Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 281712
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1212 PM CDT Sun May 28 2017

.SHORT TERM...(Today and Tonight)
Issued at 355 AM CDT Sun May 28 2017

Upper trough finally swings through the region through daybreak,
with northwest flow taking over today and tonight. With strong low
level winds and good mixing expected today, expect fairly windy
conditions at the surface as well. Based on forecast soundings, did
bump up wind gusts this afternoon, with gusts to 30 to 35 mph likely
at times. Overall, expect winds to remain below advisory level
criteria. With mostly sunny to partly cloudy skies and good mixing,
temperatures will be warmer today, but still near seasonal normals
in the 70s.

With the main upper level low wobbling southward into northern
Minnesota this afternoon and evening, a weak shortwave dives into
east central SD and southern MN in the evening. There will be enough
forcing for some isolated mid and high based showers late afternoon
in the highway 14 corridor and southwest Minnesota, expanding into
southeast SD and far northwest Iowa during the evening. Activity
tapers off in the early morning hours. Elevated instability is
fairly weak, but there should be enough for thunder mention as well.
Given the very dry airmass below 750 mb, activity will be pretty
isolated.

.LONG TERM...(Monday through Saturday)
Issued at 355 AM CDT Sun May 28 2017

Mixed signals on Monday when putting together the pieces for
potential development of showers. First, we have cooler temperatures
aloft along with increasing moisture in the lower to mid levels as
the day progresses.  There seems to be a distinct lack in larger
scale dynamic lift support for much of the day as mid-level heights
nudge just a touch upward after nighttime trough passage, but in
general have less negatives by the time diurnal support maximizes in
the afternoon to very early evening.  With most solutions showing
upwards of a few hundred J/kg MLCAPE, would expect that will see
isolated to lower end scattered showers mainly from east central SD
through southwest MN and toward the Iowa Great Lakes area. These
showers will have minimal precipitation, likely at best a few
hundredths. Winds will freshen fairly quickly in the morning with 20
to 30 knots within reach of the mixed layer.  As of now, temps aloft
have trended just a bit down, and have nudged highs again a bit
lower than the initial blend, mainly lower 60s southwest MN to upper
60s Missouri River valley.

Next lobe wraps around large upper low on Tuesday, but impact
further eastward through Minnesota. While will see an increase in
cyclonic cloudiness mainly near/east of I-29, do not look for any
meaningful showers, but will be on the watch for perhaps a couple of
sprinkles at best into parts of southwest MN or the Iowa Great Lakes
in the afternoon.  Temps look fairly similar to Monday.

Surface ridge expands across the area on Tuesday night, leading to
what should be the coolest night for the foreseeable future. A few
readings in the James River valley could touch the upper 30s, but
generally should see lower to mid 40s as winds become light,
especially near/west of I-29.

Heights begin to build a bit more aggressively on Wednesday as
surface ridge drifts eastward. Southerly flow will gradually
increase and could become a bit gusty late day toward south central
SD.  Temps will moderate quite a bit, with mainly lower to mid 70s,
perhaps upper 70s south central SD.

Wednesday night through perhaps as late as Thursday night, models
continue to cluster around some format of wave slipping through the
northwest flow ahead of ridge axis and co-locates well with push of
warm advection/low- to mid-level convergence to generate a threat
for precipitation. GFS is unlike a great deal of its fellow ensemble
members in really amplifying another wave into the western Great
Lakes by early Friday, but Canadian is actually about 18 hours
faster with a similar solution, both with a fairly active boundary
back into eastern SD and allowing a reinforcing push of cooler air
to return more quickly to the region Thursday into Friday. On the
other hand, the ECMWF is more in line with a less active solution
and a quicker veering of activity off to the east after Thursday and
setting the main boundary for wave Friday night about 200 miles
further northeast across northeast SD and Minnesota rather than
western/southern SD to southern IA. Enough difference in potential
solutions for late week and the weekend that have low confidence in
subscribing to any particular mode at this time, and have made
little if any change to initial grids beyond Thursday, but instinct
is that will be cooler again by Saturday. The transition period
around Friday could also present a threat for some severe weather
as well.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1208 PM CDT Sun May 28 2017

Diurnal CU field already becoming well established across the
terminals. Anticipating scattered showers and even a few
thunderstorms to form along an advancing cold front late this
afternoon and evening. This scattered activity will pass through
the forecast area this evening, before slowly dissipating after
dark. Coverage too low for a prevailing TAF group, however will
mention VCTS.

Winds will weaken by daybreak Monday, but are expected to increase
once again by late morning. Have some concerns that lower stratus
could pivot southeast and arrive into Sioux Falls by mid-morning.

&&

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

$$

SHORT TERM...
LONG TERM...Chapman
AVIATION...Dux



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