Alert archive / Montana / Mesoscale Discussions in 2012
Mesoscale Discussion 1521
The Storm Prediction Center issued this mesoscale discussion at Jul 20, 2012, 2:58 PM MDT for 16 counties in Montana. It was in force for 92 min.
The area
The outline as issued.
The facts
- Issued
- Jul 20, 2012, 2:58 PM MDT (20:58 UTC)
- Expired
- Jul 20, 2012, 4:30 PM MDT
- In force
- 92 min
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 40%
Counties Broadwater County, MT, Cascade County, MT, Deer Lodge County, MT, Flathead County, MT, Glacier County, MT, Granite County, MT, Jefferson County, MT, Judith Basin County, MT, Lake County, MT, Lewis and Clark County, MT, Meagher County, MT, Missoula County, MT, Pondera County, MT, Powell County, MT, Silver Bow County, MT, Teton County, MT
The radar
The Missoula radar (KMSX), 98 km from the middle of the area, began a volume at 21:00 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, 9.0 hours before the alert went out and 174 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
- 92 J/kg
- Mixed-layer CIN
- -463 J/kg
- Mixed-layer LCL
- 2595 m above ground
- 0-6 km bulk shear
- 30 kt
- 0-1 km storm-relative helicity
- 37 m²/s²
- 0-3 km storm-relative helicity
- 78 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted, in the capitals the NWS used until 2016.
275
ACUS11 KWNS 202058
SWOMCD
SPC MCD 202058
MTZ000-202230-
MESOSCALE DISCUSSION 1521
NWS STORM PREDICTION CENTER NORMAN OK
0358 PM CDT FRI JUL 20 2012
AREAS AFFECTED...WRN INTO PARTS OF CNTRL MONTANA
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 202058Z - 202230Z
PROBABILITY OF WATCH ISSUANCE...40 PERCENT
SUMMARY...TRENDS ARE BEING MONITORED FOR THE POSSIBILITY OF AN
INCREASING SEVERE THREAT WHICH COULD REQUIRE A WW LATE THIS
AFTERNOON.
DISCUSSION...DEEPENING CONVECTIVE DEVELOPMENT IS ONGOING ACROSS THE
ROCKIES... WHICH WILL GRADUALLY SHIFT ACROSS AND EAST OF THE HIGHER
TERRAIN BETWEEN NOW AND 23-00Z...AS 20 KT SOUTHERLY DEEP LAYER MEAN
FLOW BEGINS TO STRENGTHEN SOME...WITH THE NORTHEASTWARD MIGRATION OF
A 40-50 KT 500 MB JET STREAK OUT OF OREGON. THE ENVIRONMENT EAST OF
THE HIGHER TERRAIN IS NOT PARTICULARLY UNSTABLE IN TERMS OF
CAPE...BUT LAPSE RATES ARE STEEP...AND THE BOUNDARY LAYER IS
BECOMING DEEPLY WELL MIXED. AIDED BY INCREASING SHEAR...AND
LARGE-SCALE FORCING ASSOCIATED WITH THE APPROACHING SHORT WAVE
TROUGH...ISOLATED STRONG/SEVERE STORM DEVELOPMENT...INCLUDING THE
RISK FOR SUPERCELLS...DOES NOT APPEAR OUT OF THE
QUESTION...PARTICULARLY TO THE WEST AND SOUTHWEST OF CUT BANK.
..KERR/HART.. 07/20/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...BYZ...TFX...MSO...
LAT...LON 48251525 48811292 48491094 47000984 46191101 45651300
47601506 48251525SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 20, 12:38 PM MDT | Severe Thunderstorm Watch | SPC | Flathead, Lake, Lincoln, Mineral, Missoula, Sanders | 7 hr |
Nearby
Mesoscale Discussions in Montana, 2012Every mesoscale discussion in 2012
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.