Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
543 am CST sun Feb 1 2015
Short term...(today and tonight)
issued at 335 am CST sun Feb 1 2015
Snowstorm has been behaving pretty well during the night with
accumulations continuing in the warning and advisory areas.
Storm totals should range from an inch or so extreme north to
around 7 inches southeast. Even while there has been a little
dropoff in intensity in some areas including fsd...a minor secondary
surge associated with west northwesterly short wave appears to be
merging in the main snow area and is likely to cause a little
resurgence in intensity. Winds have picked up and the snow is
drifting pretty well at low levels...but the blowing snow does not
get up real high and really cut visibilities down...so will
continue to handle that part of the forecast with patchy blowing
The current warning and advisory setup is working out well and will
continue with the same. It does appear that conditions will improve
a little faster with the snow ending fairly quickly during the
middle of the day. Have chosen to let the warning far southeast in
northwest Iowa go until 6 PM as planned...and will let the advisory
out west go until the current noon expiration. In between...will
move up the expiration time of the highlights by 3 hours to 3 PM
from Yukon to fsd and in southwest Minnesota. Eventually we may be able to
cut the highlights even a little sooner. Since we are not dealing
with a blizzard...highlights extending into the time of improving
conditions may not be too bad given the drifting snow affecting
Skies will start to clear quickly from the north during the middle
of the day and it should become rather clear by early evening.
Temperatures will generally fall slowly except for a small recovery
west this afternoon after the better cooling takes place there
through this morning. Wind chills will continue to go down to 5
below southeast...and in the teens below northwest before slight
Tonight will bring mostly clear skies except for a start of warm
advection middle and high clouds from the west late. Temperatures will
drop to several degrees below zero. Wind chills might barely touch
20 below in some places late with the cooling. Since these wind
chills Wills will at worst get barely and briefly to advisory
criteria...and get there because of wind speeds which will have
dropped well into the single digits in miles per hour...will not issue a Wind
Chill Advisory. Actual low temperatures should be in the single
digits below zero...and there could be some very slight rebounding of
a couple degrees far west before daybreak as the warm advection
clouds start to arrive.
Long term...(monday through saturday)
issued at 335 am CST sun Feb 1 2015
Active weather will persist into the middle of the week as a series
of shortwave traverse the upper level northwest into the northern
The first minor shortwave clips the northeastern half of the
forecast area on Monday afternoon and evening. Stratus will build in
ahead of the wave...however middle levels look to remain pretty dry as
the wave passes through the region. Upper level support is good with
this fast moving wave...but think that snow will have a hard time
materializing. The best potential for any precipitation will be east
of i29...but chances for measurable snow are very slim. Modest
return flow will allow temperatures to moderate some...mainly in our
western half. A large range of highs across the forecast area are
expected...from the middle teens east to near 30 in south central South Dakota.
Another middle level wave dropping along the northwest flow will bring
a greater potential for some light snowfall on Tuesday. Models have
come into much better agreement in dropping the wave across our
northeastern half. While upper support is decent...moisture and
frontogenetic lift is more impressive than Monday. A stronger wave
digs across the northern plains close on the second waves heels late
Tuesday night into Wednesday. This wave tracks further south near
the Missouri Valley and i80 corridor...so will focus snow chances in
our far south. The GFS is somewhat of an outlier in tracking well
south of the forecast area. Colder air filtering back into the
region will prevent temperatures from warming much from Tuesday
night lows. Highs will only be in the teens.
Upper level ridging finally begins to rebound to our west on
Thursday and Friday...becoming more zonal on Saturday. With
southerly return flow and warm air advection developing on
Thursday...temperatures moderate some on Thursday. But by Friday and
Saturday...readings improve into the 30s and even some 40s in south
central South Dakota. Expect highs to be tempered some by the recent heavy
snowfall...so lowered all blend highs a few degrees.
Aviation...(for the 12z tafs through 12z Monday morning)
issued at 544 am CST sun Feb 1 2015
Ceilings 1-2k feet and visibilities below 3sm in snow will
improve from the north 15-21z to ceilings 2-4k feet and
visibilities p6sm. Low clouds will clear from the north
18z-02/00z. Surface gusts above 25 knots from the north
12z-02/00z. From 02/00z-12z VFR.
South Dakota...Winter Storm Warning until 6 PM CST this evening for sdz071.
Winter Storm Warning until 3 PM CST this afternoon for sdz061-
Winter Weather Advisory until noon CST today for sdz050-052>055-
Winter Weather Advisory until 3 PM CST this afternoon for sdz056.
Minnesota...Winter Storm Warning until 3 PM CST this afternoon for mnz098.
Winter Weather Advisory until 3 PM CST this afternoon for mnz080-
Iowa...Winter Storm Warning until 6 PM CST this evening for iaz002-003-
Winter Storm Warning until 3 PM CST this afternoon for iaz001.
NE...Winter Storm Warning until 6 PM CST this evening for nez013-014.