Alert archive / Colorado / Arapahoe County

Weather alerts in Arapahoe County, Colorado, 2009

210 weather alerts in 2009, from the National Weather Service and the Storm Prediction Center. An alert counts here when it covered this county.

Arapahoe County and its neighbors

Each county as a circle sized by its count in 2009. Tap one for its archive.

Alerts: 210
Warnings: 80
Watches: 31
Advisories: 40
Busiest month: June61 alerts
Busiest day: August 10, 200912 alerts

Over time

By month

Warning verification

How often warnings here had a storm report inside them, and how much warning the reports had.

1 of 11 tornado warnings covering Arapahoe County in 2009 had a tornado report inside them; 1 of 3 tornado reports fell inside a warning, on average 9 minutes after it went out.

Arapahoe County, 2009

	Warnings	With a report	False alarm ratio	Reports	Inside a warning	Mean lead time
Tornado warnings	11	1	91%	3	33%	9 min
Severe thunderstorm warnings	41	20	51%	28	89%	16 min
Flash flood warnings	2	1	50%	1	100%	16 min

Each office's whole area, 2009

	Warnings	With a report	False alarm ratio	Reports	Inside a warning	Mean lead time
NWS Denver/Boulder, CO: tornado warnings	81	16	80%	45	44%	12 min
NWS Denver/Boulder, CO: severe thunderstorm warnings	279	128	54%	321	70%	17 min
NWS Denver/Boulder, CO: flash flood warnings	19	6	68%	13	62%	43 min

An office's figures cover every county it serves, including across state lines.

Verified by the Iowa Environmental Mesonet's Cow, which matches each storm-based warning with the local storm reports inside its polygon while it was in force, within 15 km of its edge: a tornado warning counts as verified on a tornado report, a severe thunderstorm warning on hail of 1 inch or more, a gust of 58 mph or more, or wind damage, a flash flood warning on a flash flood report. The false alarm ratio is the share of warnings with no such report; "inside a warning" is the probability of detection, the share of reports that fell inside one; lead time runs from the warning's issue to each report inside it, counting zero for a report that came first. A warning with no report is not proof nothing happened: reports come from spotters, the public and damage surveys, and are thin where few people live.

The alerts

Every alert, in the order issued. Times are local, Mountain Time. Each opens its own page with the text, the map, the radar and the sounding.

