r/Winchester • u/KasperAura • 4h ago
Hi, I'm working to be a trained spotter for NWS. Let's talk about that confirmed tornado last night
Preface: I'm not an expert, just someone with the tools and know-how to track storms. I utilize the following websites and apps:
IEMBot to pull warning data and storm reports, hosted by the Iowa Environemtal Mesonet (IEW)
Weather.us for pulling past radar data, as well as the RadarScope app for current conditions
Our local NWS office's website (KLWX Baltimore/Washington, with suboffice in Sterling), as well as the Storm Prediction Center website
Social media for confirmed storm reports
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Last night, around 6:19pm, KLWX issued Tornado Warning (TOR) #17 for a part of Frederick County. This storm cell was being tracked for a while as it formed in WV and moved into VA. As it was over Lehew, WV, this warning was issued for radar-indicated rotation.
Now, what does "radar-indicated rotation" mean? Beyond your standard doppler radar, there are other radar products that can be utilized. Anyone who's watched The Weather Channel in recent years may have seen two of these products: velocity, and correlation coefficient.
In basic terms, velocity shows winds in the storm cells. Green color indicates winds that are moving towards the radar, and red indicates winds moving away from the radar. Your local NWS office looks at something like this (and many other things!) for any signs of hidden rotation. When this warning was issued, the velocity radar may have looked like this:
See how the red and green are touching, and there's a "pinhole" or "donut hole" in the middle? That was likely a contributing factor to the tornado warning being issued.
It wasn't long after, around 6:24pm, that it was upgraded from "radar-indicated" to "confirmed." Who confirmed it? Best I can tell with the current information, it was a 911 caller. At this point, it was likely near Star Tannery, around 11mi north of Stratsburg, taking its time moving at only 20mph.
Three minutes later, at 6:29pm, the warning was upgraded to a PDS TOR, or a "particularly dangerous situation" tornado warning. Consider this the midpoint between "tornado warning" and "tornado emergency." PDS is reserved for "large, extremely dangerous" tornadoes.
However, four minutes later, at 6:33pm, it was back to "radar-indicated rotation" and stayed that way until the warning expired at 6:40pm.
So... what happened? Was there a tornado on the ground? It's entirely possible. As I sit here and type this out, we've had two storm reports come in within the "polygon" area of the warning, for multiple trees down and snapped limbs. There will likely be more reports today, as part of the area is forested, mountainous, or otherwise rural. These reports can come from any number of sources: local police, the public, trained spotters/CoCoRAS, or NWS employees.
At the very least, there was definitely some strong winds. We'll likely know more information over the next couple of days.
Historically, this is Frederick County's first "PDS TOR" warning. Since 2000, the county has had four confirmed tornadoes, most famously the Middletown tornado in 2008. They can and will occur here:
TIME, DATE W LOCTM D I F/EF
1765 SEP 17, 2004 061 14:39 0 0 2 39.17 -078.17 39.20 -078.15 69
1766 SEP 17, 2004 072 15:37 0 2 1 39.03 -078.27 39.17 -078.23 69
495 APR 20, 2008 20:02 0 0 0 39.04 -078.29 39.05 -078.28 69
1035 JUN 4, 2008 13:18 0 0 0 39.30 -078.16 39.30 -078.15 691765
If any new, major info comes out about it, I'll be happy to comment under this post. Let me know if you have any questions! EDIT: buy a weather radio! They're, like, $30 and will save your life!