Alert archive / Colorado / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 31, NWS Denver/Boulder, CO

May 20, 2021Logan County, Weld County, Colorado

NWS Denver/Boulder, CO issued this severe thunderstorm warning at May 20, 2021, 7:27 PM MDT for Logan County, Weld County, Colorado. It was in force for 48 min. 7 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued
May 20, 2021, 7:27 PM MDT (01:27 UTC)
Expired
May 20, 2021, 8:15 PM MDT
In force
48 min
Issued by
NWS Denver/Boulder, CO
Area
Storm-based polygon
Hail
1.5 in
Wind
60.0 mph

Counties Logan County, CO, Weld County, CO

The radar

The Cheyenne radar (KCYS), 113 km from the middle of the area, began a volume at 01:29 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.

What was reported inside it

TimeReportWhereRemark
May 20, 7:27 PM MDTHAIL 23 Nnw Stoneham, CO
May 20, 7:29 PM MDTHAIL 0.755 Nnw Stoneham, CO
May 20, 7:29 PM MDTHAIL 3Stoneham, CO
May 20, 7:37 PM MDTHAIL 3.259 N Stoneham, CO
May 20, 7:41 PM MDTHAIL 2.753 Nnw Stoneham, CO
May 20, 7:41 PM MDTHAIL 2.753 Nnw Stoneham, COCORRECTS PREVIOUS HAIL REPORT FROM 3 NNW STONEHAM.
May 20, 7:41 PM MDTHAIL 2.753 Nnw Stoneham, CO

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Denver, CO (KDNR), launched 00:00Z, 1.5 hours before the alert went out and 98 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, Denver, CO at 00:00Z on 2021-05-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 66 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Denver, CO at 00:00Z on 2021-05-21The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 41 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
66 J/kg
Mixed-layer CIN
-60 J/kg
Mixed-layer LCL
3320 m above ground
0-6 km bulk shear
37 kt
0-1 km storm-relative helicity
41 m²/s²
0-3 km storm-relative helicity
120 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

481 
WUUS55 KBOU 210127
SVRBOU
COC075-123-210215-
/O.NEW.KBOU.SV.W.0031.210521T0127Z-210521T0215Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Denver CO
727 PM MDT Thu May 20 2021

The National Weather Service in Denver Colorado has issued a

* Severe Thunderstorm Warning for...
  East central Weld County in northeastern Colorado...
  West central Logan County in northeastern Colorado...

* Until 815 PM MDT.

* At 726 PM MDT, a severe thunderstorm was located 5 miles north of
  Stoneham, or 23 miles west of Sterling, moving northeast at 20 mph.

  HAZARD...Ping pong ball size hail and 60 mph wind gusts.

  SOURCE...Public.

  IMPACT...Expect damage to roofs, siding, and trees. People and 
           animals outdoors will be injured. Expect hail damage to 
           roofs, siding, windows, and vehicles.

* Locations impacted include...
  Stoneham and Westplains. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 4058 10368 4065 10378 4098 10357 4074 10330
TIME...MOT...LOC 0126Z 220DEG 19KT 4069 10364 

HAIL...1.50IN
WIND...60MPH
 
$$

DIRENZO
2 follow-up statements
392 
WWUS55 KBOU 210149
SVSBOU

Severe Weather Statement
National Weather Service Denver CO
749 PM MDT Thu May 20 2021

COC075-123-210215-
/O.CON.KBOU.SV.W.0031.000000T0000Z-210521T0215Z/
Weld CO-Logan CO-
749 PM MDT Thu May 20 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 815 PM MDT
FOR EASTERN WELD AND WEST CENTRAL LOGAN COUNTIES...

At 748 PM MDT, a severe thunderstorm was located 6 miles south of
Westplains, or 21 miles northwest of Sterling, moving northeast at 20
mph.

This is a very dangerous storm.

HAZARD...Baseball size hail and 60 mph wind gusts.

SOURCE...Trained weather spotters.

IMPACT...People and animals outdoors will be severely injured. 
         Expect shattered windows, extensive damage to roofs, 
         siding, and vehicles.

Locations impacted include...
Westplains.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm is producing large hail. SEEK SHELTER NOW inside a sturdy
structure and stay away from windows.

&&

LAT...LON 4067 10362 4076 10371 4098 10357 4074 10330
TIME...MOT...LOC 0148Z 220DEG 19KT 4078 10354 

HAIL...2.75IN
WIND...60MPH
 
$$

DIRENZO
965 
WWUS55 KBOU 210204
SVSBOU

Severe Weather Statement
National Weather Service Denver CO
804 PM MDT Thu May 20 2021

COC123-210213-
/O.CAN.KBOU.SV.W.0031.000000T0000Z-210521T0215Z/
Weld CO-
804 PM MDT Thu May 20 2021

...THE SEVERE THUNDERSTORM WARNING FOR EASTERN WELD COUNTY IS
CANCELLED...
    
The severe thunderstorm which prompted the warning has moved out of 
the warned area. Therefore, the warning has been cancelled.

LAT...LON 4077 10354 4079 10357 4088 10357 4096 10355
      4078 10335
TIME...MOT...LOC 0203Z 219DEG 20KT 4085 10350 

$$

COC075-210215-
/O.CON.KBOU.SV.W.0031.000000T0000Z-210521T0215Z/
Logan CO-
804 PM MDT Thu May 20 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 815 PM MDT
FOR WEST CENTRAL LOGAN COUNTY...

At 803 PM MDT, a severe thunderstorm was located over Westplains, or
22 miles northwest of Sterling, moving northeast at 25 mph.

This is a very dangerous storm.

HAZARD...Baseball size hail and 60 mph wind gusts.

SOURCE...Trained weather spotters.

IMPACT...People and animals outdoors will be severely injured. 
         Expect shattered windows, extensive damage to roofs, 
         siding, and vehicles.

Locations impacted include...
Westplains.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm is producing large hail. SEEK SHELTER NOW inside a sturdy
structure and stay away from windows.

&&

LAT...LON 4077 10354 4079 10357 4088 10357 4096 10355
      4078 10335
TIME...MOT...LOC 0203Z 219DEG 20KT 4085 10350 

HAIL...2.75IN
WIND...60MPH
 
$$

DIRENZO

The office that day

Everything else NWS Denver/Boulder, CO issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 20, 7:14 PM MDTSpecial Weather StatementBOULogan31 min
May 20, 8:15 PM MDTSevere Thunderstorm WarningBOULogan30 min
May 21, 3:51 PM MDTSevere Thunderstorm WarningBOUMorgan, Washington24 min
May 21, 5:30 PM MDTSpecial Weather StatementBOULincoln30 min

Nearby

Severe Thunderstorm Warnings in Colorado, 2021Every severe thunderstorm warning 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.