Area Forecast Discussion
Issued by NWS Des Moines, IA

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718
FXUS63 KDMX 272340
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
640 PM CDT Mon Mar 27 2017

...Updated for 00z Aviation Discussion...

.SHORT TERM.../Tonight through Tuesday/
Issued at 355 PM CDT Mon Mar 27 2017

The low pressure system that helped continue the abundance of cloud
cover and showers across the south moved off to Illinois, being
replaced by a weak inverted high pressure ridge moving into Western
Iowa. Clearing/erosion of western/northwestern edge of the cloud
deck proved slower than overnight hi-res guidance suggested,
resulting in continued blanketed cloud cover over the state and
keeping highs down in the upper 40s/low 50s. Hi-res guidance has
continued to appear overly aggressive in clearing out cloud cover
over northern and western Iowa, especially taking into consideration
performance through the day today.  Have thusly kept with generally
overcast skies across the CWA with low level moisture remaining and
only mid-upper level drying to occur. While cloud cover will remain
overnight limiting dense fog potential, with the ridge passing
through have introduced patchy fog across a fair amount of the CWA,
and especially the north where winds will be lightest.

While winds will be easterly tomorrow, with the thinner cloud
deck temperatures should be able to jump a few more degrees into
the mid 50s in most locations. A bit more erosion of the
northern/northwestern edge of the cloud deck will likely occur as
well Tuesday before the next system once again keeps the region
blanketed in cloud cover.

.LONG TERM.../Tuesday night through Monday/
Issued at 355 PM CDT Mon Mar 27 2017

Primary focus in the long term will continue to be on the relatively
active weather pattern...with cool and wet conditions continuing
over Iowa and the central Midwest.

Tuesday Night thru Thursday Night: Forecast Confidence = Medium/High

The next in the wave train of low pressure systems is expected to
slowly track across the southern plains from Tuesday night into
early Friday.  While the most robust low level moisture and
potential for severe wx will likely remain well south of
Iowa...persistent WAA/isentropic upglide and deep moisture
convergence will lead to widespread precipitation development by
early Wednesday morning. Periods of deformation zone precipitation
will then continue off and on right into early Friday.  While most
of the precip will likely fall as rain...kept a mention of a
rain/snow mix across far northern Iowa on early Thursday morning.
Little or no snow accumulation expected. Total rainfall in this
period will likely range from 1-2" across the southern half of the
state...with 0.25" to 1.0" across the north. Did not see much river
response with the weekend rainfall...but with soils more saturated
now...will need to keep an eye on river trends by midweek. With
overcast and rainy conditions...highs on Wed/Thu are expected to be
a bit below climo avgs...generally in the 40s to perhaps the lower
50s south.  Overall...rather dreary and raw.

Friday and Friday Night: Forecast Confidence = Medium

A brief lull in the action is expected on Friday as weak high
pressure builds into the region.  However...model soundings and time
sections still show considerable RH/saturation in the lower
levels...thus expecting partly to mostly cloudy conditions to
continue.  If we can eek out a little sun...highs expected to rise a
few degrees into upper 40s to lower 50s on Friday.

Saturday thru Monday: Forecast Confidence = Low

Higher uncertainty in the forecast late in the period as the
deterministic and ensemble solutions track yet another closed low
across the southern U.S.  Have maintained chance PoPs in the
forecast for Saturday into Sunday for now...but the overall trend of
the solutions have been slower and further south with this low.
Plenty of time to fine tune this period in the upcoming days.

&&

.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 635 PM CDT Mon Mar 27 2017

Made notable changes for KMCW, KFOD, and KALO by reducing vsbys
overnight tonight. If clearing becomes more pronounced, especially
KMCW and possibly KFOD may reach 1/2 SM vsbys or less. Fog should
lift by 15z Tue. CIGs likely to hover near 3000 ft, meaning it
will be difficult to pin down MVFR vs VFR with confidence for
Tuesday afternoon/evening until 12Z and 18Z Tue TAF packages.

&&

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

$$

SHORT TERM...Curtis
LONG TERM...Small
AVIATION...Kotenberg



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