Winter Storm and Heavy Snow in Iowa, March 15, 2021

Area Forecast Discussion
National Weather Service Des Moines IA
1202 AM CDT Mon Mar 15 2021

...Updated 06z Aviation...

.SHORT TERM.../Tonight through Monday/
Issued at 308 PM CDT Sun Mar 14 2021

Confidence: Medium to High

Winter concerns continue with storm entering the region today and
another expected midweek.  Today's event is evolving more or less as
expected so far with a wing of warm air advection and moisture
rapidly spreading north into the US30 to US20 corridor this morning.
The moisture transport is still attempting to overcome the dry
airmass in the north, but should edge north this afternoon. Already
have raised PoP there today. Overall the  tonight is on track
with a continued cooling of the column as moisture encounters a
continually drying airmass. The net effect will be to cool the
column as strong east southeast flow aloft encounters a moisture
surge tonight from the south. That's the easy portion of the
forecast. The difficult part remains the transition zone/sharp cut
off of amounts as well as surface winds and visibility heading
into the early morning hours Monday through 18z over the north.
Complicating the forecast today is the strong ridge of high
pressure aloft over the Northern Plains...extending southeast into
the southeast US. Though the storm will continue to edge
northeast overnight, the receding high will likely result in a
stronger surface pressure gradient near the surface from 09z to
16z Monday over the northeast along with a more pronounced frontal
zone aloft. With very strong isentropic lift and frontal forcing
tonight as the next surge of moisture moves over the region,
snowfall amounts may actually end up higher over the north. The
other result of this would be rather robust snowfall rates as the
wedge of forcing moves northeast overnight. HREF progs suggest
that 1-1.5 inch rates an hour are likely over the north overnight
with an area of greater than an inch per hour from 10 to 14z over
the I35 corridor from roughly Ames north to the Iowa Minnesota
border. This would also affect US20 east of I35 from 12z through
15z and portions of US30 overnight into tomorrow morning. With the
potential for visibility down to 1/2 to 1/4 miles at times, any
morning travel over the north half of Iowa will be difficult to
dangerous at times with the snowfall rates and visibility.
Moderate snowfall is expected to continue over the northeast
Monday morning in a corridor from Mason City southeast toward
Waterloo where the worst conditions will finally lift northeast of
our area by 18z in the far northeast. With all those
considerations and slightly higher snowfall amounts expected a few
miles south and east of the present warning areas, have expanded
the warning south and east to include areas along US20 and east to
Waterloo/Cedar Falls. Highs tomorrow will be held in the lower
30s north to about 40 to 45 in the south. By Monday night the
precipitation pulls out with only lingering clouds and lows
dipping into the mid 20s north and in the lower 30s south. Though
conditions are favorable for fog Monday night into Tuesday
morning, will forgo and deep analysis right now due to time
constraints. Needless to say, any remelt of snow with cooling
overnight lows will likely lead to saturation and potentially some
areas of thicker fog.

.LONG TERM.../Monday night through Sunday/
Issued at 308 PM CDT Sun Mar 14 2021

Confidence: Medium

Models continue to have challenges with the midweek storm, now
keeping the track south of Iowa. The Euro has been warmer throughout
the column while the GFS has been cold enough to at least support a
mix.  It has backed off the snowfall expectations of previous runs
and now is focusing accumulations over the southern areas of the
state. With confidence remaining low into midweek, will need to
evaluate details in the coming shifts once tonight/Monday's storm
has exited. Overall, next week shows a gradual warming trend with
a return of west southwest flow aloft into late week and the
weekend. This is reflected in both deterministic model runs of
the GFS/Euro and should lead to a return to highs in the 50s/lower
60s in the south with at least 40s to lower 50s north by weekend.
The snowmelt this week will quickly end up in area streams and
rivers, so expect some increase in flow and river levels as some
of the moisture also helps to recharge the dry soil moisture. Dry
weather is expected Friday into the weekend as well.

&&

.AVIATION.../For the 06Z TAFS through 06Z Monday night/
Issued at 1200 AM CDT Mon Mar 15 2021

Conditions will continue to deteriorate at the terminal sites as
the overnight progresses and through most of Monday. Moderate to
heavy rain showers will be accompanied with IFR CIGs at DSM and
OTM. A mix of rain and snow is likely for a period of time. FOD,
MCW, and ALO will eventually transition to snow, also with IFR
CIGs and visibility. Wind gusts up to 30 kts possible at most of
the TAF sites. The precipitation should move out late Monday
afternoon, but expect IFR CIGs to linger. Overall, poor aviation
conditions.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 4 PM CDT this afternoon for
IAZ044>050-057>062.

Winter Storm Warning until 4 PM CDT this afternoon for
IAZ004>007-015>017-023>028-033>039.

&&

SHORT TERM...REV
LONG TERM...REV
AVIATION...Krull

Hazardous Weather Outlook
National Weather Service Des Moines IA
704 PM CDT Sun Mar 14 2021

IAZ070>075-081>086-092>097-160015-
Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-Clarke-Lucas-
Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-Appanoose-Davis-
704 PM CDT Sun Mar 14 2021

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

Breezy east winds will gust over 30 mph at times into early this
evening.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Rain and possibly accumulating snow are possible toward midweek.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

IAZ044>050-057>062-160015-
Crawford-Carroll-Greene-Boone-Story-Marshall-Tama-Audubon-Guthrie-
Dallas-Polk-Jasper-Poweshiek-
704 PM CDT Sun Mar 14 2021

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

A Winter Weather Advisory is in effect for the area late tonight
into Monday. Please refer to the National Weather Service website
at weather.gov/desmoines for further details.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

A Winter Weather Advisory is in effect for the area on Monday.
Please refer to the National Weather Service website at
weather.gov/desmoines for further details.

Rain and possibly accumulating snow are possible toward midweek.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed, but snowfall reports are
always appreciated.

IAZ004>007-015>017-023>028-033>039-160015-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-
704 PM CDT Sun Mar 14 2021

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Tonight

A Winter Storm Warning is in effect for the area late tonight
into Monday. Please refer to the National Weather Service website
at weather.gov/desmoines for further details.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

A Winter Storm Warning is in effect for the area on Monday.
Please refer to the National Weather Service website at
weather.gov/desmoines for further details.

Rain and possibly accumulating snow are possible toward midweek.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed, but snowfall reports are
always appreciated.