Hail and Damaging Winds in Iowa, June 22, 2021

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
235 PM CDT Tue Jun 22 2021

.SHORT TERM...(This Evening through Wednesday)
Issued at 233 PM CDT Tue Jun 22 2021

Mid afternoon objective analysis shows a relatively stationary
boundary roughly draped along the SD/NE border eastward toward Le
Mars and eventually southeastward toward Storm Lake. Along and south
of it, a notable agitated Cu field has developed along with
festering weak convection. Biggest question regarding today's
convection continues to be the quality and depth of moisture and
thus the resultant instability. Surface obs across the region show
dewpoints largely in the mid to upper 50s with some pooling of
moisture noted along the front with a few lower 60 dewpoints. This
has resulted in 500-1000 J/kg of MLCAPE via RAP mesoanalysis. Should
established deep convection result, effective shear around or in
excess of 45 kts will be more than sufficient for rotating updrafts.

High res CAMs in decent agreement for more robust convective
development in the 3-5 pm time frame just a bit north of Hwy 20 with
Bunkers RM vectors taking storms quickly off to the south/southeast.
With relatively straight and enlarged hodographs in the mid to upper
levels, may see a tendency for a few cell splits as well. Despite
the rather skinny and meager instability profiles, this enhanced
deep layer shear may compensate to allow for a hail report up to
ping pong ball size and damaging wind up to 60 mph. While the
presence of a boundary would typically spark some tornado concern,
LCLs likely too high for a higher concern with regards to that.

Any severe potential would likely be confined to prior to 8 pm with
perhaps some lingering elevated convection through the remainder of
the evening. Otherwise, quiet overnight period expected with some
hint at fog or lower stratus late tonight into Wednesday morning,
given the dry ambient conditions and lack of support by SREF
probabilities, not sold on this idea just yet.

A very warm day for Wednesday as 850 mb temperatures warm into the
upper 10th percentile of climatology. Would expect widespread 90s
for afternoon highs with a few locations near and west of the James
River perhaps exceeding the century mark. Dewpoints won't be overly
oppressive so any Heat Advisory criteria may be a bit more localized
and thus have opted against an advisory.

Mid level lapse rates will also begin to steepen through the
afternoon and evening Wednesday with a wave likely sparking at least
isolated to scattered convection over the High Plains. Guidance in
fair agreement with taking this convection eastward through the
evening and early overnight hours with consensus for any stronger
activity to remain south of the MO River. With this said, not
impossible to get a stronger wind gust into our MO River counties
with forecast soundings showing a strong inverted V characteristic.
This is covered by a Marginal Risk from SPC.

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 233 PM CDT Tue Jun 22 2021

Thursday forecast remains a question mark with a strong dependence
on any convective evolution from Wednesday night and the eventual
placement of the synoptic boundary for the daytime hours Thursday.
Along and ahead of this boundary, moderate to perhaps strong
instability will remain in place and while deep layer effective
shear may be somewhat limited, will continue to carry a
strong/severe thunderstorm risk. SPC has highlighted the southeast
half of our coverage area in a Marginal/Slight which seems like a
reasonable start and will likely evolve as higher confidence in
boundary placement occurs. Currently, NW IA and surrounding areas
likely carry the highest precipitation and severe weather potential.
Temperatures Thursday also in flux but roughly mid 80s to lower 90s
seem reasonable for now.

Upper level troughing carves in for Friday with some continued
precipitation chances. Still some model discrepancy on where this
trough axis sets up but some pairing from the GFS/ECMWF for a
favorable placement for our area for occasional bouts of
precipitation through the weekend. This will also keep temperatures
near or below normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1140 AM CDT Tue Jun 22 2021

Main concern through the first half of the aviation period will
revolve around thunderstorm chances across NW IA and NE NEB late
this afternoon and evening including at KSUX. Any storms that do
develop will carry the risk for large hail and perhaps
gusty/erratic winds along with brief heavy rain and lightning.
Have continued to pencil in a most likely time for impact at KSUX
but this will be monitored through the afternoon hours.

Late tonight into early Wednesday morning, at least some hint in
guidance of patchy fog and/or low stratus below the inversion but
with dry ambient conditions and a lack of support in SREF
probabilities, will leave this out of the TAF at this time.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

SHORT TERM...Kalin
LONG TERM...Kalin
AVIATION...Kalin

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
240 PM CDT Tue Jun 22 2021

IAZ001>003-MNZ071-072-080-081-089-090-097-098-SDZ038>040-050-052>068-
231945-
Lyon-Osceola-Dickinson-Lincoln-Murray-Cottonwood-Nobles-Jackson-
Pipestone-Rock-Beadle-Kingsbury-Brookings-Gregory-Jerauld-Sanborn-
Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook-Minnehaha-
Charles Mix-Douglas-Hutchinson-Turner-Bon Homme-
240 PM CDT Tue Jun 22 2021

This Hazardous Weather Outlook is for northwest Iowa, southwest
Minnesota, central South Dakota, east central South Dakota, south
central South Dakota and southeast South Dakota.

.DAY ONE...This afternoon and tonight.

Hazardous weather is not expected at this time.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Well above average temperatures return mid week, with readings
near 100 degrees along and west of the James River Valley on
Wednesday.

There is a chance for thunderstorms Wednesday night into Thursday
night. While there is uncertainty in exact location and timing, a
few strong to severe thunderstorms will be possible.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

IAZ012>014-020>022-031-032-NEZ013-014-SDZ069>071-231945-
Sioux-O'Brien-Clay-Plymouth-Cherokee-Buena Vista-Woodbury-Ida-Dixon-
Dakota-Yankton-Union-
240 PM CDT Tue Jun 22 2021

This Hazardous Weather Outlook is for northwest Iowa, west central
Iowa, northeast Nebraska and southeast South Dakota.

.DAY ONE...This afternoon and tonight.

A few strong to severe thunderstorms will be possible during the
late afternoon and early evening. Hail up to ping pong ball size and
wind gusts to 60 mph will be possible with the strongest storms.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Well above average temperatures return mid week, with highs in the
90s on Wednesday.

There is a chance for thunderstorms Wednesday night into Thursday
night. While there is uncertainty in exact location and timing, a
few strong to severe thunderstorms will be possible.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed late this afternoon and early
evening. Any reports of large hail or damaging winds are greatly
appreciated.