6/26/2015 RUC Convective Parameters and Upscale Events in Southern Ontario Mike Leduc Environment Canada

6/26/2015 Outline Motivation Define Upscale Event Hypothesis for RUC STP index and upscale events Preliminary (Partial) Results SREF and STP

6/26/2015 OSPC Severe Weather Program Challenges –Area of responsibility –Watches and warnings –Limited staffing flexibility –Message preparation software problems –Translation Fast Moving storms can overwhelm system if not anticipated soon enough.

6/26/2015 Define Upscale Event Events that produce continuous damage reports for 3 hours or more moving quickly. Implies supercells or squall lines. (Apologies to Bob Johns and his definition of derecho) This threshold defines an event that severely taxes our warning system in Ontario.

6/26/2015 Upscale Events As one would expect these upscale events usually associated with higher values shear helicity. Both Squall lines and supercell type events seemed to be associated with STP (significant tornado potential) >1 How good would STP be in identifying all upscale events?

6/26/2015 RUC Sig Tor Potential (effective layer) STP = (mlCAPE/1500 J kg-1) * ((2000-mlLCL)/1500 m) * (ESRH/150 m2 s-2) * (EBWD/20 m s-1) * ((200+mlCIN)/150 J kg-1) Product of 3 key elements –CAPE –Effective Shear and Helicity –Shear threshold of 20 m/s and helicity threshold of 150 m2/s-2 match thresholds from diagram. STP number limited if CIN’s and LCL’s are too high.

6/26/2015 If we are using STP to estimate potential of upscale events then we are looking at situations where convection DOES initiate thus CIN not a factor. Great Lakes environment in summer fairly uniform values of LCL’s in bigger events. If we are looking for both bow echoes and supercells this height not important Given above – STP a function of CAPE Shear helicity.

6/26/2015 Graph of CAPE versus shear LI -2 LI -5 LI -8 LI KTS 40 Weisman

6/26/2015 Organized storms bows and supercells have shears greater than 20 m/s.

6/26/2015 STP hypothesis Nearly all our recent “upscale” events STP>1 STP greater than 1 with shear greater than 20m/s matches the Weisman graph so could be an index to anticipate not just tornadic supercells but also bow echo type storms.

6/26/2015 Experiment Define Southern Ontario south of line from Sault Ste Marie to east of North Bay

6/26/ z July STP

6/26/2015 Experiment Examine RUC data for convective season in Southern Ontario. Log whenever STP>1 for convective season May to October. 3 hourly intervals examined. –Functionalities in RUC archive data made this relatively easy to do.

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Experiment Determine closest hour to storm initiation. Log STP MLCAPE 0-1 SRH 0-6 ESHR for previous hour Using radar /damage reports determine what happened on that day. Often need to look at downstream locations Quebec/south of lakes –Upscale Event?

6/26/2015 Sample of Ontario days where STP>1

6/26/ Results 59 days where RUC STP exceeds 1 in southern Ontario. 2 days with upscale events with STP<1

6/26/2015 Results Upscale Events 21events were labeled as upscale –9 convection began in Ontario but they became upscale downstream (nrn U.S./Srn PQ) On 19 out of 21 days the upscaling was correctly anticipated by defined RUC criteria.

6/26/2015 Marginal Events 9 Other days where RUC numbers predicted upscale – Multiple damage reports but did not meet upscale definition. – 4 days with tornadoes.

6/26/2015 The Other 31 days 9 storms were considered correct nulls STP >1 but shear was less than 40 knots. The rest were false alarms –For this study no consideration of meteorology of situation

6/26/2015 Preliminary Conclusions STP>1 correctly nowcast 19 of 21 storms that went upscale. Just by itself STP has a high FAR of detecting upscale, but combined with other factors could be less than 50 percent

6/26/2015 Examples Summer 2010

6/26/2015 July NY State outhernTierTornadoes.html

6/26/2015 July Tornado watch issued Windsor area based on dynamics (including STP) No convection developed STP max moved eastward across Lake Erie 4 tornadoes (2 EF2’s) reported in NY state

6/26/ z July STP

6/26/ z July STP

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June Tornados southeast of Georgian Bay Tornado potential thought to be low because of presence of cloud shield from previous night MCS. Wind dynamics very good. Small clearing area lower MI allowed enough heating to develop. STP index tracked this area into Ontario 2 EF2 tornadoes reported southeast of Georgian Bay

6/26/ z June

6/26/ z June

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SREF (Short Range Ensemble Forecast) convective parameters Many examples from summer 2010 of STP quite accurately picking out upscale events up to 87 hours in advance. Worked particularly well in the Plains

6/26/2015 June Georgian Bay SREF 45 hr lead time

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SREF and July Western NY 18 Hour Lead Time

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Conclusions RUC nowcasts of STP>1 In the southern Great Lakes shows a high POD of upscale events (but with significant FAR) SREF STP>1 useful even out to 87 hours (day 4) A potentially useful number for planning purposes.

6/26/2015 THE END