Splitting of Supercells and Prob Severe/Tor/Wind

A supercell that had been warned on split with the northern storm moving into the more favorable area of instability and the updraft rapidly strengthened to severe. Noticed that Prob Tor has increased to 9% on the northern storm and Prob Hail/Wind are 99%/89% respectively.  Issued a severe thunderstorm warning shortly after the last scan on this animation. Will be monitoring that northern storm for ProbTor. Have seen some upstream storms with strengthening with rotation.

More to come...

Supercell

ProbSevereWindTor with severe storm

Looked at Prob Severe Tor/Wind/Hail with MRMS reflectivity. The Hail probabilities actually increased to 90% prior to warning issuance. MESH values were around 1.56 inches. Prob Wind was a lower (78%) value. Did see where there was a TBSS in the dual pol and reflectivity products indicative of hail. Issued severe thunderstorm warning shortly after the probs showed this. Did notice that Prob Tor was around 1% but monitoring the velocities as the cell is located near the warm front and wind shear is sufficient to support it.

More to come...

Supercell

Prob Severe & Wind Flurry of readouts

Looking at the Probabilistic products during the latest warning operations, if there are 2 or more cells within warnings, it is definitely useful to compare the parameters in the readout and probabilities. It would helpful if the color table for the Prob Severe, Hail, and Wind could have a better gradient in colors from 70% and above. Also, did not find it useful to have MESH in the Prob Wind product readout, nor did I find it useful to have the flash rate especially with the GLM data available for us to use. This image also displays why having so much on the readout for Prob Severe is too much on the screen.

Supercell

ProbSevere running hot in Iowa

ProbSevere has been running hot, with probability of hail and probability of wind, pulsing into the 30-50% and 60-80%, respectively for many storms across the DMX WFO.  Thus far no severe reports have been received.  In discussing the environment with the DMX team, we are wondering if the shear is too high for the amount of instability, which is shearing the tops off developing storms, preventing storm organization.  The tops being sheared off can be seen in 1 minute GOES-16 visible imagery (not shown).  One silver lining would be ProbSevere Version 2 probabilities are 10-40% lower than the ProbSevere Version 1--illustrating the better calibration of probabilities in ProbSevere Version 2 relative to Version 1 (although still too high for the small sample size of a few hours this afternoon in the DMX region).

-J. Sieglaff

KOUN Experimental Tornado Warning

The forecaster covering the southern Norman WFO noticed the tornado probability from ProbSevere Version 2 (All Hazards) rapidly increasing between 2114 and 2124 UTC Wednesday afternoon (Figue 1).  The rapid increase in tornado probabilities was due to rapidly strengthening low-level circulation.  ProbSevere here aided the forecaster to issue an experimental tornado warning--increasing lead-time and confidence in his decision making.  Storm chaser live video showed a tornado developed at 2139 UTC.

Figure 1. KFDR storm-relative velocity and ProbSevere Version 2 tornado probability valid 2114 - 2124 UTC 02 May 2018.

-J. Sieglaff

ProbSevere Aids in Experimental Tornado Warning

The forecasters in the Wichita, KS CWA noted ProbSevere tornado probability rapidly increased on a supercell thunderstorm that developed just ahead of a large severe squall line.  Figure 1 shows KICT 0.5 degree storm-relative velocity and ProbSevere probability of tornado contours rapidly increasing from 13% at 2048 UTC to 70% at 2056 UTC.  The velocity data shows a very strong, tight circulation.   The jump of the probability of tornado alerted the warning forecaster and after a very quick radar interrogation, he issued an experimental tornado warning at 2100 UTC.

Figure 1.  KITC 0.5 degree storm relative velocity and ProbSevere Version 2 tornado probability, highlighting the supercell ahead of the squall line valid 2048-2056 UTC 02 May 2018.

-J. Sieglaff

ProbSevere example over far Southwestern Oklahoma

Thunderstorms were developing along and ahead of the dryline over the far eastern Texas panhandle and pushing into the western Norman, OK WFO.  ProbSevere All Hazards (aka ProbSevere Version 2) showed severe hail and severe wind threats increasing between 1938 and 2000 UTC 02 May 2018 (Figure 1).  The forecasters over the Norman WFO were evaluating some other products at this time, but were keeping an eye on the ProbSevere values.  The forecasters noted the good lead-time provided by ProbSevere as the first severe hail report was received at 2010 UTC (1.00").

Figure 1. MRMS Composite Reflectivity and ProbSevere Version 2 (All Hazards) contours valid 1938 - 2000 UTC 02 May 2018.  The storm of interest very near the southwestern portion of the Norman WFO is highlighted with AWIPS ProbSevere storm attribute readout.

-J. Sieglaff

Spin up of another tornado from a long-lived supercell

A long-lived supercell thunderstorm transversed across the northern Wichita, KS WFO and into the Topeka, KS WFO Tuesday evening.  This supercell had exhibited ProbSevere All Hazards probability of tornado values that cycled with the intensity of the low and mid level circulation.  Between 2342 UTC and 2358 UTC the probability of tornado increased from near 50% to over 90% as both low and mid-level rotation quickly strengthened (Figure 1).  This storm produced at tornado at 0004 UTC 02 May 2018.  Forecasters have noticed with many of the long-lived supercells, the cycling of probability of tornado values related to cycling of mesocyclone strength.  This is giving forecasters good confidence in how to use the probability of tornado information in their decision making.

