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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
406 am CDT Friday Aug 22 2014

Short term...(today and tonight)
issued at 406 am CDT Friday Aug 22 2014

Main focus in the short term will be a fairly potent wave expected
to impact the forecast area beginning this evening. Large trough
over the intermountain west this morning will eject a shortwave from
The Four Corners region into the Central High plains this afternoon.
Meanwhile surface low pressure deepens in western Kansas and lifts
northward into Nebraska in the evening. An attendant warm front will
also lift northward towards the Missouri Valley late tonight.

Muggy conditions will persist today...with middle to upper 60s
dewpoints increasing through the day today as flow continues to tap
into moisture. Expect dewpoints well into the low or middle 70s across
our southeastern half by this afternoon. With high temperatures
warming once again into the 80s...heat index values will reach the
middle to upper 90s in parts of northwest Iowa and far southeast South
Dakota. Could see a few initial high based convection fire earlier
in the day in Nebraska and clip our southern border. However...later
this evening as the low level jet begins increasing and the front
starts lifting northward...convection will slowly build northward
into the Missouri Valley...becoming categorical across our
southwestern half overnight. Main change was to slow down the timing
several hours with nearly every model supporting a slower
progression of the boundary lifting north. Strong instability
especially in our south could bump cape values to 2500 j/kg...with
initial meager shear increasing overnight as the low level jet increases. A
few isolated embedded severe storms will be possible late tonight
near the Missouri Valley as the front nears the area...however the
bulk of the threat will remain south of the County Warning Area. Main severe threat
would be marginal hail and gusts to 65 miles per hour. Lows tonight will be in
the middle 60s to near 70.

Long term...(saturday through thursday)
issued at 406 am CDT Friday Aug 22 2014

In general...00z GFS run is much more progressive than the other
solutions...and given its outlying solution...have discounted it and
have attempted to reduce the blends influence. Warm and muggy
pattern continues this weekend ahead of a slow moving trough moving
out of the Pacific northwest into the northern rockies. Leading
shortwave lifting into the region in southwest flow appears to
mainly be focused west...and while the east remains unstable...lack
of forcing and strong enough cap should limit convection spreading
east. As such...have scaled back probability of precipitation east of I-29 throughout the
day on Saturday. As previous forecast mentioned...precipitable water values are
near 2 inches...which is around 2 Standard deviations above normal.
With strong warm air advection throughout the day Saturday...there
is the potential for regenerating cells along the warm front lifting
north through the area. Closer to the center of the short
wave...clouds and convection will keep temperatures down...while
further to the east temperatures will approach 90.

On Saturday night into Sunday...upper low approaches from the west
but ridge to the east is fairly strong so the low lifts more north
than translating east. With the focus further to the west...have cut
probability of precipitation back some especially throughout the day on Sunday. Cold front
moves through on Sunday with much cooler and drier air working into
the region behind the front. Temperatures appear to remain below
normal through the better portion of next week...with the best
chance of precipitation on Wednesday as weak upper level trough
migrates through the area.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1109 PM CDT Thursday Aug 21 2014

Weak boundary has slowed up around ksux...but should remain inert
with any convective activity to the east. Northerly push behind
boundary...but will overall have a very limited impact on low
level moisture. Areas of fog would appear fairly likely...but for
the most part should remain with MVFR visibilities with moisture
layer becoming more shallow...with greatest threat for IFR
visibilities around ksux. Do not expect ceilings with fog due to
shallow nature. Convection likely to return to ksux in the end of
the taf period with increasing low level jet and boundary stalled
to south.


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


Short term...
long term...

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