Alert archive / Pennsylvania / Chester County

Weather alerts in Chester County, Pennsylvania, 2011

251 weather alerts in 2011, from the National Weather Service and the Storm Prediction Center. An alert counts here when it covered this county.

Chester County and its neighbors

Each county as a circle sized by its count in 2011. Tap one for its archive.

Alerts
251
Warnings
88
Watches
17
Advisories
40
Busiest month
August71 alerts
Busiest day
April 28, 201113 alerts

Over time

By month

Warning verification

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

0 of 2 tornado warnings covering Chester County in 2011 had a tornado report inside them.

Chester County, 2011

WarningsWith a reportFalse alarm ratioReportsInside a warningMean lead time
Tornado warnings20100%0
Severe thunderstorm warnings322619%1385%26 min
Flash flood warnings110100%0

Each office's whole area, 2011

WarningsWith a reportFalse alarm ratioReportsInside a warningMean lead time
NWS Philadelphia/Mount Holly: tornado warnings29293%729%17 min
NWS Philadelphia/Mount Holly: severe thunderstorm warnings30716447%36186%25 min
NWS Philadelphia/Mount Holly: flash flood warnings681282%2167%70 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, Eastern Time. Each opens its own page with the text, the map, the radar and the sounding.

IssuedProductOfficeLasted
Jan 18, 12:29 AM ESTMesoscale DiscussionSPC6 hr
Jan 21, 1:24 PM ESTSpecial Weather StatementPHI36 min
Jan 26, 2:19 PM ESTMesoscale DiscussionSPC6 hr
Feb 1, 8:39 PM ESTMesoscale DiscussionSPC6 hr
Feb 25, 11:36 AM ESTMesoscale DiscussionSPC84 min
Feb 25, 12:11 PM ESTSpecial Weather StatementPHI64 min
Feb 28, 9:23 AM ESTSpecial Weather StatementPHI112 min
Mar 6, 3:14 PM ESTSpecial Weather StatementPHI61 min
Mar 6, 5:33 PM ESTAreal Flood AdvisoryPHI4 hr
Mar 6, 9:30 PM ESTAreal Flood AdvisoryPHI7 hr
Mar 6, 10:11 PM ESTAreal Flood WarningPHI9 hr
Mar 10, 7:28 AM ESTAreal Flood AdvisoryPHI6 hr
Mar 10, 1:17 PM ESTAreal Flood AdvisoryPHI5 hr
Mar 10, 4:36 PM ESTAreal Flood WarningPHI37 hr
Mar 10, 4:55 PM ESTRiver Flood WarningPHI17 hr
Mar 10, 8:02 PM ESTRiver Flood WarningPHI22 hr
Mar 10, 9:31 PM ESTRiver Flood WarningPHI12 hr
Mar 21, 6:12 AM EDTSpecial Weather StatementPHI63 min
Mar 23, 6:53 PM EDTSpecial Weather StatementPHI112 min
Mar 23, 8:30 PM EDTSpecial Weather StatementPHI2 hr
Apr 5, 5:01 AM EDTSevere Thunderstorm WarningPHI74 min
Apr 5, 5:03 AM EDTMesoscale DiscussionSPC27 min
Apr 5, 5:07 AM EDTSevere Thunderstorm WatchSPC2 hr
Apr 5, 5:23 AM EDTSevere Thunderstorm WarningPHI67 min
Apr 5, 8:55 AM EDTSpecial Weather StatementPHI65 min
Apr 5, 9:37 AM EDTSpecial Weather StatementPHI53 min
Apr 11, 8:04 PM EDTSpecial Weather StatementPHI56 min
Apr 16, 4:29 PM EDTMesoscale DiscussionSPC31 min
Apr 16, 4:41 PM EDTTornado WatchSPC6 hr
Apr 16, 6:22 PM EDTAreal Flood WarningPHI12 hr
