Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 041147
AFDFSD

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
647 AM CDT Thu Jun 4 2020

.SHORT TERM...(Today and Tonight)
Issued at 403 AM CDT Thu Jun 4 2020

Today will be another warm day with highs in the 80s. Areas south of
I-90 will be closer to 90 due to mild southerly surface winds.
Zonal flow aloft prevents major weather systems from impacting the
area over the next 36 hours. That being said, a strong upper jet
streak will be positioned across Montana and North Dakota throughout
the day. The region sits under the right jet exit region, favoring
synoptic subsidence, despite a relatively buoyant air mass. High-
resolution models agree that several vorticity maxima will move
through the southern periphery of this jet, especially during the
late afternoon and evening hours. Each of these could provide enough
lift to overcome capping, which would trigger several thunderstorms,
some of which could be strong due to 1000 to 2000 J/kg of CAPE and
40 to 50 kt of effective bulk shear. The lack of confidence in the
timing and positioning of these small-scale vorticity maxima is
the main challenge in the short term. Given a lack of model
agreement, have retained a broad-brushed Slight risk for severe
weather, with large hail and gusty winds as the main threats.
High-based storms with only modest low-level shear should keep the
tornado threat low.

The first half of the overnight could remain active with any
thunderstorms growing upscale as they move southeastward into
northwest Iowa. Gusty outflow winds and lightning would likely
become the main concerns with the stronger storms. By the early
morning hours, this activity moves out of the region. A surface
high slides into the Northern Plains Friday morning, causing a
drier and slightly cooler air mass to move in.

.LONG TERM...(Friday through Wednesday)
Issued at 403 AM CDT Thu Jun 4 2020

Friday looks to be quite pleasant with dew points in the 50s, mostly
clear skies, and light northeast winds. Chances for rainfall look
minimal due to quiet northwesterly flow ahead of a building ridge
aloft.

More active weather returns for the weekend. Saturday will start out
partly sunny, but high cloud cover increases throughout the day.
A shortwave enters the high Plains in the southwesterly flow
downstream of its parent West Coast trough. This wave is expected
to provide lift for numerous thunderstorms across the western
half of South Dakota during the afternoon. Storms would move
eastward during the evening and early overnight hours, with some
risk for strong storms west of I-29 Saturday night. The ridges
begins breaking down on Sunday, which enhances the southerly
surface mixing. Afternoon temperatures in the 90s are forecast
with summery dew points in the upper 60s. A strong cap should
minimize thunderstorm activity Sunday.

A slow-moving cold front edges eastward early next week, and this
could bring heavy rainfall Monday and Tuesday due to training
convection. Details are still quite fluid with this system, and
there has been very little model consensus over the past 48 hours
with heavy rainfall positioning, so have remained near consensus
guidance with widespread chance PoPs. A major pattern change is
then forecast for the middle of next week with notably colder
conditions as the deep trough that was previously over the West
Coast moves over the central CONUS. High temperatures are forecast
to be in the low 70s which would be below seasonal averages for
the first time in over a week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 645 AM CDT Thu Jun 4 2020

Prevailing winds will be light over the next 24 hours, with mostly
clear skies. This evening into the early overnight could bring
some high clouds due to scattered thunderstorms in the area.
Hail, lightning, and brief erratic wind gusts would be possible in
the strongest storms. Timing-wise, a majority of models show the
storms being most widespread between 05/0100z and 05/0900z.
Friday morning is forecast to be dry with decreasing cloud cover.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...VandenBoogart
LONG TERM...VandenBoogart
AVIATION...VandenBoogart


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