ProbSevere and Mature Convection

Just some comments and thoughts being relayed about the use of ProbSevere and mature convection.  The EWP participants have found the ProbSevere model useful in its stated goal--providing probability a storm will first produce severe weather in the following 60 minutes.  In the ProbSevere training it was stated the model will likely have some utility in the application of continued severe threat and/or storm decay because, even after the satellite growth rates are no longer used when the storm is mature--the model continues to generate probabilities using the environmental conditions and the MRMS MESH.  But the model has not been validated in such a manner--so it was really up to participants to comment on utility in those scenarios.  Thus far a clear distinction appears to be emerging:  the ProbSevere output is useful for discrete mature storms like supercells but not so for upscale growth of storms--convective lines.  An example of mature supercells with continued high ProbSevere values valid at 2330 UTC 7 May 2014 near the Red River is shown in the Figure 1.

Figure 1.  NOAA/CIMSS ProbSevere, MRMS composite reflectivity, and NWS warnings valid 2330 UTC 7 May 2014.  This is an example of continued utility of ProbSevere output for mature supercell thunderstorms.

It will be interesting to see if these observations continue through the experiment.  If so, the next generation of training should reflect this distinction.

-Sieglaff

CYS SVR threat decreasing

The line of storms that has produced a TOR in NE CO and SVRs in our CYS area has shown a slow weakening trend.  Many of these cells are now outside the CO total lightning coverage area so we can not view this.

Of  interest is an area of stronger storms with multiple SVR and TOR form NE CO into the North Platte, NE CWA…

These cells developed in a much more favorable environment…heating into the 60s and 70s today.  Areas under the “old” convection in WY/CO are in the 40s and 50s.

Also of interest:

The deeper Nearcast instability is now mainly centered in NE.   Best threat for further convective development and more strong to severe storms looks like it will be mainly focused just to the east (and to some extent southeast into NE CO) of the CYS CWA for the duration of the afternoon/evening.

db

CI Picking Up in Radar Void Area

I am watching a void area on the radar (bottom image) to see if there is any additional development northeast of Denver. CI values have picked up a bit (top image) in this general vicinity with some 70% probabilities. In that last few minutes probabilities have dropped. Waiting to see the outcome…

Jared Maples

New storms developing over central Texas

While mature supercells ebb and flow over the KOUN and KCYS/KBOU EWP WFOs, new convection was developing along the dryline in the San Angelo, Texas WFO.  Given the goals of the NOAA/CIMSS ProbSevere model of providing the probability a storm will first produce severe in the following 60 minutes (although EWP participants are noting utility of the ProbSevere model for supercell maintenance/severe threat as the model still uses NWP and radar information for those storms), the developing storms further south have become of more interest.

A developing storm exhibited strong vertical growth rates and strong glaciation rates within a favorable environment.  The ProbSevere model had increasing probabilities associated with storm, exceeding 50% at 2242 UTC 7 May 2014 (Figure 1) with further increase up to 97% when the NWS in San Angelo issued a severe thunderstorm warning at 2257 UTC 7 May 2014--15 minutes after the ProbSevere values jumped above 50%.

Figure 1.  NOAA/CIMSS ProbSevere, MRMS composite reflectivity, and NWS severe thunderstorm warnings valid 2242 - 2257 UTC 7 May 2014.

-Sieglaff

Expanded Lightning Jump View: 2234 UTC (CO/WY)

A wider look at the lightning jump grid at 2234 UTC of the NE Boulder CWA… All tracked storms (with greater than 10 flashes per min and within the 150 km LMA domain) are shown.  Three tracked cells show some type of sigma jump at this same time.  Two in green – 1-sigma (or standard deviation) and one smaller cluster, orange, with a 3-sigma jump.

The three-sigma jump storm corresponds with a ProbSevere 92% and MESH of 1.65 in.

-K. Calhoun, Week 1 Coordinator & Lightning Jump PI

CI miss and hit

First isolated cell builds with a CI of 40-50%.

Initial cell continues to grow with a CI of 80-90%.

Initial cell reaches a CI of >90% with a new cell developing to the southwest showing a CI 80-90%.

Initial cell eventially goes “poof”, with secondary cell continuing to grow and show a CI of >90%.

Second cell continues to grow with CI still >90% on the southwest flank.

Second cell continues to grow. A warning was eventially issued for this storm.

Scott Rudge.

persistent OTs

Convection in CO, NE, WY has exhibited persistent (30 min) OTs as of the 22:15 vis sat pic.

  

These have been over persistent strong…and at times severe…storms.  OTs have not always meant the storms were severe…and have seen SVR and even TOR under cells that have not had OTs detected.

db

Storms firing in southern Kansas

While not within the OUN WFO, EWP forecasters noticed a storm in southern Kansas developing as observed by the KTLX radar.  The NOAA/CIMSS ProbSevere model probability jumped to 74% at 2158 UTC with strong vertical growth rates and increasing MRMS MESH values (Figure 1).  The probabilities continued to increase and eventually the NWS Wichita office issued a severe thunderstorm warning at 2211 UTC 7 May 2014 (13 minutes after the probabilities increased to 74% (first time above 50%)) and was at 96% when the warning was issued.

Figure 1.  Animation of NOAA/CIMSS ProbSevere, 0.5 degree KTLX reflectivity and NWS warnings valid 2158 - 2112 UTC 7 May 2014.

-Sieglaff

CI providing lead time to initiation

As seen in the first image, CI is picking up on come cloud cover out ahead of the main convection. Probabilities were 50% and higher in this area at the time. Shortly after, thunderstorms began to develop just to the south of the main line that had already been warned on. These new storms later merged with the northern cell to produce more of a cluster. This example shows how the CI tool has some skill at time that cirrus isn’t inhibiting detection and can also raise awareness on development in a messy area.

More warnings and experimental warnings over southwestern Oklahoma

The storms over southwestern Oklahoma have recently increased in intensity and have warranted NWS and EWP severe thunderstorm warnings, with multiple reports of quarter to golf ball sized hail.  The ProbSevere values for these storms with golf ball sized hail are well in excess of 90%--even some at 100% for times.  The evolution of these storms and the generation of severe thunderstorm warnings is demonstrated in Figure 1.

Figure 1.  NOAA/CIMSS ProbSevere, 0.5 degree KTLX reflectivity, and NWS/EWP warnings valid 2132 - 2140 UTC 7 May 2014. 

A question was posed to the forecasters on the KOUN desk within EWP today, "There have been a number of storms with ProbSevere values in excess of 50% today, some of which seem to be false alarms, is this hampering the use of the product?"   The forecasters replied,

"No I like that the storms with the highest ProbSevere probabilities are in excess of 90% and these are the ones producing golf ball sized hail--these are not marginal hail stones.  The ProbSevere is drawing me to which storms are likely to need severe warnings in the near future.  The false alarm storms, while they have high probabilities today, are in the 70-85% range--which makes them different than these with 90+% probabilities.  I've easily been able to adjust to the probabilities and use them appropriately.  Also I know the ProbSevere model has not been validated as a tool to reissue severe warnings, but I like how the probabilities diminish a bit when the radar intensity decreases and then come back up if the storm re-intensifies.  If you look at this display (Figure 3) it has high probabilities on the right storms, but the ones further west are only (correctly )10-20%"

Figure 3.  NOAA/CIMSS ProbSevere and MRMS composite reflectivity valid 2204 UTC 7 May 2014.  This was the display the NWS forecaster in the EWP was referring to when he was discussing the ProbSevere continuing to identify the severe storms, but had much lower probabilities for the storms further north and west.

-Sieglaff