Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 252047

Area Forecast Discussion
National Weather Service Des Moines IA
347 PM CDT Thu May 25 2017

.SHORT TERM.../Tonight through Friday/
Issued at 341 PM CDT Thu May 25 2017

Main concern during the short term period is POPs and timing

Surface pressure ridge will continue moving eastward away from the
CWA, allowing the next weather system to our west to advance
closer. Two shortwaves are progged to move across the CWA during
the short term period. The first one is presently reflected by
the sprinkles and light showers along and west of the Missouri
River. Moisture is less plentiful toward the east, so expect the
areal coverage of echoes to decrease in time as the feature moves

Second shortwave is progged to traverse the state beginning Friday
morning. It will have a pressure trof / weak front reflection at
the surface. This shortwave is expected to be more potent from a
dynamic and thermodynamic perspective, and have more moisture
associated with it. Remaining convection from the developing CO-
KS-NE MCS may also be associated with it. Have tried to go middle
of the road in terms of POPs, as not all models are in agreement
with precip chances. Some, such as the GFS and NAM seem too
aggressive while others such as the ECMWF seem too dry. CAMs also
support at least scattered showers and some thunderstorms during
the day Friday especially from midday into the afternoon.

Have lowered max temps especially across the east on Friday due to
longer period of cloud cover and precip.

.LONG TERM.../Friday night through Thursday/
Issued at 341 PM CDT Thu May 25 2017

Relatively quiet weather pattern considering it`s late May into
early June. The main concern is storm potential Saturday across
southern Iowa where a low threat for severe storms exist. Leaned
slightly more toward the NAM/ECMWF Friday night into Saturday and
then a blend of the GFS/ECMWF.

After a brief visit from a surface high pressure Friday night into
Saturday morning.  A shortwave looks to cut across Iowa during the
day providing low chances for showers and thunderstorms. This is
associated with a much stronger vort max and trough to move across
the Central and Southern Plains. This locations will have a much
greater severe weather potential Saturday into Saturday evening
but certainly can`t rule out a brief window during peak heating
across far southern Iowa for an isolated severe threat. Some
elevated instability tries to develop with weak moisture
convergence to provide a little lift. A cold front and parent
trough will move across the region by Sunday morning but system
remains moisture starved and any precip chances end by 12z Sunday.
Decent mixing develops behind the trough during the afternoon
Sunday. Nudged up winds and temperatures Sunday and may need to go
even warmer with the dry air and mixing as high as 850mb

Monday into Wednesday.... Large and deep upper level trough of low
pressure builds into the Great Lakes region and brings across a
couple shortwaves to possibly impact the forecast area Monday into
Tuesday. However, an upper level ridge will begin to take over
the weather pattern and likely keep any significant shortwave to
the east of the state early next week. Thus, low confidence with
any widespread rain and even convection for the beginning of June.


.AVIATION.../For the 18Z TAFS through 18Z Friday afternoon/
Issued at 1257 PM CDT Thu May 25 2017

Isolated showers may affect the area late today through tonight, but
probability and expected coverage are too low for even VCSH at this
point. Low clouds will begin to move back in toward the end of the
TAF period, with MVFR cigs possible after 12Z Friday.





LONG TERM...Podrazik
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