Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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442
FXUS63 KFSD 152304
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
604 PM CDT Sun Apr 15 2018

.SHORT TERM...(This evening through Monday)
Issued at 331 PM CDT Sun Apr 15 2018

Well...we`ve (mostly) made it through our historic April `18
blizzard. Several locations picked up over a foot of snow (some as
high as 20 inches), along with serious issues from blowing and
drifting snow. A very impressive WV imagery display shows the main
upper level wave over IA/IL/WI. Will continue to carry the chance of
either light snow or flurries into the evening hours for areas along
and east of I-29 before forecast soundings show the column
finally drying out. Any additional accumulations should be fairly
minimal.

Large scale subsidence builds in by the overnight hours as a brief
period of upper level ridging nudges in from the west. This will
allow for clearing skies overnight and finally a slackening of the
winds. Look for unseasonably cold overnight lows, generally in the
low to mid teens. Trended temperatures toward the lower end of
guidance. Given the lighter winds, clearing skies, added boundary
layer moisture, and building surface high pressure, can`t rule
out some fog, mainly in areas east of the I-29. Added mention of
fog for now but may need be adjusted based on cloud cover and wind
trends.

Quiet weather will...thankfully...arrive Monday as the region will
be under the full influence of ridging across the central US. Don`t
expected any miracles when it comes to temperatures though as
fresh snow cover and 925 mb temperatures from 0 to -5 C will keep
afternoon highs mainly in the 30s. This would be a rather
depressing 20 to 25 degrees below normal for this time of year.

.LONG TERM...(Monday night through Sunday)
Issued at 331 PM CDT Sun Apr 15 2018

Most of Tuesday should be rather uneventful as well with a mix of
sun and clouds and high temperatures generally in the mid 30s and
40s. Adjusted temperatures down again closer to Consraw values
given snow cover and impact of climatology on populated guidance.
Clouds begin to increase by late in the day and this is where
things could get rather painful again. Large trough currently off
the coast of the Pac NW will have rotated into the rockies with a
vort max ejecting by late Tuesday and pointed at our region.

Models continue to disagree on the finer details with the track and
evolution of this wave. Latest GFS is quicker with the timing of the
system compared to the other deterministic models, with subtle
difference in the track also noted from model to model. All
advertise a very robust band of precipitation somewhere in the Tri-
state area sparked by an impressive PV anomoly and frontogenetic
forcing. ECMWF and NAM are a little further south with their
latest solution, closer to the Sioux City to Spencer line, and if
this trend continues the forecast may need to be adjusted in that
direction. Thermal profiles suggest the precipitation starting as
rain before switching to wintry mix and then to snow. GFS
soundings are most aggressive with the freezing rain threat,
particularly over NW Iowa, but will be something that needs to be
watched. Long story short, a band of moderate to potentially heavy
snow looks probable Wednesday, with the current most favored
location south of I-90. Northwest winds will also be on the breezy
to windy side and raised winds closer to Consmos values.

System exits by Thursday morning with another period of relatively
quiet weather as upper level ridging sets in again. Temperatures
will remain below normal however with highs largely in the 30s and
40s. Another significant system looks to arrive into the central
US next weekend, although latest models have trended south,
perhaps only grazing our coverage area.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 555 PM CDT Sun Apr 15 2018

A few flurries from the I-29 corridor and eastward during the
evening, otherwise, skies will clear from the west overnight. With
light winds cannot rule out patchy fog development, with most
recent model guidance suggesting the greatest potential being
over the James River Valley.

&&

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

$$

SHORT TERM...Kalin
LONG TERM...Kalin
AVIATION...JM



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