Apr 16, 6:38 PM EDTMesoscale DiscussionSPC97 min
Apr 16, 9:11 PM EDTSevere Thunderstorm WarningPHI64 min
Apr 16, 9:18 PM EDTRiver Flood WarningPHI11 hr
Apr 16, 9:58 PM EDTMesoscale DiscussionSPC62 min
Apr 17, 3:56 AM EDTAreal Flood WarningPHI6 hr
Apr 17, 6:07 AM EDTAreal Flood WarningPHI3 hr
Apr 17, 6:37 AM EDTRiver Flood WarningPHI7 hr
Apr 23, 7:43 AM EDTSpecial Weather StatementPHI2 hr
Apr 24, 2:12 PM EDTMesoscale DiscussionSPC93 min
Apr 24, 3:40 PM EDTSevere Thunderstorm WatchSPC5 hr
Apr 24, 6:10 PM EDTMesoscale DiscussionSPC65 min
Apr 27, 3:55 PM EDTMesoscale DiscussionSPC65 min
Apr 27, 6:50 PM EDTMesoscale DiscussionSPC55 min
Apr 27, 8:15 PM EDTSevere Thunderstorm WatchSPC8 hr
Apr 28, 3:32 AM EDTMesoscale DiscussionSPC28 min
Apr 28, 4:05 AM EDTSevere Thunderstorm WatchSPC6 hr
Apr 28, 6:12 AM EDTSpecial Weather StatementPHI63 min
Apr 28, 6:21 AM EDTMesoscale DiscussionSPC54 min
Apr 28, 6:23 AM EDTSpecial Weather StatementPHI52 min
Apr 28, 6:56 AM EDTSevere Thunderstorm WarningPHI34 min
Apr 28, 9:45 AM EDTSevere Thunderstorm WatchSPC6 hr
Apr 28, 10:00 AM EDTSevere Thunderstorm WarningPHI60 min
Apr 28, 10:48 AM EDTAreal Flood AdvisoryPHI3 hr
Apr 28, 10:57 AM EDTSevere Thunderstorm WarningPHI63 min
Apr 28, 11:49 AM EDTMesoscale DiscussionSPC56 min
Apr 28, 12:11 PM EDTSevere Thunderstorm WarningPHI31 min
May 3, 9:43 PM EDTSpecial Weather StatementPHI47 min
May 7, 5:20 PM EDTSpecial Weather StatementPHI85 min
May 14, 11:46 PM EDTSpecial Weather StatementPHI89 min
May 15, 9:17 PM EDTSpecial Weather StatementPHI58 min
May 15, 10:16 PM EDTAreal Flood AdvisoryPHI3 hr
May 16, 3:04 PM EDTSpecial Weather StatementPHI56 min
May 16, 3:19 PM EDTAreal Flood AdvisoryPHI3 hr
May 18, 3:08 PM EDTMesoscale DiscussionSPC67 min
May 19, 12:20 PM EDTSevere Thunderstorm WatchSPC8 hr
May 19, 2:17 PM EDTMesoscale DiscussionSPC58 min
May 19, 3:01 PM EDTAreal Flood AdvisoryPHI3 hr
May 19, 3:15 PM EDTSpecial Weather StatementPHI60 min
May 19, 5:02 PM EDTMesoscale DiscussionSPC58 min
May 23, 4:40 PM EDTMesoscale DiscussionSPC95 min
May 23, 6:21 PM EDTSpecial Weather StatementPHI54 min
May 27, 6:14 PM EDTMesoscale DiscussionSPC2 hr
Jun 1, 12:58 PM EDTTornado WatchSPC7 hr
Jun 1, 2:42 PM EDTSevere Thunderstorm WarningPHI52 min
Jun 1, 4:55 PM EDTSevere Thunderstorm WarningPHI26 min
Jun 9, 1:45 PM EDTMesoscale DiscussionSPC90 min
Jun 9, 2:34 PM EDTSevere Thunderstorm WatchSPC7 hr
Jun 9, 6:24 PM EDTSevere Thunderstorm WarningPHI66 min
Jun 9, 6:44 PM EDTSevere Thunderstorm WarningPHI61 min
Jun 9, 7:17 PM EDTMesoscale DiscussionSPC58 min
Jun 9, 7:27 PM EDTSevere Thunderstorm WarningPHI48 min
Jun 9, 7:42 PM EDTSevere Thunderstorm WarningPHI33 min
Jun 10, 5:28 PM EDTMesoscale DiscussionSPC92 min
Jun 11, 6:17 AM EDTSpecial Weather StatementPHI58 min
Jun 11, 9:06 PM EDTSpecial Weather StatementPHI54 min
