorm chances Sunday into Monday and Tuesday are the primary
focus through the period. The Pacific northwest upper low has been
trending further north as it ejects out to the east/northeast. The
impact of this is the subtropical high bubble will not be suppressed
as far south as previously expected by Monday with the surface boundary
likely to stall over central to southern Iowa. The boundary will
lift back north a bit on Monday before a cold front moves through
Monday night into Tuesday.

The tropical connection has been strengthening this morning with middle
level moisture advection surging north in the increasing monsoonal
flow. The initial surge of this moisture will pass just northwest of
the forecast area late this afternoon and tonight. This flow will
veer Sunday into Sunday night and become more focused into central
Iowa. In addition...lower level Gulf moisture will be streaming
north into the state during this period and the combination of the
Pacific and Gulf moisture will push precipitable water values in excess of 2
inches late Sunday into Monday. The precipitable waters in conjunction with deep
warm cloud depths and storm motions of 25 kts or less will be
favorable for efficient rain producing storms. Storm motions nearly
parallel to the boundary will lead to potential training storms. The
greatest threat with this system is switching to a heavy to very
heavy rain threat. Severe weather is also possible especially with
peak heating storms as MLCAPES of 2500 j/kg or greater develop. A
few supercells may develop with the initial activity Sunday
afternoon with effective shear values of 30 to 35 kts. The effective
srh is not projected to be as high as the previous nights guidance
thus the primary threats will be large hail and damaging wind gusts
with upper level wind profiles becoming unidirectional. The boundary
will push south Monday night though a few thunderstorms will linger
into southern Iowa on Tuesday. Another system arrives Thursday with
another chance for showers and thunderstorms. This system will drive
even cooler weather into the area with highs in the 60s to lower 70s
by Friday which is a big switch from the 80s to lower 90s expected
on Sunday.

&&

Aviation...05/12z
issued at 623 am CDT Sat Sep 5 2015

VFR conditions expected at sites through period. Winds will
remain southerly with gusts up to 20kts in the afternoon...before
decreasing after 00z.

&&

Dmx watches/warnings/advisories...
none.

&&

$$

Short term...awb
long term...donavon
aviation...awb

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