Alert archive / Colorado / Tornado Warnings in 2017

Tornado Warning 18, NWS Denver/Boulder, CO

August 12, 2017Washington County, Colorado

NWS Denver/Boulder, CO issued this tornado warning at Aug 12, 2017, 5:30 PM MDT for Washington County, Colorado. It was in force for 30 min. 2 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: Aug 12, 2017, 5:30 PM MDT (23:30 UTC)
Expired: Aug 12, 2017, 6:00 PM MDT
In force: 30 min
Issued by: NWS Denver/Boulder, CO
Area: Storm-based polygon
Tornado: Observed
Hail: 1.25 in

County Washington County, CO

The radar

The Goodland radar (KGLD), 113 km from the middle of the area, began a volume at 23:32 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

Time	Report	Where	Remark
Aug 12, 5:40 PM MDT	HAIL 1	1 Sse Arickaree School, CO
Aug 12, 5:42 PM MDT	HAIL 1.5	3 S Arickaree School, CO

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

The watch it was issued in

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

Issued	Product	Office	Lasted
Aug 12, 2:59 PM MDT	Severe Thunderstorm Watch	SPC	7 hr

The nearest sounding before it

Denver, CO (KDEN), launched 12:00Z, 11.5 hours before the alert went out and 32 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 166 J/kg
Mixed-layer CIN: -274 J/kg
Mixed-layer LCL: 1194 m above ground
0-6 km bulk shear: 30 kt
0-1 km storm-relative helicity: 53 m²/s²
0-3 km storm-relative helicity: 46 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

913 
WFUS55 KBOU 122330
TORBOU
COC121-130000-
/O.NEW.KBOU.TO.W.0018.170812T2330Z-170813T0000Z/

BULLETIN - EAS ACTIVATION REQUESTED
Tornado Warning
National Weather Service Denver CO
530 PM MDT SAT AUG 12 2017

The National Weather Service in Denver Colorado has issued a

* Tornado Warning for...
  Southeastern Washington County in northeastern Colorado...

* Until 600 PM MDT

* At 530 PM MDT, a confirmed tornado was located near Arickaree
  School, or 29 miles north of Flagler, moving southeast at 25 mph.

  HAZARD...Tornado and half dollar size hail. 

  SOURCE...Weather spotters confirmed tornado. 

  IMPACT...Expect damage to mobile homes, roofs, and vehicles. 

* Locations impacted include...
  Arickaree School and Cope. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This Tornado Warning replaces the Severe Thunderstorm Warning issued
for the same area.

To repeat, a tornado is on the ground. TAKE COVER NOW! Move to a
basement or an interior room on the lowest floor of a sturdy
building. Avoid windows. If you are outdoors, in a mobile home, or in
a vehicle, move to the closest substantial shelter and protect
yourself from flying debris.

&&

LAT...LON 3957 10311 3981 10310 3982 10281 3967 10280
      3957 10281
TIME...MOT...LOC 2330Z 310DEG 22KT 3971 10298 

TORNADO...OBSERVED
HAIL...1.25IN

$$

RPK

2 follow-up statements

706 
WWUS55 KBOU 122346
SVSBOU

Severe Weather Statement
National Weather Service Denver CO
546 PM MDT SAT AUG 12 2017

COC121-130000-
/O.CON.KBOU.TO.W.0018.000000T0000Z-170813T0000Z/
Washington CO-
546 PM MDT SAT AUG 12 2017

...A TORNADO WARNING REMAINS IN EFFECT UNTIL 600 PM MDT FOR
SOUTHEASTERN WASHINGTON COUNTY...
    
At 546 PM MDT, a severe thunderstorm capable of producing a tornado
was located 7 miles south of Arickaree School, or 24 miles north of
Flagler, moving south at 15 mph.

HAZARD...TORNADO and half dollar size hail. 

SOURCE...Radar indicated rotation. 

IMPACT...Expect damage to mobile homes, roofs, and vehicles. 

Locations impacted include...
Arickaree School and Cope. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW! Move to a basement or an interior room on the lowest
floor of a sturdy building. Avoid windows. If you are outdoors, in a
mobile home, or in a vehicle, move to the closest substantial shelter
and protect yourself from flying debris.

&&

LAT...LON 3978 10310 3978 10281 3967 10280 3957 10281
      3957 10311
TIME...MOT...LOC 2346Z 359DEG 14KT 3964 10299 

TORNADO...RADAR INDICATED
HAIL...1.25IN

$$

RPK

134 
WWUS55 KBOU 122358
SVSBOU

Severe Weather Statement
National Weather Service Denver CO
558 PM MDT SAT AUG 12 2017

COC121-130008-
/O.EXP.KBOU.TO.W.0018.000000T0000Z-170813T0000Z/
Washington CO-
558 PM MDT SAT AUG 12 2017

...THE TORNADO WARNING FOR SOUTHEASTERN WASHINGTON COUNTY WILL EXPIRE
AT 600 PM MDT...
                
The storm which prompted the warning has weakened below severe
limits, and no longer appears capable of producing a tornado.
Therefore the warning will be allowed to expire.

A severe thunderstorm watch remains in effect until 1100 PM MDT for
northeastern Colorado.

LAT...LON 3978 10310 3978 10281 3967 10280 3957 10281
      3957 10311
TIME...MOT...LOC 2358Z 310DEG 22KT 3959 10292 

$$

RPK

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 11, 7:28 PM MDT	Special Weather Statement	BOU	Weld	62 min
Aug 11, 7:40 PM MDT	Severe Thunderstorm Warning	BOU	Weld	16 min
Aug 12, 2:41 PM MDT	Special Weather Statement	BOU	Weld	34 min
Aug 12, 3:06 PM MDT	Areal Flood Advisory	BOU	Weld	3 hr
Aug 12, 3:18 PM MDT	Special Weather Statement	BOU	Jefferson	27 min
Aug 12, 3:38 PM MDT	Areal Flood Advisory	BOU	Jefferson	97 min
Aug 12, 3:57 PM MDT	Special Weather Statement	BOU	Broomfield	33 min
Aug 12, 4:33 PM MDT	Severe Thunderstorm Warning	BOU	Washington	42 min
Aug 12, 4:54 PM MDT	Severe Thunderstorm Warning	BOU	Washington	51 min
Aug 12, 4:59 PM MDT	Severe Thunderstorm Warning	BOU	Adams	31 min
Aug 12, 5:04 PM MDT	Areal Flood Advisory	BOU	Adams, Arapahoe	116 min
Aug 12, 5:26 PM MDT	Special Weather Statement	BOU	Elbert	49 min
Aug 12, 5:35 PM MDT	Severe Thunderstorm Warning	BOU	Elbert, Lincoln	40 min
Aug 12, 5:38 PM MDT	Severe Thunderstorm Warning	BOU	Lincoln, Washington	52 min
Aug 12, 5:52 PM MDT	Areal Flood Advisory	BOU	Elbert, Lincoln, Washington	4 hr
Aug 12, 5:57 PM MDT	Severe Thunderstorm Warning	BOU	Lincoln	29 min

Nearby

Tornado Warnings in Colorado, 2017 Every tornado warning in 2017 Tornadoes in 2017

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.