FXUS63 KDMX 201055

Area Forecast Discussion
National Weather Service Des Moines IA
555 AM CDT Thu Jun 20 2019

.DISCUSSION.../Today through Wednesday/
Issued at 359 AM CDT Thu Jun 20 2019

A weak default ridge of high pressure is currently situated over
central Iowa and wedged between low pressure to the east and low
pressure to the west. Areas of dense fog have developed in the weak
flow regime with several locations south of Highway 30. Expect this
fog to expand a bit yet this morning before rapidly dissipating
between 7-9 am. Have issued a Dense Fog Advisory which is in effect
through 9 am. Thunderstorms are currently moving across central
Nebraska and central South Dakota near the nose of the low level jet
and region of theta-e advection. This area will continue to move
east and impact mainly northern Iowa this morning.

The focus for the forecast period remains the severe weather and
heavy rain potential today through Sunday night. For today,
instability will increase through the mid Missouri Valley including
west central Iowa. Numerous CAMs continue to suggest an organized
storm or two developing near the warm front the riding southeast
along the instability gradient into west central and central Iowa.
If this storms do develop, the near storm environment would support
rotating updrafts and possibly tornadoes, though the 0-1 km shear is
not ideal at around 20 kts. The updraft helicity swaths are
impressive on the HRRR so will certainly continue to monitor the
tornadic potential.

An MCS is expected to arrive late tonight into Friday morning and
should be able to maintain strength as a 40 kt low level jet is
focused into the state. A few severe storms will be possible with
this round along with an inch or more or rain. A stout elevated
mixed layer(EML)will follow the MCS and should effectively cap any
surface based development through much of the afternoon and early
evening. Any widespread redevelopment(mainly elevated) Friday night
likely will not occur until the LLJ intensifies again after 03z.
Again a few severe storms and locally heavy rainfall will be
possible. The EML will intensify on Saturday and should once again
keep much of the day precipitation free and again redevelopment may
not occur again until Saturday night as a short wave arrives and mid
level cooling occurs and eroding the EML. The late Saturday night
through Sunday night remains on track to be the most active period
as the primary upper level system ejects from out west and into the
Plains. While a few severe storms will again be possible, the main
threat may evolve into heavy rain potential. Still some uncertainty
yet for this period though regarding how strong the upper level
system fragment will be along with temporal and spatial issues yet
and has led to the longer range guidance (ECMWF/GFS) not being quite
as robust for this timeframe.

The system will begin to move out Monday with some lingering
precipitation around. Mostly dry conditions and summer like
temperatures will follow Tuesday and into mid nest week.


.AVIATION.../For the 12Z TAFS through 12Z Friday morning/
Issued at 553 AM CDT Thu Jun 20 2019

Areas of fog this morning are expected to quickly dissipate
between 12-14z. A few showers and thunderstorms possible mainly
over northern sites today then another round possible, especially
late tonight. Light wind this morning will become southeasterly.


Dense Fog Advisory until 9 AM CDT this morning for IAZ045>048-




NWS DMX Office Area Forecast Discussion