Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 221133 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
633 AM CDT Fri Mar 22 2024

.KEY MESSAGES...

- First system winding down early this morning, while next one
  begins approaching on Saturday. An inch or two accumulation
  expected already during the day on Saturday.

- No appreciable change with the weekend storm system. Onset of
  the brunt of the storm begins Saturday night into Sunday. Snow,
  heavy at times combined with stronger winds will begin to cause
  impactful conditions on Sunday into Sunday night.

- There is a 60 to 100 percent probability of wind gusts of at
  least 30 MPH across most of the forecast area by Sunday night
  through the first half of the day on Monday presenting a
  blowing/drifting snow component to this weekend`s storm system.
  Travel will likely become difficult to impossible Sunday/Monday.

&&

.UPDATE...
Issued at 629 AM CDT Fri Mar 22 2024

See updated aviation discussion below.

&&

.SHORT TERM /TODAY THROUGH SATURDAY AFTERNOON/...
Issued at 513 AM CDT Fri Mar 22 2024

Snow has winded down to basically flurries across the northern CWA.
Had already cancelled Brown/McPherson/Edmunds from the Winter
Weather Advisory, with the eastern segment remaining in place
through 12Z this morning. May be able to cancel that a bit early.
Current forecast PoPs fade to "no weather" by 12Z this morning, but
may have to insert mention of scattered flurries based on upstream
obs/radar, and abundance of clouds producing flurries. As for the
cloud cover, increased sky grids this morning based on current
trends. Latest HREF cloud cover ensemble mean does suggest high
potential for low clouds to stick around in a "mostly cloudy or
cloudy" fashion through at least the morning hours, with some degree
of clearing trying to get going this afternoon.

Low temps tonight are rather trick, especially across the
north/northeast where there is a fresh few inches of snow. The
aforementioned HREF cloud cover product does suggest a trend towards
mostly clear skies over eastern areas this evening. So, if there is
a period of mostly clear skies before the onset of mid/high clouds
later tonight, there could be a period of radiational cooling with
temps dropping down into the single digits at least. Did opt to go
towards lower percentile guidance for lows tonight over northern and
eastern areas where snow was received.

Snow looks to be moving into the area already on Saturday, with
likely to categorical (60-100%) PoPs in place. NBM mean 24-hr
snowfall ending at 00Z Sunday is around 1 to 2 inches across much of
the CWA. Highest probabilities for an inch or greater are showing up
across central/north central SD, with values generally ranging from
50-75% over the north central SD counties. Official forecast does
show about 1 to 2 inches across the area during the day Saturday.

&&

.LONG TERM /SATURDAY EVENING THROUGH THURSDAY/...
Issued at 513 AM CDT Fri Mar 22 2024

The main forecast challenge in this period will continue to remain
focused on the highly anticipated impactful winter storm progged to
move into the region this weekend and linger into early next week.
Both deterministic and ensemble guidance remains fairly agreeable on
the placement and timing of this storm system as it shifts out
the Rockies into the Plains and Upper Midwest. As mentioned in
previously released forecast packages, we`ll be dealing with a
classic Colorado surface low that will organize and strengthen
over the Front Range on Sunday and shift out into the Central
Plains Sunday Night and Monday morning. Guidance then hooks it
toward the northeast into eastern Nebraska and western Iowa during
the day Monday before continuing it`s northeast trajectory toward
southeast Minnesota and western Wisconsin Monday night and into
the western Great Lakes early Tuesday.

As this period starts out Saturday night into Sunday morning,
southwest flow aloft begins to commence in a more pronounced fashion
across South Dakota as the upper level trough moves across the Great
Basin and into the Rockies. Snow, possibly heavy at times will be
ongoing across our CWA at this time frame...or it`s expected to be
increasing in intensity with time in a more widespread pattern as we
get into Sunday morning. One aspect at this point we`ll have to
watch is how much relatively warmer air could make its way into our
far southern zones. It`s possible some parts of south central South
Dakota and points northeast into the James Valley(south of Hwy 212)
see temperatures reach above 32 degrees and effectively cut snow
ratios below 10:1 for a time during the day on Sunday. This would
have an impact on snowfall amounts. As the sfc low shifts out into
the Plains Sunday morning, it will be butting up against a sfc high
over parts of Manitoba and Ontario. A tighter gradient develops
across the region through the overnight and into Sunday where we can
expect to see strong sustained easterlies creating blowing snow and
visibility issues in the falling snow. These winds eventually become
north to northeasterly as the sfc low makes its way into Iowa by
Sunday night into Monday. TROWAL induced snowfall will continue at
this point over our CWA with a tight gradient in place. Although NBM
winds may be a tad overdone at this point by Sunday night, we`ll run
with them as is for now as concerns for blizzard conditions remain
on the forefront going into the overnight hours into Monday morning.
Snowfall will continue through the day on Monday, but intensity will
slowly diminish through the day as the precipitation chances
gradually come to an end from west to east beginning Monday
afternoon through the overnight into early Tuesday.

NBM probabilities for seeing given snowfall amounts remain
impressive with this storm system. Just taking the 6 inch figure as
an example, which is the snowfall criteria for a Winter Storm
Warning, the probability of seeing at least this amount is at or
exceeds the 50 percent chance for the majority of our forecast area.
So, that means a good chunk of the area this office serves could see
a half a foot or more of snow from this event. Therefore, went ahead
with the issuance of a Winter Storm Watch at this point in time
beginning Saturday night through Monday night. With the concern for
stronger winds and blowing and drifting snow, included the mention
of blizzard conditions possible. Conditions should gradually improve
on Tuesday into the middle of next week. Don`t expect temperatures
to recover much thanks to the new blanket of snow on the ground.
Below average readings are anticipated to persist through most of
next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 629 AM CDT Fri Mar 22 2024

Terminals KABR,KATY,KPIR,KMBG

A mixed of IFR and MVFR cigs early in the TAF period will improve
to low end VFR before 18Z. Isolated flurries may briefly restrict
visibilities to 6SM early in the TAF period. Light snow may move
into western South Dakota late tonight, possibly impacting KPIR
after 9Z.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Watch from Saturday evening through late Monday
     night for SDZ003>011-015>023-033>037-045-048-051.

MN...Winter Storm Watch from Saturday evening through late Monday
     night for MNZ039-046.

&&

$$

UPDATE...SD
SHORT TERM...TMT
LONG TERM...Vipond
AVIATION...SD


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