Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 191052

Area Forecast Discussion
National Weather Service Des Moines IA
552 AM CDT Wed Jun 19 2019

.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 evening.

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 12Z TAFS through 12Z Thursday morning/
Issued at 548 AM CDT Wed Jun 19 2019

A few patches of IFR/MVFR cigs this morning and fog with vsbys in
the 3-5sm range this morning. Showers and a few thunderstorms will
be possible, especially in vicinity of KOTM. Cigs may fall to MVFR
at times in that area. Mainly VFR conditions are expected over
northern Iowa through much of the period with the exception of
some fog redevelopment tonight. The wind will be from the
east/northeast at 10kts or less.




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