Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 251112

Area Forecast Discussion
National Weather Service Sioux Falls SD
612 AM CDT Fri May 25 2018

.SHORT TERM...(Today and Tonight)
Issued at 402 AM CDT Fri May 25 2018

Weak surface boundary between James River and I-29 early this
morning, with subtle shortwave seen in water vapor imagery in the
western Dakotas triggering small area of ACCAS/isolated storms in
western SD as of 08Z. Wave shifts into southern Minnesota by mid
afternoon, and while surface boundary washes out a bit with mixing,
some hi-res models still have a hint of it near the Hwy 60 corridor
by 21Z. May also be some outflow boundaries lingering around from
convection which has moved across southern Minnesota early this

Strong mixing and fairly abundant sunshine should allow temperatures
to climb into the upper 80s/lower 90s, which soundings suggest would
be enough to break a weak cap across the area. As a result, CAMs
indicate isolated to scattered convection developing by mid-late
afternoon, mainly in our northern and eastern areas. Have introduced
some low pops to account for this possibility, though confidence in
favored location of development is low. Overall shear remains on the
weak side with nearly uni-directional wind profile, but could be
locally enhanced near aforementioned surface boundaries, or any
additional outflow generated if afternoon storms do develop. Thus,
think risk of severe storms is low, but not zero, with primarily an
isolated wind threat as mid level lapse rates not supportive of
large hail development and soundings depict inverted-v look beneath
mid-level cloud bases.

Any afternoon convection should diminish toward sunset as the wave
slides further east and daytime heating is lost.

.LONG TERM...(Saturday through Thursday)
Issued at 402 AM CDT Fri May 25 2018

Upper ridge builds into the region for the weekend, bringing well
above normal temperatures into early next week. Highs in the 90s
still look to be widespread Saturday and Sunday, with some locales
possibly pushing record levels on Sunday. Dew points currently
expected to be in the mid-upper 50s Saturday afternoon, climbing a
little higher Sunday as low level flow turns more southerly again.
May have to watch for some areas reaching heat advisory criteria,
though readings remain a few degrees shy at this time. Will continue
to highlight the upcoming early season warmth online and in the HWO.

Models hinting at a low chance of storms scraping our far northern
areas early Sunday, initially triggered by low level jet in the
western/central Dakotas Saturday night, then sliding around the
periphery of the upper ridge through Sunday morning. GFS is most
robust with this activity and seems overdone, but other models
showing potential for isolated activity so will carry the low pop
toward the Hwy 14 corridor.

Sunday night/Monday, western extent of the upper ridge begins to
break down as a piece of energy swing around a deep trough over the
Intermountain West. This could bring spotty showers/storms to the
area for the Memorial Day holiday itself, but precipitation chances
grow later Monday night through Tuesday night as the broad western
trough shifts east into the northern Plains. This should bring some
relief from the weekend heat, though at this point still expecting
highs largely in the 80s as May comes to a close. Could have some
decent instability during the day on Tuesday, though mid-level lapse
rates are rather weak, as is deep shear, so overall severe threat
looks low with this system.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 609 AM CDT Fri May 25 2018

VFR conditions with occasional scattered mid level clouds
expected through the TAF period.




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