Issued	Product	Office	Lasted
Jan 12, 12:58 AM MST	Winter Weather Advisory	BOU	15 hr
Jan 12, 8:49 AM MST	Winter Weather Advisory	BOU	2 hr
Jan 19, 10:21 AM MST	Red Flag Warning	BOU	7 hr
Jan 22, 5:44 AM MST	Red Flag Warning	BOU	12 hr
Feb 5, 2:08 PM MST	Red Flag Warning	BOU	29 hr
Feb 17, 12:16 PM MST	Red Flag Warning	BOU	6 hr
Feb 20, 4:35 AM MST	Red Flag Warning	BOU	12 hr
Feb 25, 5:42 AM MST	Red Flag Warning	BOU	12 hr
Mar 2, 3:05 PM MST	Red Flag Warning	BOU	26 hr
Mar 3, 3:01 PM MST	Fire Weather Watch	BOU	24 hr
Mar 4, 3:34 AM MST	Red Flag Warning	BOU	17 hr
Mar 4, 2:42 PM MST	Red Flag Warning	BOU	27 hr
Mar 6, 3:50 AM MST	Red Flag Warning	BOU	14 hr
Mar 14, 3:13 AM MDT	Fire Weather Watch	BOU	25 hr
Mar 15, 4:01 AM MDT	Red Flag Warning	BOU	16 hr
Mar 21, 2:47 PM MDT	Red Flag Warning	BOU	30 hr
Mar 23, 1:38 PM MDT	High Wind Warning	BOU	28 hr
Mar 24, 3:59 PM MDT	Winter Storm Watch	BOU	20 hr
Mar 25, 11:47 AM MDT	Winter Storm Warning	BOU	29 hr
Mar 26, 2:57 AM MDT	Blizzard Warning	BOU	33 hr
Mar 26, 6:55 AM MDT	Mesoscale Discussion	SPC	3 hr
Mar 26, 10:35 AM MDT	Mesoscale Discussion	SPC	5 hr
Mar 26, 4:46 PM MDT	Winter Weather Advisory	BOU	13 hr
Mar 31, 4:27 AM MDT	Winter Weather Advisory	BOU	44 hr
Apr 2, 4:20 AM MDT	Winter Storm Watch	BOU	32 hr
Apr 3, 4:22 AM MDT	Winter Storm Warning	BOU	32 hr
Apr 3, 11:50 AM MDT	Blizzard Warning	BOU	42 hr
Apr 15, 4:18 AM MDT	Winter Storm Watch	BOU	31 hr
Apr 16, 4:41 AM MDT	Winter Storm Warning	BOU	61 hr
Apr 16, 1:10 PM MDT	Mesoscale Discussion	SPC	95 min
Apr 26, 10:07 PM MDT	Winter Weather Advisory	BOU	11 hr
Apr 28, 4:45 PM MDT	Mesoscale Discussion	SPC	3 hr
May 22, 3:40 PM MDT	Areal Flood Advisory	BOU	94 min
May 24, 3:31 PM MDT	Areal Flood Advisory	BOU	119 min
May 24, 4:17 PM MDT	Special Weather Statement	BOU	43 min
May 24, 5:27 PM MDT	Areal Flood Advisory	BOU	93 min
May 25, 12:13 PM MDT	Areal Flood Advisory	BOU	77 min
May 30, 4:18 PM MDT	Mesoscale Discussion	SPC	87 min
May 30, 4:52 PM MDT	Areal Flood Advisory	BOU	83 min
Jun 2, 11:18 AM MDT	Areal Flood Advisory	BOU	8 hr
Jun 4, 1:27 PM MDT	Severe Thunderstorm Watch	SPC	8 hr
Jun 4, 5:16 PM MDT	Mesoscale Discussion	SPC	89 min
Jun 5, 2:18 PM MDT	Mesoscale Discussion	SPC	87 min
Jun 7, 10:44 AM MDT	Mesoscale Discussion	SPC	61 min
Jun 7, 11:02 AM MDT	Severe Thunderstorm Watch	SPC	6 hr
Jun 7, 1:28 PM MDT	Severe Thunderstorm Warning	BOU	62 min
Jun 7, 1:40 PM MDT	Tornado Warning	BOU	35 min
Jun 7, 1:53 PM MDT	Tornado Warning	BOU	37 min
Jun 7, 2:24 PM MDT	Tornado Warning	BOU	51 min
Jun 7, 2:30 PM MDT	Mesoscale Discussion	SPC	60 min
Jun 7, 3:12 PM MDT	Tornado Warning	BOU	33 min
Jun 8, 2:03 PM MDT	Mesoscale Discussion	SPC	87 min
Jun 10, 3:02 PM MDT	Areal Flood Advisory	BOU	88 min
Jun 10, 6:47 PM MDT	Areal Flood Advisory	BOU	88 min
Jun 11, 11:34 AM MDT	Mesoscale Discussion	SPC	86 min
Jun 11, 1:12 PM MDT	Tornado Warning	BOU	48 min
Jun 11, 1:41 PM MDT	Tornado Warning	BOU	49 min
Jun 11, 2:00 PM MDT	Tornado Watch	SPC	7 hr
Jun 11, 2:25 PM MDT	Areal Flood Advisory	BOU	95 min
Jun 11, 2:27 PM MDT	Tornado Warning	BOU	48 min
Jun 11, 5:48 PM MDT	Mesoscale Discussion	SPC	57 min
Jun 11, 11:04 PM MDT	Severe Thunderstorm Warning	BOU	56 min
Jun 11, 11:35 PM MDT	Areal Flood Advisory	BOU	2 hr
Jun 11, 11:59 PM MDT	Severe Thunderstorm Warning	BOU	61 min
Jun 12, 4:04 PM MDT	Severe Thunderstorm Watch	SPC	6 hr
Jun 12, 6:56 PM MDT	Mesoscale Discussion	SPC	64 min
Jun 13, 12:41 PM MDT	Mesoscale Discussion	SPC	64 min
Jun 13, 1:56 PM MDT	Tornado Watch	SPC	9 hr
Jun 13, 6:42 PM MDT	Mesoscale Discussion	SPC	63 min
Jun 14, 1:06 PM MDT	Mesoscale Discussion	SPC	54 min
Jun 14, 1:50 PM MDT	Tornado Watch	SPC	7 hr
Jun 14, 3:13 PM MDT	Tornado Warning	BOU	32 min
Jun 14, 3:45 PM MDT	Severe Thunderstorm Warning	BOU	45 min
