Forecaster Thoughts – John Billet (2009 Week 3)

Being part of the EWP was very worthwhile with the four separate test beds each offering unique opportunities. The phased array radar was extremely useful. The highlight of the week for the phased array was Wednesday night’s live event. I was working with Kevin Brown from the Norman office using the phased array to simulate test warnings for the storms. There are a number of very good features with the phased array, the fast temporal updates of 1 minute per volume scan and the higher resolution brings much better identification to features. The radar has the ability to quickly change where the range folding was occurring from one volume scan to the next which meant at most just one minute of bad data. We were able to view animated cross sections through WDSSII and actually watch the reflectivity cores rise and then come back down to the ground causing downburst signatures. The current phased array radar only has one panel so it had limited viewing as the number of storms increased. We only looked briefly at a tornadic storm in the CASA area but focused on the storm coming south from Oklahoma City to Norman which also had tornadic potential. This storm we could see the original outflow move out ahead of the storm then slow down as the storm caught up and reintensified. This is when the tornado developed which we could clearly track in the velocity and as it got close to the radar we even saw the debris swirl on the radar.

The CASA network with 4 low power Doppler radars each about 40 km apart was surprisingly useful. The fact that a 3DVAR wind analysis is done with the radar scans was very helpful. This analysis clearly showed gust fronts and rear flank downdrafts. It also picked up very well on the tornado. I had some hesitation about the system because it completes a volume scan in 1 minute and if there are numerous echoes in range it only does 1 to 2 elevation scans. I think in hail situations this could be a problem. The software is programmed to look for individual cells then scan up several cuts but we had too many cells in the area so that only 1 or 2 elevations were possible. There is also a numerical forecast of various fields which utilizes the radar data and goes out 1 hour in the future. This helps significantly improve situational awareness.

While the previous two systems are only available at Norman there are two other systems which we at Wakefield hope to access locally. The enhanced lightning detection network which includes in cloud and cloud to ground strokes has one domain centered over Washington DC. The VILMA or lightning density product helped with updraft detection and provides another reality check on storm structure. Being a coastal office and talking with the scientist about the fact that in cloud lightning almost always precedes any ground strokes, we could use this product to give some lead time at the beaches during the summer time about when lightning might occur. The lightning tied to individual cells producing trends helped in predicting intensification or weakening of cells. If the cell numbers could be color coded to indicate increasing or decreasing lightning trends this would help with quick identification of which cells might be increasing.

The final data set was multi sensor multi radar data. For now one domain is centered over Washington DC and covers all of our CWA. Some of the most useful products included real time MESH or hail forecast tracks and instantaneous size estimates. In the cases and two real time events it appeared a good estimator of hail size something always needed. These tracks could also be very useful in the proper shaping for a polygon warning. The circulation tracks are so dense it was hard to use it much but would like to look at it in more detail. There are numerous other products as well which will need to be examined but we ran out of time in Norman. We are working to set this up here for real-time use.

John Billet (NWS Wakefield VA – 2009 Week 3 Evaluator)

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