On 21 Jun, 2013, at 18:39, Shawn Milrad wrote: Hi all, As you might have heard, the foothills of southern Alberta (including the city of Calgary) are in the midst of incredibly bad flooding, leading to 100,000+ people being evacuated in Calgary alone. Info from the Calgary Herald here: http://www.calgaryherald.com/news/LIVE+Flood+waters+siege+Calgary+southern+Alberta/8550481/story.html, and a great map with flood pictures here: http://www.calgaryherald.com/news/flood-map/index.html. Also, a few videos are posted here: http://www.theweathernetwork.com/news/articles/alberta-floods-your-dramatic-photos-and-videos/8084/ This event was primarily brought on 200+ mm (8+ inches) of rainfall in the foothills each of the past two days (see attached radar-estimated 24-hour precipitation totals from Environment Canada, one from 18 UTC 19 Jun - 18 UTC 20 Jun, and one from 18 UTC 20 Jun- 18 UTC 21 Jun (today)). Much of the water then flowed downstream along the Elbow and Bow rivers towards larger communities, forcing the City of Calgary to declare a state of emergency for only the 2nd time ever, and first time since 2005. Meteorologically, I used Kyle Griffin's GFS analysis site to produce a theta on the Dynamic Tropopause (DT) map (attached) which clearly shows a large Rex block over western Canada and the NW US during the period in question. This forced the closed low (also seen on the attached 500 mb height analysis) to sit and spin over eastern Washington and Idaho as a "sideways negatively tilted" (I made this term up haha) trough, essentially setting up strong CVA from the east into southern Alberta. The strong forcing combined with persistent upslope flow allowed an anomalously moist (+3SD) stream of air (see attached PW standardized anomaly plot) to approach the area from the east. The anomalous PW plume appears to be able to be traced back to the Gulf just by looking at the PW plot. I have not played with the HYSPLIT trajectories yet, but that would be an interesting diagnostic. Seems to me that this is the only possible setup to get persistent convective rains into this region. Another interesting thing that comes to mind is how much of the top-side ridging in the Rex Block was related to the very anomalous Alaska heat earlier in the week, and associated the downstream development from the Pacific discussed a few days ago. Comments welcome....(and apologies for the synoptic semi-novel). -Shawn ********************************************************************** On Fri, Jun 21, 2013 at 2:05 PM, Bosart, Lance F wrote: Hi Shawn, Let's try this again... SLP, 1000-500 hPa thickness, PW, and 250 hPa wind analyses for 0000 and 1200 UTC 20 June 2013, courtesy of Heather Archambault, show the deep upslope flow against the Canadian Rockies that resulted between a lee cyclone over Montana and the western Dakotas and a sprawling east-west oriented anticyclone over southwestern Canada. Heather's DT and 250 hPa PV and irrotational wind analyses (attached), both for 0600 UTC 20 June, show that the upslope flow is strongest north of the PV hook and has a very well diabatically driven upper-level outflow signature in the 250 hPa irrotational wind field As Shawn has already noted, Heather Archambault's DT theta/wind/925-850 hPa layer-mean vorticity loop (http://www.atmos.albany.edu/student/heathera/dt/nam/7_to_22_jun13.html) nicely shows the connection between the Alaskan ridging and associated heat wave discussed previously on map and this heavy rain event in the Calgary area. As the Alaskan ridge begins to build northward on the DT on 12-13 June, one Pacific DT disturbance undercuts the ridge on 13 June while a second DT disturbance moves southward over eastern Alaska on 13-14 June. Both DT disturbances interact with one another and amalgamate west of Washington State by 15 June as strong ridging building continues across Alaska. The resulting amalgamated DT disturbance remains quasi stationary through 17 June and only begins to move toward the Pacific Northwest on 18 June in response to yet another DT disturbance dropping southward across eastern Alaska. As the DT disturbance crossing the Pacific Northwest continues eastward and evolves into a PV hook, backward-tilted anticyclonic wave breaking (what else can we call this process?) occurs over southwestern Canada on 19-20 June which completes PV hook evolution. The surface reflection of this PV hook formation process drives warm, moist air poleward east of the U.S. Rockies after which this air turns westward toward the southern Canadian Rockies immediately on the northern side of the PV hook and along the corridor of strongest low-level easterly geostrophic flow between the lee cyclone over Montana and the anticyclone to the north. it seems as though high-impact rainstorms are occurring in multiple places around the world right now. Can anyone quantify where these rainstorms in the aggregate fall in global climate space? Lance ********************************************************************** On 21 June, 2013 20:50:13 GMT Gregory Carbin wrote: To further add to this post... Moisture channel and IR loops of the event are available here: http://www.spc.noaa.gov/exper/archive/looper.php?date=20130619&type=wv http://www.spc.noaa.gov/exper/archive/looper.php?date=20130619&type=ir NESDIS PW and PW Anomaly Loops can be seen here: http://www.osdpd.noaa.gov/bTPW/US_TPWPCT.html And, the University of Calgary Suominet plot of GPS PW is available here: http://www.suominet.ucar.edu/pw_plots.html?site=SA10 The log for site SA10 2013 is here... http://www.suominet.ucar.edu/data/staYrHr/SA10nrt_2013.plot ... and appears to show a max GPS PW value of 28.7mm occurring at 5:45 UTC, 20-June-2013. An incredible event! -Greg