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Forecast Discussion

Forecast Discussion for FSD NWS Office

FXUS63 KFSD 301129

National Weather Service Sioux Falls SD
629 AM CDT Thu Mar 30 2023

.SHORT TERM...(Today through Friday Night)
Issued at 357 AM CDT Thu Mar 30 2023

Key Messages:

1. Multi-faceted, multi hazard system impacts the region today
through Friday night. Isolated severe weather, locally heavy rain,
moderate to heavy snow, are possible. Strong winds are expected.

2. Reprieve for the weekend, with a warmer temps Sunday.

3. Another system may impact the region early to mid next week.
Confidence remains low in details.

Short Term Discussion:

Through Daybreak: Clouds continue tracking northeast along the
first WAA push as mid level ridge builds. Winds are strengthening
with tightening surface pressure gradient as surface high moves
east. With southerly flow and WAA, have started to see
temperatures begin to rise, with most of the area solidly in the
20s at 08z/3AM CDT. Although we`re seeing some returns on radar,
dry sub cloud layer has been precluding precip from reaching the
ground thus far.

Today into This Evening: Mid level trough continues to deepen across
the southwestern US, moving northeast through the day. By this
afternoon, surface low begins to eject out of the Rockies into
western KS and NE. In response, warm front treks north with ample
WAA, leading to a warm day for most of the area. Folks near the Hwy
14 corridor likely stay in the upper 30s, increasing to the
lower/mid 60s along Hwy 20. Temperatures will likely also be
dependent on cloud cover, with models varying on coverage across our
southern CWA. LLJ also cranks up in the east (northwestern IA and
southwestern MN) through the early afternoon. Cloud cover and
subsequent warming plays a role in the possible convective threat as
well. With the LLJ, WAA, and increasing dew points, expect some
shower activity east of I-29 today and into the afternoon. Rumbles
of thunder are possible.

Attention will turn to the possible severe weather threat - mainly
this evening and into tonight - with elevated convection likely
forming in NE and marching northeastward. Most models continue to
show a high shear/low CAPE environment through most of the
afternoon, with instability tracking northward during the evening.
If convection to our south can form and if instability gradient
shifts north/storms can break the cap, can`t rule out isolated
strong to severe storms from northeastern NE stretching northeast
into southeastern SD/southwestern MN/northwestern IA (outlined by
the 06z SPC Day 1 Marginal Risk). Hail would be the main threat
given lapse rates over 7 deg C per km. Additionally, could see some
locally heavy rainfall, especially with convection.

Tonight: Temperatures begin to fall along the Hwy 14 corridor to
below freezing, leading to a transition to freezing rain. Soundings
support a fairly long period of freezing rain, with little to no
sleet and/or snow mixing in. One uncertainty tonight with respect to
precip will be the potential dry slotting and periodic loss of
saturation. This could lead to drizzle/freezing drizzle. One other
uncertainty remains the temperatures, and just how quickly they fall
both aloft and at the surface. Lows in the upper 20s to lower 30s in
the north and west, with northwestern IA staying mild in the
mid/upper 40s. Instability aloft, albeit weak, could be enough to
lead to some convective precip, which could create some moderate to
heavy precip in addition to thunder.

Friday: Highs on Friday will range from near 30 east of the James
and along Hwy 14, to the upper 50s and lower 60s in northwestern IA
(who stays in the warm sector the longest). Increasing CAA could
lead to falling temperatures through the day as surface low travels
east. Winds strengthen and turn northwesterly during the afternoon,
which will lead to blowing/drifting snow. Transition from either
rain or freezing rain to snow occurs through the day, with most of
the area switching to snow by the evening. The exact timing is
uncertain due to timing issues with CAA. Snow will be heavy at
times, and northwesterly winds ramping up in the afternoon will
likely lead to blowing/drifting snow and reduced visibility.

Although could see some thunderstorms along and east of Hwy 75 in
northwestern IA/southwestern MN, severe threat has shifted just to
the east of our area. Can`t rule out a stronger storm with initial
development, if convection can get going mid morning, although this
scenario seems unlikely.