Jun 11, 9:22 PM EDTAreal Flood AdvisoryPHI3 hr
Jun 12, 12:39 AM EDTSpecial Weather StatementPHI66 min
Jun 12, 1:48 PM EDTSevere Thunderstorm WatchSPC6 hr
Jun 22, 2:15 AM EDTSpecial Weather StatementPHI60 min
Jun 22, 3:05 AM EDTAreal Flood AdvisoryPHI115 min
Jun 22, 2:03 PM EDTMesoscale DiscussionSPC117 min
Jun 23, 10:04 AM EDTMesoscale DiscussionSPC116 min
Jun 24, 11:42 AM EDTMesoscale DiscussionSPC3 hr
Jun 24, 12:46 PM EDTSevere Thunderstorm WatchSPC7 hr
Jun 24, 4:13 PM EDTMesoscale DiscussionSPC92 min
Jul 7, 4:35 PM EDTSevere Thunderstorm WarningPHI55 min
Jul 7, 5:12 PM EDTSevere Thunderstorm WarningPHI63 min
Jul 8, 11:44 AM EDTMesoscale DiscussionSPC61 min
Jul 8, 1:51 PM EDTSevere Thunderstorm WatchSPC7 hr
Jul 8, 2:25 PM EDTAreal Flood AdvisoryPHI7 hr
Jul 8, 2:56 PM EDTAreal Flood AdvisoryPHI3 hr
Jul 8, 4:29 PM EDTAreal Flood AdvisoryPHI4 hr
Jul 8, 5:52 PM EDTMesoscale DiscussionSPC83 min
Jul 11, 9:49 PM EDTSpecial Weather StatementPHI56 min
Jul 19, 8:07 PM EDTSevere Thunderstorm WarningPHI53 min
Jul 23, 6:48 PM EDTSpecial Weather StatementPHI57 min
Jul 23, 7:32 PM EDTSpecial Weather StatementPHI58 min
Jul 23, 7:55 PM EDTSevere Thunderstorm WarningPHI30 min
Jul 25, 1:12 PM EDTMesoscale DiscussionSPC2 hr
Jul 25, 5:42 PM EDTMesoscale DiscussionSPC63 min
Jul 25, 6:23 PM EDTAreal Flood AdvisoryPHI3 hr
Jul 29, 2:40 PM EDTSevere Thunderstorm WatchSPC8 hr
Jul 29, 4:40 PM EDTMesoscale DiscussionSPC95 min
Jul 31, 10:00 PM EDTSpecial Weather StatementPHI60 min
Aug 1, 3:22 PM EDTMesoscale DiscussionSPC83 min
Aug 1, 4:33 PM EDTSevere Thunderstorm WarningPHI87 min
Aug 1, 5:11 PM EDTAreal Flood AdvisoryPHI2 hr
Aug 1, 5:37 PM EDTSevere Thunderstorm WarningPHI53 min
Aug 1, 6:18 PM EDTMesoscale DiscussionSPC57 min
Aug 1, 6:20 PM EDTSevere Thunderstorm WarningPHI46 min
Aug 3, 9:53 PM EDTSpecial Weather StatementPHI52 min
Aug 3, 10:33 PM EDTSpecial Weather StatementPHI117 min
Aug 7, 1:32 AM EDTAreal Flood AdvisoryPHI3 hr
Aug 8, 6:49 PM EDTSpecial Weather StatementPHI86 min
Aug 9, 11:46 AM EDTSpecial Weather StatementPHI59 min
Aug 9, 12:18 PM EDTSevere Thunderstorm WarningPHI57 min
Aug 9, 12:48 PM EDTMesoscale DiscussionSPC57 min
Aug 9, 3:05 PM EDTMesoscale DiscussionSPC55 min
Aug 9, 4:16 PM EDTSevere Thunderstorm WatchSPC5 hr
Aug 9, 5:48 PM EDTSpecial Weather StatementPHI87 min
Aug 9, 7:07 PM EDTMesoscale DiscussionSPC83 min
Aug 13, 1:20 PM EDTSpecial Weather StatementPHI115 min
Aug 13, 2:07 PM EDTMesoscale DiscussionSPC113 min
Aug 13, 4:32 PM EDTSpecial Weather StatementPHI88 min
Aug 14, 12:37 AM EDTAreal Flood AdvisoryPHI3 hr
Aug 14, 1:12 AM EDTFlash Flood WarningPHI4 hr
Aug 14, 1:00 PM EDTAreal Flood WarningPHI8 hr
Aug 15, 1:05 PM EDTAreal Flood AdvisoryPHI4 hr
Aug 18, 4:48 AM EDTSpecial Weather StatementPHI57 min
Aug 18, 6:04 AM EDTSpecial Weather StatementPHI41 min
Aug 18, 6:35 AM EDTAreal Flood AdvisoryPHI3 hr
