Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 242355

Area Forecast Discussion
National Weather Service Sioux Falls SD
655 PM CDT TUE MAY 24 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 313 PM CDT Tue May 24 2016

A warm and pleasant evening is expected across the region with a
weak bit of subsidence shifting across the area. Southwest upper
level flow however will direct yet another shortwave into the
Missouri Valley a little after midnight and lift it northeast
through the forecast area overnight into Wednesday morning. Weak
surface boundary remains stalled across central SD and another
boundary parked across southern Kansas. As the surface low in
Colorado lifts northeast this evening and the low level jet kicks
in...the boundary to our south lifts northward. Convection is
expected to develop across Nebraska later this afternoon and evening
and push into south central SD and the Mo Valley region late evening
into the early morning hours.

The big question will be whether convection can get going this
evening ahead of the main wave. The HRRR and GFS develops scattered
convection by mid evening in southeast SD to the south of
I90...likely triggering off of the diffuse boundary in south central
SD. Convergence is very weak here and a bit more defined in central
Nebraska. Modest instability has developed along with steep lapse
rates, however effective shear is pretty marginal and some weak
capping exists. If elevated thunderstorms do manage to develop in
south central or near the Missouri Valley this evening, a few storms
could become strong to severe with half dollar hail and gusts up to
60 mph. Did leave an isolated to scattered thunderstorm mention in
the forecast near the Missouri Valley. The experimental HRRR,
NAMDNG, NAM, and ECMWF however, keeps the region dry through the

Tonight, showers and thunderstorms will become likely as the wave
lifts through the region. Storms will track northeast and while the
severe threat wanes quickly after midnight with effective shear
values dropping quickly, fairly high precipitable water values above
1.25 inches will keep the threat for heavy rainfall going.
Fortunately, it does look like activity will be moving fairly
quickly. Still, with recent heavy rainfall in northwest Iowa and
southwest Minnesota, will need to watch for flash flooding concerns.

Wednesday`s forecast is a tricky one. Ongoing convection in the
morning will lift to the northeast by mid/late morning. With clouds
becoming scattered to broken and potentially allowing temperatures
to heat back into the low to mid 80s with dewpoints in the low 60s,
we potentially become moderately unstable. Without much in the way of
lift, temperatures will need to heat out fully, so any thunderstorm
development will be quite conditional on how early morning
convection impacts the airmass in its wake. This will also make it
difficult to go above chance pops given the uncertainty.  Severe
storms will again be possible in the afternoon if anything manages
to form. Shear looks a little better than this evening, but still
somewhat marginal.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 313 PM CDT Tue May 24 2016

Wednesday evening thunderstorms are expected to wane steadily later
in the night with the exit of the short wave and the inflow from the
west and northwest of somewhat drier and more stable air. After
coordinating it looks like we can go for no mention of storms in
the area for Thursday morning, then a threat Thursday afternoon and
night, as that moisture and instability increase from the southeast.
Meanwhile, an upper low moving from the four corners area into the
southern plains will begin to move north northeast and amplify the
moisture availability as it approaches SD and IA. This will likely
bring widespread showers and storms to the area for parts of the
Friday through Saturday time frame. Will hold pops to the loaded
extended values of likely at most for now because of the usual
timing issues that far ahead, but one or two periods in that time
frame should have rain affecting most of the area.

Some severe storm threat seems possible with late Thursday and
Thursday evening storms, given the recovering instability and likely
good heating. Friday through Saturday severe threat is uncertain,
with modest shear ahead of the approaching upper low, but possibly
weak heating in the broadly increasing moisture field.

The Friday and Saturday system should pull northeast and leave a
mostly rain free Sunday, but will leave some fairly small chance
mainly in southwest MN for Sunday in case the upper low is slow to
pull out. Monday is uncertain, with a strong wave digging into the
Pacific Northwest area suggesting plains ridging and not much
convection. However, instability should also start to increase
again, so a chance of storms seems appropriate.

Modestly warm and humid conditions, certainly not really worthy of
summer yet, will keep high temperatures well into the 70s or low
80s, with lows in the 50s to low 60s. The cooler days will be the
cloudiest, such as Friday and Saturday.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 645 PM CDT Tue May 24 2016

VFR conditions are expected to persist through early Wednesday
morning. Convection may try to develop later this evening ahead of
a larger complex of storms anticipated to move eastward overnight.

While the widespread severe weather risk is low. A stronger wind
gust or marginal hail producing storm is possible as these storms
move through. Convection will push east of the Interstate 29
terminals by mid-morning and expectations are that stratus will
move in through mid-day.

Depending on how overnight storms progress, we`ll again have a
risk for more thunderstorms Wednesday afternoon.


.FSD Watches/Warnings/Advisories...


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