Friday Night: With wrapping low and LLJ paired with increasing
CAA on the backside of the system as it moves to the east, expect
winds to ramp up quickly. NBM continues to have values near and
above Wind Headline criteria; however, not convinced via soundings
that we`ll be able to consistently mix to 850mb (where the
strongest winds lie) to keep these values in. Have reduced with
the NBM 10th percentile (although this is still possibly too
high), previous forecast, and CONSShort. Trends will need to be
monitored for possible headlines. Regardless of headline
potential, winds will be strong through the night, leading to
blowing and drifting snow.

QPF through the event has come in lower this forecast period than
previous forecast, and thus have seen a decrease in snow totals
tonight through Friday night. Models have shifted the axis of
heavier snow to the north and west as well with the low track a
touch further to the north. For our area, amounts look highest west
of the James and along the Buffalo Ridge (where over 4 inches
possible). Probabilities of 6+ inches have dropped a touch, to just
over 50% in our far northwest. Also, with saturation issues and
temperatures a touch warmer aloft, have seen an increase in ice
amounts. Could see a tenth of an inch of ice from south central SD
to the Buffalo Ridge, with about a 30% chance of over a tenth along
Hwy 14. Did not make any changes to headlines at this point,
maintaining the Winter Storm Watch for possible Blizzard Conditions.
Did ponder an expansion of the headline to the I-90 corridor with
NWS Twin Cities; however, given downward trend in snow amounts and
lower confidence in ice accumulations, held off for this package.

Folks should prepare today for all possible hazards, and keep an eye
on the forecast through the day for updates. Be prepared to alter
local and regional travel plans tonight into the weekend.

.LONG TERM...(Saturday through Wednesday)
Issued at 357 AM CDT Thu Mar 30 2023

Saturday: Low continues to move off to the east Saturday, bringing
the return of zonal flow. CAA on the backside of the low will keep
us on the cooler side, especially early in the day and into the
afternoon across the eastern portion of the forecast area. Any
lingering snowfall should come to an end as the low moves to the
east as well. Highs Saturday in the 30s and 40s, with lows falling
into the 20s and 30s. Increasing clouds and breezy conditions
return, with blowing snow possible Saturday night (depending on how
much new snow falls across the region Friday/night).

Sunday: WAA returns as a mid level short wave is progged to swing
across the International Border into ND. Clouds increase ahead of
this, but other than breezy conditions, no impacts expected. Warmer
day on tap with the WAA and southerly/westerly flow. Highs in the
40s and 50s (close to normal!), with lows in the 20s and 30s.

Early/Mid Next Week: Temps generally below/near normal. Slightly
cooler Monday with CAA behind the wave and cold surface high
sliding south. Highs in the upper 30s to upper 50s, warmest in
northwestern IA. By Monday night, trough builds into the western
US, deepening through Monday night into early Tuesday. Models are
in somewhat agreement with the overall evolutionary trends of the
system, but timing and track still have enough variance for low
confidence. This system, depending on timing and track, could be
another multi- faceted event. Regardless of precip, it will be
windy. Folks should keep an eye on the forecast for early/mid next
week, especially if you have regional travel plans.


.AVIATION...(For the 12Z TAFS through 12Z Friday Morning)
Issued at 621 AM CDT Thu Mar 30 2023

VFR conditions begin the TAF period, with a mix of stratus and
cirrus. MVFR and lower stratus develops east of I-29 this
afternoon, filling in to the west through the evening. MVFR and
lower conditions expected through Friday.

Winds increase through the morning, with a lull (relatively)
through the latter half of the period as low pressure slides
across the area. Expect the strongest winds in northwestern IA.
LLWS is possible for northwestern IA and southwestern MN this
evening as the LLJ strengthens, but have left out of KFSD and
KSUX, as these sites look to be on the far eastern edge.

Precip (rain) develops across southwestern MN and northwestern IA
later today. Although added with this package, low confidence
remains in convection potential this evening for KFSD and KSUX.
Any thunderstorm could further reduce visibility/ceilings, as well
as create brief erratic winds.


SD...Winter Storm Watch from Friday morning through late Friday night
     for SDZ040-055-056.

     Winter Storm Watch from Friday morning through late Friday night
     for SDZ038-039-050-052>054-057>060-063-064.

MN...Winter Storm Watch from Friday morning through late Friday night
     for MNZ071-072-080-081-097.




NWS FSD Area Forecast Discussion