Harrisburg, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

266
FXUS63 KFSD 220452
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1052 PM CST Sat Dec 21 2024

.KEY MESSAGES...

- Sunday will be warmer and dry with high temperatures ranging
  from the freezing mark near the Highway 14 corridor to the mid
  40s along the Missouri River.

- There is a 20-30 percent chance of a wintry mix Sunday night
  along and east of a line from Marshall to Worthington to
  Spencer. While any accumulation will be very light, roads may
  become slick, impacting the Monday morning commute.

- Temperatures will warm through the upcoming week and be well
  above late December normals. Sporadic 20 percent precipitation
  chances return Thursday into next weekend. Precipitation
  coverage and type will depend on storm track, but some
  temperatures above freezing may allow for increased rain
  chances.

&&

.DISCUSSION...
Issued at 238 PM CST Sat Dec 21 2024

TONIGHT...southerly breezes will continue tonight with a tight
surface pressure gradient across the region. This, in
combination with increasing mid-high level clouds will keep
temperatures 10-15 degrees warmer than this morning.

SUNDAY...a 500 hPa closed low will drop southeastward from
central MT to southern MN. At the surface, low pressure will
skirt along the NE/SD border and across northern IA. Very strong
warm air advection ahead of this system will allow for well
above normal temperatures...with highs ranging from the freezing
mark along Highway 14 to the mid 40s along the Missouri River.

Overall, this system is quite moisture starved with the 12Z
HREF showing non-zero perception probabilities north and east
of the forecast area. That said, new 12Z deterministic guidance
(especially the NAM) is a bit more bullish with bringing some
precipitation across parts of southwest MN into northwest IA
Sunday night.

As the low-levels begin to saturate, soundings show a prominent
warm nose of +3 to +5 Celsius around 850 hPa. If saturation
occurs quickly enough, this could result in light freezing
rain/drizzle for areas along and east of a line from Marshall to
Worthington to Spencer after 9 pm. Thermal profiles eventually
cool to below freezing on the backside of the departing low,
allowing any remaining precipitation to change over to
sleet/snow. That said, there are still questions concerning
saturation within the -12 to -18 C ice production layer that
could wreck havoc on the p-type forecast. Total liquid
accumulations look to be very minimal (a couple hundredths at
best), but could still be enough to create slick roads,
impacting Monday morning`s commute.

MONDAY through CHRISTMAS DAY...a somewhat messy progressive
synoptic flow pattern will keep the immediate region dry and
warm. The coolest temperatures will reside along the Highway 14
corridor into southwest Minnesota, coincident with the current
snowpack, but afternoon highs are expected to top the freezing
mark region wide by Christmas Day.

THURSDAY into next WEEKEND...12Z medium-range guidance (GFS/
ECMWF) ejects a couple of 500 hPa lows into the central CONUS
from the Four Corners region. Large run-to-run variability
coupled with timing/strength differences precludes straying from
NBM POPs, but this results in low-confidence sporadic 20
percent chances each day, especially east of I-29. Ensemble
guidance has been consistent in keeping temperatures well above
late December normals, so any precipitation has a higher
probability of falling as rain. Those with holiday travel plans
will want to monitor the forecast for changes as details become
clearer.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1052 PM CST Sat Dec 21 2024

VFR conditions will prevail through this period, but locations
toward Highway 14 may see MVFR-IFR stratus sag southward into
the area prior to sunrise Sunday.

Occasional southerly gusts to around 20kt continue in areas
east of I-29 tonight and Sunday, perhaps slightly higher toward
25kt in higher elevations of southwest Minnesota overnight into
early Sunday morning. The gusty winds should diminish as we
approach sunset Sunday evening.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.

&&

$$

DISCUSSION...Rogers
AVIATION...JH