EWP Blog

We are in the process of educating our guests on the gridded probabilistic warning concept. Our IOP will probably begin around 6pm, over the Ohio Valley. Hoping there are still storms around when we begin, as the training today is taking a little longer than we planned. We also need to take a dinner break! So I’m going take notes on the blog to capture some of the PW training discussion.

Some good questions already – what probability numbers should be used? Forecasters need to be calibrated since they haven’t really thought about this.

How will we verify events in sparsely populated areas like the desert Southwest?

The spreading polygon is opposite to a probability contour. If the initial warning is set to, e.g., 50%, as the warning grows larger down the swath, the probabilities are actually smaller due to the uncertainty. If you look at a probability grid, the 50% contour will actually come to a point rather than spread out with time.

We’ll try do a demo live case, with NSSL driving first, and then letting each forecaster try it out, before the forecasters go through the archive case with the job sheet. The archive case will be doneon Tuesday.

Greg Stumpf (EWP Weekly Coordinator, 28 April – 2 May)

The storm merger has occurred but there are still distinct inflow notches aligned east-west on the south side of a >50dBZ contiguous low-level core. We’re seeing the strong SR inbounds in the core but no outbounds south of the core due to poor signal.

Liz’s binary TOR threshold is 30% so she dropped the probabilities to just above that level. This means absolute probabilities will not be consistent between forecasters. Should they be relative to a personal TOR warning threshold?

Oh, when Liz made a loop, the edit polygons dialogue box also looped in an annoying way.

The end. NO tornado observed yet though dust was rising in some chaser’s streaming videos.

Jim LaDue (EWP Weekly Coordinator-in-Training)

Live stream from a chaser east of GLD shows a wall cloud northest of Thomas, KS.

Liz took over prob warn and as expected, is experiencing a big learning curve. Warnings may not be totally accurate. We’ll need at least an hour for each forecaster to get up to adequate skill in WG.

Jim LaDue (EWP Weekly Coordinator-in-Training)

At 2005 UTC, we had a storm merger east of GLD. THe lead supercell was starting to produce a moderate low-level meso and I decided to update my TOR probabilities to start at 50% which happens to be my personal tornado warning threshold. The environment was marginally favorable for meso induced tornadoes and pretty favorable for supercells in general. So my impression of the environment was not great. There were no spotter reports despite potentially good coverage. Thus I kept my tornado warning probabilities just above my threshold and not higher.

Greg and Liz were wondering what made me set a 50% probability of a tornado as a mental threshold of a tornado warning. I replied that I felt that I wanted to be more than half confident that a tornado would occur inside my threat area as it expanded and moved downstream. However I’ve been issuing tornado warning proababilities well before I reached the 50% threshold.

I found another challenge in maintaining my storm motions between threat types for the same storm. I became preoccupied with updating the TOR threat area and storm motion as the storm turned more to the right. After I updated the TOR threat area, I became distracted by an out of date hail threat area with the left mover. However, I should’ve updated the storm motion for the hail threat area for the same storm I had followed with the TOR threat. Since I didn’t, the two motions, and subsequent threat swaths were in totally different directions.

Jim LaDue (EWP Weekly Coordinator-in-Training)

Liz, Greg and I are tracking a pair of storms northeast of GLD. The lead storm is a supercell while the trailing storm is more obviously multicellular consisting of ordinary cells. We’re raising many questions about the probability warning guidance issue.

Questions include:

• Liz asks how does she maintain some kind of connection with her user? Greg counters that the warning meteorologist should be separated from the user. Afterall there are many types of users, each with their own thresholds for warning. There will still be a need for some kind of binary product that the lowest common dissemination method (e.g., NOAA wx radio) can still transmit. Liz is not comfortable with losing the connection with the user. Greg says someone will likely be filling this role.
• Can we set a threshold probability in the prob warning tool for which when passed, the tool flags the swath as an official binary warning?
• Can a forecaster set his/her own threshold warning probability?
• Liz wonders if we can save each forecaster’s warning thresholds so that we can see how each one thinks? My 50% is your 30%, for example. This process may shed light on forecaster differences (biases) in the assessment of probabilities.
• Can metadata be added to each threat area ID so that any input not easily translated to grids can be added? Greg suggested that it could be a blog for each threat area. We’re thinking that metadata could include special call-to-action statements, forecaster reasoning, adding context to the event and others.
• Liz wonders how we could translate any of this metadata to something that is consistent with text in current warnings.

Greg would like to have the individual threat area translucent overlays (H,W,T) to be separated out so that we can toggle each threat area type on and off.

Jim and Liz would like product legends to be simplified. Hard to get time and elevation cut/height to stand out.

Jim would like to be able to change from irregular polygon to ellipse in mid process.

Jim LaDue (EWP Weekly Coordinator-in-Training)