Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 141134
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
534 AM CST Sat Jan 14 2017

.SHORT TERM.../Today through Tonight/
Issued at 359 AM CST Sat Jan 14 2017

Precipitation has moved into far northern Missouri early this
morning and is clipping into south central Iowa. This
precipitation is in response to a region of theta-e advection and
weak short wave energy. Likely will have a brief period of a
wintry mix over the south as warm layer temperatures aloft are in
the 1-2C range. The forcing and precipitation will move quickly
out of the area toward 6am and will be followed by dry air
intrusion for high pressure to the north. The high pressure will
settle into southern Minnesota and northern Iowa this afternoon
and through tonight and will delay the onset of precipitation
overnight as the associated dry air remains entrenched. Return
flow will develop late tonight over the far south/southwest
therefore have retained low pops over that region. Again, a wintry
mix will be possible as the warm nose aloft reasserts itself.

Generally kept high temperatures today below guidance as mid-level
clouds will have an impact. High temperatures are expected to be
in the low to mid 20s north to the low 30s south.

.LONG TERM.../Sunday through Friday/
Issued at 359 AM CST Sat Jan 14 2017

The primary focus was on the potential ice storm and winter storm
Sunday into Monday. Models remain in decent agreement with the
overall synoptic trends but have delayed any precipitation into
the state much later in the day Sunday. Therefore, delayed the
onset of precipitation roughly 6 hours across the entire forecast
area and thus the Winter Storm Watch (more on this below). Further
north, the precipitation delay looks even late Sunday night into
early Monday. With the large stubborn surface high to the north,
this has slowed the northeastward progression of the surface low
and thus the atmosphere remaining significantly dry until Sunday
afternoon and evening for at least central to northern portions of
the CWA.

Sunday into Tuesday...Some weak mid-level Theta-e advection and
isentropic upglide enter the southern portion of the state b/t
15-18z Sunday. CSQ to OTM forecast soundings per GFS suggest the
deeper saturation moves into this location closer to midday
Sunday and into the afternoon hours. Primary precip type remains
freezing rain with some sleet possible early in the event as the
warm layer aloft ranges around +1.0C to +1.5C over central to
southern Iowa. Surface temperatures remain in the upper 20s to
around 30 for much of the Sunday into Sunday night and with the
existing very cold ground, suspect icing should be quick to occur
when the precipitation onset. Currently a similar scenario ongoing
in KS/MO area. By late Sunday night, strong and deep forcing move
across the state with the surface low tracking east-northeast
from OK to eastern KS to south- central Iowa/northern MO by 00z
Tuesday. The ECMWF is slightly further north in the surface low
track and associated upper level vort max. Regardless, all models
remain consistent on a long duration period of freezing
rain/wintry mix between 03z-15z Monday, from south to north.
Strong WAA aloft yields 850mb temperatures as warm as +3C or
higher towards Monday morning over much of central and the warm
layer aloft is roughly 4kft-5kft deep with the refreezing surface
layer up to around 1000 feet. Thus, freezing rain seems inevitable
over central to southern Iowa. Further north, the WAA tongue
creeps into this location and likely to provide a decent period of
FZRA towards sunrise Monday morning through midday. The onset of
precipitation past 06z Monday remains a sleet, snow mix with the
warm layer aloft barely warming to 0.5C and a very thin layer as
well in northern Iowa. Regardless, the morning commute Monday over
much of the central portion of the state is likely to be
extremely hazardous, especially on any untreated roads. Delayed
the start time of the Winter Storm Watch until 18z Sunday for the
southern two tiers of counties and 21z to 03z for the remainder of
the CWA. WAA at the surface finally should switch precipitation
over to all rain by around 15z Monday over central to southern
Iowa and thus kept the ending time of 18z for the southern two-
thirds of the CWA. With the persisting wintry precipitation into
Monday afternoon and evening, extended the end time until 00z
Tuesday for the northern sections of the forecast area.

Wedensday through Friday...much warmer temperatures are
anticipated during this time frame with an upper level ridge
placing the state within some decent southwest flow. High
temperatures look to rebound into the 40s to even 50s by the end
of the work week.

&&

.AVIATION.../For the 12Z TAFS through 12Z Sunday morning/
Issued at 534 AM CST Sat Jan 14 2017

MVFR cigs will gradually erode over southern Iowa this morning as
dry air from high pressure to the north arrives. Generally light
winds and VFR conditions through the remainder of the period
though cigs will begin to lower over far southern Iowa ahead of a
winter storm that will be approaching the area.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Sunday afternoon through Monday morning
for IAZ046-057>061-070>075.

Winter Storm Watch from Sunday evening through Monday morning
for IAZ036>039-047>050-062.

Winter Storm Watch from Sunday evening through Monday afternoon
for IAZ004>007-015>017-023>028-033>035.

Winter Storm Watch from Sunday afternoon through Monday morning
for IAZ081>086-092>097.

Winter Storm Watch from Sunday afternoon through Monday
afternoon for IAZ044-045.

&&

$$

SHORT TERM...Donavon
LONG TERM...Podrazik
AVIATION...Donavon



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