995
FXUS63 KFSD 231752
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1152 AM CST Sun Feb 23 2025

.KEY MESSAGES...

- High temperatures in the 50s to mid 60s (15-25F above normal)
  are expected through this last week of February.

- Watch for refreeze of melted snow causing scattered slick spots
  as nighttime temperatures fall back below freezing.

- Predominately dry conditions will persist through the week. Low
  (20%-30%) chances for light rain Monday (north of I-90) and
  again Tuesday night into early Wednesday.

- Areas of elevated fire danger are possible through the week
  ahead as snow melt continues and temperatures remain mild. The
  better chance will be near & west of the James River through
  Tuesday, but may expand toward I-29 & points east by late week.

&&

.DISCUSSION...
Issued at 340 AM CST Sun Feb 23 2025

A very mild pattern will prevail across the northern Plains
through much of the week ahead, with any temperatures close to
what we saw last week confined to well north of the Canadian
border. Instead, 850-925mb temperatures in the +5C to +15C range
will support several days of highs in the 50s to lower 60s, with
some mid-upper 60s possible toward south central SD at times. NBM
remains on cool side of the NBM 50th percentile, while observed
high temperatures the past few days have been closer to, or even
warmer than the NBM 75th percentile. This cold bias may continue
for at least the next several days as the blend`s bias-correction
may still be feeling the effects of our recent arctic blast. Thus
have coordinated with neighbors to favor highs closer to the NBM
75th percentile through much of the week ahead, pushing further
toward the 90th percentile today and Tuesday when warm advection
between waves is maximized over the area.

The current weak wave over the region is responsible for fairly
expansive mid-level clouds early this morning, which thus far has
been helping to keep any fog at bay. Expect the clouds to slowly
decrease from the northwest as the wave exits this morning, which
could still allow for patchy low lying fog development by around
daybreak. Our warm daytime temperatures should quickly melt our
remaining snow over the next 2-3 days, and while our nights will
also be quite mild for this time of year, any areas falling back
below freezing will see a risk of refreeze of the melted snow on
untreated surfaces. Also cannot rule out the potential for patchy
fog again tonight, but again looking at a fair amount of mid-high
level cloud cover until late tonight-early Monday which may
inhibit development.

RAIN CHANCES: Each subsequent wave (Monday, then Tuesday night
into early Wednesday) appears to be slightly stronger then the one
before. However, we still seem to be lacking sufficient moisture
to produce much more than a few spotty hundredths of an inch of
rainfall with ensembles showing <20% chance of rainfall exceeding
0.10" in either 24-hour period. Chances for light rain will
largely be confined to areas near/north the Hwy 14 corridor on
Monday, but 20-40% chances for measurable rain expand as far south
as Hwy 20 Tuesday night.

FIRE DANGER: Several high-res models are indicating the potential
for stronger wind gusts topping 30kt (35 MPH) Monday afternoon,
especially into areas west of the James River Valley as weak cold
advection/deeper mixing develops behind the departing wave. Have
blended in some of this higher guidance to nudge NBM winds upward,
resulting in an area of High to Very High Grassland Fire Danger
in areas where vegetation has been snow-free for several days.

The warm air looks to remain in place into at least Friday when
the next wave is slated to dive into the northern Plains. Some
discrepancy among the deterministic models on when the wave and
associated cooler air arrive, though even the more aggressive
(faster) GFS shows high temperatures Friday in the 50s to lower
60s. Friday also looks to be on the windier side, and with snow
cover expected to be gone and fine fuels having plenty of time to
dry, could see the High to Very High fire danger expand over much
of the forecast area.

MARCH IN LIKE A LION OR LAMB? Cooler air does arrive behind the
wave Friday which brings temperatures closer to seasonal normals
Saturday, but the cooldown may be brief as mild air could return
again early next week. For the local area, March should arrive
like a lamb on Saturday and into early next week as northern
stream ridging dominates the flow pattern across the northern
Plains. A strong cut-off upper low over the Desert Southwest
Saturday moves across the southern Rockies and into the southern
Plains early next week, but even solutions which are weaker with
this system favor dry conditions in our area for the first weekend
of March.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1152 AM CST Sun Feb 23 2025

VFR conditions are expected through the rest of the afternoon with
light southwesterly winds around 10-12 kts. Winds become westerly
after midnight and remain around 10 kts or less. High cirrus clouds
continue to flow in from the northwest through the afternoon and
overnight. Ceilings are expected to gradually lower after 24.12Z as
a weak wave approaches bringing chances for light precipitation
after the end of the current period. However, they are expected
to remain above 7000 ft AGL.

Light winds and plentiful moisture left behind from today`s melting
snow increases the risk of fog development overnight and into Monday
morning. Confidence in fog development is higher at KSUX and KFSD
and have included mention in the TAFs. KHON confidence is lower
and have left fog out at this time. Current guidance indicates
the fog will be patchy in nature, however we will continue to
monitor the trends.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...AJP