Area Forecast Discussion
Issued by NWS Des Moines, IA

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919
FXUS63 KDMX 241202
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
602 AM CST Fri Feb 24 2017

.SHORT TERM.../Today through Tonight/
Issued at 358 AM CST Fri Feb 24 2017

It was a very active night across central Iowa with near blizzard
conditions north and at least near severe convection all occurring
at the same time. The convective treat has ended but a transient
burst of strong theta-e advection produced seasonally strong
elevated convection in a swath from SW into NE Iowa. With MUCapes
500-1000 j/kg and effective shear around 50kts several produced
supercell characteristics with pea-dime size hail covering the
ground in some instances, a few occurring to a depth of an inch in 5
minutes or less.

The magnitude of the convection has diminished confidence however,
and while the event is certainly not over, it has appeared to rob
the strength of the deformation zone precip. The coldest cloud tops
are now north and west of Iowa with the dry slot more pronounced.
This will likely lead to more of a mix for a period this morning
with freezing drizzle likely more prominent than snow until the
deformation zone reorganizes somewhat. The surface air temp freezing
line is now along and NW of a Harlan-Boone-Charles City line at 09z
with 32F road temps similarly oriented.  This lead to concerns about
the fate of the Blizzard Warning, but calls to local law enforcement
agencies in the warning and videos posted on social media indicate
plenty of blowing snow and near zero visibilities from already
fallen snow, especially in rural areas, with wind gusts often 35 mph
plus. The Iowa DOT also recently noted Travel Not Advised from Story
City to the MN border. Thus will leave the Blizzard Warning
unchanged with additional snow anticipated later today. The Winter
Weather Advisory is somewhat questionable, but may be needed for
different reasons than earlier anticipated, at least initially with
freezing drizzle rather than snow, so will leave that intact as
well. The deformation zone will eventually sag south and east
starting ice introduction again and end any freezing drizzle threat,
which would be coincident with increasing wind as the current
surface low north of Quincy IL continues to move away. Regarding
additional snow amounts generally have 1-4 more inches, although
isolated spots toward the MN border could see slightly more. Snow of
varied intensities is expected to persist until the kinematic
deformation zone forcing finally exits this evening.

.LONG TERM.../Saturday through Thursday/
Issued at 358 AM CST Fri Feb 24 2017

Any lingering blowing snow will end quite early Saturday morning
as winds decrease with a zone of high pressure passing to the
south of Iowa. As we head into next week, confidence is low with
models being rather inconsistent run to run and compared to each
other. A weak shortwave will try to spread a bit of rain over
southeast Iowa Sunday after which weak ridging will build over the
region briefly. Temperatures will gradually trend upward from
near or below normal this weekend to above normal by Tuesday. In
the wake of this weak shortwave, winds will become from the south
and southeast drawing moisture northward as a longwave trough over
the western US approaches. Isentropic lift will spread
precipitation across the state from south to north later Monday
which will last into the first part of Tuesday as low pressure
moves through the region. The Canadian is a bit faster with
bringing precipitation into the area Monday and have lowered PoPs
across the area from initial guidance.

As this longwave trough moves off to the east, flow will become from
the northwest. This will set the stage for several fast moving
shortwave to cross the area. The first will pass over the area on
Thursday with a rain/snow mix possible. The next will pass the area
late Friday skirting the northeastern part of the state.
Temperatures from the middle part to the end of the week will be
within several degrees of typical values for early March.&&

&&

.AVIATION.../For the 12Z TAFS through 12Z Saturday morning/
Issued at 601 AM CST Fri Feb 24 2017

Widespread MVFR to IFR conditions remain in place across Iowa this
morning due to ceilings and visibility restrictions due to fog,
drizzle and/or snow and blowing snow. Little change in category is
anticipated through today but it will become more driven by
ceilings and light snow/blowing snow. North winds will remain
strong and gusty, often 30kts plus. Conditions should improve
later tonight however with VFR and gradually diminishing winds.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight CST tonight for IAZ028-
037>039-047>050-057>060-070.

Blizzard Warning until midnight CST tonight for IAZ004>007-
015>017-023>027-033>036-044>046.

&&

$$

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



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