Alert archive / Montana / Severe Thunderstorm Warnings in 2020

Severe Thunderstorm Warning 9, NWS Glasgow, MT

May 20, 20204 counties in Montana

NWS Glasgow, MT issued this severe thunderstorm warning at May 20, 2020, 9:33 PM MDT for 4 counties in Montana. It was in force for 57 min. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued
May 20, 2020, 9:33 PM MDT (03:33 UTC)
Expired
May 20, 2020, 10:30 PM MDT
In force
57 min
Issued by
NWS Glasgow, MT
Area
Storm-based polygon
Tornado
Possible
Hail
0.75 in
Wind
70.0 mph

Counties Daniels County, MT, Phillips County, MT, Roosevelt County, MT, Valley County, MT

The radar

The Glasgow radar (KGGW), 35 km from the middle of the area, began a volume at 03:31 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 watch it was issued in

The SPC watch in force over the same counties when this warning went out.

IssuedProductOfficeLasted
May 20, 3:11 PM MDTSevere Thunderstorm WatchSPC8 hr

The nearest sounding before it

Glasgow Intl Airport, MT (KGGW), launched 00:00Z, 3.6 hours before the alert went out and 33 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, Glasgow Intl Airport, MT at 00:00Z on 2020-05-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 975 joules per kilogram.LCLLFCEL10008507005003002001001 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, Glasgow Intl Airport, MT at 00:00Z on 2020-05-21The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 2 square meters per square second.19395878Sfc1 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
975 J/kg
Mixed-layer CIN
-43 J/kg
Mixed-layer LCL
1692 m above ground
0-6 km bulk shear
30 kt
0-1 km storm-relative helicity
2 m²/s²
0-3 km storm-relative helicity
35 m²/s²
Significant tornado parameter
-0.0
Supercell composite
-0.4

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Glasgow, MT wrote its last area forecast discussion before this severe thunderstorm warning went out at May 20, 7:47 PM MDT, 1 hour 46 minutes earlier.

Area forecast discussion, May 20, 7:47 PM MDT, 1 hour 46 minutes before
Area Forecast Discussion
National Weather Service Glasgow MT
747 PM MDT Wed May 20 2020

.DISCUSSION...
Evening update...
Adjusted POPs to follow the line that's approaching from the
south, and now beginning to cross the southern border of the CWA,
across the area this evening into the early overnight hours.

97

Previous discussion...
Just at this forecast issuance time, the Storm Prediction Center
has coordinated with us, and a severe weather watch has just been
issued for most of northeast Montana.

All ingredients for strong to severe thunderstorms are location
over the region. Moist SE surface wind. Upper-level flow from the
west and southwest. Low surface pressure axis through the area.
Unstable atmosphere.

Although some disagreement between models still exist regarding
timing and placement of the strongest storms, a general idea of
where the risk of severe thunderstorms is set across the area.

Storms will move from south to north. Multiple waves will spread
through the CWA. Best guess places the strongest storms with the
heaviest QPF 0.50 to 1.00 inch in a band from Prairie County, up
through Valley County.

This activity is expected to persist through the evening hours,
then begin to diminish away toward the north during the overnight
hours tonight and early morning hours tomorrow.

Precipitation chances for the remainder of the week drop off
significantly, but another system set up for more rain showers
across southern and eastern portions of the region through the
weekend.

&&

.AVIATION...
FLIGHT CONDITION: mostly VFR, but periods of MVFR or IFR with
thunderstorms this evening. After 9z, all TAF sites should be VFR
through Thursday afternoon.

WINDS: from the south 5-15 kts overnight, except stronger and
gusty near storms. On Thursday, winds should be from the southwest
10-20 kts.

SYNOPSIS: A line of thunderstorms will move northward through the
area this evening and out during the overnight hours. This line of
storms will bring strong winds and hail, along with frequent
lightning. The intensity of the storms should decrease after
about 5 or 6z. Another round of showers cannot be ruled out late
in the day on Thursday.

97

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

weather.gov/glasgow

In the hours before

Local storm report, May 20, 9:07 PM MDT, 26 minutes before
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GLASGOW MT
907 PM MDT WED MAY 20 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0825 PM     TSTM WND GST     2 WNW JORDAN            47.33N 106.95W
05/20/2020  M62 MPH          GARFIELD           MT   ASOS

            ASOS STATION KJDN JORDAN. TIME ESTIMATED.

&&

RUX
Local storm report, May 20, 9:21 PM MDT, 12 minutes before
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Local storm report, May 20, 9:25 PM MDT, 8 minutes before
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Local storm report, May 20, 9:27 PM MDT, 6 minutes before
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Local storm report, May 20, 9:28 PM MDT, 5 minutes before
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Local storm report, May 20, 9:30 PM MDT, 3 minutes before
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The office that day

Everything else NWS Glasgow, MT issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 20, 6:55 PM MDTSevere Thunderstorm WarningGGWPrairie30 min
May 20, 7:28 PM MDTSevere Thunderstorm WarningGGWDawson, Garfield, McCone, Prairie62 min
May 20, 7:35 PM MDTSevere Thunderstorm WarningGGWGarfield, Petroleum, Phillips55 min
May 20, 8:18 PM MDTSevere Thunderstorm WarningGGWGarfield, McCone, Prairie, Valley57 min
May 20, 8:36 PM MDTSevere Thunderstorm WarningGGWDawson, McCone, Richland, Roosevelt, Wibaux39 min
May 20, 8:44 PM MDTSevere Thunderstorm WarningGGWDawson, Garfield, McCone, Phillips, Richland, Roosevelt and 1 more76 min
May 20, 9:17 PM MDTTornado WarningGGWValley13 min
May 20, 9:35 PM MDTSevere Thunderstorm WarningGGWDaniels, Roosevelt, Sheridan55 min
May 20, 10:02 PM MDTAreal Flood AdvisoryGGWGarfield, Valley3 hr
May 20, 10:21 PM MDTSpecial Weather StatementGGWRoosevelt54 min
May 20, 10:33 PM MDTSpecial Weather StatementGGW57 min
May 20, 10:54 PM MDTSpecial Weather StatementGGWDaniels66 min
May 20, 11:09 PM MDTSpecial Weather StatementGGWPhillips, Valley81 min
May 21, 3:04 PM MDTSpecial Weather StatementGGWValley26 min
May 21, 3:36 PM MDTSpecial Weather StatementGGWValley39 min
May 21, 3:51 PM MDTSpecial Weather StatementGGWDaniels39 min

Nearby

Severe Thunderstorm Warnings in Montana, 2020Every severe thunderstorm warning in 2020

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.