New Blog

I have a new website:

www.wxforecastnow.com

This will be my new web home where I have a storm chase photo album, forum, weather forecast tools, and my new blog:

www.wxforecastnow.com/wxblog

In addition to the usual storm chase posts, I also have a general "weather" category and a "wxforecastnow.com news" category.

5 June 2009 Wyoming Tornado

June 5th turned out to be a spectacular tornado day. We left the Denver area during the early afternoon hours and targeted Cheyenne, WY. Storms ended up firing just a tad further north than we expected and we intercepted this storm just as a beautiful wall cloud was present. The tornado developed to our west while we sat on HYW 85 and waited for it to cross the road. The tornado was on the ground for approximately 25 minutes and it crossed the road about 1/8 mile to our north. Our group (TWISTEX) sampled the tornado as it roped out and crossed HWY 85. We had a full deployment surrounding the tornado with mobile mesonets and one of Tim's probes likely took a direct hit. This was a very successful chase day.

Lull in Activity

Here we are approaching the heart of storm season '09 and zonal flow dominates the synoptic weather pattern... leading to very little supercell and tornado activity. The long range forecasts look grim with zonal flow and then a forecasted ridge building in by May 16-17 and beyond. There may be a couple of "marginal" at best plays out there over the next 7 days, but overall the upper level flow and good moisture don't align correctly for supercells. The TWISTEX project is still working out some technical issues with COM ports on our new mobile mesonet system, but we are close to resolution. I plan to be back out on the road once the forecasted ridge breaks down. If the cap looks breakable on Tue in eastern Colorado, I may poke my nose out there and see if I can't catch me a supercell... we'll see.

 

Cedar Hill, TX Tornadoes - 29 April 2009

 This turned out to be quite an eventful day. Our main goal was to test out the mobile mesonet software that I've been working on all winter, but we got to see and collect data near tornadoes. We met up with the rest of the group in Plainview, TX at 2pm targeting storms that would fire on the dryline and move off and interact with an outflow boundary from early day convection to the east. A storm fired on the dryline as expected and it slowly moved towards our location throughout the afternoon. We sat at Chubby's BBQ in Plainview for a few hours, had some amazing West Texas BBQ, and watched as our storm slowly gained strength. While it was west of Plainview, the storm had a high base as it's inflow environment was about 85/55. A mid level mesocylone was apparent on radar as the storm approached our location. Our group left Plainview and got east of the storm while it become outflow dominant and took on HP characteristics. It cycled and a new wall cloud formed with a lower base shortly after while the storm began to take on more of a classic supercell character. At this stage there were many gustnadoes along the RFD boundary and even a organized anticyclonic whirl developed on the south end of the storm. The 2nd cycle was uneventful other than dust whirls and a nice wall cloud. At this point it appears that RDF boundary from our supercell surged ahead because it was rather cold and negatively buoyant and I believe this interacted with the outflow boundary from earlier in the day. Just to the south and east of our location, a large, low, dark rain free base quickly developed. The structure was amazing with rapid inflow from the east. We quickly found ourselves in the forward flank downdraft region of the new dominate cell. A few large (1.5") hail stones fell at our location. We quickly drove south to get in front of the "main show". I noticed some rapid downward motion and a "waterfall" effect in the clouds to our south and west. An RFD dry slot quickly developed and cut in what appeared to be from the south and southeast. Within minutes, a rope like "needle" tornado quickly formed and dissipated. Then minutes later the main tornado developed and took on a cone-like appearance for a while with a little bit of dust being kicked up below. The main tornado became a slender cone and condensation descended to the surface.  Our group traveled towards the tornado trying to get in it's path. We sample data within the forward flank downdraft all the way to about 1/2 to 1/4 of a mile north of the tornado as it roped out. We now noticed a new tornado developed maybe a mile or less to our east. As the main tornado crossed the road in front of us just to our south, we were going to get right up behind it to sample data, but the tornado showed a bit of erratic motion so we backed off and stayed about 1/4 mile away. Both tornadoes dissipated and we noticed new development to our east. The roads we were driving on were dirt and we should not have been out there without 4-wheel drive, but we found ourselves stuck after the hook echo passed over and caused our road to essentially become like cookie dough with 3 inches of cake batter on top. We had a Hummer H3 try to "ram" us out of there from behind, but we slowly slide towards a deep ditch and had to abandon that effort. After hours of trying every "MacGyver-like" method to pull us out of there... including ropes, winches, pulleys, Hummers, and large 4 wheel drive trucks without success we were forced to give up. However, a very kind local farmer saved us by coming out and pulling us 2 miles through the mud with his tractor. We were very appreciative as the sun was setting. This was a very memorable chase and I'd put it up there with my top 3 favorites (Manchester, SD being #1).   

Moderate Risk for severe weather today KS and OK

Severe thunderstorms including supercells with large hail and tornadoes are possible today over southeastern KS and eastern OK. Storms are starting to fire now on the dryline in north central Oklahoma. Here's a cool 3D image of initiation. I don't think this storm is surviving at the moment, but it's a cool image anyways.

Moderate Risk - Tornado Warned Storms Southeast US Today

Scattered supercell thunderstorms are currently present over the southeastern US. The most organized storm at 5pm Eastern time was tornado warned, had just crossed I-20, and is heading towards the Georgia state line. The storm has a fat "hook echo" on it indicating that it is a classic/HP storm. Radar returns to 70 dBZ suggest there is BIG hail in this thing... look out!

Gearing up for storm season

I went to the National Storm Chaser's Convention last weekend in Denver. It was a real nice time and I met lots of great people. I got to hang out with Reed Timmer and Chris Chittick from http://www.tornadovideos.net/ for a while. They were cool guys and I look forward to seeing them out there on the road this spring. Sorry if I talked your head off Reed! I've been isolated from storms for too long!

