Harrisburg, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

700
FXUS63 KFSD 040458
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1058 PM CST Tue Dec 3 2024

.KEY MESSAGES...

- Becoming much colder and windy on Wednesday with wind gusts of
  40 to 50 mph and falling daytime temperatures expected.

- Scattered flurries/very light snow are expected Wednesday
  morning, possibly mixing in with light freezing drizzle for
  brief periods. At this time, impacts are expected to be minor
  with brief reductions to the visibility possibly below a mile,
  with snowfall amounts up to a quarter to a half an inch
  expected.

- Sub-zero wind chills return late Wednesday afternoon and continue
  through Thursday morning.

- Much milder temperatures for Friday through Sunday.

- Cooler with low confidence precipitation chances for the
  beginning of next week.

&&

.UPDATE...
Issued at 1047 PM CST Tue Dec 3 2024

Majority of the forecast remains unchanged, though model
guidance has trended towards stronger winds also reaching areas
along and west of the James River Valley. Have expanded the wind
advisory to include those counties, keeping start and end times
the same.

Lastly, some model guidance has come in showing less saturation
in the dendritic growth zone, rather saturated below -12 deg C
leading to concern for freezing drizzle. Saturation depths
beneath the DGZ are rather thin, so while it can`t fully be
ruled out the impacts look to remain minimal aside from patchy
slick surface if the freezing drizzle is at all able to develop.
Did include metnion of FZDZ in the grids, with the area most as
risk in SW MN, where the low-level saturation is highest.


&&

.DISCUSSION...
Issued at 255 PM CST Tue Dec 3 2024

Mild overnight temperatures are expected as a wave dives south out
of Canada. An initial cool front will move through overnight but
with winds remaining up and temperatures with this front still
fairly mild lows will inly dip into the 20s. The main wave will drop
into the Great Lakes region tomorrow afternoon which will drive a
more substantial front into the area from late Wednesday morning
into the evening. This will cause falling afternoon temperatures with
wind chill values below zero north of I-90 by late afternoon and
below zero south of I-90 during the evening. Values will not be cold
enough to warrant a wind chill advisory. The main concern for
Wednesday will be wind speeds. The latest model soundings indicating
35 to 45 knots in the mixed layer so suspect surface wind gusts of
40 to 50 mph at times for many locations.

Also of concern will be the potential for flurries and patchy light
snow. Two main forces driving this potential will be some weak
instability at the top of the mixed layer as well as a deepening
dendritic layer. The first forcing mechanism will be most prominent
in the morning and afternoon and more likely in southwest MN. Some
brief reduced visibility will be likely if a small band of
instability driven flurries/light snow can develop. Snowfall amounts
should be a quarter inch or less with the better chances again in
southwest MN. The deepening dendritic layer may also allow for
flurries over many locations but model soundings seem to struggle
to generate moisture in this layer so confidence on widespread
flurries is a little lower.

Cold high pressure settles south Wednesday night into Thursday
morning, bringing light winds, especially west of I-29, and colder
temperatures. Suspect some locations will fall below zero with the
better chances near and west of the James River. A cold day is in
store with highs in the teens to mid 20s. There will be a small
chance for a little light snow as some weak warm advection develops
in central SD Thursday afternoon. Confidence low in accumulation as
a significant dry layer appears to be in place below the main warm
advection.

Mild westerly flow will develop on Friday and continue into the
weekend. Highs in the 40s are expected both Saturday and Sunday.
Precipitation is not expected during this time.

A system moves into the area Sunday night into Tuesday with marginal
agreement on placement and timing. For now chances will remain at 20
percent or less through the period and will monitor trends to
determine if anything impactful could develop. For now this is not
expected.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1047 PM CST Tue Dec 3 2024

As strong winds continue to move through aloft, will see LLWS
continue for a few more hours before decreasing from north to south
as stronger northwest gusts are able to reach the surface. An MVFR
stratus deck is currently observed moving into far NE SD as of
0430Z, with MVFR cigs moving in throughout the early morning hours.
Timing of the MVFR cigs looks mostly unchanged, reaching areas along
the highway 14 corridor by 3 AM, I-29 corridor by 5/6 AM, and
highway 20 by around 8 AM. Scattered flurries/sprinkles will be
accompanying the front during the morning hours, possibly briefly
mixing in with freezing drizzle. Chances for sprinkles/flurries
decrease in areal coverage throughout the afternoon hours.

Lastly, the front has just about finished swinging winds around to
become out of northwest, with winds increasing after sunrise. Gusts
of 35 to 45 mph are expected east of the James River Valley during
the day before decreasing by late afternoon and early evening hours.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from 6 AM to 6 PM CST Wednesday for SDZ038>040-
     050-052>071.
MN...Wind Advisory from 6 AM to 9 PM CST Wednesday for MNZ071-072-
     080-081-089-090-097-098.
IA...Wind Advisory from 6 AM to 9 PM CST Wednesday for IAZ001>003-
     012>014-020>022-031-032.
NE...Wind Advisory from 6 AM to 9 PM CST Wednesday for NEZ014.
     Wind Advisory from 6 AM to 6 PM CST Wednesday for NEZ013.

&&

$$

UPDATE...APT
DISCUSSION...08
AVIATION...APT