Jun 14, 4:26 PM MDT	Severe Thunderstorm Warning	BOU	49 min
Jun 15, 2:00 PM MDT	Tornado Warning	BOU	30 min
Jun 15, 2:15 PM MDT	Mesoscale Discussion	SPC	30 min
Jun 15, 2:34 PM MDT	Tornado Watch	SPC	8 hr
Jun 17, 1:29 PM MDT	Mesoscale Discussion	SPC	61 min
Jun 17, 2:30 PM MDT	Tornado Watch	SPC	8 hr
Jun 17, 4:43 PM MDT	Mesoscale Discussion	SPC	92 min
Jun 23, 2:51 PM MDT	Severe Thunderstorm Watch	SPC	6 hr
Jun 23, 4:02 PM MDT	Severe Thunderstorm Warning	BOU	58 min
Jun 23, 4:14 PM MDT	Areal Flood Advisory	BOU	91 min
Jun 23, 4:59 PM MDT	Severe Thunderstorm Warning	BOU	50 min
Jun 23, 6:13 PM MDT	Mesoscale Discussion	SPC	62 min
Jun 23, 7:17 PM MDT	Areal Flood Advisory	BOU	12 hr
Jun 25, 1:06 PM MDT	Mesoscale Discussion	SPC	54 min
Jun 25, 1:30 PM MDT	Severe Thunderstorm Watch	SPC	7 hr
Jun 25, 2:05 PM MDT	Severe Thunderstorm Warning	BOU	40 min
Jun 25, 2:14 PM MDT	Areal Flood Advisory	BOU	53 min
Jun 25, 2:48 PM MDT	Flash Flood Warning	BOU	2 hr
Jun 25, 4:22 PM MDT	Mesoscale Discussion	SPC	53 min
Jun 25, 5:50 PM MDT	Mesoscale Discussion	SPC	55 min
Jun 26, 2:23 PM MDT	Mesoscale Discussion	SPC	67 min
Jun 26, 2:38 PM MDT	Special Weather Statement	BOU	37 min
Jun 26, 2:38 PM MDT	Severe Thunderstorm Watch	SPC	5 hr
Jun 26, 2:57 PM MDT	Tornado Warning	BOU	22 min
Jun 26, 2:58 PM MDT	Severe Thunderstorm Warning	BOU	47 min
Jun 26, 3:26 PM MDT	Severe Thunderstorm Warning	BOU	34 min
Jun 28, 2:27 PM MDT	Mesoscale Discussion	SPC	63 min
Jul 2, 6:29 PM MDT	Mesoscale Discussion	SPC	61 min
Jul 3, 5:18 PM MDT	Areal Flood Advisory	BOU	57 min
Jul 3, 5:25 PM MDT	Mesoscale Discussion	SPC	65 min
Jul 3, 5:29 PM MDT	Severe Thunderstorm Warning	BOU	46 min
Jul 3, 6:16 PM MDT	Severe Thunderstorm Warning	BOU	44 min
Jul 4, 1:52 PM MDT	Mesoscale Discussion	SPC	113 min
Jul 5, 1:44 PM MDT	Severe Thunderstorm Watch	SPC	6 hr
Jul 5, 4:55 PM MDT	Severe Thunderstorm Warning	BOU	65 min
Jul 5, 5:17 PM MDT	Severe Thunderstorm Warning	BOU	58 min
Jul 5, 6:15 PM MDT	Mesoscale Discussion	SPC	60 min
Jul 6, 12:22 PM MDT	Mesoscale Discussion	SPC	113 min
Jul 6, 1:40 PM MDT	Mesoscale Discussion	SPC	95 min
Jul 6, 2:07 PM MDT	Severe Thunderstorm Watch	SPC	6 hr
Jul 6, 5:21 PM MDT	Severe Thunderstorm Warning	BOU	34 min
Jul 6, 5:33 PM MDT	Areal Flood Advisory	BOU	87 min
Jul 6, 5:35 PM MDT	Mesoscale Discussion	SPC	55 min
Jul 6, 6:13 PM MDT	Severe Thunderstorm Warning	BOU	41 min
Jul 10, 8:57 PM MDT	Severe Thunderstorm Warning	BOU	31 min
Jul 10, 9:00 PM MDT	Areal Flood Advisory	BOU	90 min
Jul 10, 9:31 PM MDT	Special Weather Statement	BOU	29 min
Jul 11, 3:35 PM MDT	Mesoscale Discussion	SPC	55 min
Jul 11, 3:56 PM MDT	Severe Thunderstorm Watch	SPC	9 hr
Jul 12, 2:05 PM MDT	Mesoscale Discussion	SPC	85 min
Jul 13, 12:07 PM MDT	Mesoscale Discussion	SPC	83 min
Jul 13, 1:45 PM MDT	Severe Thunderstorm Watch	SPC	6 hr
Jul 13, 2:17 PM MDT	Severe Thunderstorm Warning	BOU	43 min
Jul 13, 3:14 PM MDT	Severe Thunderstorm Warning	BOU	41 min
Jul 15, 5:29 PM MDT	Special Weather Statement	BOU	46 min
Jul 17, 12:06 PM MDT	Mesoscale Discussion	SPC	84 min
Jul 17, 12:59 PM MDT	Tornado Watch	SPC	6 hr
Jul 20, 10:22 PM MDT	Tornado Warning	BOU	25 min
Jul 20, 10:24 PM MDT	Severe Thunderstorm Warning	BOU	51 min
Jul 20, 10:39 PM MDT	Areal Flood Advisory	BOU	81 min
Jul 20, 10:43 PM MDT	Severe Thunderstorm Warning	BOU	47 min
Jul 20, 10:56 PM MDT	Mesoscale Discussion	SPC	94 min
Jul 20, 11:18 PM MDT	Areal Flood Advisory	BOU	117 min
Jul 21, 12:02 AM MDT	Areal Flood Advisory	BOU	88 min
Jul 21, 2:44 PM MDT	Mesoscale Discussion	SPC	61 min
Jul 23, 1:25 PM MDT	Mesoscale Discussion	SPC	65 min
Jul 25, 9:15 PM MDT	Areal Flood Advisory	BOU	58 min
Jul 27, 4:08 PM MDT	Severe Thunderstorm Warning	BOU	45 min
