Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 210347
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
947 PM MDT Thu Jul 20 2017

.UPDATE...
Issued at 945 PM MDT Thu Jul 20 2017

Have cancelled the Severe Thunderstorm Watch that was in effect
for northwestern South Dakota. Storms in that are are becoming
much weaker and less organized.

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 259 PM MDT Thu Jul 20 2017

Latest analysis shows low pressure centered over eastern Montana.
A warm front extends eastward from the low into northern North
Dakota and a dry line extends southward from the low into eastern
Wyoming. The dry line will push into western South Dakota this
evening followed by a weak cold front that will push southeastward
across the region overnight. Thunderstorms have already developed
in southeastern Montana and along the warm front in North Dakota.
Deep shear profiles and increasing instability this afternoon
point to the possibility of severe thunderstorms over parts of the
forecast area overnight. A severe thunderstorm watch has already
been issued for parts of far northwestern South Dakota, which need
to be extended farther south later this evening. The surface low
will be centered over south central South Dakota on Friday morning
so may see some storms linger over the eastern CWA during the
morning. Might see some breezy areas in the area of the tighter
sfc pressure gradient to the west of the low especially during the
morning. Drier air will flow into the region as high pressure
moves in behind the departing low.

Saturday through Thursday, a flat upper ridge on Saturday will
begins to amplify Sunday into early next week. Isolated -TSRA may
occur, but most areas will remain dry. Temperatures will be 5-10F
above average with perhaps Monday looking to be the warmest day.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 513 PM MDT Thu Jul 20 2017

Thunderstorms currently over northeastern Wyoming and northwestern
South Dakota will continue to move southeastward across the rest
of western South Dakota tonight. Severe thunderstorms are possible
through this evening, with large hail and damaging wind gusts.
Outside of any thunderstorms, VFR conditions are expected.


&&

.FIRE WEATHER...
Issued at 259 PM MDT Thu Jul 20 2017

Drier air will push into the area Friday and Saturday with a few
breezy areas possible. Minimum RH will dip to 15-25% on Friday
afternoon.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from 11 AM MDT /noon CDT/ to 7 PM MDT /8 PM CDT/
     Friday for SDZ032-043-046-047-049.

WY...None.
&&

$$

Update...10
DISCUSSION...10
AVIATION...10
FIRE WEATHER...10



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