UW Overshooting Top Algorithm Hits Storm Prior to Springfield, MA Tornado

Yesterday, 1 June 2011, climatologically rare tornadoes hit New England. The University of Wisconsin Overshooting Top algorithm identified an overshooting top with a severe thunderstorm at 2002 UTC 1 June 2011, just west of Springfield, MA (right). The overshooting top magnitude is filled atop the GOES visible imagery. The overshooting top identification occurred 28 minutes ahead of the first tornado report in Westfield, MA at 2030 UTC (a western suburb of Springfield).

UW Nearcast Product and Developing Convection

The GOES Sounder Nearcasting product is being used today on the EFP CI-desk to identify possible forcing mechanisms for the deep convection. In the image below the nearcasting theta-e difference is shown, valid 1700 UTC 01 June 2011. Strong convection has been ongoing and continually developing in eastern to north-central Kansas along the minimum (maximum instability) and northeastward toward the strong gradient in the nearcasting theta-e difference. It was noted this gradient is also coincident with a strong dewpoint gradient at 850 hPa. It is believed southerly flow across this gradient is helping force the convection. Further east across the Mid Atlantic region, convection was developing largely in the minimum of the theta-e difference, with a strong gradient to the west as low-level moisture decreases behind the front. It has also been noted there are many other areas of strong potential instability indicated by the nearcasting product, however there is not deep convection associated with many of these areas. One hypothesis is there needs to be not only instability present, but also a forcing mechanism. Possible forcing mechanisms maybe inferred by a strong gradient in the instability indicated by the nearcasting product, suggestion strong temperature and/or moisture advection.

NSSL-WRF Simulated ABI Imagery and CI forecast

This morning on the EFP CI-desk, the simulated ABI imagery from the NSSL-WRF provided guidance on location and timing of initial CI location for many of the forecasters. As can be seen in the image below, there was a tight cluster of forecasted first CI location points over the higher terrain of northern New Mexico. The simulated ABI band 13 image valid at 1900 UTC shows newly developing convention over northern New Mexico. A few other forecasters favored convective initiation along the moisture gradient in the lower troposphere in eastern Kansas. (Ongoing storms northwest of Salina, Kansas were excluded from the forecast area.)

UW CTC Highlights Most Rapid Development of Convective Line

The UW Cloud-Top Cooling (CTC) rate cannot only be used to nowcast convection initiation, but also highlight the most rapid vertical growth along a line of developing convective clouds. Below is the GOES visible imagery/UW CTC valid at 1732 UTC 31 May 2011 and base radar reflectivity at the same time. The entire line of towering cumulus over central Michigan looks similar on visible imagery, but the UW CTC highlights (green circle) the most rapidly growing and hence precipitating portion of the line (also green circle).

Simulated ABI Radiances Compared to GOES Observations

This week there is no EWP running so all support is geared towards the EFP. Early Tuesday on the CI desk of EFP, the NSSL-WRF simulated ABI radiances were compared to the current GOES observations for judging the timing/placement of the upper level vorticity maxima/upper level dry intrusion over the Central US, as well as impact of cloud cover on convective intiation forecasts over the western Great Lakes.

Below are the 15 UTC simulated ABI brightness temperatures (top) and observed GOES brightness temperatures (bottom). The consensus of the forecasters on the CI desk was the NSSL-WRF had excellent placement of the upper level vorticity as depicted by the water vapor channels. On the other hand, the NSSL-WRF struggled to capture the intensity and magnitude of a band of clouds and decaying convection over the Upper Mississippi Valley/western Great Lakes. The images below show the GOES observed clouds are much more expansive and have colder brightness temperatures than the simulated ABI clouds from the NSSL-WRF. Discussion is ongoing on how these clouds will impact convective initiation timing and location later today.







FLASH utility to toggle between images

Discussing RGB imagery

A forecaster from Austria visited the HWT this week and I asked him to give a short briefing on the use of satellite data over Europe to the EWP forecasters to help them understand some of the capabilities that we will have with GOES-R with respect to the utility of RGB imagery. Over Europe, the use of radar and surface data is relatively limited to the level that we use it here in the US because of the difficulty in obtaining data from the private companies, not to mention other neighboring countries. Scientists and forecasters in Europe have found innovative ways to combine imagery into products that help identify surface features, cloud types, volcanic ash, as well as moisture and jet streaks. These techniques are not commonly used within normal WFO operations within the US, mainly because of the lack of spectral data available from our current operational satellites. EWP forecasters got the chance to have a look at what they use routinely over Europe and found the briefing very interesting and are excited to use this sort of information in the future.

