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Area forecast discussion
National Weather Service Sioux Falls South Dakota
421 PM CDT Thursday Apr 24 2014
Short term...(this evening through friday)
issued at 409 PM CDT Thursday Apr 24 2014
Relatively mixy conditions are expected to subside this evening as
low pressure shifts east and gradient weakens. High pressure center
is expected to shift east south of the forecast area tonight into
Friday. With good radiative conditions overnight...considered adding
fog mention in northwest Iowa where mixing is not as strong and heavier
rain fell. Still think that a fair amount of the moisture will be
able to mix out over the next few hours...so for now left mention
out. With relatively weak flow and winds aloft generally in the 10
- 15 knot range....should be a relatively pleasant Spring day across
the area on Friday with 850 hpa temperatures in the upper single digits.
Still will see a slightly elevated fire danger on Friday with
relatively dry air resulting in relative humidity values of 20-30 percent.
Long term...(friday night through thursday)
issued at 409 PM CDT Thursday Apr 24 2014
Ridging shifts eastward on Saturday as a deep Pacific trough
advances into The Four Corners region. Windy conditions develop as
east southeast winds increase to around 20 to 25 miles per hour with higher
gusts by the afternoon. Moisture gradually increases during the
day...resulting in increased middle and high clouds. Temperatures will
again be quite mild...especially near the Missouri Valley where a bit
more sunshine and warming is expected. Highs will be mainly in the
60s...with some 70s in our south.
Unsettled weather pattern sets up for the first half of next week as
the Pacific trough emerges in the Central High plains...lifts
northward to near central portions of Nebraska and South Dakota then
slowly wobbles eastward. Still seeing model differences...
particularly in the gradual progression east and away from the
area. The general consensus with the 12z runs is for a more
northerly track...which results in slightly milder temperatures and
a greater potential for thunderstorms. Additionally...models are
also trending towards a slower exit of the upper low which will
result in rain chances lingering into the end of the forecast period
Greater moisture advection will lead to some middle level instability
on Saturday evening and overnight. Strong directional shear and
steep middle level lapse rates suggest that a few strong or severe
storms will be possible if storms can manage to initiate. Storms
become more likely across the area overnight as the upper low
emerges into the plains. Could see precipitation briefly taper off
late Sunday morning into the afternoon...however as much stronger
lift and forcing pushes into the Missouri Valley...showers and
storms will again become numerous throughout the forecast area.
Shear remains strong at around 40 knots...though more
unidirectional...along with decent instability will pose the
potential for some isolated strong to severe storms. Moisture will
be more copious on Sunday than Saturday...so think that
precipitation will be more widespread and lift across the area
through the early morning hours.
Cloudy skies and rain chances persist through at least Tuesday as
the large system drifts eastward across the region. While the more
northerly track will result in a milder system overall...
temperatures will be below normal Monday and beyond. Did trend highs
and lows slightly warmer...but expect highs to generally top out in
the 50s Tuesday through Thursday.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1245 PM CDT Thursday Apr 24 2014
IFR conditions across southwest Minnesota into northwest Iowa
should gradually improve to VFR late this afternoon and evening as
a surface ridge builds into the area. Brisk northwest winds across
southeast South Dakota are expected to decrease through the
evening hours with sunset. VFR conditions are expected to remain
through the overnight into Friday morning with light westerly
issued at 313 am CDT Thursday Apr 24 2014
Red flag warning conditions across central and southeastern South
Dakota should abate with sunset this evening as mixing ceases and
strong northwest winds subside. Relative humidity values are expected to recover
throughout the evening.
South Dakota...red flag warning until 7 PM CDT this evening for sdz255-256-258.
NE...red flag warning until 7 PM CDT this evening for nez249.