Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 202015

Area Forecast Discussion
National Weather Service Sioux Falls SD
315 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 18Z TAFS through 18Z Monday afternoon)
Issued at 1250 PM CDT Sun May 20 2018

MVFR conditions will continue to impact much of the region
through the TAF period. While VFR conditions will continue in south
central SD into the highway 14 corridor of east central SD and
southwest MN this afternoon, the stratus is expected to spread
northward late this evening and tonight. After 15z Monday morning,
stratus will begin to clear gradually in southeast SD, but the
KFSD and KSUX will likely see MVFR or IFR ceilings throughout the
TAF period. A few sprinkles or spotty light rain showers will
also be possible today and tonight, but probability is too low for
mention in TAF.




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