Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 111733
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1133 AM CST Wed Jan 11 2017

.SHORT TERM.../Today through Tonight/
Issued at 337 AM CST Wed Jan 11 2017

Another low confidence forecast today with subtle forcing and varied
degrees of moisture in amount and depth. Right entrance region lift
through the Dakotas speed max and weak waves streaming over the
Rockies continue to spread sporadic mid and high level lift into the
MO Valley.  The primary burst of theta-e advection and
frontogenetical forcing brought a quick burst of light snow to NE IA
overnight, but has exited into WI leaving behind broad weaker warm
advection. 1-3km moisture is also limited so there isn`t much
precipitation potential for the time being. However mid level
forcing strengthens somewhat later today as the jet exits into the
Great Lakes pushing the front now roughly along a Sioux City-Charles
City line out of the state by 00z. The models also suggest current
SD/MN stratus may move or further develop into IA just behind the
front in the cold advection. While neither of these mechanisms is
too significant, light mid level precip or lower based drizzle could
potentially develop central and southeast from midday into the
afternoon. Thus have slight chances for either light rain or a
wintry mix depending on surface temps. Temps will remain fairly flat
north of the front, but may rebound to 40F or more again southeast
before cold air encompasses the entire state again tonight.

Remnants of the stronger wave currently approaching the Rockies from
the west will reach IA tonight bringing mid level kinematic forcing,
but will be undercut by spotty moisture and cold advection. Forecast
soundings suggest high 0-1km RH and possibly stratus into the night
with the cold advection and temps in this layer would be at or below
-10C making it fairly easy to produce light snow or
flurries. Thus have widespread slights and low end chances to
account for these possibilities.

.LONG TERM.../Thursday through Tuesday/
Issued at 337 AM CST Wed Jan 11 2017

On Thursday an upper trough will swing through the region as a
surface high pushes in bringing a reinforcing shot of cold air to
Iowa.  Models are suggesting light snow/flurries across the North
but the forcing in either North or East of Iowa and soundings show
drying from the mid levels to the surface during the morning hours
so I am not really putting much credence in pops for Thursday.  It
will however be very cold and unpleasant.

Friday is an interesting day as we`ll have a surface high in place
that will be shifting East as an upper ridge builds into the
Southern Plains advecting warmer and more moist air
Northward...probably into at least central Missouri.  North of the
state a weak shortwave will move out of the Northern Plains towards
Minnesota and Northern Iowa.  There is some forcing with this
feature that moves across the aforementioned area but moisture is
lacking.  However...as cold as it will be...we will not need much
moisture to squeeze out some light snow or flurries.  For the most
part Iowa will be in between the Southern Plains ridge and the
Northern Plains shortwave so I am not looking at much in the way of
precip /snow/ but certainly a couple tenths or so will be possible.

The weekend into early next week looks the most active and
interesting.  A strong low will dig into the desert Southwest
buckling the ridge over the Southern Plains and pushing the warmer
and more moist air Northward into Iowa.  Just how far North still
remains to be seen but models are all consistent in the large scale
features developing as well as their location.  At this point it
does not look like much will happen over Iowa through Sunday though
far Southern Iowa will not be out of the woods as far as precip
potential and models diverge on solutions here.  The Euro keeps the
low further South as it moves out of the SW U.S. while the GFS lifts
the low Northeast pushing the moisture as far north as Highway 30.
This looks overdone but certainly far Southern Iowa could see
something Saturday night.  Thermal profiles suggest a wintery mix if
it does occur.

As we get into Sunday night and Monday the upper low finally lifts
out of the SW U.S. the Euro is further East with the low than the
GFS and thus the energy that gets ejected out of the trough with the
Euro model shift more South and East of Iowa while the GFS drives it
right up the I-35 corridor then into Eastern Iowa.  Depending on
which model verifies ptype will either be snow and a wintery mess
lifting into Iowa.  Ptype Sunday night will be snow but as the upper
low lifts further on Monday there will be some portion of the
forecast area in the warm sector and precip will eventually mix with
or chance to rain in the South and remain snow in the North with a
wintery mix somewhere across central Iowa.  Colder air will spill on
on the backside of the low Monday night likely changing precip back
to snow before finally pushing East on Tuesday.  The overall trend
of the models has been to slow things down which further complicates
ptype issues but in any event Sunday through Tuesday will not be a
fun period as this system moves through.  At least there doesn`t
appear to be any arctic air around so temps will not be frigid
behind this in fact highs next week will be above normal with
readings in the 30`s by Tuesday and 30-40 Wednesday.

&&

.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1133 AM CST Wed Jan 11 2017

Main concerns are cigs...winds and ptype. 10 to 20 kt winds and
lower cigs are developing immediately behind the boundary through
01z as it passes southeast of area. Saturation has not been realized
though better chances yet through 23z at KALO so with low confidence
will continue VCSH for light precip there. Otherwise light snow
expected over northern Iowa aft 06z with KFOD...KMCW... and KALO
possibly being affected through 13z. Some reduction in vsby to
MVFR also expected at these sites.

&&

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

$$

SHORT TERM...Small
LONG TERM...FAB
AVIATION...REV



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