Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 140529
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1129 PM CST Fri Jan 13 2017

.SHORT TERM.../Tonight through Saturday/
Issued at 408 PM CST Fri Jan 13 2017

Overall a relatively quiet period through tonight. Initially, a weak
wave/vort max will continue to work through the upper level flow
this afternoon. Through the morning it struggled to produce light
snow at the surface due to a relatively large dry air mass at the
surface, though was able to saturate enough to result in light snow
across the north. This will continue through the afternoon as it
treks eastward and exits the state. Minimal accumulations can be
expected.

Have dropped lows a degree or two overnight in part due to
temperatures today lagging behind original forecasts. While winds
will be light, did not go crazy given expected continued cloud cover
through the night. Have also removed nearly all POPs across the far
SE as models continued the general trend of slowing down
progressions with the high situated to the north. That said, while
models do not show accumulating precip in current runs, soundings
continue to show a mostly saturated layer below 850mb resulting in a
saturated layer about 1 to 1.5km deep. While iffy for drizzle,
cannot rule out at least a bit making appearances overnight across
S/SE areas.

.LONG TERM.../Saturday night through Friday/
Issued at 408 PM CST Fri Jan 13 2017

Main focus for the mid/long range continues to be on the storm
for Sunday into Monday. Little changes noted in overall
expectations. Some timing/placement differences mainly in the push
of the parent low across the central US toward late Monday into
Tuesday which impacts the amount of light lingering precipitation
expected across the area mainly Tuesday. Otherwise still have the
deep upper trough still dropping through the Baja region of Mexico
and the SW US...closing off then lifting slowly northeastward
through the southern plains. This will still send moisture
streaming northward into the state by late Saturday into
Sunday...with the overrunning scenario still expected. Very cold
air in place at the onset of precipitation could lead to a brief
mix of snow/sleet, however surface temps should warm enough
initially Sunday for the main precip type through the day into
Sunday night across central/southern Iowa to be freezing rain.
Some weak instability noted far south by Sunday afternoon, so
could see some enhanced precip areas. Overall main pushes of
moisture and precipitation to move in Sunday night into Monday.
This is when the main icing is expected to occur with temperatures
remaining in the 20s to right around 30 degrees.

Surface low to push out into the central plains by midday Monday
with the associated warm front lifting northward toward Iowa. This
will send surface temperatures warming to above freezing across
much of the state through the day. Therefore we expect freezing
rain to transition to all rain through the day, with some wintry
mix/snow still possible in far northern areas where colder air
still expected. Expect icing could still continue for awhile after
temps rise above freezing due to very cold ground/road temps that
have been in place. Frost depth here at the office around 18
inches, and sub-surface temps likely to remain below freezing
until temps warm further Monday. Overall have around a half inch
to inch of QPF expected with this system, with snow amounts of
around a trace to 3 inches across northern portions of the CWA,
and icing amounts from a few hundredths across northern Iowa to
0.30-0.40 inches in the far south/southwest. Details regarding
thermal properties of this storm could still cause adjustments to
these totals.

Additionally have looked at analogs for this storm, and one of the
top ones suggests a similar look to this storm as one that hit the
state back in mid-December of 2007. That storm was a bit colder
than this storm and likely had more of the precipitation fall as
ice versus rain, than this storm will bring. However it did give a
good representation of where icing/snow fell and targeted much of
the same areas with the greatest icing occurring across
southern/southwest IA and snow across north central and northwest
Iowa. Will have to watch the push of warm air, as that will be the
main detail that can change amounts the most across the watch
area. For now have not made any changes to the watch, main thing
that could be needed is an extension in the end time as we move
toward issuing any advisory/warning products in the next few
shifts as light winter mixed precip/snow hangs on through the day
Monday across the north and into Monday night.

&&

.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1128 PM CST Fri Jan 13 2017

Changes on the way for cigs. Lowering MVFR cigs have spread north
into the area this evening and expanded toward US Highway
20...including KDSM...KOTM. HIRES models suggest that KALO may
just hit MVFR category aft 08z. Patchy cigs below 2000 ft expected
near KOTM 08z through 11z. There may also be a brief period of
patchy light FZDZ at KOTM between 08-11z though confidence remains
low with regard to occurrence. Gradually this push of higher
moisture will move east and cigs will lift to VFR over the area
between 12-14z remaining south sites. KFOD and KMCW likely to
remain VFR. Winds not an issue and should remain light through the
period. /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Sunday morning through Monday morning
for IAZ044>049-057>062-070>075-081>086-092>097.

Winter Storm Watch from Sunday afternoon through Monday morning
for IAZ004>007-015>017-023>028-033>039-050.

&&

$$

SHORT TERM...Curtis
LONG TERM...Beerends
AVIATION...REV



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