Area Forecast Discussion
Issued by NWS Sioux Falls, SD

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

000
FXUS63 KFSD 181122
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
622 AM CDT Mon Mar 18 2024

.KEY MESSAGES...

- Low relative humidity down to 20-25% along with lighter winds
  will yield high to very high fire danger today. High to very
  high fire danger will continue through Tuesday.

- Colder air drives south Tuesday into Wednesday. This has a
  high chance of bringing near to below normal temperatures from
  Wednesday through next weekend.

- Chances for precipitation return to the area late Wednesday through
  the weekend. Uncertainty remains for the time being so those
  with weekend travel plains will want to continue to monitor
  the latest forecast for the most up to date information.

&&

.DISCUSSION...
Issued at 341 AM CDT Mon Mar 18 2024

Low level stratus continues to produce flurries early this morning
and some breezy winds. This stratus deck will continue to push
through the area for the rest of the overnight and into the morning
hours. Should see this low level stratus deck completely exit the
area by the afternoon hours. This will leave partly sunny skies in
place as mid to upper level clouds filter in aloft ahead of an
incoming of an upper level jet max diving out of Canada. At the
surface, a surface high pressure system will be sliding through the
area mostly during the morning hours. Southwesterly return flow on
the back side of the high will take over for the afternoon hours
with winds becoming breezy during the late afternoon hours. High
temperatures will warm to the 40s and low 50s while dew points
remain in the single digits. This will make for low relative
humidity (RH) values all the way down to 20-25%. While RH will meet
critical fire danger levels, winds winds will only meet criteria for
a brief period of time late this afternoon. Thus have foregone any
fire related headlines for today.

As the previously mentioned wave dives southward out of Canada this
evening, warm air advection (WAA) will strengthen out ahead of it.
Despite the strong WAA, this wave will exhibit large scale decent
rather then large scale ascent characterized by divergence of Q-
vectors aloft. BUFKIT soundings also depict dry air throughout the
troposphere so no precipitation is expected. This wave will still
drag a cold front through the area tonight which will keep low
temperatures down to the 30s.

Tuesday will still be a warmer day despite cold air advection (CAA)
in the wake of the passing cold front. With 850 mb temperatures on
either side of 0 degrees C, highs will warm into the 50s across most
of the area. High temperatures up to around 60 degrees F look to
occur along the Missouri River Valley. Northwest winds within the
cold advective regime will result in breezy to gusty winds with
gusts up to around 35 mph. While winds will meet critical fire
danger levels, RH may not. Although temperatures will be warmer, dew
points will warm as well up to the low 30s, thus keeping RH values
down to only around 30-35%. Dew points could lower more and bring
conditions closer to meeting red flag criteria if mixing is strong
enough. For now, do not have high enough confidence to lower dew
points at this time. Will watch trends during this period of time.
Winds will wane during the evening hours as mixing ceases. Low
temperatures will be on the cold side, falling to the teens and 20s
overnight.

Wednesday will be a cooler and mostly quiet day as surface high
pressure slides through the Upper Midwest. High temperatures will
only warm to the 30s and 40s across the area. The next chance for
precipitation will come Wednesday night as a shortwave trough ejects
out of the Rockies and into the Northern Plains. Soundings show dry
low levels but medium range guidance shows stronger frontogenesis
(FGEN) from about 925-700 mb along with increasing WAA. Think the
stronger forcing may overcome the dry low levels to some degree and
thus have increased PoPs a bit to reflect this potential. Low
temperatures will fall to the 20s overnight.

The bulk of accumulating precipitation will fall on Thursday as the
shortwave trough pushes through the forecast area. Although strong
forcing resides over the area, ensembles keep the bulk of the
precipitation just northeast of the forecast area, across
northeastern South Dakota and western Minnesota. With a strong
thermal gradient across the area, temperatures look to warm to
around the mid 30s across southwest Minnesota while temperatures
into the 40s and 50s will reside across southeast South Dakota,
northwest Iowa, and far northeast Nebraska. This will keep a mix of
rain and snow across the area. However, bufkit soundings show that
the best low level moisture will reside across southwest Minnesota
and dry out towards south central South Dakota. This will keep
mostly snow confined to southwest Minnesota with a rain/snow mix
back into southeast South Dakota and northwest Iowa. Ensembles
generally support this as their probabilities for exceeding an inch
of snow are highest across southwest Minnesota for our area.
However, the models highest probabilities lie across western
Minnesota. Still, have maintained a moderate chances (40-70% chance)
for precipitation to fall and accumulate in this system. Like the
previous discussion alluded to, shifts in the track of the system
remain possible which can also affect snowfall totals.

Friday will be a quiet day with highs in the 30s and 40s but a
thermal gradient will reside across the front range of the Rockies.
Medium range guidance depicts a strong jet streak aloft embedded
within an ejecting upper wave over the weekend. This wave will
interact with the thermal gradient and spawn a surface low pressure
system that will be responsible for the next chance for
precipitation. While there is decent agreement in the overall
synoptic set up, mesoscale details along with the track of the
surface low are uncertain at this time. Have left model blended PoPs
for the weekend but there is potential for a stronger system to
impact the region. Will continue to monitor trends over the coming
days.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 621 AM CDT Mon Mar 18 2024

VFR conditions are expected for the TAF period. Low level stratus
with isolated flurries begins the TAF period this morning. The
stratus is sitting at predominately VFR levels though isolated
observations have reported the stratus dipping down to 3,000 ft.
This stratus will push southeastward and exit the area throughout
the morning hours. Although winds begin the period out of the
northwest, they will turn to out of the southwest by this afternoon.
Speeds will still be light at 10-15 knots but gusts will reach up to
about 20-25 knots along the highway-14 corridor, including KHON,
late this afternoon.

The low level jet (LLJ) will ramp up this evening and night,
creating low level wind shear (LLWS) at all TAF sites. The LLWS will
finish out the TAF period along with a cold front passing through
the area. Winds will turn back to out of the northwest at the end of
the TAF period.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...Meyers


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.