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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
644 am CDT Sat Oct 25 2014

Short term...(today and tonight)
issued at 317 am CDT Sat Oct 25 2014

Quiet weather expected today into tonight with high pressure in
control. Some cirrus out there early this morning...but expect this
to push northeast of the way to a sunny day. Some of
the warmer bias corrected temperatures have been performing best
recently...and see no reason why that should not be the case again
today. Thus going with highs in the upper 60s and low 70s. With the
high pressure overhead...winds will be light as should be
a great day for outdoor activities.

Tonight...the high pressure begins to shift east with southeasterly
return flow developing. Coolest lows will be across portions of
southwest Minnesota and northwest Iowa where flow will stay weaker
longer...and looking at readings around 40 there. Elsewhere should
see an early drop into the middle and upper 40s...with nearly steady
temperatures the remainder of the night. Generally looking at a
clear night...although with increasing low level moisture...could
begin to see stratus development west of the James River and along
the Missouri River towards 12z.

Long term...(sunday through friday)
issued at 317 am CDT Sat Oct 25 2014

Stratus or stratocumulus is a concern on Sunday...placed in the
early morning west of the James River Valley...then moving
eastward throughout the day across our forecast area. Moisture
transport in the low levels is quite strong ahead of upper
troughing to the west of the area...and one does not have to go
too far southward to see some 50s to lower 60s surface dew points
in Kansas and OK. So the question remains is will potential low cloud
development hinder high temperatures for Sunday. The answer is
yes it least for locations east of I 29 where the bulk
of stratocumulus could be by middle afternoon. Therefore only mixed
temperatures to about 900mb for those locations...which gives
highs a couple of degrees either side of 70. But venturing along
and west of I 29...higher mixing should give readings well into
the 70s...especially along and west of a Sioux City to Huron line.
The low level jet is Stout on Sunday...with 35 to 45 knots common
at 900mb. Therefore expecting a breezy to windy day translating
from west to east as the day progresses. The fire weather situation
is not setup very good for red flag pretty high
humidity values are prevailing east of the James River Valley
where the wind speeds will be the strongest in the afternoon.
Behind a surface trough...winds will shift to the west in the
Lower Brule area in the afternoon drying the air mass out a
bit...but wind speeds will also become much lighter in our western
zones. So the humidity and winds are not juxtaposed very well to
produce very high or extreme fire danger in our area.

This surface trough moves across the forecast area Sunday night
producing light winds. Did not want to drop low temperatures too
far though as middle and high level clouds will be on the increase
overnight as the upper trough moves into the Western Plains.

The upper trough moves eastward across this region Monday and
Monday evening as an open wave. The middle and upper qg forcing is
rather diffuse and not very organized...with jet stream
orientation not favorable for our location. There is strong
frontogenesis however...with the usual sloping front as 850mb
frontogenesis favors our southern zones...and 600mb frontogenesis
in our north. Maximized the probability of precipitation along the 700mb zone which
resides generally from Tyndall and Yankton South Dakota...northeastward
through Sioux Falls and Onward to Windom Minnesota. Not enough dynamics
with this system to go likely or higher probability of precipitation yet kept
probability of precipitation in the slight chance to chance categories. With the
anticipated extensive cloud cover...highs on Monday will of
course be cooler than sundays highs...with 60 to 65 common.

Temperatures will be markedly cooler on Tuesday...with mixing only
giving upper 40s to middle 50s. Also noteworthy is the northwest
surface flow will be quite brisk...with winds easily in the 20 to
30 miles per hour range. But similar to Sunday...minimum humidity values look
way too high for any red flag fire weather concerns.

After Tuesday...the European model (ecmwf) and GFS are actually in not too bad
agreement overall...although they do begin do diverge pretty bad
right at the end of the extended period. A weak wave looks to
harmlessly pass across our forecast area on Wednesday and
Wednesday evening...with the GFS as usual being a bit quicker. But
left conditions dry at any rate...and high temperatures staying
mainly in the 50s for Wednesday and Thursday. As eluded too of the bigger question Marks for temperatures is at
the end of the extended on Friday with fairly chilly high
pressure nosing down from south central Canada. The European model (ecmwf) develops
an upper wave across the western Great Lakes Thursday night...then
dives it southward on Friday which would really allow some cool
air to intrude into our area. With the propensity of the GFS to be
too progressive...blended some cooler European model (ecmwf) temperatures into the
mix for late next week...which gives only upper 40s to lower 50s
for highs.


Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 640 am CDT Sat Oct 25 2014

Expecting VFR conditions through the period with generally light
winds. A southeasterly breeze will begin increasing later tonight
with a developing low level jet...and may be close to low level
wind shear criteria late. Also could see low stratus begin forming
or moving into the Missouri River corridor around 12z...but feel
like best chance of this will be after the taf period beyond will keep things VFR for now.


Fsd watches/warnings/advisories...
South Dakota...none.


Short term...chenard
long term...mj

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