Figure 1.  KICT 0.5 degree storm relative velocity and ProbSevere All Hazards probability of tornado 2342 - 2358 UTC 01 May 2018.

-J. Sieglaff

Possible Tornadic Circulation in southern Dodge City, KS WFO

Early Tuesday evening, 0-1 km storm relative helicity had increased over the Central and Southern Plains.  The DDC crew noticed a rapid jump in ProbSevere All Hazards probability of tornado between 2328 and 2336 UTC--going from 10% to 70% in the 8 minute time period (Figure 1) in Comanche county, Kansas.  The forecast crew said the rapid increase alerted them to a rapidly intensifying low-level circulation and prompted an experimental tornado warning at 2339 UTC.

Figure 1.  KDDC 0.5 degree storm relative velocity and ProbSevere All Hazards probability of tornado contours 2328 - 2336 UTC 01 May 2018.

-J. Sieglaff

A few quick ProbSevere All Hazards Comments from a Forecaster

With such a busy afternoon of severe weather over the WFOs of interest, I was able to ask a forecaster if he had any comments on performance of ProbSevere All Hazards so far today.  He said, "it is performing very well and I am very happy to see ProbSevere All Hazards performing well with left moving supercells after storm splits, as often algorithms struggle with these types of storms".  He also added, "I was going to severe warning on this right moving supercell, and noticed ProbSevere All Hazards probability of tornado was up to 40%, while I wasn't confident enough to go tornado warning, I added the tornado possible tag to my severe warning".

-J. Sieglaff

Experimental Tornado Warning in Hastings, NE

One forecaster in the Hastings, NE WFO issued an experimental tornado warning based on his interrogation of base velocity data at 2137 UTC 01 May 2018.  The forecaster noted the ProbSevere All Hazards probability of tornado was low (9%) at the time he decided to issue the warning (2134 UTC), but then jumped to 40% in the following scan (see Figure 1).  The probability of tornado values continued to increase into the 60% range.  The forecaster commented, he realized the rotation increase he noted in base data took a few minutes to be captured in the MRMS AzShear fields and hence ProbSevere All Hazards.  In this case he said the probability of tornado confirmed his decision to warn and it gave him confidence in the probability of tornado, but to keep aware of the latency in base data into derived products.  This storm did produce a brief tornado shortly after the warning issuance.

Figure 1. KUEX 0.5 degree storm-relative velocity and ProbSevere All Hazards probability of tornado contours over Nebraska 2132-2142 UTC 01 May 2018.

-J. Sieglaff

ProbSevere All Hazards Alerts Dodge City Forecaster

One of the forecasters covering the Dodge City, KS noticed a rapidly developing storm just ahead of the main line around 2050 UTC.  The base reflectivity was only near 50 dBZ and MRMS MESH was less than 0.20", but the forecaster noted the appearance of a ProbSevere AllHazards contour of 48% at 2046 UTC.  The ProbSevere All Hazards probability then rapidly increased to 84% only 6 minutes later--due to rapidly increasing total lightning, strong satellite growth rates, and very favorable thermodynamic environment for severe hail (see Figure 1).  The forecaster said, "this caused me to interrogate the storm further using all-tilts and noticed a strengthening trend aloft".  The forecaster added, "ProbSevere All Hazards drew my attention to this storm, that combined with the ProbSevere All Hazards reaching high probabilities with other storms before MRMS MESH was exceeding 1.00" and getting reports of severe hail gave me the confidence to issue an experimental severe thunderstorm warning earlier than I would have using only an all-tilts interrogation of the storm".

Figure 1.  MRMS Composite reflectivity and ProbSevere All Hazards contours 2046 - 2052 UTC 01 May 2018.  The storm of interest AWIPS read-out demonstrates the jumps in probability of severe hail as well as rapidly increasing total lightning flash rates.

-J. Sieglaff

ProbSevere All Hazards Providing Lead-Time in Kansas

Severe thunderstorms explosively developed along the dry line over central Kansas Tuesday afternoon.  The HWT forecasters are centered on the Hastings, NE and Dodge City, KS WFOs.  Forecasters from both WFOs have noticed ProbSevere All Hazards was exhibiting rapid jumps to to probabilities in excess of 90%, while MRMS MESH values remained in the 0.50" to 0.75" range (see Figures 1 and 2 below).  The forecasters remarked they were pleased with the lead-time ProbSevere All Hazards was providing, despite the MESH still being below severe size (1.00").  The jumps in the probability of hail from ProbSevere All Hazards can be attributed to 1) intense GOES-16 vertical growth rates, 2) rapid increases in total lightning flash rates, and 3) the environmental parameters from Numerical Weather Prediction (NWP) used are extremely favorable for severe hail.

Figure 1.  Storm over Hastings, NE CWA at 2012 UTC 01 May 2018.  Notice ProbSevere All Hazards is 88%, while MRMS is only 0.37".  This example illustrates the power of utilizing other observations of deep convection, specifically satellite derived growth rates and total lightning flash rates, as well as environmental conditions from NWP data.

Figure 2.  Storm over Dodge City, KS CWA at 2014 UTC 01 May 2018.  Notice ProbSevere All Hazards is 95%, while MRMS is only 0.73".  This example also illustrates the power of utilizing other observations of deep convection, specifically satellite derived growth rates and total lightning flash rates, as well as environmental conditions from NWP data.

-J. Sieglaff