Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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503
FXUS63 KFSD 292309
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
609 PM CDT SUN MAY 29 2016

.SHORT TERM...(This evening through Monday)
Issued at 357 PM CDT Sun May 29 2016

Very subtle surface boundary is moving across the eastern sections
of northwest IA this afternoon which will continue to produce a few
showers and isolated thunderstorms. Otherwise the focus of attention
shifts to tonight, when fairly strong low level warm air advection
and positive thetae advection lifts northeastward across the
forecast area. The accompanying low level jet is not real strong.
But still the various hi-res CAMs are producing a fair amount of
convection by overnight and late tonight of high based storms in
the central portion of our forecast area. Therefore low end likely
pops are warranted in southeast SD and much of northwest IA, and
also in the southern sections of southwest MN by very late
tonight. Elsewhere, scattered pops are warranted in our far
northern and southern zones. Earlier tonight during the evening
hours, thoughts are that any small chances for convection will be
confined to our southwest zones along the leading edge of a thetae
ridge extending from south central to west central SD. But that
skittish activity will likely wane by sunset.

Memorial Day is rather problematic in terms of thunderstorm chances.
There could be some elevated convection leftover in our eastern
zones early in the day from the night time activity. But otherwise a
lot may not go on until possibly extremely late in the day. By late
afternoon, height falls begin to take shape as a well advertised
upper trough/short wave moves eastward into the western plains. But
with a broad southerly flow, there really is no low level focusing
mechanism through the day on Monday until very late. Have the
highest pops, which are high end scattered in northwest IA toward
evening on the nose of the low level jet, and across our extreme west
in central SD just ahead of the surface cold front. But otherwise a
bulk of Memorial Day will likely not hold a lot of chances for
rainfall with very mild temperatures in the lower 80s.

.LONG TERM...(Monday night through Sunday)
Issued at 357 PM CDT Sun May 29 2016

Monday night still looks to be the most active period of the
upcoming week. As in the short-term, relied more heavily on high-res
model ideas for progression of precip chances. This would focus our
more organized early evening chances in the thermal ridge ahead of
advancing cold front in central South Dakota. Here 4km NAM depicts
instability in 1500-2000 J/kg range at peak heating, but deep layer
shear on the weak side around 30 kt in the early evening. Thus would
anticipate primarily hail/wind threat across our western areas in
the evening. Also have a pretty robust moisture return boosting our
precipitable water values back into 1.0-1.5 inch range by Monday
evening. This could lead to locally heavy rainfall, with localized
flash flooding not out of the question given the nearly saturated
ground due to recent rains.

In addition to holding off eastward extent of initial development,
the high-res models progress the system eastward more quickly, with
a strong push of post-frontal dry air shunting most of the storm
activity east of the forecast area shortly after daybreak. Holding
on to some low pops east of Brookings to Tyndall line Tuesday to
give some credence to slower solutions, but overall expect to see
dry conditions for most of our forecast area on Tuesday. This will
be the start of a short cool-down, with highs only in the lower to
mid 70s.

Wednesday should be the coolest day of the week, with most areas
topping out in the 60s. With cool pocket aloft cannot completely
rule out spotty instability showers in our far north as waves of
energy rotate around the south side of upper low lifting out of
northern Minnesota. Warmer air begins to then push back into the
area Thursday, with highs by Friday-Sunday climbing back to around
80 degrees. Looks like dry conditions will dominate the mid to late
part of the week, though do have a couple of periods with low rain
chances. First is Thursday night, when slight moisture return with a
weak low level warm front could spark a few elevated showers south
of Highway 18. Second would be Friday night, as a mid level wave
drops southeast through the region. Depending on timing, this wave
could have fair amount of instability and shear to work with, so
will have to watch this period for possible severe threat. Looks as
though this should push east of the area by Saturday, though, with a
nice weekend on tap at this point.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 604 PM CDT Sun May 29 2016

primarily VFR conditions are expected through the TAF period,
however scattered thunderstorms may develop across portions of the
area overnight. This activity will affect mainly the KFSD site.

&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...MJ
LONG TERM...JH
AVIATION...JM



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