End of week debrief... 27 May

Today we had our end of week debrief for the EWP. We did have a fairly robust discussion yesterday regarding the 24 May event, so we tried to gather some additional information from the forecasters. We covered each of the products and how they performed within warning operations this week.

Convective Initiation

- (26 May event) CI did not so well over AL/TN... high FAR, low POD in morning... Forecaster theorized this may have something to do with the less dramatic temperature differences between the surface and clouds during the morning hours.

- CI did much better during rapid scan.

- The UAH version was much more agressive that the UW version.

- Having a probabilistic approach versus a yes/no would help.

- Forecaster used the UW CTC/CI product to issue a severe weather statement... ended up putting a warning on it afterwards.

- This could be important for not just severe weather... the CI products could be very useful for the onset of lightning as sort of a proxy for the growth of a certain dBZ threshold above say a -10 C level if it had faster updates.

- "I'm assuming that performance should improve pretty dramatically once you get the rapid updates with the next-generation satellites, but now I guess it would work best in a clean environment in the plains. I could also see the probabilities a good way to go."

- Maybe contouring SATCAST probabilities would be a good.

- "Based on what it's designed to do, I can see this working in a typical summer afternoon in Florida, not just over the plains."

- Could help identify waterspout candidates because they're harder to see on radar.

- For non-severe faster moving systems it may be useful in detecting regions of heavy rain.

- Would be a good idea to get west coast offices to look at these things since they rely heavily on satellite data because of a lack of surface observations.

Pseudo-GLM

- When we saw cell mergers there was a rapid increase in flash rate over a 5 minute time period and updraft speed from the 3D-VAR analysis.

- A lot of times we would have flash rate increases over the anvil areas downstream... it could help you focus on the new electrification of the storm as well as where new cells might develop or updrafts cores move... would give 10-15 minutes lead time before it showed on radar.

- 10-15 minutes lead time on the first CG.

- "There's a lot of potential use for these types of products... but there is definitely more room for improvement with additional research, as well as increased temporal or spatial resolution."

- It may be difficult to display the rate of change product, not everyone will be looking at the same storm, so having a gridded history would be really useful that you could click on and get an idea of how that storm has evolved.

- Having polarity information would be very useful.

- "Need more research on the forecasting applications of this data."

- Would be interesting to see the PGLM over mini-supercells as well as some winter cases looking at rainfall rates and updraft strengths.

- Ratio of IC-CG would be very useful... being able to query a cell or cluster for it's trend would be helpful.

- The classic MCCs, it would be interesting to see how that related to severe and heavy rain potential.

- Using the PGLM might be useful for a poor man's microwave information in distinguishing areas of convective and trailing stratiform.

- Would have a lot of utility in mountainous regions where flash flooding is a big issue, especially if there is no radar coverage.

- The sum product was not very useful, mainly because of the color scale... everything becomes white... Forecaster used it as a sort of storm total tool, much like precip.

Overshooting-top / Thermal Couplet

- (26 May event) One couplet was over some leading cells along the PN/MD line... the clouds behind that were masked by cirrus and may have limited the detection. When it did trigger, it well differentiated that cell from the rest of the scene.

Nearcast

- (26 May event) The theta-e and precipitable water differences really indicated the marginality of the storms in the foothills... where the maximum stuff intersected that is where we saw the most sustained convection and highest flash rates. It was definitely a good indicator of flash flooding over the area.

- "A lot of the time to increase my lead time in the morning, I like to take a look at PW and WV... so I found that this was a nice utility because it was indicative of finding areas of greatly deep instability, or moisture source regions."

- "One on storm on tuesday, there was strong theta-e gradient that the storm was moving into and that gave me confidence in that the storm would intensify."

- It's a simple way to identify areas of warm advection and instability... this is why the forecaster found it useful in warning operations.

NSSL-WRF Band Difference

- The band difference has a lot of potential... you can get a head start by looking at the trends in the data that help you anticipate what's going to happen.

Overall

- "I enjoyed seeing the combination of the satellite products interacting with the radar and lightning products... it's a great planning tool."

- Need to come up with some pre-made default procedures for the experimental products... it's tough for forecasters to come in cold and learn how to load all of the products and then go into forecasting operations. The forecasters especially applauded the creation of the "ultimate-CI" procedure from last week and that should be saved.

- Create articulate presentations that forecasters can view beforehand rather than having "powerpoint death" on Mondays... this will also maximize the time forecasters have to look at the products.

