Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 250330

Area Forecast Discussion
National Weather Service Sioux Falls SD
1030 PM CDT Thu May 24 2018

.SHORT TERM...(This evening through Friday)
Issued at 244 PM CDT Thu May 24 2018

The right entrance region of the upper level jet was spreading
northward through central Nebraska this afternoon. Just ahead of
this was an area of weak mid level convergence along the eastern
fringes of the strong EML. This has allowed the ACCAS field to
expand into southeast SD and scattered showers and isolated
thunderstorms have developed. As elevated as these storms are they
will likely struggle to become severe, but a few stronger storms
will be possible with hail to quarters, wind gusts to 50 mph and
brief heavy rainfall. As this wave lifts north drier air was working
in in the low and mid levels into central SD and central Nebraska. A
relatively weak boundary was shifting east into central and eastern
SD late this afternoon and could serve as a focus for thunderstorm
development if surface heating is substantial enough. Soundings
suggest that something close to 87 to 88 degrees will be needed to
break the cap. If this happens CAPE values of 2500 J/kg and about 20
knots of shear will provide enough energy to bring the chance for
hail to the size of golf balls as well as 65 mph winds. This threat
is conditional on breaking the cap and there is still a threat for
thunderstorms to struggle to develop. At 3 pm there was very little
cumulus activity along this front.

Hot and dry pattern for Friday into the weekend as upper level ridge
builds across the plains.  Could see a few fair weather cumulus
develop across the east, where there is a bit more moisture in the
boundary layer.  Further to the west, looks mostly sunny with full
heating.  850 hpa temps approach 20C by late in the day, leading to
highs in the upper 80s to lower 90s.

.LONG TERM...(Friday night through Thursday)
Issued at 244 PM CDT Thu May 24 2018

Temperatures continue to warm aloft into the weekend, leading to
slightly warmer conditions.  Surface high across the central plains
gradually shifts east through the day on Saturday leading to
increasing southerly flow and increasing moisture.  Because of this,
have slightly higher temperatures on Saturday, but higher heat index
values on Sunday.  At this point, end up a few degrees shy of heat
advisory criteria, but will still be important to keep heat safety
in mind given the early nature of this heat wave.

Upper ridge starts to break down on Monday as upper level low across
the west slowly works east.  There are timing differences on how
quickly this system approaches, with the GFS being a bit quicker
than the ECMWF. There is an outside chance of a storm on Monday, but
more widespread activity looks to be possible on Tuesday into
Wednesday.  While instability looks to be a little stronger than
this week, shear profiles look to be week limiting overall severe


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1030 PM CDT Thu May 24 2018

VFR conditions expected through the TAF period.




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