449
FXUS63 KABR 052337
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
537 PM CST Wed Feb 5 2025

.KEY MESSAGES...

- There is a 35% to 50% chance of snow this evening over
  northeastern South Dakota and west central Minnesota. Less than
  one inch of snow is expected.

- Northwest winds will increase into the 15 to 30 mph range across
  central South Dakota tonight, then across eastern South Dakota
  and west central Minnesota on Thursday. Gusts may reach as high
  as 40 mph.

- Our next chance of precipitation will be Friday into Saturday.
  Probabilities of snow accumulation exceeding 6 inches have
  increased to 60-90% over portions of northern South Dakota into
  west central Minnesota.

- Arctic air is set to move in for the start of next week, with
  highs in the single digits Monday through Wednesday.

&&

.UPDATE...
Issued at 532 PM CST Wed Feb 5 2025

Changing wind direction and speeds are resulting from the surface
trough shifts across eastern SD. We`ll continue to monitor the
exiting wintry mix (mainly snow) over our northeastern counties
over the next couple of hours and nearing now over central SD
early this evening. The main change in the ongoing forecast has
been to winds.

&&

.SHORT TERM /THIS EVENING THROUGH THURSDAY NIGHT/...
Issued at 306 PM CST Wed Feb 5 2025

An upper level shortwave trough will swing across the Northern
Plains tonight, with a more west to east oriented wave setting up
over the northern CWA on Thursday before weak ridging pushes the
wave northward Thursday night.

At the surface, a low pressure system is currently situated over
eastern Wyoming, with a frontal boundary extending from it to the
northeast across South Dakota. This boundary has been aided by upper
level energy and steep lapse rates to be the focus for scattered
snow/sleet showers today, and this continues across mainly the
eastern half of the CWA this afternoon. As the boundary eventually
sets up more north to south oriented over the eastern CWA this
evening, will see a better chance for snow development, especially
across far northeastern South Dakota into west central Minnesota,
where up to one half inch or so of accumulation is possible by
midnight. High pressure will begin to nose in from the northwest
overnight, with a tight enough pressure gradient developing ahead of
it to produce wind gusts in excess of 35 mph across central South
Dakota tonight, then across eastern South Dakota and west central
Minnesota on Thursday. The winds will taper off Thursday night as
the high drops over the Northern Plains. After the chance for snow
this evening, no precipitation is expected through Thursday night.

Low temperatures tonight will be in the single digits to around 12
degrees. High temperatures on Thursday will range from the mid teens
across west central Minnesota, to the upper 30s across south central
South Dakota. Lows Thursday night will be in the single digits to
the mid teens.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 306 PM CST Wed Feb 5 2025

The main concern in the long term will be the storm system bringing
accumulating snow to the area, with the bulk of it occurring late
Friday into early Saturday. Clusters seem to be coming together
better and overall agree that by Friday evening, the shortwave`s
axis is forecasted to extend from MT and southward through Idaho
with zonal flow over the Northern Plains on the PVA side of the
system. These winds will turn more southwest as the shortwave inches
closer to the Northern Plains through the overnight. By 12Z
Saturday, the axis of the shortwave will extend from ND through NE.
Cluster 2, made up of majority GEPS, seems to be the outlier with
the wave being slower and a bit westward at this time compared to
the other ensembles. This wave will continue to track east through
the day Saturday with most of the Northern Plains on the backside of
the wave by Saturday evening with west winds turning to the
northwest. It is also noted a west to east jet streak will be over
the area with speeds of 100-120kts Friday afternoon and evening with
speeds still around 90-110kts through early Saturday morning. So the
combination of the strong shortwave and jet streak will provide
ample lift and upper level divergence.

By 00Z Friday, Clusters agree that the center of the elongated low
will stretch from WY and southeastward to CO, with the Northern
Plains on the northeastern side of the low, as precipitation will
continue to track eastward over the CWA. Between 06-12Z Saturday
looks to be the time period when we expect to see the bulk of the
snow fall (75-90% pops) as the CWA will transition from being on the
northeastern side of the low to being on the northern side of this
low, as the low is forecasted to be centered over KS by 12Z
Saturday. With an inverted trough extending northward from the low
(and this strong lift aloft) all the Clusters do agree that the
higher QPF/higher snow totals will be over northern to northeastern
SD into west central MN in this narrow WAA/deformation zone where
700mb FGEN is noted.

Latest QPF, mean NBM runs from 0.35 over Pierre to as much as 0.45
over 8D3 for the 24 hours ending Saturday evening. NBM 75th runs
between 0.4" to 0.5" over the northern/northeastern portions of the
state. Friday evening and onward, NAM/GFS soundings in this area
indicate a deep saturated column above, through, and below the DGZ
(and some points all within the DGZ) and ample amounts of omega
(mentioned above). This along with the FGEN gives confidence to
increase the SLR`s, and with collab from WPC, they range between 15-
18:1. This is why snow totals will be higher than the 10:1 totals on
ENS/GEFS which only show ~4-6 inches per mean. To add additional
confidence, NAEFS indicates 1-2 standard deviations above climo for
mean specific humidity at 850-925mb Saturday and EC EFI highlights
0.7-0.8 with a shift of tails of zero for QPF. Values of 0.7 to 0.9
with a shift of tails of zero is also noted for snowfall in this
area for Saturday. This also helps confidence as this means an
anomalous event, but nothing extreme or record breaking relative
to the EC reforecasts from a 5 week period (2004-2025) centered
on the week this forecast was initialized, for now. However, WPC
has upped the totals quite a bit (running in the 90th percentile
of NBM`s numbers) in this deformation zone to as high as
0.50-0.60" over the northern portion of the CWA. This seems high
for what is going on/overall models were mentioning and the
progressive nature of this low. So I did lower them a bit back to
around NBM mean-75th percentile over the northern and northeastern
CWA. This results in 4- 6 inches for the 25th percentile to 9-11
inches for the 75th percentile across northern and northeastern SD
into west central MN. Given still some uncertainty, most areas
have 5-6 inch spread between the 25-75th given a few days out. So
stay tuned!

With this heavy snow threat, the winter storm outlook highlights a
30-50% chance of exceeding warning criteria over northern to
northeastern SD/western MN on Saturday with a 30-50% chance of
exceeding warning criteria over the far eastern CWA Sunday. WSSI
highlights widespread 10 to areas of 20% for moderate impacts,
meaning expect disruptions to daily life with hazardous riving
conditons and closures may occur.

Temps will range in the teens and 20s Friday through the weekend
with another blast of arctic air early to at least the middle of
next week with highs only in the single digits by Tuesday. We also
will have weak systems that could bring slight chances of snow to
the area as well.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 532 PM CST Wed Feb 5 2025

Terminals KABR,KATY,KPIR,KMBG

VFR to MVFR conditions will continue at ABR and ATY, lingering at
ATY through around 06Z before a clearing sky returns to the entire
area. Wind gusts of 20 to around 30kts are expected during the
daytime hours Thursday. Low level wind shear, with winds just
above the surface around 40kts, is possible at MBG from 11-16Z
Thursday.

&&

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

$$

UPDATE...KF
SHORT TERM...Parkin
LONG TERM...MMM
AVIATION...KF