Winter Storm in Minnesota, December 28 to 30, 2019

Area Forecast Discussion
National Weather Service Aberdeen SD
346 AM CST Sat Dec 28 2019

.SHORT TERM...(Today through Monday)
Issued at 345 AM CST Sat Dec 28 2019

Forecast challenges surround p-type, timing and coverage throughout
the period.

Currently, it's cloudy and snowing over the CWA. A few areas have
started out as freezing rain/sleet before the bottom of the column
has saturated/cooled enough for p-type to change over to snow.
Temperatures on relatively light southeast surface winds are holding
generally in the 20s to low 30s this morning.

The back edge of the snowfield for this first wave of wintry
precipitation is up through the i-90 corridor all the way up to
KPIR. That dry/void of radar-discernible light precipitation area
will continue to push northward across the CWA today, leaving some
light freezing rain/freezing drizzle potential in play until later
this evening when the second wave of much more significant
precipitation begins to move north and west across the region, and
the north-northwesterly surface winds begin to ramp up.

Given the synoptic-scale set up and the amount of warm/moist air
riding the warm conveyor belt of this system, won't be surprised at
all if some of the precipitation later tonight into Sunday has a
convective look and feel to it. Seems like thunder and lightning
should also be accompanying a system as dynamic as this one will be.

Changes are subtle, including an increase to maxTwaloft values over
the far southeastern forecast area where the low level waa will
create a small/saturated warm tongue in the column tonight into
Sunday and allow more opportunity for p-type to be sleet and/or
freezing rain over a larger area of the cwa and for a longer period
of time. This has nudged ice accumulations up into the 0.25 to 0.30
inch range along and east of the eastern slopes of the Prairie
Coteau, and lowered snow accums there by an inch or two. The 00Z
deterministic ECMWF has also drawn a third wave of wrap-around light
snow westward into the CWA during the day on Monday (another 1-3
inch snow accum potentially) while the winds over the eastern half
of the CWA are still progged to be 15 to 25 mph with gusts to 35
mph. Stayed with a small nudge upward to probIcepresent values for
Sunday/Monday, as p-type within TROWAL-forced areas is expected to
be a frozen/snow p-type. All things considered, still looks like the
juxtaposition of worst conditions (heaviest falling snow combined
with strongest northerly winds, despite the low level thermal
inversion) is Saturday night and Sunday over all of the western half
of the CWA and over to the James River valley. Then, light to
moderate snow and breezy to windy conditions (not quite blizzard)
looks to transition to along and east of the James River valley for
Sunday night through the day Monday.

Temperatures throughout the period will be near to above normal.

.LONG TERM...(Monday night through Friday) Issued at 345 AM CST
Sat Dec 28 2019

The models are still showcasing a flow pattern aloft less amplified,
a little bit faster/progressive with weaker, more transient-type
shortwaves of low pressure. In house guidance is basically dry/void
of pops mention, although at some point in the extended, there will
probably be some smallish pops introduced for a little bit of light
snow or rain/snow mix. There are some areas where the wind speeds are
high enough that the blowing snow tool gave "patchy blowing snow".
Indeed, will have to watch the wind-favored/downslope-prone areas
closely for a couple of days after this pending big storm to ensure
local-effects blowing snow events done occur/go un-noticed.
Otherwise, perhaps the only other thing worth noting is the strong
winds signal showing up in all the GSM deterministic output this
morning for next Saturday (day 8). Again, temperatures (both
deterministic and ensemble-based) in the out periods do not look all
that cold, running generally near to a tish above climo normal most
of the time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
Issued at 1120 PM CST Fri Dec 27 2019

IFR skies/vsbys will continue to move north into the region
overnight as mixed pcpn heads north out of the Central Plains.
Freezing rain is possible, as well as some accumulating snows
through the early morning on Saturday.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Warning until 6 AM CST /5 AM MST/ Monday for
     SDZ003>011-015>023-033>037-045-048-051.

MN...Winter Storm Warning until 6 AM CST Monday for MNZ039-046.

&&

SHORT TERM...Dorn
LONG TERM...Dorn
AVIATION...TDK

Hazardous Weather Outlook...UPDATED
National Weather Service Aberdeen SD
313 PM CST Fri Dec 27 2019

SDZ003>007-009>011-015>019-033>037-045-048-051-281200-
Corson-Campbell-McPherson-Brown-Marshall-Walworth-Edmunds-Day-Dewey-
Potter-Faulk-Spink-Clark-Stanley-Sully-Hughes-Hyde-Hand-Jones-Lyman-
Buffalo-
313 PM CST Fri Dec 27 2019 /213 PM MST Fri Dec 27 2019/

This Hazardous Weather Outlook is for central South Dakota, north
central South Dakota and northeast South Dakota.

.DAY ONE...This afternoon and tonight.

Light to moderate snow and perhaps some sleet or light freezing rain
are forecast to move into the region late this evening. Roads will
likely become snow covered and slippery.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

The first wave of precipitation will move north of the area or
weaken, putting the area under some light snow or freezing drizzle
for much of the day Saturday. The snow will intensify Saturday night
and continue to fall heavy at times through Sunday before gradually
diminishing Sunday night into Monday morning. Total snow
accumulations will exceed 8 inches for most areas, and likely exceed
a foot for a good portion of the area. In addition, blizzard
conditions are possible on Sunday, especially between the Missouri
and James Rivers, as winds gust over 40 mph. Stay tuned to the
latest forecasts for updates on this potentially dangerous storm
system.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed. Weather spotters are
encouraged to submit reports to the National Weather Service in
Aberdeen. The public can submit reports on our web page, Facebook
page, or our Twitter feed.

MNZ039-046-SDZ008-020>023-281200-
Traverse-Big Stone-Roberts-Codington-Grant-Hamlin-Deuel-
313 PM CST Fri Dec 27 2019

This Hazardous Weather Outlook is for west central Minnesota and
northeast South Dakota.

.DAY ONE...This afternoon and tonight.

Light to moderate snow and perhaps some sleet or light freezing rain
are forecast to move into the region after midnight tonight. Roads
will likely become snow covered and slippery by Saturday morning.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

The first wave of precipitation will move north of the area Saturday
morning, but expect lingering light snow or freezing drizzle for
much of the day Saturday. The snow will intensify Saturday night and
continue to fall heavy at times through Sunday before gradually
diminishing Sunday night into Monday morning. Total snow
accumulations will exceed 8 inches for most areas, and likely exceed
a foot for a good portion of the area. Total ice accumulations of a
tenth of an inch to a quarter of an inch are possible. Stay tuned to
the latest forecasts for updates on this potentially dangerous storm
system.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed. Weather spotters are
encouraged to submit reports to the National Weather Service in
Aberdeen. The public can submit reports on our web page, Facebook
page, or our Twitter feed.

SRF