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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
419 am CDT Friday Jul 11 2014

Short term...(today and tonight)
issued at 416 am CDT Friday Jul 11 2014

Current round of convection continues to move eastward...with the
rain currently mostly along and east of the I 29 corridor. Upstream
weak short wave is responsible for much of this activity. So far...
redevelopment behind the main complex in our western zones has been
limited. This is likely due to perturbed low level inflow from a
second complex in central Nebraska. But fairly strong 850mb thetae
advection is still working through...and really does not exit our
far eastern zones until 15z. So am expecting some redevelopment
almost anywhere east of the James River Valley into the early
morning hours. Furthermore...latest 88d radar scans are showing a
hookup with our current convection...southwestward into the cold
pool of the Nebraska complex...which will likely fill in across our far
southern zones into early morning. Therefore all said...still have
high probability of precipitation in our eastern and southern zones through 12z...then
decreasing through the morning hours as the influence of the short
wave wanes. From late morning Onward...not expecting a lot of
convection chances in our forecast area as we are firmly planted in
between two short waves with rising middle level heights noted. Not
real confident about afternoon showers or storms in our eastern
zones along an 850mb trough only included slight chance
probability of precipitation for those areas. In our western may be too capped
for anything to develop so have them dry. With some clearing expecting temperatures to become quite warm this
afternoon. Went with the warmest guidance readings which were the
raw values and consensus raw readings...and then even in many cases
further warmed temperatures another degree or two.

Tonight...a few severe storms are possible in our far southern
zones...mainly from Sioux City and Storm Lake. Another
short wave moves eastward...and a surface to 850mb boundary sets up
during the evening and overnight hours in those areas. Currently it
looks as though wind shear is a bit limited...with the low level
flow rather weak. And if the storms are elevated...the lowest 1km of
wind shear will likely not be tapped at any rate leaving a
multicellular looking hodograph. But there is decent instability...
with 925mb-850mb mu convective available potential energy of near 2000 j/kg nudging northward from
Nebraska...coupled with plenty of low level moisture to tap.
Therefore would also not rule out some locally heavy rain in some of
our southern zones. Current thoughts are that the convection which
forms during the evening hours in our southern zones will ooze
northward along the low level a high pop chance
generally from I 90 and points southward.

Long term...(saturday through thursday)
issued at 416 am CDT Friday Jul 11 2014

A pretty strong upper level wave will continue to move across the
area on Saturday...interacting with a frontal boundary overhead.
Thus expecting good coverage of showers and thunderstorms
across the area. Expected evolution is that convection that forms
over northern Nebraska on Friday night...will move north into our
County Warning Area through Saturday morning...with some new development overhead as
well. This activity is expected to remain elevated...and with
instability pretty limited...not seeing much of a severe risk. Still
some differences among the models on location of the greatest
coverage of storms...but current consensus seems to suggest areas
from the Interstate 90 corridor and points south. These storms
should push east through the day...with the northwest half of the
area likely dry by early to middle afternoon. As the day
progresses...storms may become more surface based ahead of the cold
front with an increasing severe threat. However this appears to
happen southeast of the County Warning Area...possibly clipping our far southeast near
Storm Lake. Thus the day 2 Storm Prediction Center outlook looks good. Highs on Saturday
will be in the upper 70s to middle 80s...warmest in the west...where we
should see the greatest amount of clearing by later in the day.

One more warm day expected on our region remains ahead
of the main cold front. Looking at highs again in the upper 70s to
middle 80s. Cold front will push across during the afternoon hours.
Will need to monitor convective chances with this frontal passage.
Despite the lack of any shortwave...the combination of remaining low
level moisture and cooling temperatures aloft...may be enough to get
a few thunderstorms along the front. Deep layer shear will be around
40 kts...but instability looks pretty meager and thin...possibly
approaching 1000 j/kg. Thus at this point severe threat seems
low...but given the shear can not rule out a stronger
storm...especially if we manage slightly higher instability than
currently expected.

Much cooler air will usher into the region Sunday night into Tuesday
behind this front. Lows Sunday night will be in the 50s...and by
Monday night we may see some areas drop into the upper 40s. For
highs...looking at only the middle 60s to middle 70s on Monday and
Tuesday. These are around 15 to 20 degrees below normal for this
time of year...more typical of late September values. Ridging will
begin to build back into the area by Wednesday and
Thursday...bringing a warming trend. By Thursday we will see highs
in the upper 70s to middle 80s...although these will still be below
average. Could see a few showers or thunderstorms on Monday east of
Interstate 29 as the trough axis and coldest air aloft swing across
the area. Otherwise not really seeing any precipitation chances
Tuesday through Thursday with high pressure in control.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1041 PM CDT Thursday Jul 10 2014

Scattered thunderstorms are expected to develop across portions
of the area overnight. Confidence is low on track and timing of
convective activity...though the better chance appears to be in
the time frame of 09z to 12z around kfsd and ksux. Some models
are also hinting at MVFR ceilings developing through parts of the
area toward 12z...again more likely at ksux and kfsd. Although a
low level jet is expected to strengthen across the region
tonight...does appear at this time that criteria for low level
wind shear will not be met.


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


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

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