Area Forecast Discussion
Issued by NWS Des Moines, IA

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354
FXUS63 KDMX 241738
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1238 PM CDT Wed Aug 24 2016

...Aviation Update...

.SHORT TERM.../Today/
Issued at 413 AM CDT Wed Aug 24 2016

The primary concern certainly remains convective trends and their
associated impacts. Water vapor imagery continues to show deep flow
and moisture streaming northward ahead of NM/CO short wave with
little recent change suggesting frontal boundary noted just west of
Iowa per 08z surface analysis is in no hurry to push through Iowa
today. Most models suggest we will see a break from precipitation
into midday, but additional development is anticipated during the
afternoon.

Large scale forcing associated with this Rockies short wave is
expected to spread into Iowa during the afternoon coincident with
the H85/H7 trough. The surface front may not be too far removed from
the trough over southern Iowa resulting in more than adequate
vertical motion to trigger another round of convection. There is
certainly some concern regarding the degree of recovery today
considering upstream mid and high cloudiness, but with dewpoints
remaining 70 plus and plenty of synoptic scale lift any inhibition
is expected to be reduced sufficiently. Confidence in this scenario
is supported by several convection allowing models showing
development along the front from NE/KS into IA 20z-00z. Deep shear
will again be low so while there is some severe concerns heavy rains
may be more of an issue. Low level moisture transport and inflow
will be weaker than what occurred overnight, neither warm cloud
depths or precipitable water values are extreme and with the minimal
inflow Corfidi vectors are essentially similar to the mean wind.
However with the mean wind parallel to the slow moving boundary
repetitive training could very well occur in the vicinity of the
slow moving front.

.LONG TERM.../Tonight through Tuesday/
Issued at 413 AM CDT Wed Aug 24 2016

A slow moving cold front will roughly extend from Waterloo to
Lamoni at 00Z and from Davenport to Corydon by 06Z. Storms will
redevelop this afternoon and will be focused along this boundary.
There will be some potential for severe storms once again this
afternoon into the evening then storms will transition into a
heavy rain event. the combination of recent heavy rainfall and the
potential for more tonight has prompted the issuance of a flash
flood watch for locations along and ahead of the front at 00Z.

After a brief respite Thursday into Friday...another potent
shortwave will push across the region from Friday night through a
fair part of the weekend. This will bring more chances for storms
especially Saturday and Saturday night with lingering chances East
on Sunday. At this point the severe potential doesn`t look great
due to lack of instability but it is still several days out and
the models may change. Heavy rain is not expected at this point
but there will be a prolonged period of light to moderate rainfall
and with recent heavy rainfall this will need to be monitored as
well. Going into next week we will see a dry period with
moderating temperatures.

&&

.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1233 PM CDT Wed Aug 24 2016

Line of MVFR/IFR CIGs continues to move across the state with
surface front, dropping sites below VFR for 3-4 hour periods. Line
nearly through KFOD, a couple hours remaining for KMCW and
approaching KALO. Those 3 sites will go VFR once through. KDSM and
KOTM will deal with both low CIGs associated with front, and
expected convection this afternoon/evening. In both instances,
MVFR conditions likely from convection, but have withheld for now
waiting for coverage/timing to show itself.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 7 PM CDT this evening through Thursday
morning for Adams-Appanoose-Clarke-Davis-Decatur-Lucas-Mahaska-
Marion-Monroe-Ringgold-Taylor-Union-Wapello-Wayne.

&&

$$

SHORT TERM...Small
LONG TERM...FAB
AVIATION...Curtis



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