PDS Watch and on a Slight Risk Day?

[Jeff Duda]

There is a PDS tornado watch about to expire in TN, AL, an MS. Why? I wasn't watching the storms overnight, but in checking current severe reports, there have been NO tornado reports in the watch box. Also, if SPC is issuing a PDS tornado watch, why do they only have a slight risk for the area? I know the categorical risk has a lot to do with coverage, but has anyone ever seen a PDS tornado watch in a slight risk? (Not to say it can't be done, but I've never seen it...I would bet there are members of this forum that have, though, and I'm curious to know when and how it played out)

 

[Jeff Snyder]

Jeff -- I assume the greatest risk was from the 3:40 am (issuance time) to 7 am time frame, which would have been during the previous day's SWODY1 and before the current slight-risk SWODY1. The tor probs on that watch are very high (80%/70%), and that would certainly not be consistent with only a SLT risk. Interestingly, more of that watch's valid time occurs after 12 UTC than before 12 UTC, and all SWODY1s issued for today have have SLT risks with only a 5% tor prob.

I don't think a PDS tor watch would be issued for a SLT risk (at least unless the SLT were being upgraded to MDT or HIGH), but that may be a better topic of a W&C thread as opposed to a NOW thread.

 

[Skip Talbot]

The Day 1 extends until 12z the next morning. So the high risk was valid until 7 am this morning. The new Day 1 issued at 1am picks up at 7am. Its not midnight to midnight. So even though the current Day 1 shows a 5% tornado risk, that watch was issued at 3 am when the 30% hatched tornado probabilities were still valid.

 

[Jeff Duda]

Well, given that, and the fact that the day hadn't exactly lived up to HIGH risk standards, I'm still a little confused as to why SPC would continue to issue a PDS tornado watch.

 

[Derek Weston]

Parkersburg tornado was a in PDS watch for an area that was in a slight risk. (and.. what, 5-10% non hatched tornado area?)

 

[John MacKay]

Parkersburg tornado was a in PDS watch for an area that was in a slight risk. (and.. what, 5-10% non hatched tornado area?)

I don't know when the watch was issued, but I assume it was near when the 2000 UTC SPC outlook was issued. It originally was a hatched 10% and slight on the 600 outlook, then pulled back to 5% (non-hatched) and slight for both the 1300 and 1630 outlooks. The 2000 outlook put Parkersburg at the south end of a hatched 10% again, but upgraded the area to a moderate.