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Area Forecast Discussion (AFD)

Issued by Des Moines, IA (DMX)

FXUS63 KDMX 191748

Area Forecast Discussion
National Weather Service Des Moines IA
1248 PM CDT Wed Jun 19 2019

...Updated Aviation Discussion...

.DISCUSSION.../Today through Tuesday/
Issued at 358 AM CDT Wed Jun 19 2019

The focal point of the forecast is the precipitation lingering
today over southern Iowa then thunderstorm chances Thursday and 
into the weekend. Currently the precipitation is beginning to 
erode across central Iowa and is becoming more focused over the 
southeast third of the state. That region of the state will remain
the area of highest probability of showers and thunderstorms 
through today as an upper level system passes across Missouri 
today. Locally heavy rainfall of 2 inches is possible but much 
like Tuesday, any heavy rain should remain isolated enough to 
minimize any potential hydrologic impacts.

Strong theta-e advection returns to western and central Iowa on 
Thursday ahead of a short wave trough that will arrive later in
the day. A ribbon of strong instability should develop over the 
western half of the state by the afternoon. Convective initiation 
may occur during the afternoon as the upper level energy arrives 
and may evolve quickly into organized storms that may roll down 
the instability gradient into central Iowa. While not currently 
outlooked in SPC's SWODY2,should convection develop, it could 
quickly become severe with damaging winds, large hail and a few 
tornadoes all possible. The number 1 CIPS analog for Thursday from
the 00z NAM was from Jun 30, 1993 when several tornadoes occurred
under a similar setup. Will begin highlighting at least the 
potential for a few severe storms for Thursday afternoon and 

A more widespread potential for severe weather arrives on Friday as 
the upper level low pushes east/southeast into Montana and Wyoming 
Thu night into Friday and steepens the southwest flow aloft into
the Midwest. This will lead to a potential very active 24 to 48 
hrs over the region. Still a chance an overnight MCS will arrive 
into Iowa early Friday morning from Nebraska/South Dakota. At this
time, all signs point to the region recovering from any 
associated cold pool with the steep southwest flow continuing to 
push warm and moist air into the state. This should lead to 
vigorous redevelopment of storms by late after and evening as 
another short wave arrives. The potential for tornadoes will be 
defendant on the location of the warm front but it is now the time
of year that Iowa gets some of its most significant damaging wind
events. A significant damaging wind event or two will be 
possible, especially in vicinity of the surface warm front where 
the the 0-3km theta-e differences are the greatest. A few areas of
heavy rainfall may occur.

The boundary is expected to linger and bisect the state Saturday 
then move a bit further east on Sunday before departing by Monday 
afternoon. As previously mentioned, this could be a very active 
period as the strong southwest flow remains until the primary
upper wave lifts out early Monday. This could lead to multiple 
rounds of storms with some severe weather and heavy rainfall 
potential. The accumulative rainfall may become an issue over 
central and southern Iowa should these areas become the target of 
multiple rounds of storms. The severe weather potential is not as 
clear cut and will be defendant on environmental impacts from 
previous convection and arrival timing of upper level features. 

Low thunderstorm chances remain mentioned in the forecast for
early next week. May be able to remove those pops soon if trends
persist and drier conditions prevail as high pressure approaches 
the region late Monday into mid next week.


.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1234 PM CDT Wed Jun 19 2019

Ongoing light shower activity looks to persist over central to
southeast Iowa mainly affecting OTM and DSM. Confident MVFR to be
the prevailing CIG group as the stratus deck is slow to move 
east, but certainly might see some brief VFR ceilings as the
afternoon drags on. Fog is likely to develop by early Friday
morning and for now have only MVFR visibility mentioned at OTM,
DSM and ALO. Lower confidence with the duration and when it'll
form, but the hires models suggest sometime after 06z.