Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 211746
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1146 AM CST Mon Jan 21 2019

.SHORT TERM.../Today through Tonight/
Issued at 400 AM CST Mon Jan 21 2019

Confidence: Medium

Complex storm moving into the region overnight tonight through
Tuesday night. Early today, warm air advection has been producing a
band of light snow/flurries moving into western/central Iowa. This
will continue heading east and lift northeast, ending later this
morning. Little if any accumulation is expected with this area of
light snow. The approaching storm is still expected to bring a
variety of wintry weather to the region later this evening and
through Tuesday evening.  Initially, there will be a lack of ice
introduction from 00z through 12z over the region. Though there are
differences in the models, the Euro/GFS are in better agreement with
previous runs and have leaned on these solutions for this event.
Over the far west/northwest a mixture of light freezing drizzle
light snow will begin between 00 and 03z...expanding northeast
toward northeast Iowa by 12z. Some light icing and a light dusting
of snow will be expected by 12z. As the low tracks into northeast
Kansas by 18z, isentropic lift will fill in across the region
with a mixture of freezing rain/freezing drizzle over the south
third of the region...and a wintry mixture of light freezing
rain/drizzle changing over to snow from roughly US30 north to the
border. As the H850 low tracking across the region from 12-00z, a
period of moderate snow will occur over the north with rates
roughly a half inch per hour. In the far south, temperatures will
warm enough to change the wintry mix of ice/snow over to light
rain south of Interstate 80 for a period from mid to late morning
and most of the afternoon. Colder air will begin to filter into
the backside of the system and again create a mixture of light
freezing rain/snow from about Interstate 80 north to US 20 and
back over southwest areas. Gradually all of the precipitation will
transition over to snow in the evening hours with patchy blowing
snow on the backside. The southeast will see a changeover back to
either a light frozen mixture or light snow in the evening hours.
For the event, the greater snow totals still appear to be north of
Highway 20 and in the neighborhood of 3 to 5 inches with a few
locations possibly exceeding 6 inches of snow. With the potential
for blowing snow across the north later in the day and evening
Tuesday...the day shift may need to adjust the headlines higher
across the north for some of the counties North of US 20. Most of
the precipitation will be winding down by 06z Wednesday. In the
southeast, there is still some uncertainty as to how much impact
will occur Tuesday evening. If the changeover back to a wintry mix
of light freezing rain/snow again impacts travel - an additional
headline may be needed there for several hours. Highs today will
warm into the teens and 20s with lows tonight holding steady.
Highs Tuesday will range from the lower 20s north to the upper 30s
in the southeast.

.LONG TERM.../Tuesday through Sunday/
Issued at 400 AM CST Mon Jan 21 2019

Tail end of this messy system lingers into early Wednesday morning
and models are still differing on the speed and location of the
surface low.  The Euro has the low over north central MO while the
GFS has it lover east central/southeast IA.  With the GFS solution
we get a dry slot pushing into far southeast IA.  With the loss of
ice introduction, comes more mixed precip.  With the Euro, the
dryslot is muted and further south, in MO and about 6 hours slower.
This is then followed by the def zone sliding through central and
eastern Iowa overnight Tuesday night, changing everything back to
snow before ending early Wednesday morning.  I`m leaning more with
the GFS solution.  During the evening, eastern locations could see
an inch or so of snow. Across the southeast, where the dry slot will
play more of a role, less snow but a few hundredths of an inch of
ice is possible.

On Wednesday we will be in between events as the upper trough slides
east and weak high pressure at the surface move in.  Late Wednesday
night a weak system drops down the deep northwest flow and enters
northwest Iowa by 12Z.  This system will bring with it some weak
forcing and colder air resulting in some light snow clipping
northwest into south central Iowa.  Really not looking for much in
the way of QPF or snowfall.

With the passage of this system Wednesday night, high pressure will
build into the region and drop some arctic air into the region.
Highs Thursday will only be in the single digits north and teens
south.  Lows Thursday night will be brutal with near 20 below north
and 10 to 15 below elsewhere.  Friday will remain cold with single
digits below zero northeast to teens southwest.

Models vary from Friday night on with the Euro bringing a surface
low across northern MO and producing some light snow south while the
GFS is much further north with the low and precip being placed far
northwest. The GFS solution then drops the snow across the forecast
area through Friday night.  This slower movement is carried through
on Saturday with the Euro pushing an upper trough east of the state
by then and the GFS keeping in over south central to northeast Iowa.
The GFS would suggest more light snow.

On Sunday the GFS drops a substantial shortwave across the state
while the Euro is much weaker, further north with this wave and
slower with the resulting surface low.  Given the model uncertainty
from Friday night on, left the forecast to model blends with minor
adjustments where consensus was at least somewhat evident.  At least
there will be temp modification Sunday into early next week.

&&

.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1145 AM CST Mon Jan 21 2019

A mix of VFR and MVFR cigs across central Iowa this afternoon.
Widespread MVFR to IFR cigs will arrive overnight with the
potential for freezing drizzle and light snow. The wintry mix of
precipitation will continue into Tuesday morning. Some icing is
likely across the area. The precipitation may change to rain near
KOTM late in the period. Breezy to gusty southeast winds today
will remain breezy through the overnight.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from midnight tonight to midnight CST
Tuesday night for IAZ006-007-016-017-025>028-036>039-047>049-059-
060-072-073-081>083-092>094.

Winter Weather Advisory from 6 PM this evening to midnight CST
Tuesday night for IAZ004-005-015-023-024-033>035-044>046-057-058-
070-071.

Winter Weather Advisory from 6 AM Tuesday to midnight CST
Tuesday night for IAZ050-061-062-074-075.

Winter Weather Advisory from 6 AM to noon CST Tuesday for
IAZ084>086-095>097.

&&

$$

SHORT TERM...REV
LONG TERM...FAB
AVIATION...Donavon


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