Area Forecast Discussion
Issued by NWS Des Moines, IA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KDMX 301134
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
634 AM CDT Tue May 30 2017

.SHORT TERM.../Today through Tonight/
Issued at 319 AM CDT Tue May 30 2017

The primary concern today will be subtle precip trends during peak
heating. Iowa continues to be affected by broad, deep cyclonic flow
around the Hudson Bay upper low. GOES 16 water vapor imagery shows a
myriad of short waves rotating through the flow with one of note in
particular also showing up nicely in other IR and RGB products
across northern Minnesota. This feature will push some mid level
cloudiness into Iowa this morning. Much like previous days the
airmass will mix quickly, especially where the clouds haven`t
arrived, pushing gusts well through the 20s /kts/ once again.

Also as suggested by persistence, low but uncapped instability will
develop producing isolated showers during peak heating over northern
sections. However many convection allowing models also suggest a
weak southern stream feature may brush southeast Iowa resulting in
similar instability conditions there. Thus have added isolated
showers there as well.

The weak convection should quickly dissipate early in the evening
leading to clearing skies into the night as high pressure slides
down the Missouri Valley. Light winds and clear skies should produce
favorable radiational cooling conditions so have dropped mins north
and in the Nish Valley.

.LONG TERM.../Wednesday through Monday/
Issued at 319 AM CDT Tue May 30 2017

Surface high pressure will slide across the region on Wednesday
fostering plenty of sunshine and highs just a tad below normal for
the last day of May. As the high slides east later in the day, winds
from the northwest will become from the south. With the shift in
winds, warm air advection and moisture transport will commence back
into the region. This will initiate thunderstorms, likely an MCS
over Kansas and Nebraska, that will track across the southern part
of the forecast area. By Thursday, a weak warm front will have
pushed towards the Minnesota border with much of Iowa in the warm
sector. This will place highs near seasonal values. The
aforementioned warm front will also be an area for convection to
focus around later Thursday, with some of the storms possibly
strong. MLCAPE values late in the afternoon will reach between 1000
and 2000 J/kg, but wind shear is modest at best. Low and mid-level
wind speeds peak around 30 knots with mid-and upper level flow
fairly unidirectional. The low-level jet will be into the boundary
keeping a good moisture feed into the storms with PWs around 1.25
inches. This could bring bouts of locally heavy rain to the same
area.

Models continue to struggle with details beyond Thursday due to
uncertainties in how convection will evolve late Thursday into
Thursday night. Currently, the boundary looks to linger near
northern Iowa with another round of thunderstorms triggered by peak
heating with upscale growth into an MCS late Friday into early
Saturday. As a shortwave trough approaches the area on Saturday,
sunshine will be limited and will continue to have chances for
showers and thunderstorms. As this shortwave moves east of the area
towards Sunday, should see drier air begin to move in, which is
supported by 00z ECMWF/CMC. 00z GFS keeps rain/storm chances for
Sunday, but have limited it to some slight PoPs over the
northeast.

&&

.AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/
Issued at 634 AM CDT Tue May 30 2017

There is fairly high confidence in VFR conditions through the
period. Mid clouds will cross the state this morning with high
based diurnal cumulus clouds also developing during peak heating
of the afternoon. Isolated showers may develop, but confidence at
any particular TAF site is not great enough for even VCSH wording
as of yet. There is also some potential for radiation fog early
Wed morning, but again confidence is not there to include for now.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Small
LONG TERM...Ansorge
AVIATION...Small


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.