Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 222116
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
416 PM CDT Sat Apr 22 2017

.SHORT TERM...(This evening through Sunday)
Issued at 415 PM CDT Sat Apr 22 2017

Surface ridge of high pressure will continue to drift off to the
southeast tonight. This will turn our winds around to the south and
southwest as the night progresses. Therefore lows are a bit tricky
tonight. The coolest location overall will be northwest Iowa as the
winds will be lightest there. In fact used a blend of the ARW and
NMM for lows in northwest Iowa which cooled off the low terrained
areas to below consensus guidance readings, such as Sioux City and
Spencer. Conversely with a southwest wind in place, raised Marshall
and Windom MN above guidance, as well as Storm Lake IA.

Winds still look fairly strong on Sunday between the departing high
to our southeast and low pressure moving into the front range of the
Rockies. To the north, a stalled frontal boundary extends from
central MN through northern SD not impacting our weather yet.
Surface winds will be decidedly southwest which is an excellent
warming direction. Therefore raised consensus highs a full category
which mixes temperatures from 850mb a full 22 or 23 degrees down to
the surface. Wind speeds will average 20 to 30 mph in our western
zones, and 15 to 25 mph across the east. The southwest wind should
also help to dry dew points more then consensus, so used a blend of
the ARW and NMM again which picked up on this trend. Minimum
humidity values are dry enough to warrant a fire weather watch
however there are a couple of problems. First, our cool season
grasses have greened up. With our western zones short grass
dominated which are green, they will likely not experience any fire
starts. In our eastern zones which are more warm grass dominated,
the wind speeds are not quite strong enough to warrant a fire
weather watch.

.LONG TERM...(Sunday night through Saturday)
Issued at 415 PM CDT Sat Apr 22 2017

Gusty southerly winds will persist Sunday night, leading to a mild
overnight with lows in the mid 40s to lower 50s. Low-level jet
increasing to 30 to 40 kts ahead of wave pushing into the Dakotas
later Sunday night, and will likely remain strongest and most gusty
at/near elevation. Appears as if a fairly strong elevated mixed
layer will advect north through the night, with gradient in lapse
rate hovering near the far western/northern borders of the CWA by
morning.  While very unlikely, a couple of rogue showers could dot
Lower Brule to mid James valley locations toward daybreak.

Overall, fairly low amplitude system will be traversing the region
on Monday, with bulk of upper dynamics passing just north of the
area. Elevated mixed layer again could incite a few showers during
the morning mainly toward Highway 14 and through areas west of I-29.
Will have surface wave generally track from central SD toward
central MN by evening, dragging a cold front across the area. With
moisture return to interact with wave fairly meager, boundary
remains fairly capped to surface or near surface development,
especially further south toward the Missouri River. Potential for a
couple of late day thunderstorms limited to near this boundary, but
expect a fairly sparse coverage of any precipitation, and much less
south than north.

Upstream jet, much stronger, will be close on the heels of this
system, and is likely to bring some light rainfall into south
central SD by later Monday night, while northerly flow of cooler air
will work through the CWA.  While likely that dry air will impede
northward progression to precip development, would be possible that
a little added wet bulb effect could potentially introduce a chance
for a little mix of snow toward K9V9 early day Tuesday.  A very
frontogenetic setup on Tuesday suggests a widespread threat for
rainfall, especially near/south of I-90 and northeast through
southwest MN by later in the day. Fairly neutral mid-level thermal
profiles spill northward through areas south of I-90 during the
later morning through early afternoon, and almost takes on look of
potentially stronger banding of showers from KYKN to KMJQ, and would
not be shocked for a rogue rumble or two along southern edge of
precip shield with potential for slantwise instability.  With upper
wave to yet move through, still a strong chance for rainfall into
the evening east of I-29, then drops off fairly quickly after 06z.
Increasing northerly flow will continue to bring cooler air into
area as surface wave develops across Iowa and the Mississippi
valley. Likelihood of temperatures cool enough to force at least a
mix to snow appear possible on back edge of precipitation from east
central SD into southwest MN.  Could be dealing with some near
freezing temperatures, even with winds of 10 to 20 mph continuing
by Wednesday morning.

Wednesday into early Thursday brings the only likely dry periods,
but temperatures will remain below normal, and will be watching for
a potential freeze Wednesday night. Quite a bit of variance on
east/west location on wrap-around cloudiness and potential for
persistence of northerly winds. Unlikely to surpass the mid 50s for
highs on any accord.

Final portion of the extended range forecast is wrought with
uncertainty, but generally indicates a potential for rainfall at one
time or another from later Thursday into Saturday.  Enough variance
that made no attempt to alter grids from blended initialization,
other than to shade toward a little lesser precip threat Friday
across parts of southwest MN.  Trends have been for the GFS to
become a bit more ECMWF-like and less of an ensemble outlier from
yesterday to today, but still have a much more aggressively timed
path than other solutions.  Certainly nothing mild about the weather
pattern through at least next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1212 PM CDT Sat Apr 22 2017

18Z TAFs reflect VFR conditions through Sunday morning.

&&

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

$$

SHORT TERM...MJ
LONG TERM...Chapman
AVIATION...MJ



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