Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 230424
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1124 PM CDT Mon May 22 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 359 PM CDT Mon May 22 2017

A couple areas of ongoing showers/thunderstorms will move across the
region the remainder of this afternoon/early evening. Northern parts
of the forecast area will see the more widespread activity ahead
of low-mid level boundary dropping southward. With instability more
limited in this area due to extensive cloud cover, think the thunder
threat will be limited.

Distinct upper wave spinning through south central South Dakota will
be catalyst for more scattered activity along/south of I-90, as it
swings toward northwest Iowa through the late afternoon, interacting
with surface boundary dropping southward. May have to still watch
for an isolated stronger storm as these come together over northwest
Iowa/Highway 60 corridor over the next few hours, and our southeast
forecast area was able to heat out much more than locations farther
west and north, and thus may have slightly better instability to
work with. That said, instability profiles are still rather tall and
skinny, and with limited shear, still think the hail threat will be
quite isolated. Current activity in south central South Dakota as
been able to produce gusts nearing 40 mph at the Winner airport
shortly after 230 pm, which goes along with earlier thinking that
marginal severe wind gusts may be the greater threat across our
southeast into the very early evening.

Lagging tail of the northern rain band may linger across southwest
Minnesota and portions of the I-29 corridor into this evening. But
otherwise overnight appears rather quiet, waiting for next wave to
drop southward into the area late tonight/Tuesday. More substantial
low level moisture and lower instability will lead to mainly shower
activity. With cyclonic curvature prevailing across the area through
the day, potential for scattered showers will persist throughout the
daylight hours. Temperatures will once again be on the cooler side,
with highs in the 50s across the region, and a gusty northerly wind
making it feel a bit more raw.

.LONG TERM...(Tuesday night through Monday)
Issued at 359 PM CDT Mon May 22 2017

Lingering showers should meet a fairly quick demise on Tuesday
evening with loss of diurnal cycle, but clouds will be fairly
persistent through areas east of I-29 overnight, along with somewhat
more persistent northerly winds holding temps in the mid 40s. Toward
the James River valley and westward, clearing and proximity to
elongated ridge axis should allow a few temps to dip to the chilly
upper 30s. The upper ridge folds over and pushes the closed low away
from the region on Wednesday. Some residual moisture looks to remain
trapped below subsidence inversion from just west of I-29 and
eastward which could result in some temporary self-destructive
sunshine. However, will likely see some drier air advecting in on
northeast flow toward southwest MN which should erode a thicker
coverage, as well as slowly deepening mixing of what should be a
thin cloud layer.  Temps should recover 6 to 10 degrees from the
Tuesday chill, mainly 60s.

Trough from the Pacific NW will barrel into the ridge later
Wednesday night and Thursday, flattening the ridge over the northern
plains and driving a decent low level jet toward south central SD
later in the night. Moisture is quite limited, but do see some 700-
500 hPa lapse rates of 7.5-8.5C/km expand into southeast SD later
Wednesday night into Thursday. For now, not enough indications of
deep dynamic support to suggest much more than a minimal threat for
a mid-level shower or thunderstorm, but should see some increase in
clouds through the day Thursday. Wave shears a little closer on
Thursday night and have trended toward a low-end chance for elevated
thunderstorms mainly east of I-29 on Thursday night, and later
at night along advancing weak frontal boundary.

Focus remains at odds with precip chances Friday into Friday night,
with core of the upper trough remaining near/north of the
International border, and secondary energy digging through the
central and southern Rockies allowing for a period of flatter subtly
rising heights. Fairly "average" temperatures expected.

From Saturday on begins a trek of deviating model solutions, from
the more progressive ECMWF which slingshots the Rockies wave across
the central plains, keeping the boundary well south, and gradually
sinking the northern vortex toward the Great Lakes. Result of this
solution is a fairly dry and touch cooler solution with stronger
northwest flow by Sunday. GFS on the other end of the spectrum
really amplifies the western wave, closes off and congeals into a
strong closed low which wanders from eastern Nebraska to Wisconsin
over a 36 hour period Sunday into Monday, with an appreciable
potential of rainfall.  For now, too much uncertainty to go one way
or the other, but even GFS ensemble would suggest a much greater
probability of a non-operational GFS solution.  Only low PoPs are in
order, and likely to have temps a shade below to near normal.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1120 PM CDT Mon May 22 2017

Showers will work out of southwest Minnesota this evening,
however, additional showers along with MVFR ceilings will work
back into the region towards daybreak on Tuesday. Shower activity
will be light leading to prevailing VFR conditions. Winds will be
brisk out of the northwest throughout the daylight hours on
Tuesday.

&&

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

$$

SHORT TERM...JH
LONG TERM...Chapman
AVIATION...BT


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