Aug 3, 3:08 PM MDT	Severe Thunderstorm Warning	BOU	52 min
Aug 3, 3:20 PM MDT	Severe Thunderstorm Warning	BOU	31 min
Aug 3, 3:43 PM MDT	Severe Thunderstorm Warning	BOU	62 min
Aug 3, 4:19 PM MDT	Severe Thunderstorm Warning	BOU	56 min
Aug 5, 3:51 PM MDT	Mesoscale Discussion	SPC	84 min
Aug 5, 4:15 PM MDT	Severe Thunderstorm Watch	SPC	7 hr
Aug 5, 7:26 PM MDT	Mesoscale Discussion	SPC	64 min
Aug 5, 10:09 PM MDT	Mesoscale Discussion	SPC	66 min
Aug 6, 3:37 PM MDT	Severe Thunderstorm Warning	BOU	38 min
Aug 6, 3:48 PM MDT	Areal Flood Advisory	BOU	87 min
Aug 6, 5:28 PM MDT	Mesoscale Discussion	SPC	92 min
Aug 8, 3:34 PM MDT	Mesoscale Discussion	SPC	86 min
Aug 9, 8:56 PM MDT	Severe Thunderstorm Warning	BOU	31 min
Aug 9, 10:48 PM MDT	Special Weather Statement	BOU	27 min
Aug 9, 10:57 PM MDT	Severe Thunderstorm Warning	BOU	33 min
Aug 10, 12:47 AM MDT	Severe Thunderstorm Warning	BOU	28 min
Aug 10, 1:17 AM MDT	Severe Thunderstorm Warning	BOU	43 min
Aug 10, 1:29 AM MDT	Mesoscale Discussion	SPC	61 min
Aug 10, 1:49 AM MDT	Severe Thunderstorm Watch	SPC	6 hr
Aug 10, 1:58 AM MDT	Severe Thunderstorm Warning	BOU	32 min
Aug 10, 1:07 PM MDT	Mesoscale Discussion	SPC	83 min
Aug 10, 4:24 PM MDT	Special Weather Statement	BOU	36 min
Aug 10, 4:38 PM MDT	Mesoscale Discussion	SPC	67 min
Aug 10, 4:43 PM MDT	Severe Thunderstorm Watch	SPC	9 hr
Aug 15, 1:07 PM MDT	Mesoscale Discussion	SPC	53 min
Aug 16, 6:12 PM MDT	Mesoscale Discussion	SPC	93 min
Aug 17, 3:51 PM MDT	Mesoscale Discussion	SPC	84 min
Aug 17, 4:36 PM MDT	Severe Thunderstorm Warning	BOU	39 min
Aug 17, 5:15 PM MDT	Severe Thunderstorm Warning	BOU	33 min
Aug 17, 6:03 PM MDT	Severe Thunderstorm Warning	BOU	27 min
Aug 17, 6:27 PM MDT	Severe Thunderstorm Warning	BOU	48 min
Aug 17, 6:46 PM MDT	Severe Thunderstorm Warning	BOU	29 min
Aug 17, 7:45 PM MDT	Severe Thunderstorm Warning	BOU	45 min
Aug 18, 11:41 AM MDT	Mesoscale Discussion	SPC	2 hr
Aug 18, 12:29 PM MDT	Severe Thunderstorm Watch	SPC	9 hr
Aug 18, 1:10 PM MDT	Severe Thunderstorm Warning	BOU	22 min
Aug 25, 2:31 PM MDT	Mesoscale Discussion	SPC	89 min
Aug 25, 3:07 PM MDT	Areal Flood Advisory	BOU	83 min
Aug 25, 5:18 PM MDT	Areal Flood Advisory	BOU	117 min
Aug 25, 5:19 PM MDT	Areal Flood Advisory	BOU	116 min
Aug 29, 6:37 PM MDT	Severe Thunderstorm Warning	BOU	53 min
Aug 31, 5:39 PM MDT	Severe Thunderstorm Warning	BOU	33 min
Sep 5, 4:48 PM MDT	Flash Flood Warning	BOU	104 min
Sep 21, 9:21 PM MDT	Freeze Warning	BOU	7 hr
Sep 22, 4:31 AM MDT	Winter Storm Watch	BOU	9 hr
Sep 22, 1:06 PM MDT	Winter Weather Advisory	BOU	16 hr
Sep 29, 3:27 PM MDT	Fire Weather Watch	BOU	14 hr
Sep 30, 5:00 AM MDT	Red Flag Warning	BOU	15 hr
Sep 30, 2:21 PM MDT	Freeze Watch	BOU	13 hr
Sep 30, 2:21 PM MDT	High Wind Warning	BOU	13 hr
Oct 1, 3:05 AM MDT	Freeze Warning	BOU	29 hr
Oct 2, 3:38 PM MDT	Freeze Warning	BOU	16 hr
Oct 14, 4:12 AM MDT	Dense Fog Advisory	BOU	5 hr
Oct 14, 9:07 AM MDT	Dense Fog Advisory	BOU	113 min
Oct 20, 3:11 PM MDT	Winter Weather Advisory	BOU	36 hr
Oct 26, 3:15 PM MDT	Winter Storm Watch	BOU	12 hr
Oct 27, 3:26 AM MDT	Winter Storm Watch	BOU	25 hr
Oct 27, 3:26 AM MDT	Winter Storm Warning	BOU	69 hr
Oct 28, 9:56 PM MDT	Mesoscale Discussion	SPC	4 hr
Oct 29, 12:59 PM MDT	Blizzard Warning	BOU	16 hr
Oct 30, 1:02 AM MDT	Winter Weather Advisory	BOU	4 hr
Nov 13, 5:06 AM MST	Winter Storm Watch	BOU	34 hr
Nov 14, 10:57 AM MST	Winter Storm Warning	BOU	26 hr
Dec 5, 10:22 AM MST	Winter Weather Advisory	BOU	24 hr
Dec 7, 5:21 AM MST	Winter Weather Advisory	BOU	47 hr
Dec 8, 12:53 PM MST	Wind Chill Advisory	BOU	9 hr
Dec 9, 4:31 AM MST	Wind Chill Advisory	BOU	4 hr
Dec 21, 7:53 PM MST	Winter Weather Advisory	BOU	61 hr
Dec 24, 3:52 PM MST	Winter Weather Advisory	BOU	49 hr

