Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 251730

Area Forecast Discussion
National Weather Service Sioux Falls SD
1230 PM CDT WED MAY 25 2016

.SHORT TERM...(Today and Tonight)
Issued at 352 AM CDT Wed May 25 2016

Corfidi vectors suggest parallel stratiform MCS across the region
this morning will shift off to the east. Atmosphere behind the MCS
is conditionally unstable, with 2-3K J/kg of surface CAPE
developing.  Cap becomes fairly minimal by late this afternoon, but
still struggling to see how widespread convection could develop with
lack of trigger mechanism across the region.  Would not be surprised
if a storm or two was able to develop solely based on surface
heating, but pinpointing that location is difficult.  The best
chance for this to occur would be across the highway 14 corridor
where the capping inversion is slightly weaker, but can`t rule out
any particular location in the forecast area.

If by chance a storm is able to develop, not an overly supportive
environment for tornadoes with weak shear in the low levels;
however, models suggest steep lapse rates of 9.5-10 C/km along and
west of the James River by late afternoon. Therefore, not entirely
possible to rule out a landspout out west with initial development
in the updraft phase. Elsewhere, think that wind and especially hail
will be the primary severe threats. 0-6 km bulk shear vales around
25 knots suggest marginal organization, but think that the large
CAPE values due to the steep lapse rates from 700-500 mb will be of
greater significance.

As for highs today, have lowered highs just a touch with filtered
sunshine expected through much of the day.  This makes breaking the
cap that much more difficult.

As heating dies away tonight, atmosphere becomes capped off making
the instability difficult to realize.  Have kept some 20-30 pops
ahead of a weak boundary working through overnight, but with lack of
any upper level support, am not sure there will be a lot of
convection with the front.

.LONG TERM...(Thursday through Tuesday)
Issued at 352 AM CDT Wed May 25 2016

Thursday should be a warm day with the environment gradually
becoming more unstable with increasing shear. At this time the most
unstable air will likely be south of Interstate 90...with what
appears to be a good potential for about 2000 to 3000 j/kg CAPE and
30 to 40 knots of surface to 6 km shear.

Not a whole lot to say about the Thursday night into Friday night
time frame as much of the time will be spent with showers and
thunderstorms. Low pressure is expected to deepen across Colorado as
low pressure gradually shears out across North Dakota into southern
Canada. These two waves will work to keep the low and mid level
thermal gradient in place which will help provide additional lift
for showers and thunderstorms. While severe weather does not look
likely in the immediate area, a strengthening low level jet and
strong instability will work north towards far southeast South
Dakota and northwest Iowa on Thursday night. This may prove to be
the best chance for severe thunderstorms into the weekend.

In the outer periods (Saturday through Tuesday), an unsettled
weather pattern will continue through the period. Saturday likely to
see the best chance for rain and thunderstorms as low pressure lifts
northeast. A good chance for a dry Sunday in many locations as
subsidence and mid and upper level height rises suggest that
precipitation chances will be lower. Troughiness Monday and Tuesday
will again support the chance for thunderstorms with warm and
relatively humid air expected. overall highs will mainly be in the
70s to lower 80s with lows in the mid 50s to lower 60s.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1230 PM CDT Wed May 25 2016



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