Alert archive / Montana / Mesoscale Discussions in 2021

Mesoscale Discussion 1258

July 11, 20215 counties in Montana

The Storm Prediction Center issued this mesoscale discussion at Jul 11, 2021, 2:53 PM MDT for 5 counties in Montana. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
Jul 11, 2021, 2:53 PM MDT (20:53 UTC)
Expired
Jul 11, 2021, 5:00 PM MDT
In force
2 hr
Issued by
the Storm Prediction Center
Concerning
Severe potential...watch unlikely
Chance of a watch
20%

Counties Blaine County, MT, Glacier County, MT, Hill County, MT, Liberty County, MT, Toole County, MT

The radar

The Great Falls radar (KTFX), 148 km from the middle of the area, began a volume at 20:56 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 nearest sounding before it

Great_falls, MT (KTFX), launched 12:00Z, 8.9 hours before the alert went out and 145 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-pSkew-T log-p diagram, Great_falls, MT at 12:00Z on 2021-07-11Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Great_falls, MT at 12:00Z on 2021-07-11The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -10 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
3738 m above ground
0-6 km bulk shear
21 kt
0-1 km storm-relative helicity
-10 m²/s²
0-3 km storm-relative helicity
104 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

488 
ACUS11 KWNS 112053
SWOMCD
SPC MCD 112053 
MTZ000-112300-

Mesoscale Discussion 1258
NWS Storm Prediction Center Norman OK
0353 PM CDT Sun Jul 11 2021

Areas affected...Far Northern Montana

Concerning...Severe potential...Watch unlikely 

Valid 112053Z - 112300Z

Probability of Watch Issuance...20 percent

SUMMARY...A couple of severe storms are likely to move across far
northern Montana, posing a threat of severe hail and wind.  Given
the limited spatiotemporal threat, a watch is unlikely.

DISCUSSION...Rapid thunderstorm development has occurred over the
high terrain of the northern Rockies near the Canadian border ahead
of a potent shortwave trough.  Despite the limited moisture and
instability, strong forcing for ascent and sufficient deep-layer
shear will continue to support a supercell or two across far
northern Montana through the afternoon and evening hours.  Hail will
probably be the primary threat initially, but a severe wind threat
may evolve with time given the deep, well-mixed boundary layer
across the area.

..Jirak/Guyer.. 07/11/2021

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

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

LAT...LON   49001328 48561330 48391114 48400891 48420855 49000864
            48980944 48991161 49001328

Nearby

Mesoscale Discussions in Montana, 2021Every mesoscale discussion in 2021

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.