By product

Every kind of product issued here, grouped by hazard. Each opens the same place narrowed to that product.

Product	Alerts
Severe storms
Severe Thunderstorm Warning	41
Tornado Warning	11
Severe Thunderstorm Watch	14
Tornado Watch	6
Mesoscale Discussion	53
Special Weather Statement	6
Flooding
Flash Flood Warning	2
Areal Flood Advisory	24
Winter
Blizzard Warning	3
Winter Storm Warning	5
Winter Storm Watch	7
Winter Weather Advisory	12
Cold
Freeze Warning	3
Freeze Watch	1
Wind Chill Advisory	2
Wind and dust
High Wind Warning	2
Fire
Red Flag Warning	13
Fire Weather Watch	3
Fog and smoke
Dense Fog Advisory	2

The busiest days

Days with the most alerts issued, by UTC date.

Nearby

Alerts in force now Tornadoes on record Forecast The radar archive 2008 2010

Sources

National Weather Service watches, warnings, advisories and statements from the Iowa Environmental Mesonet's VTEC archive, which reconstructs tornado, severe thunderstorm, flash flood and marine warnings back to 1986 from the NWS text archive. Storm Prediction Center watches and mesoscale discussions from SPC's archive through the Mesonet. County centers from the US Census Bureau. Warning verification from the Mesonet's Cow. Rebuilt daily.