Aug 18, 5:48 PM EDTSevere Thunderstorm WarningPHI57 min
Aug 18, 6:18 PM EDTSpecial Weather StatementPHI57 min
Aug 18, 6:39 PM EDTSevere Thunderstorm WarningPHI66 min
Aug 18, 6:39 PM EDTMesoscale DiscussionSPC96 min
Aug 18, 6:59 PM EDTFlash Flood WarningPHI2 hr
Aug 18, 7:14 PM EDTSevere Thunderstorm WarningPHI50 min
Aug 18, 7:28 PM EDTSpecial Weather StatementPHI62 min
Aug 18, 8:26 PM EDTAreal Flood AdvisoryPHI112 min
Aug 19, 12:02 AM EDTSpecial Weather StatementPHI58 min
Aug 19, 12:50 AM EDTSpecial Weather StatementPHI40 min
Aug 19, 1:14 AM EDTAreal Flood AdvisoryPHI3 hr
Aug 19, 12:43 PM EDTMesoscale DiscussionSPC62 min
Aug 19, 1:04 PM EDTSevere Thunderstorm WatchSPC8 hr
Aug 19, 5:35 PM EDTSevere Thunderstorm WarningPHI55 min
Aug 19, 5:39 PM EDTAreal Flood AdvisoryPHI3 hr
Aug 19, 5:42 PM EDTSevere Thunderstorm WarningPHI48 min
Aug 19, 6:14 PM EDTSevere Thunderstorm WarningPHI65 min
Aug 19, 6:42 PM EDTMesoscale DiscussionSPC63 min
Aug 19, 8:54 PM EDTAreal Flood WarningPHI4 hr
Aug 21, 11:54 AM EDTMesoscale DiscussionSPC2 hr
Aug 21, 12:52 PM EDTSevere Thunderstorm WatchSPC8 hr
Aug 21, 1:25 PM EDTAreal Flood AdvisoryPHI110 min
Aug 21, 1:47 PM EDTSevere Thunderstorm WarningPHI58 min
Aug 21, 2:43 PM EDTSevere Thunderstorm WarningPHI62 min
Aug 21, 4:35 PM EDTAreal Flood AdvisoryPHI3 hr
Aug 21, 7:12 PM EDTMesoscale DiscussionSPC63 min
Aug 21, 7:35 PM EDTAreal Flood AdvisoryPHI115 min
Aug 25, 9:35 AM EDTSpecial Weather StatementPHI55 min
Aug 25, 10:00 AM EDTAreal Flood AdvisoryPHI3 hr
Aug 27, 3:47 PM EDTAreal Flood AdvisoryPHI118 min
Aug 27, 4:06 PM EDTRiver Flood WarningPHI36 hr
Aug 27, 4:06 PM EDTRiver Flood WarningPHI37 hr
Aug 27, 5:37 PM EDTRiver Flood WarningPHI19 hr
Aug 27, 5:42 PM EDTAreal Flood WarningPHI6 hr
Aug 27, 7:31 PM EDTMesoscale DiscussionSPC89 min
Aug 27, 7:56 PM EDTTornado WatchSPC9 hr
Aug 27, 8:28 PM EDTFlash Flood WarningPHI12 hr
Aug 27, 9:43 PM EDTAreal Flood WarningPHI6 hr
Aug 27, 10:14 PM EDTTornado WarningPHI31 min
Aug 27, 10:23 PM EDTTornado WarningPHI37 min
Aug 27, 11:37 PM EDTFlash Flood WarningPHI12 hr
Aug 28, 3:50 AM EDTFlash Flood WarningPHI10 hr
Aug 28, 11:07 AM EDTAreal Flood WarningPHI18 hr
Sep 5, 6:03 PM EDTSpecial Weather StatementPHI117 min
Sep 5, 10:53 PM EDTAreal Flood AdvisoryPHI3 hr
Sep 6, 1:42 AM EDTAreal Flood AdvisoryPHI3 hr
Sep 6, 5:43 PM EDTAreal Flood AdvisoryPHI3 hr
Sep 6, 6:44 PM EDTAreal Flood WarningPHI15 hr
Sep 6, 7:03 PM EDTRiver Flood WarningPHI16 hr
Sep 6, 11:13 PM EDTRiver Flood WarningPHI3 days
Sep 7, 12:59 AM EDTRiver Flood WarningPHI41 hr
Sep 7, 2:39 PM EDTSpecial Weather StatementPHI66 min
Sep 7, 3:06 PM EDTFlash Flood WarningPHI4 hr
Sep 7, 3:33 PM EDTFlash Flood WarningPHI4 hr
Sep 7, 3:36 PM EDTMesoscale DiscussionSPC84 min
Sep 7, 3:49 PM EDTSpecial Weather StatementPHI56 min
Sep 7, 6:07 PM EDTRiver Flood WarningPHI10 hr
Sep 7, 7:21 PM EDTAreal Flood WarningPHI14 hr
