As we mark the final day of the 2012 Atlantic Hurricane Season, we have witnessed a few mid-latitude storms that have included elements of convection and even hurricane-force winds. After working with the Ocean Prediction Center (OPC) last winter, I was amazed at how many hurricane-force extratropical storms occur during a typical winter. Could you imagine if we named all of those? These storms are winter’s version of the hurricane, but are far more expansive than their southern cousins. This post will focus on two storms in particular that have kept the forecasters at OPC quite busy in the last few days.
I created a four day animation of the complicated West Coast trough (large-scale storm system) that spit out a couple different waves of low pressure that included wind gusts along the CA and OR coasts over 70 mph and very heavy rainfall. The main highlight of this animation is the Vaisala GLD-360 30-minute accumulated lightning that is overlaid on the infrared satellite image where you can see multiple lightning pulses in the frontal bands, then a secondary area in the cold-air cumulus under the cold-core upper lows. It is interesting to observe how the lightning diminishes in frequency as the convective elements move into the near-shore waters. Can anyone guess as to why this occurs?
On the Atlantic side, a storm rapidly intensified as it passed just east of New Foundland overnight. The SEVIRI RGB Air Mass animation above shows this evolution with the Vaisala GLD-360 15-minute lightning accumulation overlaid to get a better idea of how the convection evolved along the cold front east of Bermuda. The main highlight in this imagery is the intense pinks/reds that are indicative of a significant stratospheric intrusion. This intrusion originates farther west over Quebec and moved towards the developing potential vorticity (PV) anomaly that was moving offshore of New England and Nova Scotia. This interaction led to explosive cyclogenesis in the Northwest Atlantic with the storm deepening from 995 mb at 12z on 11/29/12 to 950 mb at 12z on 11/30/12. That qualifies as a cyclonic “bomb” dropping 45 mb in 24 hours south of 60N! Very impressive!
To further demonstrate this storm’s power, I have overlaid the ASCAT high resolution winds on the Air Mass image to show how close the surface winds match up to the red-coloring associated with the stratospheric drying. The highest winds observed in this image are near the tip of southern Greenland (coincidentally called the “Tip Jet”) where ASCAT picked up winds near 65 knots or 75 mph. The larger area of brown with some embedded dark red wind barbs are winds of 50-60 knots (58-70 mph). Notice the large gap in ASCAT coverage in the eastern quadrant of the cyclone. It is quite possible that this area is experiencing winds in excess 60-65 knots!
The final image of this post is the 20z AIRS pass showing the higher concentrations of stratospheric ozone especially closer to the source region for this particular intrusion. I would expect to see much more ozone farther east, but the largest concentration of greater than 350 Dobson Units is sitting over eastern Quebec and New Foundland, which would indicate to me that this system is still maturing.
Considering the relative lack of interesting weather across the lower 48, the Pacific and Atlantic basins are quite active, keeping the forecasters at OPC quite busy over the next few days. Thanks for reading!