Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
550 am CST Wednesday Jan 28 2015
Short term...(today and tonight)
issued at 316 am CST Wednesday Jan 28 2015
Tricky temperature forecast today...which will be largely dependent
on the extent of cloud coverage. Very mild 925 mb temperatures above
zero and southerly winds at the surface will tap into some continued
seasonably warm temperatures. The question is how much cloud cover
will impact warming today. The most recent hrrr has a good handle on
clouds early this morning...which will shift eastward into the
midday hours. Think the the northeastern half of the forecast
area...from east central South Dakota into southwest Minnesota and the Iowa Great
Lakes are will hold onto mostly cloudy skies the bulk of the day.
Kept temperatures on the conservative side of guidance in this area.
If clouds look less abundant...could see readings warm above
forecast highs. Elsewhere...mostly sunny to partly cloudy skies
through middle afternoon will give way to clouds with the anticipated
frontal passage late afternoon. South central South Dakota into the Missouri
Valley will have the best potential to warm into the low to middle 50s.
With the front tracking through the area middle afternoon into this
evening...clouds will roll back into the region. Northwest winds
expected to become quite windy behind the front with 40 to 50 knots
winds just off the surface. At the surface...winds will likely be
near advisory level...especially with gusts around 40 or 45 miles per hour.
Given that the strongest winds are expected in the early morning
hours and are marginal for an advisory...will hold off issuing any
headlines for now.
With low level stratus blanketing the area overnight...a fast moving
shortwave drops across southwest Minnesota late evening into the
early morning hours. Not much moisture in place...and while the low
stratus does thicken...the cloud mass remains largely outside the
snow growth zone. Could see a few snow isolated showers develop
mainly in our Minnesota counties...with some patch drizzle also possible.
Surface temperatures will be near or just above freezing in this
Long term...(thursday through tuesday)
issued at 316 am CST Wednesday Jan 28 2015
The shortwave exits the area on Thursday with surface high pressure
building into the region. It will be breezy with a tight gradient
across the area and good mixing in a cold air advection regime. In
response to the colder air filtering into the region behind the
exiting shortwave...high temperatures will be a good 10 to 15
degrees cooler than today...topping out in the upper 20s from east
central South Dakota through southwestern Minnesota...to upper 30s through the MO
river corridor. Winds will die off on Thursday night...leading to a
cold night with lows in the Lower/Middle teens through the eastern two
thirds of the County Warning Area. To the west...it will not be quite as cold with
an ensuing southeasterly flow behind the exiting high
pressure...with lows generally lower 20s. Friday will see warming
with a strengthening southerly flow on the backside of the high.
High temperatures will run lower 30s northeast to as warm as the middle
40s through south central South Dakota.
On Saturday northern stream upper level energy drops out of western
Canada and slides southward as southern stream energy lifts to the
north...converging over the Central Plains. Still some model
differences on how this scenario evolves...but does potentially
bring precipitation to at least our southern and eastern County Warning Area for
later on Saturday afternoon and Saturday night. Precipitation type
looks to be mainly in the form of snow...with cooling thermal
profiles as low pressure over the James Bay begins to drive colder
air southward. At this point snowfall amounts look to be in the
range of 2 to 3 inches in our southeast...though will have to watch
the track of this system for greater snowfall amounts if it trends
farther to the north. It still wont be unreasonably cold on Saturday
with highs mainly in the 30s...but by Saturday night and Sunday much
colder air will have settled into the region with highs on Sunday
mostly in the teens. The cold air then looks to linger through next
Monday...with some moderation possible by Tuesday.
Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 540 am CST Wednesday Jan 28 2015
MVFR/IFR ceilings are tracking along our far eastern counties
early this morning. This stratus is not expected to expand much
further west this morning...however a fast moving front will track
west to east through the forecast area 18z through 00z this
afternoon/evening and usher in addition low level clouds behind
it. Strong northwest winds behind the front will average 20 to 25
knots with frequent gusts 30+ knots in the evening and overnight.