Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 172318

Area Forecast Discussion
National Weather Service Sioux Falls SD
518 PM CST Fri Nov 17 2017

.SHORT TERM...(This evening through Saturday)
Issued at 302 PM CST Fri Nov 17 2017

Main forecast challenges look like they will take place in the next
12-18 hours with quiet weather expected in the extended.

A positively tilted open wave is beginning to translate into the
Plains with a surface cold front now just about through our far
southeast counties as of 2 pm. Light radar returns, mainly sprinkles
or trace rain amounts, have been observed along and north of I-90
associated with the mid level 850-700 mb front.

An additional round of precipitation looks to develop along this mid
level front later this evening and overnight as a better vorticity
max moves overhead. Initially it looks like a fractured area of 700
mb frontogenesis will lead to some light precipitation north of I-90
but then the best forcing shifts to the southern half of our area.
Precipitation type this evening should start off as rain before
cooler air advecting in could change things over to a mix or snow
toward the end of the period. The question that is still somewhat
unanswered is to what extent does the colder/drier air cut off
precipitation before it has a chance to switch over. Bufkit
soundings are very borderline either way with this potential. Any
snow that does fall shouldn`t amount to much as far as accumulation,
potentially just a slushy dusting across the southern counties.
Latest SREF plumes also support this with even the max members
showing only very light amounts.

As drier air continues to filter in, skies will clear out Saturday.
NW winds will also be on the increase with soundings indicating the
capability of mixing down gusts in the 30 to 35 mph range. While
Saturday will feature more sunshine, it will feel like a fairly raw
day with cooler temperatures in the 30s and low 40s and wind chills
teens and 20s.

.LONG TERM...(Saturday night through Friday)
Issued at 302 PM CST Fri Nov 17 2017

As previously mentioned, the extended forecast looks very quiet with
the main challenge pertaining to temperatures. The surface cold
front from tonight continues to drive south bringing with it any
meaningful source of moisture. Our region then sits in an altering
zonal/NW flow regime with a void of any significant waves. What this
means for sensible weather is a lack of precipitation but also a
good variation in day to day temperatures. Generally, the week will
start off 5-15 degrees above normal with highs in the 40s and 50s
before dropping back to below normal temperatures Tuesday.

By Wednesday, the trend of moderating temperatures will commence
again with highs back into the 40s and 50s by the Thanksgiving
holiday. Still would take these numbers with a grain of salt as
model spread still remains high. Ensembles member high temperatures
continue to have a standard deviation of as much as 8 standard
deviations. Regardless, it looks like the entire upcoming week,
including Thanksgiving, will be dry.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 515 PM CST Fri Nov 17 2017

A narrow band of light rain or sprinkles continues to move
through portions of the area this evening. Generally guidance
continues to focus the stronger forcing south of Interstate 90,
and will include prevailing very light rain at Sioux City into the
overnight hours. HON may be brushed with a bit of light rain or
sprinkles, but any duration will be limited. At Sioux Falls,
precipitation chances have dwindled, but could still see a bit of
light rain or perhaps a few snow flakes late this evening, but
closer to the midnight hour.

Not anticipating any restrictions through the overnight hours.
Models are hinting at diurnal CU building in by late Saturday
morning and continuing into the afternoon hours. These may begin
in the MVFR level, but will rise into VFR levels.




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