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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
957 PM CDT Sat Mar 28 2015

Update...
issued at 948 PM CDT Sat Mar 28 2015

The cold front is presently located through far western South
Dakota late this evening...though radar beginning to show returns
out ahead of the system through central South Dakota into north
central Nebraska. Not sure if much of this is reaching the ground
with dry air in the lower levels...however based on radar and
latest hi res models did pull low probability of precipitation farther south than previous
forecast. In addition...removed any mention of thunder for the
last half on the night with lighting activity that was occurring
earlier over the western part of the state having subsided...as
well as later model runs indicating minimal instability over our
area.

&&

Short term...(this evening through sunday)
issued at 258 PM CDT Sat Mar 28 2015

Strong low level jet of 50 to 60 knots is expected to develop across
the Central Plains tonight ahead of a cold front moving through the
area. With the passage of the front...small amount of elevated
instability that may result in scattered showers/isolated
thunderstorms developing. Moisture is certainly a limiting
factor...though any showers that develop would be quite problematic
as there would likely be evaporative cooling on top of the strong
winds aloft. If the downdraft was able to surface...there would be
the potential for a severe wind gust or two. Best chances for any
shower activity is across the northern portions of the forecast area
closer to the middle level wave...or across eastern portions of the
forecast area where moisture is slightly more abundant.

Strong northwest winds are expected to develop behind the cold
front...and could gust near 50 knots or so immediately behind the
front as strong winds couple with low level cold air advection. The
cold air advection is relatively quick...and shifts through the
forecast area by 18z. However...mechanical mixing takes over at
that point drawing momentum down from aloft. Gradient winds aloft
gradually decrease through the day...and expect a gradual downward
trend in the winds through the day as momentum aloft decreases. The
most substantial reduction in winds will be across central South
Dakota...where mixing will not counteract the winds as much. Have
went ahead and issued a Wind Advisory for the entire forecast
area...but left it going through the afternoon hours in the eastern
portion as mechanical mixing will still make it possible to meet
advisory conditions through the afternoon hours.

Other concern is fire weather with strong northwest winds developing
mixing down drier air from aloft. Model guidance in dew points is
relatively poor...but sided with the drier guidance values. Even
though that is the case...still ended up on the high side of things
in terms of relative humidity for red flag conditions. Opted to continue with the
Fire Weather Watch with dormant fuels and strong northwest winds.
Have also expanded the Fire Weather Watch to south central South
Dakota zone...though decreasing winds through the afternoon will be
a limiting factor.

Long term...(sunday night through saturday)
issued at 258 PM CDT Sat Mar 28 2015

A weak ridge of high pressure will move through Sunday night into
Monday with westerly winds developing again on Monday. Will not be
as strong but still expecting some 15 to 25 miles per hour westerly winds in
the afternoon. Will be a very mild day as well and expect highs to
range from the middle 60s in southwest Minnesota to the middle 70s down
the Missouri River valley.

Another weak ridge of high pressure will pass through late Monday
night into Tuesday morning. With the drought like conditions in
place will lower lows just a touch as well as raise highs just a
touch. Tuesday could end up being the nicest day of the 7 day
period with fairly light winds and mild readings from 65 to 75
degrees.

In the outer periods(wednesday through saturday)...a fairly active
period aloft as troughiness becomes established. However not a while
lot of precipitation potential for much of the period. A fairly
strong wave will move into the northern plains Wednesday which will
deepen a bit and merge with the semi permanent low centered over
central Canada. A few thunderstorms...especially over northwest
Iowa...will be possible Wednesday afternoon and early Wednesday
evening as this wave moves through. As this occurs a wave moving
through The Rockies will track into the Central Plains Thursday
night into Friday which could bring a threat for precipitation to
the southern County Warning Area. This might be a wave to watch as there are hints
of deeper moisture and strong warming getting into southeast
Nebraska so if for some reason this wave comes out a little farther
north there could be a greater impact. Friday into Saturday will
start a cool down...just a matter of how much. The European model (ecmwf) and GFS not
very agreeable at this time so not ready to bite on trending in any
particular direction just yet...albeit the 12z European model (ecmwf) now starting to
hint at cooler conditions both Friday and Saturday so will aim for
highs in the 50s both days.

&&

Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 607 PM CDT Sat Mar 28 2015

A strong cold front will push across the area later
tonight...with a 50 to 60 knots low level jet developing out ahead of
the boundary. This will result in a few hours of low level wind
shear at all the taf sites. There will also be a possibility of
isolated showers with the boundary...mainly north of the
Interstate 90 corridor...and very strong winds could briefly mix
down to the surface with these showers. Otherwise...strong
northwesterly winds will develop behind the front...gusting to
around 40 kts through much of the day on Sunday.

&&

Fire weather...
issued at 258 PM CDT Sat Mar 28 2015

Despite the chance for light rainfall across the area
overnight...very strong northwest will develop behind a cold front
moving through the area. Wind gusts to 50 miles per hour will be possible
through the morning hours...gradually decreasing through the day.
Relative humidity values are expected to fall to 20-40 percent Sunday
afternoon...with the lowest rhs in central South Dakota. With
dormant fuels and strong winds...elected to keep the Fire Weather
Watch in effect for Sunday....and expanded it to include south
central South Dakota. While winds will be decreasing there through
the afternoon hours...relative humidity values will lead to dangerous conditions.

&&

Fsd watches/warnings/advisories...
South Dakota...Fire Weather Watch from Sunday afternoon through Sunday evening
for sdz255>258.

Wind Advisory from 7 am to 7 PM CDT Sunday for sdz040-055-056-
061-062-066-067-069>071.

Wind Advisory from 4 am to 1 PM CDT Sunday for sdz038-039-050-
052>054-057>060-063>065-068.

Minnesota...Fire Weather Watch from Sunday afternoon through Sunday evening
for mnz900.

Wind Advisory from 7 am to 7 PM CDT Sunday for mnz071-072-080-
081-089-090-097-098.

Iowa...Fire Weather Watch from Sunday afternoon through Sunday evening
for iaz300-301.

Wind Advisory from 7 am to 7 PM CDT Sunday for iaz001>003-
012>014-020>022-031-032.

NE...Fire Weather Watch from Sunday afternoon through Sunday evening
for nez249.

Wind Advisory from 7 am to 7 PM CDT Sunday for nez013-014.

&&

$$

Update...jm
short term...
long term...08
aviation...jm

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