Alert archive / Montana / Mesoscale Discussions in 2017

Mesoscale Discussion 970

June 8, 201712 counties in Montana

The Storm Prediction Center issued this mesoscale discussion at Jun 8, 2017, 4:24 PM MDT for 12 counties in Montana. It was in force for 96 min.

The area

The outline as issued.

The facts

Issued: Jun 8, 2017, 4:24 PM MDT (22:24 UTC)
Expired: Jun 8, 2017, 6:00 PM MDT
In force: 96 min
Issued by: the Storm Prediction Center
Chance of a watch: 60%

Counties Cascade County, MT, Chouteau County, MT, Glacier County, MT, Granite County, MT, Hill County, MT, Lewis and Clark County, MT, Liberty County, MT, Missoula County, MT, Pondera County, MT, Powell County, MT, Teton County, MT, Toole County, MT

The radar

The Great Falls radar (KTFX), 76 km from the middle of the area, began a volume at 22:24 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 307Jun 8, 4:45 PM MDT

The nearest sounding before it

Great_falls, MT (KTFX), launched 12:00Z, 10.4 hours before the alert went out and 135 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 8 J/kg
Mixed-layer CIN: -444 J/kg
Mixed-layer LCL: 2385 m above ground
0-6 km bulk shear: 16 kt
0-1 km storm-relative helicity: 9 m²/s²
0-3 km storm-relative helicity: 3 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

956 
ACUS11 KWNS 082224
SWOMCD
SPC MCD 082224 
MTZ000-090000-

Mesoscale Discussion 0970
NWS Storm Prediction Center Norman OK
0524 PM CDT Thu Jun 08 2017

Areas affected...Portions of western/central Montana

Concerning...Severe potential...Watch possible 

Valid 082224Z - 090000Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms will continue to develop across the region
late this afternoon into this evening. As storms progress northeast,
they are expected to strengthen, with some potential for damaging
winds and large hail. Watch issuance may be needed within the next
hour or so.

DISCUSSION...Despite mid/high-level cloud cover having overspread
the region today, surface temperatures have warmed into the 80s
across much of western/central Montana. Increasing forcing for
ascent associated with an approaching shortwave trough and maturing
orographic circulations have fostered the development of
thunderstorms across the higher terrain of western Montana. As these
storms progress north/northeast, they will encounter an environment
characterized by steep low/mid-level lapse rates and adequate
boundary layer moisture (e.g., surface dew points in the upper 40s
to 50s). In turn, MLCAPE values upwards of 1000-1500 J/kg will
support vigorous updraft accelerations, and strong, uni-directional
south/southwesterly mid-level flow will encourage splitting/bowing
structures, enhancing the threat of damaging winds. Related to this
strong mid/upper flow, favorable effective shear may yield a few
rotating updrafts in any semi-discrete cores, resulting in some
instances of large hail. Considering this increasing threat of
severe weather, convective trends are being monitored for potential
watch issuance.

..Picca/Weiss.. 06/08/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...TFX...MSO...

LAT...LON   46661393 46991411 49001399 49011068 48890997 47770991
            47091092 46161292 46331363 46661393

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 8, 4:46 PM MDT	Severe Thunderstorm Watch	SPC	Cascade, Chouteau, Flathead, Glacier, Hill, Lake and 6 more	6 hr

Nearby

Mesoscale Discussions in Montana, 2017 Every mesoscale discussion in 2017

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.