Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 240853

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
253 AM MDT Mon Jul 24 2017

.DISCUSSION...(Today Through Sunday)
Issued at 251 AM MDT Mon Jul 24 2017

08z surface analysis had low pressure over southern SK with
meandering frontal boundary south into eastern WY and then
southeast into central NE. Water vapour showed well-defined
shortwave over southeast MT. 500J/kg MUCAPE supporting small
convective cluster ahead of wave moving into west central into
northwest SD. This activity will continue to move east-northeast
early this morning, weakening slowly as 25-35kt low level jets
wanes with sunrise. This convection will certainly splay out an
outflow boundary, which will play havoc with TSRA chance
locations later today and tonight.

Today and tonight, SK low drags frontal boundary into the CWA with
dry line likely surging out of WY during peak boundary layer mixing
late this afternoon. Few breezy spots ahead of features over south
central SD. Boundary may be focus for afternoon convection given 1-
1.5KJ/kg MLCAPE on the SD plains. However, drier air moving in from
the southwest will keep MLCIN on the high side, so coverage will be
limited and focused on aforementioned boundaries. A marginal threat
for gusty winds is expected. Forecast soundings indicate readings
above 100F for areas east of the Black Hills. Heat indices from 100-
105F over central SD, so will hoist excessive heat advisory.

Tuesday, upper ridge flattens as surface boundaries consolidate
across southern portions of the CWA. Shortwave will move from the
Rockies into the CWA late in the day. PW`s rise to 150-200% of
normal as moisture pools along boundary creating 1-2KJ/kg MLCAPE and
little MLCIN by 00z. 850-300mb steering flow 10-15kts and parallel
to expected boundaries. Could see some training storms and/or
locally heavy rain. 0-6km bulk shear sufficient for isolated severe
storms before system mushes into a blob Tuesday evening.
Temperatures will be near guidance.

Wednesday and Thursday, slightly cooler temperatures expected with
TSRA possible as upper ridges reestablishes itself west of the

Friday through Sunday, upper ridge builds back with warmer
temperatures and small chances for TSRA.


.AVIATION...(For the 06Z TAFS Through 06Z Monday Night)
Issued At 1109 PM MDT Sun Jul 23 2017

Scattered thunderstorms will move across northeast Wyoming into
the Black Hills and northwest South Dakota overnight into early
Monday morning. Local MVFR conditions and gusty winds with the
thunderstorms, otherwise VFR conditions expected.


SD...Heat Advisory from 2 PM MDT /3 PM CDT/ this afternoon to 7 PM
     MDT /8 PM CDT/ this evening for SDZ014-031-032-043-046-049-



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