Alert archive / Montana / Mesoscale Discussions in 2021
Mesoscale Discussion 558
The Storm Prediction Center issued this mesoscale discussion at May 7, 2021, 2:25 PM MDT for Clark County, Idaho; 11 counties in Montana. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- May 7, 2021, 2:25 PM MDT (20:25 UTC)
- Expired
- May 7, 2021, 4:30 PM MDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
Counties Clark County, ID, Beaverhead County, MT, Broadwater County, MT, Gallatin County, MT, Golden Valley County, MT, Jefferson County, MT, Madison County, MT, Meagher County, MT, Park County, MT, Stillwater County, MT, Sweet Grass County, MT, Wheatland County, MT
The radar
The Billings radar (KBLX), 202 km from the middle of the area, began a volume at 20:28 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, 8.4 hours before the alert went out and 235 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.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 2449 m above ground
- 0-6 km bulk shear
- 40 kt
- 0-1 km storm-relative helicity
- 39 m²/s²
- 0-3 km storm-relative helicity
- 48 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
500
ACUS11 KWNS 072026
SWOMCD
SPC MCD 072025
MTZ000-WYZ000-IDZ000-072230-
Mesoscale Discussion 0558
NWS Storm Prediction Center Norman OK
0325 PM CDT Fri May 07 2021
Areas affected...Southern Montana...far northeast Idaho...and far
northwest Wyoming
Concerning...Severe potential...Watch unlikely
Valid 072025Z - 072230Z
Probability of Watch Issuance...5 percent
SUMMARY...Developing thunderstorms may produce isolated strong to
severe winds as well occasional severe hail. This threat should
remain relatively isolated, and a watch is not expected.
DISCUSSION...Recent GOES imagery and lightning observations show a
few convective cells developing within the Sawtooth mountain range
of northeast ID/southwest MT. Recent RAP forecast soundings suggest
minimal instability (100-200 J/kg MLCAPE) is in place across the
region, but is sufficient for initiating storms given orographic
lift and ascent along a cold front. Gradual boundary-layer warming
(and slight moistening) is noted across southern MT, and should help
improve MLCAPE through the late afternoon hours. Stronger flow aloft
will support effective bulk shear values on the order of 30-40 knots
as parcel ascents deepen with time. Latest RAP mesoanalyses show a
narrow plume of 0-3 km lapse rates near 8 C/km ahead of the
developing storms, which should support the potential for sporadic
strong to severe winds with any mature convection. A veering wind
profile in the lowest 5-6 km may support one or two organized
mesocyclones and the potential for isolated severe hail, though the
limited instability introduces considerable uncertainty for this
scenario. Overall, the coverage of this threat is expected to be
fairly isolated, precluding the need for a watch.
..Moore/Thompson.. 05/07/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BYZ...RIW...TFX...PIH...MSO...
LAT...LON 44561340 45381310 46251190 46791051 46760874 46100825
45370868 44841000 44441139 44121286 44561340Nearby
Mesoscale Discussions in Montana, 2021Mesoscale Discussions in Idaho, 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.