Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
1141 am CST Sat Mar 8 2014
Short term...(today and tonight)
issued at 354 am CST Sat Mar 8 2014
Focus in the near term is on temperatures and cloud cover concerns.
Models did not initialize well with low lying stratus pouring out of
North Dakota into South Dakota. Expect this area of cloud cover to
quickly work into at least the northern half of the forecast area
this morning...and potentially further south. This increased cloud
cover will limit the amount of warming across the north and eastern
portions of the forecast area...and have sided with cooler guidance
values in these areas. Across central South Dakota...expect to see
some clearing throughout the afternoon hours and along with limited
snow cover should see some nice warming. With surface ridge passing
over the area...winds should be relatively light till tonight when
pressure gradient increases and wind speeds increase.
Strongest winds are expected in exposed areas along the Buffalo
Ridge. With relatively cool temperatures since the last snowfall
event...added blowing snow to the forecast after 06z tonight. With
increasing winds...expect temperatures to rise leading to lows in
the early to middle evening hours.
Long term...(sunday through friday)
issued at 354 am CST Sat Mar 8 2014
Continues to look warm on Sunday as ridging and southerly flow
returns to the area. Two things that could potentially inhibit
warming will be snow cover and clouds. Tough call over the deeper
snowpack across southwest Minnesota and adjacent areas of northwest
Iowa...but will continue with middle to upper 40s in those areas.
Record temperatures with over 6 inches of snow on the ground are
right around 50...so makes sense to stay below that in those deeper
snow covered areas. Over the snow free areas across south central
South Dakota and along the Missouri River...bumped highs up a few
degrees with 60s likely. Could even seem upper 60s towards
Chamberlain and Gregory. Tougher call is on the edge of the snowpack
from Huron to Sioux Falls...but will continue with 50s in those
areas. Overall think cloud cover will be thin and high enough to
only have a minimal impact on temperatures...with the greatest
impact in the north...where these clouds may be slightly thicker.
These middle and high clouds will sink south on Sunday night...before
lifting back north on Monday. So expecting partly to even mostly
cloudy skies. Highs Monday have a slightly better chance of being
impacted by the clouds...as they should be thicker. 925 mb
temperatures will also run a bit cooler on Monday. These negatives
will be offset by continued decreased snow cover though. So went
with highs similar to Sunday in the snow covered areas...and a
little cooler than Sunday in the snow free area due to the above
factors. Still well above average across the area though.
Our next precipitation threat will be Monday night into Tuesday.
Pretty strong frontogenesis as a cold front drops south...combined
with lift ahead of the approaching wave and in the right entrance of
an upper jet...should set the stage for a period of light to
moderate precipitation. GFS...European model (ecmwf) and Gem in pretty good
agreement...and thus bumped probability of precipitation into the high likely to
categorical range. Expecting precipitation to start in our west
around midnight...then spread towards Sioux Falls by early morning.
Precipitation will then exit from northwest to southeast from middle
morning into the early afternoon hours. Precipitation type is up in
the air...but would expect it to start as rain. Then as cold air
filters in behind the front we should mix with and change to
snow...although it will be a wet snow with temperatures right around
or just above freezing. Tough to pin down details this far out...and
still differences among models as to how much quantitative precipitation forecast falls as snow. If
this was all snow...quantitative precipitation forecast could be high enough for several inches of
accumulation somewhere. But thought now is that the combination of
rain to begin...and then low ratios after the changeover...should
limit amounts to just an inch or two...with the best chance of that
along and north of Interstate 90. But will need to continue to
monitor thermal trends over the coming days.
Cooler air moves in behind the front for Tuesday and Wednesday. Kept
the cooler temperatures of 30s and 40s going on Tuesday...as cloud
cover and the potential New Light snow cover should limit warming.
Should be a couple to several degrees warmer on Wednesday...with
models trending a bit quicker with the exit of the colder low level
temperatures. Pretty good model and ensemble agreement that we
return to above normal temperatures by Thursday and Friday...with
40s and 50s common. After the precipitation exits Tuesday...the rest
of the work week continues to look dry.
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1141 am CST Sat Mar 8 2014
VFR stratus 4-6kft expected to mainly affect northeast half of the
forecast area today...with forecast soundings showing moisture layer
gradually thinning through the afternoon. Will carry broken ceiling
at or above 4kft at khon and kfsd...though these sites will both be
on the edge of the stratus deck and could vary between scattered and
broken throughout the afternoon. Lower MVFR stratus in central South
Dakota working slowly eastward...but also slowly dissipating along
the southern edge...so uncertainty remains whether MVFR conditions
will reach khon. Have scattered 2kft deck mention indicate potential
timing if the cloud deck holds together...but will leave conditions
VFR unless MVFR conditions begin to appear more likely through the
Generally light winds today becoming south-southwest tonight. Higher
elevations in southwest Minnesota likely to tap into stronger winds
aloft...with gusts of 25kt or more becoming more likely after 06z
tonight. These stronger gusts will diminish slightly toward end of
this taf period...though gusts of 20-25kt still expected east of US
Highway 75. Stronger winds in southwest Minnesota tonight could lead to
areas MVFR-locally IFR visibility in blowing snow.