Area Forecast Discussion
Issued by NWS Des Moines, IA

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483
FXUS63 KDMX 281047
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
547 AM CDT Sun May 28 2017

...Updated for 12z Aviation Discussion...

.SHORT TERM.../Today through Tonight/
Issued at 303 AM CDT Sun May 28 2017

Shortwave trough pivoting through the state early this morning so
far only has a band of clouds associated with it. While there are
some light radar returns over northern Iowa as of about 8z, no
surface observations are reporting rain and with cloud bases at or
above 10000, this is not surprising. This shortwave will be east of
the area by sunrise and in its wake, will see winds from the
northwest increase this morning and be gusty this afternoon. As with
previous forecasts and in coordination with neighboring offices,
have increased winds from initial guidance due to deep mixing up to
between 7000 and 8000 feet. Winds at these levels peak between 25
and 30 knots in the afternoon so will likely realize these gusts to
the surface. Other than the breezy conditions today, it will be
rather pleasant with ample sunshine and seasonable temperatures in
the middle 70s to near 80 degrees over central Iowa.

Winds will subside after sunset this evening and become primarily
from the west. A very weak shortwave will approach the area and may
bring an isolated shower to far northwest Iowa this evening.
Otherwise, it will be partly to mostly clear overnight with lows in
the low and middle 50s.

.LONG TERM.../Monday through Saturday/
Issued at 303 AM CDT Sun May 28 2017

The first several days of the period will be dominated by broad,
deep cyclonic flow as the upper low moves from the Great Lakes
toward Hudson Bay. Models suggest an elongated PV trough embedded
in the flow through northern IA at 12z which should push to the
south by afternoon. Cooler air aloft following behind may result
in unorganized diurnal showers from the afternoon into early
evening north. Remnants of the PV trough axis may also linger into
Tuesday with smaller, more compact short waves continuing to drop
into the mean trough. Similar shallow showers may form again
northeast during peak heating with another token period of low
PoPs. The broad cyclonic flow will finally give way to surface
high pressure sliding through the MO Valley into Wednesday
precluding any further mention of diurnal PoPs. This pattern will
keep both temperatures and humidity levels below seasonal norms
through the end of the month.

The pattern will finally become progressive enough to initiate
warm advection once again late Wednesday Night into Thursday with
heights slowing rising as ridging reaches the Rockies. The upper
level flow through the end of the week will be fairly weak and
nondescript with the ECMWF less aggressive holding onto fringe NW
flow into IA. The convection looks weak and elevated initially
but the surface based potential will increase into Friday or
Saturday. Confidence in timing and details is not great at this
time range, but in a broader temporal sense confidence is higher
that there will be a period of increased instability and potential
for surface based convection. This will also return temperatures
and dewpoints to values more typical for early June. The 00z ECMWF
and GFS offer different timing, but both suggest at least a
moderately unstable airmass ahead of a frontal passage. The GFS is
faster highlighting more significant warm advection convection
Thursday Night, a surface based potential with a frontal passage
Friday, and surface high pressure trying to return from the north
into Saturday. The ECMWF suggests the same, but just shy of a day
slower. There could be a few severe storms during this window
considering the degree of instability, but the overall severe
threat does not appear great due to weak winds aloft, especially
if the weaker flow of the ECMWF materializes. This results in an
extended period of variable PoPs from early Thursday through the
end of the period, and especially south into Saturday per the
slower ECMWF timing and GFS suggesting a short wave along the
baroclinic zone through the lower MO Valley.

&&

.AVIATION.../For the 12Z TAFS through 12Z Monday morning/
Issued at 548 AM CDT Sun May 28 2017

Main impact in the TAF period will be winds from the northwest
that will increase this morning and become gusty at all terminals.
Winds will lessen toward sunset and become from the west
overnight. Otherwise, VFR conditions will prevail through the TAF
period at all terminals.

&&

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

$$

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



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