Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
608 PM CDT Thursday Oct 8 2015
Short term...(this evening through friday)
issued at 329 PM CDT Thursday Oct 8 2015
Middle level frontogenetic band continues to hang on through the
Missouri Valley...between exiting jet through the Great Lakes and
the energy diving into Wyoming. Fairly dry air below middle cloud deck
until the lower clouds which have been pushing southward into eastern South Dakota
and SW Minnesota. Been a fairly strong correlation of the 80 percent 850-
925 relative humidity gradient on the rap/NAM with the area covered by stratus
early this afternoon...with exception of a bit slower advance
through SW Minnesota. Cloud forecast challenging...in that the current
slow erosive trend may cease with mixing cycle...and as winds below
the trapping inversion trend toward more northerly. Rap/NAM suggest
that areas near i29 and eastward may find areas of lower clouds
holding on into the early morning hours...but approach of low level
ridge axis should be limiting feature.
The only precipitation threat in the short term would be the
remainder of the afternoon and very early evening...as middle level
frontogenetic band slowly sags southward. Most likely would not be
more than a brief sprinkle...but have carried a most minimal
measurable pop along the far southern portions of the County Warning Area.
Otherwise...as surface ridge builds in from the northwest
overnight...fairly dry airmass...recent dry period...and slow west
to east clearing will allow temperatures to drop. If middle 30s materialize as
expected around the middle James Valley eastward along Highway 14...
would likely find some fairly widespread frost developing...given
the current higher dewpoints. Not looking for a hard freeze. Will
issue a frost advisory for a small area at this time...as clearing
becoming a bit more questionable toward the I 29 corridor.
Should be able to shake any remaining lower clouds fairly quickly in
the morning across the east...leaving slowly moving surface ridge to
slip east. Another very pleasant fall day with temperatures in the 60s to
around 70. Will see an increase in higher level clouds from the west
during the midday and afternoon hours.
Long term...(friday night through thursday)
issued at 329 PM CDT Thursday Oct 8 2015
Friday night into Saturday will see southerly winds remain fairly
strong so a warm night and warm day can be anticipated with very
little cloud cover expected. Lows in the upper 40s to middle 50s with
highs from the middle 70s to middle 80s.
A fairly strong but moisture starved wave will move through on
Sunday. Very warm air and potentially deep mixing will develop
ahead of the incoming cool front so went ahead and raised highs just
a touch in the east...mainly middle 80s...and lowered dew points back
closer to 50. This brings afternoon humidity values down to around
30 percent and with winds expected to gust from the south at about
30 to 35 miles per hour...especially in northwest Iowa...some fire weather
concerns could crop up.
In the outer periods (monday through thursday)...a fairly strong
wave will pass on Sunday night into Monday with west northwest flow
aloft becoming predominant through the rest of the week. With the
stronger flow...troughing and colder associated air remaining to the
north temperatures will continue to stay above normal through late
next week. The west northwest flow aloft also suggests dry
conditions so not planning on having any threat for precipitation.
Monday should be pretty windy after the frontal passage with breezy
conditions into Tuesday. Wednesday and Thursday not looking nearly
as strong with winds.
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 605 PM CDT Thursday Oct 8 2015
Winds will continue to drop off through the early evening hours.
Otherwise...MVFR stratus is drifting southward into the
area...most likely affecting locations from the Interstate 29
corridor and eastward through the night time hours. Clouds will
then lift by middle to late morning on Friday.
South Dakota...frost advisory from 4 am to 9 am CDT Friday for sdz038-039-052-