Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 210452
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1152 PM CDT Sun May 20 2018

.SHORT TERM...(This evening through Monday)
Issued at 311 PM CDT Sun May 20 2018

Surface high centered over northern Minnesota will continue to shift
eastward into the Great Lakes, while a surface trough and vort max
continue to slide east-northeast through the forecast area this
evening. Soundings indicate decent forcing and deep saturated layer
along and east of I-29 tonight into Monday; therefore have kept
spotty/isolated showers across this area. With easterly surface flow
prevailing tonight, expect mostly cloudy skies tonight and for most
of the day on Monday. Overnight lows will generally be in the upper
40s and lower 50s.

Upper-level ridge will dominate the area by Monday, bringing
mostly dry conditions after midday. Return flow of the departing
surface high over the Great Lakes area will bring warm southerly
winds and mid-level moisture back into the region. Highs will
range from the upper 60s to upper 70s.

.LONG TERM...(Monday night through Sunday)
Issued at 311 PM CDT Sun May 20 2018

A more active pattern will take shape this week with multiple
opportunities for showers and thunderstorms to the region, along
with warmer temperatures.

Upper-level flow remains mostly zonal with fast-moving impulses of
energy, at least through mid-week. By Monday night, a surface low
pressure over the central Plains will be lifting a warm front
northward into the area. Guidance continues to suggest late evening
convection along the lower Missouri river valley on the nose of the
LLJ coming from central Nebraska and increasing low-level warm
advection. The shear for this time-frame looks minimal, but decent
dynamic will favor spotty thunderstorms, some of them could become
strong.  Actually, showers and thunderstorms look more favorable
Tuesday evening. As the front lift farther north on Tuesday,
increasing theta-e advection, moderate deep layer shear, MUCAPE
(2500-3000 J/kg) and a reinforced LLJ may induce deep convection
Tuesday night into Wednesday. Again, will need to monitor for severe
weather potential.

There are some differences Wednesday and beyond with timing of
embedded shortwaves and intensity of any convection. Better chances
for showers and thunderstorms look to be Thursday night into Friday
night. Amplified upper trough over the Northern Plains will approach
the area, bringing chances for thunderstorms along and ahead of the
frontal boundary. Still quite of uncertainty regarding the intensity
and extent of precipitation by the end of the week.

With the upper ridge in place for majority of the week, temperatures
will be near to above normal through the period. Daytime highs will
generally be in the 80s, and overnight lows in the 50s and 60s.
With H850 temperatures from 15-20 C, Wednesday and Thursday will
be the warmest days of the period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1133 PM CDT Sun May 20 2018

Messy night and morning ahead for aviation interests. Widespread
MVFR ceilings will continue to lower, settling into IFR at FSD and
LIFR at SUX. Things are a bit better at HON, where ceilings are
expected to stay MVFR, though the morning hours will see fuel
alternate considerations come into play. Wind won`t be a concern
at all, which in this case is deleterious as some sites are
starting to show some signs of fog. With this stagnant air comes
the expectation for FSD and SUX to eventually be impacted by fog
in addition to the previously mentioned IFR ceilings. The return
of the sun and the upper wave finally moving off to the northeast
will herald improvements by tomorrow afternoon, with ceilings
expected to scatter out west to east by Monday evening.

&&

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

$$

SHORT TERM...05
LONG TERM...05
AVIATION...Ferguson


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