95th American Meteorological Society Annual Meeting Phoenix, AZ 6 January 2015

 What are the Petals?  How Are They Used  Who Uses Them  Example Case  Verification

 Observed CG Lightning strikes  SCIT history (movement and intensity)  Convective indices (helicity)  Gamma distribution function (alpha,beta)  Cosine function ( f )  Formulated together in GFE (Graphical Forecast Editor) to create a 2 hour thunder probability grid (images at the top are actual rose petal images which are very symmetric. Plumes are typically not due to wind shear. We currently make Petals)

 Cosine function Provides uniform distribution on either side of the center line of the cell motion track. Uses SCIT cell movement history to determine width of the petal (longer history = confidence = more narrow petal)  Gamma distribution function Provides decreasing probabilities downstream. Alpha and Beta parameters determine the rate of the decrease and are adjusted based on CG rate and Cell speed.

In this Petal there are three Observed CG strikes. They are shown as the red grids in the lower left corner. Thunder probabilities are set to 100 at those grids. Storm motion is from 250 (Southwest). The yellow contours are the downstream Thunder probabilities

Same Petal as on previous slide except this is filled to show the thunder probability gradients. Dark purple is 100%, yellow is around 25%.

Timing Balloons/Petals

 Update Probability of Severe (ProbSvr) and Tornado (ProbTor) Warning Issuance (locally defined as the probability that a warning will be issued for that grid)  Conditional (given a Thunderstorm) Probabilities for Severe (CondProbSvr) and Tornado(CondProbTor) and the background Thunderstorm probability (ProbThunder) grids are updated by forecasters

 Petals update the 1 and 2 hour Thunderstorm probability grids (ProbThunder1)  As petals are updated every 10 minutes, the ProbSvr and ProbTor grids are updated.  ProbSvr=ProbThunder1 * CondProbSvr  ProbTor=ProbSvr * CondProbTor  Used to update 1 hour PoP and Wx grids

 OkArkSkyWarn.org. EM’s can base text/ alerts based on ProbSvr values. County based maximum values currently with points supported through (OHMARS)  In Severe weather briefings during ongoing events  Enhanced short term 1 or 2 hour Wx and PoP grids  Public via DSP (chicklet) page  Private Companies (CommPower and iNotify) See Poster #3 Poster session #1 Kenneth Galluppi on Improving Weather Messaging

 Dry line moving from west to east across the area.  Tornado watch issued at 19z  First storm begins to develop at 1930z just southwest of the Tulsa CWA

A. Original ProbThunder B. Petals A v B = Max (A,B) Petal Enhanced Probabilities Downstream From Obs CG

A= Conditional probability That a given thunderstorm Will require a Severe Thunderstorm Warning B= ProbThunder grid from previous slide A * B = Probability that A Severe Thunderstorm Warning will be issued. Enhanced by the Petals at 1940Z on Apr 27, 2014

Original ProbSvr. Higher Probabilities in reds and lower in yellows and greens. Point A is Just ahead of forecast dryline and Point B is just behind it

Petals Only (no background values) Red grids are observed CG The contours range from 100% around the red CG obs points, to 20% on the outside edge. Each Petal is a 2 Hour Forecast of the probability of a Thunderstorm. 4 Hour loop from 1930 – 2220 UTC

ProbSvr loop From Cells originally develop directly on the dryline over Point B. A little west of the higher probabilites. The petals quickly updated the probabilities SVR and TOR warning polygons take the grid values to 100%. You can see petal influence ahead of the warning issuance.

Point A ProbThunder and ProbSvr Time Series

Point B ProbThunder and ProbSvr Time Series

Verification Petals yellow contours Obs CG in reds/ pinks Obs CG shaded by # strikes Red = 10+ Strikes are given a 10km radius Thunderstorm is defined as ‘hearing’ thunder. Stronger long lived cells verify best Cell movement (SCIT) biggest source of error

Later in event cells became more organized and verification improved (lower Brier) along the center of the petal where higher probabilities were. Fewer overall grids in the petal verified but those that didn’t were mainly on the outer edges.

 Lightning Derived Thunderstorm Petals Do Provide An Added Service  A Good First Effort to Create an Automated Method To Bridge the Watch to Warning Gap With Decent Verification Numbers  Enhances First 2 Hours of the Forecast Where HRRR/RAP Are Not As Useful.  Shared with Pleasant Hill, MO (EAX), Charleston WV (RLX), Salt Lake (SLC) and Others.

Dr. Vincent Dimiceli (Deceased 2013) Associate Professor of Mathematics Oral Roberts University, Tulsa, OK