771
FXUS63 KABR 031127
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
527 AM CST Mon Mar 3 2025

.KEY MESSAGES...

- Above normal temperatures are expected again Today.

- Light rain/drizzle moves into the region tonight, with a band of moderate
  rainfall from central to northeast South Dakota. As the night
  progresses, there will be a transition of precipitation to a mix
  and then snow. Ice is possible during this transition.
  Accumulation ranges for snow are between a dusting to 2 inches
  with locally higher amounts in south central SD.

- Northerly winds of 35-45 mph are also expected Tuesday into
  Tuesday night. The combination of the snow and wind may lead
  to visibilities reduced below 1 mile at times.

&&

.SHORT TERM /TODAY THROUGH TUESDAY AFTERNOON/...
Issued at 327 AM CST Mon Mar 3 2025

Stratus is just starting to move northwards out of western
Nebraska/Kansas/Oklahoma, while another pocket lies situated across
east Texas/Louisiana and into the gulf.  This low level moisture
advects north on the strength of a 30-40kt low level jet. By the
afternoon this low level moisture is expected to make it into the
Watertown/Sisseton hills region. Otherwise the region will
experience full sun with an inverted trough developing across
eastern South Dakota as a surface low takes shape over eastern
Colorado.

The track of this low is more of a bee-line eastwards through
Kansas, which is not a trajectory for a Colorado Low that would
typically generate significant moisture for the region. That said,
there still appears to be impacts thanks to a transition in
precipitation types early to mid-day Tuesday. There is a pool of
cool air to the north, which will get drawn into the north side of
the inverted trough. Thus, while the heavier precipitation is
expected to reside south of the forecast area, any moisture that
does develop this far north will occur within in a complex
environment of temperature gradients and variable dendritic growth
zone heights and levels of saturation within the profile.

CAMS support this myriad of precipitation types, with each member
showing some sort of transition from rain to a possible period of
freezing rain to snow. We can see this in some of the NAM BUFKIT
soundings too, as the cooling results in profiles that lack
saturation in the dendritic growth zone but 4-5kft thick stratus,
primarily up in the Sisseton hills. For Aberdeen/Pierre, the NAM
profiles show a more rapid transition because the profile saturation
takes longer, so it suggests going over mainly to snow more rapidly.
That said, these profiles may not be capturing the setup of a mid-
level southwest to northeast deformation zone that sets up somewhere
across central/northeast South Dakota. This is where we can
anticipate light to moderate perception to develop, with more
widespread light shower activity outside the deformation zone. The
issue of "who gets what" has a high uncertainty thanks to the fact
that it is a narrow feature and slowly migratory, but its exact
location is kind of up in the air for central/northeast South Dakota
because it could set up about 50 miles to either side of a line from
somewhere between Sisseton/Aberdeen to Miller/Pierre.

Moisture equivalent amounts have also taken a bit of an upwards
tick. The 25th/75th percentiles from the NBM haven`t really shifted
that much however, and confidence on "who gets how much" is anyones
guess with the 25th percentile around 0 and the 75th percentile at
about a half inch. HREF isn`t much better, and this again is all
owing the the mesoscale nature of this deformation zone.

NBM still shows a diurnal trend during the day Tuesday, which will
be fighting low level cold advection, though precipitation is mostly
done out west with diminishing clouds. Seems less likely in the far
east however. Will lean on the CAMS for hourly temperatures during
the day.

As for headlines, its not very clear which is the best product since
we have a combination of winds and mixed precipitation with the
probability of 2 inches of snow or greater only about 40-60 percent
across the far south of the CWA. The probability of 4 accumulation or
greater is only a little bullseye in Jones county. Outside of
falling snow, little impact other than terrible road conditions are
anticipated thanks to the mix with ice potential before the change
over. At this point, will let the day shift have one more go at
available information before making the call.

&&

.LONG TERM /TUESDAY EVENING THROUGH SUNDAY/...
Issued at 327 AM CST Mon Mar 3 2025

The precipitation occurring during the day Tuesday will mainly be
over eastern SD by the evening, with the NBM showing 15-45% chance
for precipitation east of the James River Valley. This precipitation
then moves out of the state overnight. Temperatures during this time
look to be around freezing and then cool once the sun starts to
sets, which helps the precipitation type to stay as snow Tuesday
evening into Wednesday. The snow accumulations during this time look
to stay light and be around/less than a half inch, though the
clusters show a 20-40% chance for greater than a half inch. Winds
during this time continue to be stronger as a tighter pressure
gradient between the surface low in MO and high in ND stays over
central and eastern SD through Wednesday. These winds and gusts look
to be over 30kts Tuesday evening and as the tight pressure gradient
moves east, the winds start to dissipate from west to east overnight
into Wednesday. These stronger winds could cause blowing snow and
reduced visibility in areas, but this will depend on how wet the
falling snow is Tuesday evening into Wednesday morning. If the snow
is wet, the winds might not be strong enough to loft it into the
air, but if it is drier snow, the winds will loft it easier.

A surface high pressure is over SD through the day Thursday, with a
surface low moving over KS overnight Thursday into Friday. An area
of precipitation develops on the north side of this surface low, and
is over southern SD through Friday. Depending on the location of the
low, the deterministic models vary how far into south central SD the
precipitation occurs, with the NBM mainly keeping the precipitation
to the south of HWY 212, with chances of up to 35% over south
central SD. Temperatures start above freezing and then cool once the
sun sets causing the precipitation to start as rain then transition
to a mix of rain and snow and then just snow overnight. QPF looks to
be light over south central SD during this time, leading to lower
precipitation amounts. The clusters have a 20-40% chance of more
than 0.1in of snow over south central SD and the NBM showing only
0.1in of snow occurring in far southern portions of south central
SD.

There is a warming trend in the temperatures starting Wednesday. As
an upper-level ridge starts to develop over the west coast Saturday
and moves east towards SD, the weekend high temperatures look to be
10-20 degrees warmer than normal. With this upper-level ridge
starting to push in, the chance for precipitation stays low after
Friday.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 523 AM CST Mon Mar 3 2025

Terminals KABR,KATY,KPIR,KMBG

VFR conditions initially with winds shifting to northerly
(easterly for KATY). CIGS will gradually lower, first at KATY
late this afternoon to MVFR/IFR and then for the other sites
overnight. Precipitation though 12Z should be primarily rain will
MVFR VISBY outside of KATY which will have fog and drizzle and
lower VISBY, though there will be a transition to freezing rain
and snow towards the very end of the TAF period.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

$$

SHORT TERM...Connelly
LONG TERM...Vernon
AVIATION...Connelly