NUCAPS shows environment favorable for elevated convection

As of around 20Z .  presence of a cold pocket aloft and relatively low precipitable water values around a half an inch confirm elevated convection along with the scattered reports of severe hail in eastern Idaho.   Cloud to ground lightning strikes are largely outnumbered by intercloud lightning activity.

John Pendergrast

Missed hail event in Oregon

There was a 1″ hail report at 2236z north of Elgin, OR. The highest ProbSvr value was 3% with a MESH of a quarter-inch. Attached is the 2222z radar scan and ProbSvr overlay.

Williams & MacGyver

Thoughts on Overshooting Tops and 1 min imagery

I was trying to think of how to use the overshooting top algorithm in warning ops.  The current 15 minute data it is useless to me.  I would be interested in the trend and the duration of the overshooting top for issuing warnings.  The longer the overshooting top, the more likely it will have severe weather.  As a result, the only data that would work for me is 1 min data.  I can compare this to the radar data as I get it.  I do not think that the 5 min data will work as it will wash out trends and the true nature of the atmosphere.

This made me think of QLCS and HSLC tornadoes.  If I had near real time one minute satellite data, I could find the strongest updraft in the line.  This could have a huge impact on these warnings, the FAR and POD for these storms.  The other thing that would help this would be a local maximum cloud top algorithm.  For example, make a 200 km x 200 km grid.  Use some nearest neighbour algorithm and find a local max in cloud tops.  This could lead to lead time with QLCS and HSLC storms.

Williams and MacGyv

Lightning Jump to 8 sigma

Click on the animated gif below to see how the lightning jump algorithm increased from 0 sigma at 2210Z to 4 sigma at 2211Z to 8 sigma at 2212Z. This was a great clue that the updraft of the storm was strengthening and that a warning may be necessary. We used this information in conjunction with the Prob Severe which was showing an increasing trend to go ahead and pull the trigger on a severe thunderstorm warning. It was interesting that although Prob Severe was showing an increasing trend, it was not over the 80% threshold. In this case, the lightning jump algorithm alerted us more than Prob Severe whereas we’ve seen other cases today where Prob Severe has been high and the lightning jump algorithm has been lower than expected.

-Helen Hunt

Quarter Hail producer near Pocatello spiked on CIMSS Prob SVR Model

In about a 5 minute span the cell highlighted in blue showed a severe potential of only 20 percent but increased to 89 percent and produced reported one inch hail near Chubbuck south of Pocatello.   Interestingly the Lightning Jump detection algorithm did not indicate a significant rise in total lightning activity with this developing cell during the same time.

John Pendergrast

TBSS and ProbSvr comparison

ProbSvr climbed above 50% at about the same time a TBSS became evident:

Issued a warning based on the TBSS signature in conjunction with the ProbSvr value quickly climbing (it reached ~80% with MESH of ~1.25″).

Williams & MacGyver

ENI, LJA & ProbSevere Used in Warning Decision

Overlaying point ’20’ with the West ENI DTA cell flash rate polygon showed significant increases in lightning activity in the time series product at at 2100Z and 2115Z. This was a good indicator that we needed to keep an eye on the storms and consider a warning due to a strengthening updraft. We probably should have issued the warning when we saw the first significant increase around 2100Z instead of waiting until 2115Z.

The lightning jump algorithm product shown below displayed a value of 2 sigma at 2113Z on the same storm. I would have expected a higher sigma value, but the algorithm takes into account the big dip that we see at 2110Z, which averages out to an overall lower sigma value.

The NOAA/CIMSS prob severe model percent increased to 87% (shown in magenta) at 2102Z. We did not issue the warning until 2115Z, but probably could have gotten a longer lead time had we issued it when the prob severe first increased at 2102Z.

The warning has not verified yet, but it is in a very rural area.

-Helen Hunt

NUCAPS vs. RAP

Finally got the NUCAPS data.  Was waiting for this data to compare with local sounding from BOI.  Had to mix the low levels to actual values.  After this, it was clear why convection was not going on to our northern CWA….there is some warm air across the northern CWA.  This sounding isnt as dry in the low levels, suggesting that there is not as high of a chance for wind.

Williams & MacGyver

KPDT – fast jump in ProbSvr values

Timeline of values:
2042z – 31%
2046z – 54%
2050z – 70%
Levelled off at 72% thereafter

The problem is that this is likely a very sparsely populated area, so even if there were to be severe weather, it probably won’t be reported. Will be hard to verify…

Growth rates show up as N/A for this cell, which has been the case for all cells that ProbSvr pegs in this area so far.

Williams & MacGyver

Hello Williams and MacGyver,

I just wanted to let you know that the satellite data are truncated west of 110W, so you won’t be seeing any growth rates in Oregon or Idaho. We plan to have it running truly CONUS-wide by next year. Hopefully you’ll be able to work somewhere east of that 110W in the next few days, to evaluate the satellite contribution to probabilities.

KPDT ProbSvr followup

ProvSvr maxed out at 88%, MESH at about 1.5″ 2029z-2039z.

Wondering if best practice is to lengthen duration of warning in cases when using ProbSvr, since there is some extra lead time compared to when one might issue a warning without it. In our case, we issued at a 30 minute warning (fairly typical) when a 45 minute warning may have been more appropriate given how much sooner ProbSvr can flag a severe potential.

Williams & MacGyver