My buddy Sean Poling gave me a few pictures from last season so I thought I'd post them here given the lack of storms this time of year. The pictures were taken in Kansas on May 22, 2008. Maybe he will comment on them since I wasn't there (I was still at Snoqualmie Pass, WA at that point). Looks like he intercepted a nice supercell with an RFD dry-slot and a developing tornado. Sean, comment about your storm. (BTW I didn't add all the shots... it appears the storm went HP at some point as one of the shots has a really wet RFD).

Oklahoma Supercells 10 Feb 2009

Wow! is this really February? A line a tornadic supercells is barreling through central Oklahoma at the moment. There are 4 distinct supercells with well developed hook echoes on this radar image. The storms are fast movers... with speeds of 45 kt. This could be a dangerous situation as they move through the Oklahoma City area. Looks like the month of May out there!

Rear Flank Downdraft 101

I've had several people comment on "what the heck is an RFD and why do we care!". Well, I'm going to do my best at explaining what they are and why they're important to storm and tornado research. First lets look at each term. Rear - the rear side with respect to storm motion. Flank - side or lateral. Downdraft - downward flowing air. So an RFD is an area of downward flowing air found near the rear and side of a supercell thunderstorm. More specifically, it is found from the rear to right side of the storm's main updraft with respect to motion. The picture shows an RFD. The view is looking north and the lower gray cloud straight ahead on the road is a wall cloud. Wall clouds form on the interface between the updraft and RFD. To the left is clearing behind the storm and the RFD scours away clouds wrapping counter-clockwise around the rotating updraft forming a clear slot or notch (visual evidence of the RFD). RFD winds hit the ground and spread out along the surface. Storm chasers look for this signature, which manifests as a horse shoe shaped cloud, as a precursor to tornado formation in supercell thunderstorms. Once the RFD develops, it will do one of two things... 1). focus the broad storm scale rotation near the surface into a tight circulation (i. e. tornado) or 2). cause the storm scale circulation to become less focused near the surface and essentially kill off low level rotation (no tornado). This is why the RFD is so important to tornado formation (at least we think that is true at the moment). It takes a special RFD to form a tornado... and a REALLY special RFD to form a long-lived damaging tornado. The basics are this: an RFD that is neutral or positively buoyant (think of a balloon that either hovers in place or moves upwards on its own) will readily rotate inward and upward into the storms main rotating updraft. These downdrafts are special because most downdrafts fall out of the sky because the air in the downdraft is heavier than it's surroundings due to evaporative cooling. However, a warm RFD is forced downward by something else... most likely vertical pressure differences. So once this warm, buoyant air is forced down to the surface, it spirals in to a common point under the updraft and is recycled. It had angular momentum as it rotated downward (or developed it due to other reasons). As the RFD air spirals inward to the center of the updraft... angular momentum is conserved. You can test the physics of this at home by sitting in your computer chair and start spinning with your legs out. While spinning, bring your legs inward. You will quickly begin to rotate faster. This is due to the conservation of angular momentum. It is theorized that the same thing happens with the warm RFD air. However, more commonly RFD air is colder than its surroundings and the opposite effect will occur. Evaporatively cooled air (from rain and dry air) can contribute to this. Cold RFDs will hit the ground and be too heavy for the updraft to recycle much of the air. The RFD will surge away from the updraft and the conservation of angular momentum will cause the rotation to slow down (do the computer chair experiment starting with your legs in and then push them out... you will start fast and then rotate slower). So RFDs are very important to the development of tornadoes and the demise of rotation. In fact, it is likely that the RFD that causes tornadoes to develop in time will cause the tornado to rope out and die. Warm RFD's that initially fuel the tornado turn colder in time and snuff off the circulation. This is where lots of current tornado research is being done today. Why are some RFDs cold and others warm? Why do they transition over time. Why can one storm produce multiple RFDs over time that are sometimes warm and other times cold. There are lots of questions to be answered.

Alta Vista, CO tornado

Since it's the middle of winter and I'm thinking a lot about storms, I thought I would post a few shots and some radar data from my tornado intercept last August. I'm glad to be back out on the Plains after being away for 4 years. .. Here's a view of the Alta Vista, CO tornado developing (view is from the west looking east). A nice RFD notch can be seen with a dust whirl developing underneath. The tornado was a mile to my east. The storm was a neat little LP supercell that had a very compact base as seen from Dann's shots on the other side of the storm. Note that the pictures were taken by an iphone camera. Not bad quality for a phone, huh. I wasn't prepared to chase on this day. Keri & Tommy were in Florida with our main camera and we had just moved back to CO from WA. All of our stuff was still in boxes. Anyways, it was a fun chase, got to see a tornado, and get some half way decent pictures.

Here's the Pueblo, CO radar image from 4:19 local time. The storm was very sheared out west to east and had no visible hook echoes. It was an LP storm with all of its precipitation well downshear from the main updraft. There were also lots of surface boundaries in the vicinity. Once of which was a large north to south boundary that was likely a combined dry line - outflow boundary. This played a role in convective initiation and possibly tornadogenesis.




Finally, here's a picture of the tornado when it was mature. The funnel was not visible from my perspective. Notice that swirl-like cloud above and left of the tornado... that was a long-lived feature on this storm and was likely the low level mesocyclone. Rapid cloud based rotation was present for about an hour prior to the tornado. This was a very interesting storm from many aspects.

Alta Vista tornadic LP supercell

Photo taken by Dann Cianca of the Alta Vista, CO LP supercell that later goes on to produce a tornado on 13 Aug. 2008. I've drawn in where I think a mini-RFD surge was occurring. I was located just left of where I labelled "RFD" and got blasted by a warm and dry RFD surge as the tornado developed.