Sep 8, 9:32 AM EDTAreal Flood WarningPHI15 hr
Sep 11, 6:38 PM EDTMesoscale DiscussionSPC97 min
Sep 11, 8:46 PM EDTAreal Flood AdvisoryPHI3 hr
Sep 11, 9:00 PM EDTFlash Flood WarningPHI3 hr
Sep 11, 9:14 PM EDTFlash Flood WarningPHI110 min
Sep 11, 9:14 PM EDTSpecial Weather StatementPHI61 min
Sep 11, 9:24 PM EDTSevere Thunderstorm WarningPHI51 min
Sep 11, 9:56 PM EDTFlash Flood WarningPHI4 hr
Sep 11, 10:29 PM EDTSevere Thunderstorm WarningPHI46 min
Sep 11, 10:44 PM EDTAreal Flood AdvisoryPHI107 min
Sep 11, 11:10 PM EDTSevere Thunderstorm WarningPHI65 min
Sep 14, 3:22 PM EDTMesoscale DiscussionSPC53 min
Sep 14, 7:53 PM EDTSpecial Weather StatementPHI112 min
Sep 23, 10:13 AM EDTAreal Flood AdvisoryPHI5 hr
Sep 23, 5:27 PM EDTAreal Flood WarningPHI12 hr
Sep 23, 11:58 PM EDTRiver Flood WarningPHI5 hr
Sep 24, 4:13 AM EDTRiver Flood WarningPHI7 hr
Sep 24, 4:44 AM EDTRiver Flood WarningPHI14 hr
Sep 24, 5:29 AM EDTAreal Flood WarningPHI5 hr
Sep 28, 3:20 PM EDTSpecial Weather StatementPHI55 min
Sep 28, 3:59 PM EDTSpecial Weather StatementPHI61 min
Sep 28, 4:33 PM EDTAreal Flood AdvisoryPHI2 hr
Sep 28, 4:36 PM EDTFlash Flood WarningPHI3 hr
Sep 28, 4:45 PM EDTMesoscale DiscussionSPC60 min
Sep 28, 7:44 PM EDTAreal Flood WarningPHI3 hr
Sep 28, 11:07 PM EDTSpecial Weather StatementPHI53 min
Sep 29, 12:35 PM EDTSpecial Weather StatementPHI55 min
Oct 1, 8:47 PM EDTSpecial Weather StatementPHI58 min
Oct 2, 1:26 AM EDTSpecial Weather StatementPHI2 hr
Oct 2, 3:35 AM EDTAreal Flood AdvisoryPHI4 hr
Oct 2, 4:56 AM EDTSpecial Weather StatementPHI3 hr
Oct 14, 12:25 PM EDTSpecial Weather StatementPHI80 min
Nov 22, 5:54 PM ESTAreal Flood AdvisoryPHI6 hr
Nov 22, 9:56 PM ESTAreal Flood WarningPHI6 hr
Nov 23, 12:35 AM ESTAreal Flood AdvisoryPHI6 hr
Nov 23, 3:08 AM ESTSpecial Weather StatementPHI3 hr
Nov 23, 3:44 AM ESTAreal Flood WarningPHI8 hr
Nov 23, 5:54 AM ESTRiver Flood WarningPHI16 hr
Nov 23, 6:34 AM ESTRiver Flood WarningPHI7 hr
Nov 23, 6:57 AM ESTRiver Flood WarningPHI16 hr
Nov 23, 11:50 AM ESTAreal Flood WarningPHI4 hr
Nov 29, 12:48 PM ESTSpecial Weather StatementPHI57 min
Nov 29, 4:27 PM ESTAreal Flood AdvisoryPHI4 hr
Dec 7, 6:51 AM ESTAreal Flood AdvisoryPHI4 hr
Dec 7, 4:37 PM ESTAreal Flood AdvisoryPHI4 hr
Dec 7, 8:04 PM ESTAreal Flood WarningPHI18 hr
Dec 7, 11:40 PM ESTRiver Flood WarningPHI8 hr
Dec 8, 2:21 AM ESTRiver Flood WarningPHI10 hr
Dec 8, 2:51 AM ESTRiver Flood WarningPHI13 hr
Dec 21, 9:54 PM ESTSpecial Weather StatementPHI51 min
Dec 23, 3:18 AM ESTAreal Flood WarningPHI3 hr
Dec 27, 6:01 PM ESTAreal Flood WarningPHI3 hr

By product

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

The busiest days

Days with the most alerts issued, by UTC date.

Nearby

Alerts in force nowTornadoes on recordForecastThe radar archive20102012

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.