- Would also be useful to create very short WES cases to send out beforehand that the forecasters can go through before they arrive.

- Forecaster would like to see the derived sounder products within the HWT AWIPS next year.

Psuedo-GLM Products in the Mid-Atlantic

Forecasters conducted warning operations in the Sterling, VA and State College, PA CWAs, which allowed for analysis of the pseudo-GLM products (from the DCLMA). Although the earliest convection initiated along and just west of the Appalachian Mountains (out of range of the LMA), storms soon formed within range. Isolated storms initiated and developed rapidly ahead of the main line. The pseudo-GLM products detected IC flashes ~10 min prior to the first CG flashes in two of these storms. These storms continued to intensify and eventually merged into a line, further increasing the flash rates.




As the discrete cells merged into a line, flashes remained frequent, and the pseudo-GLM products helped confirm the strength of individual cells within the line. Greater flash rates also helped identify areas of new convection as they formed along the line.



Forecasters also observed that the pseudo-GLM swaths (i.e., 60 min sum of flashes) helped to illustrate persistent cells and identify the most intense portions of the line.



The above screen captures illustrate several four panel displays used to compare individual products in AWIPS. The pseudo-GLM products often were plotted alongside the 3-D Var updraft and vorticity tracks, as well as the multi-radar multi-sensor hail swaths and reflectivity at -10 C.

Scott Rudlosky

EWP forecaster debrief... 26 May

This afternoon we had an extensive debrief session with the EWP forecasters regarding the tornado outbreak from this past Tuesday (24 May). We asked them in detail what they saw for each of the products, and these are the responses/comments we received for the GOES-R products...

Convective Initiation

- We were seeing 10-15 minute lead times from the UAH CI product along the dryline prior to any echoes above 35 dBZ on radar. The UWCI was much more conservative and missed a few instances of CI, but it had less false alarms and similar lead times when it did trigger for CI.

- UAH CI did show some signals after initiation behind the dryline, but nothing really continued to grow. However, forecaster mentioned how this would be very useful in warning operations to help increase situational awareness for future development when you may be focusing primarily on the first storms.

- Forecaster mentioned how he was watching the UAH CI this morning over the SE and it was giving negative lead times and UWCI was not flagging anything at all. However, he did want to emphasize that on Tuesday GOES-E was in rapid-scan operations and was not this morning, so that could be why the lead times were so poor.

Pseudo-GLM

- Very useful as a situational awareness tool during warning ops... Forecasters saw rapid increases in the instantaneous flash rates prior to increases in reflectivity and other products such as the 3D-VAR updraft strength and various MRMS products.

- Forecaster mentioned that it would be nice to have a line graph display for this to help identify jumps better. (Kristin and I did mention that we have heard that forecasters would not like this in the past since it would remove them from the D2D during warning ops... forecaster responded with that you can do this as a percentage change product within the storm interrogator software within AWIPS which could mitigate this.)

- Forecasters found that the track product (that we currently use as a proxy for a jump graphic) was not very useful in detecting 'jumps' mainly because of the resolution of the product... the rapid changes could not be seen because they would generally overlap on the same pixel.

- There were moments that some data outages occurred within the OKLMA network that caused some false instances of 'jumps' and lack of signal. It was theorized that the sensors were becoming attenuated in heavy rain and not transmitting data since they are daisy-chained. Also, one tower was hit by a tornado and caused a large break in the chain, so the OKLMA is down until further notice, possibly throughout the remainder of the experiment.

Overshooting-tops / Thermal Couplet

- Not many were seen, but those that were tended to be near the center of the upper low.

- Those that were seen did coincide with instances of increases in reflectivity aloft.

- Usefulness within warning ops very minimal because of lack of detections.

CI over New York

Another busy day for the EWP forecasters, as severe thunderstorms have erupted over the mid-Atlantic region. As so, screen captures from AWIPS have been tough to come by. Therefore, these next screen shots come from NAWIPS.

SATCAST CI has performed very well over the New York and Pennsylvania areas this afternoon. The following satellite image is from 1945 UTC. SATCAST forecasted CI over south central New York. Approximately 13 minutes later, radar reflectivity exceeded 35 dBZ on the base scan. While not the largest lead time, in another large CAPE environment, SATCAST is performing well.


SATCAST is performing quite well today pinpointing areas where storms will develop in the future. Even in Florida, where the dynamics are not as impressive, storms developed with help from convergence by the sea breeze, and SATCAST provided a very good forecast.