Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 181936
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
236 PM CDT Mon Mar 18 2024

.KEY MESSAGES...

- Relative humidity (RH) recovers into the 30-40% range Tuesday
  afternoon. Winds will be northwesterly gusting to 25-30 mph.
  Grassland fire danger index will remain in the High to very
  high category, but due to the higher RH, no headlines are
  planned at this time.

- A push of cold air Tuesday into Wednesday will result int
  temperatures slightly below normal Wednesday through next
  weekend.

- Confidence is increasing in precipitation beginning late
  Wednesday night through into the early part of next week.

- Uncertainty remains high for the weekend and early week
  precipitation forecast. Those with weekend travel plans will
  want to continue to monitor the latest forecast for the most
  up to date information.

&&

.DISCUSSION...
Issued at 232 PM CDT Mon Mar 18 2024

THIS AFTERNOON: Some scattered high stratus will drift in from the
north this afternoon on the backside of a high pressure that moved
through the area today. A low pressure system over Manitoba will
drag a cold front through the area beginning late this evening into
the overnight hours. Lows for tonight will be in the 20-30s.

TUESDAY: Winds at the surface will turn to the northwest and will
increase with a push of CAA behind the front. Look for winds to be
around 10 mph increasing to 15-20 mph in the afternoon. Good mixing
will help us to tap into the stronger winds in the 850-800 mb level,
resulting in afternoon gusts 25-30 mph. Dew points recover overnight
and settle into the mid to upper 20s by afternoon. Relative Humidity
(RH) recovers on pace with dew points, with minimum RH for the
afternoon in the 30-40% range. Despite the CAA, highs will still
warm into upper 40s to 50s, with 60s along the Missouri River and
southward. Grassland fire danger index remains in the High to Very
High category, but thanks to the higher RH it does not look like we
will meet minimum requirements for a Fire Weather headline as of
this forecast package. Should we mix down more of the drier air
aloft, dew points and RH may decrease enough to warrant a headline.
This will need to be monitored throughout the afternoon.
Significantly cooler lows for Tuesday night, teens to 20s.

WEDNESDAY: Moisture flows in from the northwest for Wednesday,
increasing RH and easing grassland fire danger index into the
Moderate to High category. Continued CAA cools temperatures at the
850 mb level into the negative single digits Celsius. Highs for
Wednesday will be slightly cooler than average, in the 30 to
low 40s. Lows will be in the low to upper 20s, with the coldest
temperatures for both highs and lows across southwestern
Minnesota. Throughout the day an inverted trough will push into
the area from the northwest. This will set the stage for an
active pattern that will persist into early next week. Bufkit
soundings indicate the column will saturate from the top down
through the afternoon and evening hours Wednesday. Saturation in
the DGZ could spawn some light snow showers as early as
Wednesday evening. However, there is a stout dry layer beneath
the stratus deck, which will need to saturate out before we`ll
see anything reach the ground. Deterministic and ensemble
guidance are split on Wednesday evening light precipitation
chances, with the GFS and EC only indicating a 10-30%
probability of measurable precipitation (24 Hr QPF >= 0.01 in).

THURSDAY and BEYOND: Currently, it looks like full column saturation
will happen during the overnight hours into Thursday morning. Here
the guidance begins to converge on 80-100% probability of
precipitation beginning Thursday. The majority of this first wave of
precipitation will fall along and north of I-90, but as far south as
Highway 20 still has a 50-80% probability of measurable
precipitation. Thursday evening a short wave and surface low moves
out of Wyoming and into western South Dakota. This wave has a
much more focused area of frontogenesis, and therefore a higher
probability of producing precipitation. There remains slight
variance on the amplitude of the upper trough and surface low
track, but the three main models indicate high probability
(70-100%) of precipitation across the region for Thursday night
into Friday morning, with southwestern Minnesota having the best
probability (70-100%) to see QPF up to a tenth of an inch.

A lull follows Friday evening into Saturday morning before a strong
push of WAA triggers another round of precipitation Saturday evening
into Sunday. At the same time, a stronger upper wave digs south as
it moves onshore over the Pacific Northwest. A strong surface
low will then eject out onto the central plains out of New
Mexico and Colorado by late Sunday night. There is a fair amount
of variance in solutions, but guidance is in good agreement
that a stronger precipitation event will unfold for Monday and
Tuesday. Please note:
the systems responsible for the upcoming precipitation are still
off shore over the Pacific Ocean. There remains high uncertainty
in the details and there will be changes to this forecast in the
coming days as things move closer to shore and are better
sampled. But confidence is beginning to increase that we will
see multiple days of precipitation, likely in the form of snow,
possibly interspersed with mixed precipitation or rain south of
I-90.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1223 PM CDT Mon Mar 18 2024

VFR conditions are expected for this period. Afternoon scattered
stratus will give way to clear skies overnight. Near the end of the
period, a thicker deck of stratus builds in over southwestern
Minnesota, but they should not impact any TAF sites. Winds will be
southwesterly sustained at 10-15 kts with gusts 15-20 kts. Winds
become northwesterly overnight with the passage of a cold front. A
brief lull in winds before they increase again to sustained 10-15
kts in the afternoon with gusts 20-25 kts.

LLWS is a concern for all three sites beginning around 19.03Z
Tuesday morning. Directional and speed shear between 35-40 kts is
expected to continue through 19.09Z.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...AJP


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