Ramblings of a Graduate Student

Today VORTEX 2 operated in western Texas in the Lubbock vicinity. Here, an outflow boundary marked the boundary between extremely warm, moist air to the south and relatively cooler and drier air to the north. Unfortunately, the wind shear aloft was not great for supercell thunderstorms, so thunderstorms had a low probability of what is known as supercell tornadoes. However, these storms did have a lot of wind associated with them. Several mobile mesonets reported wind gusts in excess of 70 mph with at least one recording a gust greater than 80 mph. In addition to the strong winds, numerous gustnadoes were observed along with at least one landspout.

However, these storms in Texas were not the major weather story of the day. For that, we have to look to Oklahoma City, OK where over 11″ of rain has fallen in less than 24 hours. (It is still raining at the time of this writing!) Most of the rain – nearly 9″ of it – fell in around a 6 hour period. As you can imagine, this led to major flooding across the Oklahoma City metro area. Numerous high-water rescues were made today, roadways closed, and houses flooded.

Today’s flooding in Oklahoma City, along with the flooding in Nashville, TN during the weekend of 30 April – 2 May, are referred to as 500 year floods. This does not mean that a flood of this magnitude occurs only once every 500 years. It *is* possible to have two 500 year floods in a single year. What a 500 year flood means is that the probability of a flood of this magnitude occurring during any given year is 0.2%. What is the probability of a city having two 500 year floods occurring in the same year? Well, that’s simply 0.002 * 0.002 = 0.0004%. This would be equivalent to a 250,000 year flood! Yikes! Hopefully this means Oklahoma City won’t have a flood like this again this year – but it remains possible.

In any event, the events of today have underscored why Oklahoma City, OK is known for having some of the most wild weather on earth. In the last 6 months there has been a blizzard, an ice storm, two tornado outbreaks, a multi-million dollar hail storm, and now a 500 year flood. If you live in or around the Oklahoma City, OK area, I sure hope you have an emergency/disaster preparedness plan. If not, you might want to consider creating one…

The armada spent the night in Colby, KS.  This morning the decision that faced them was to either target storms that might develop in the northern Texas panhandle and then move south, or to target the storms in NE CO / SE WY and which would move southeast.  Being in Colby, KS and the realization that the severe weather threat tomorrow afternoon and evening appeared to be better over the northern target than the southern one, the armada chose to target the northern choice.  The feeling was while the meteorology was slightly better to the south, the driving down there to chase storms away from where they would need to be the next day it wasn’t worth it.

The armada headed to Byers, CO with the intent of chasing storms that might develop in and around the Denver area.  Enroute to this target, the armada realized that the low clouds and storms already developing by lunch time would probably spell doom for any threat of supercells.  Based on this they headed to Greeley, CO and waited for the next wave of thunderstorms.  Unfortunately, the next wave of thunderstorms also developed too early and left a rain-cooled atmosphere in its wake.  This cool air ruined any chance for supercells in this area, so the armada set its sights on storms developing north of Cheyenne.

These new thunderstorms were slowly becoming supercells and exhibited transient mesocyclone features.  By the time they got up to Cheyenne, WY and headed east on I80, these storms were bonified supercells (albeit weak ones).  The armada set up a deployment and collected some data as the storm moved into Nebraska.  Interestingly, while not a true supercellular tornado, one of the mobile mesonet probes observed a brief landspout tornado!

About the time they armada was going to call it quits for the day, a new thunderstorm developed extremely quickly to their west in the Cheyenne, WY area along colliding outflow boundaries.  This storm quickly became a supercell and tracked through the north and east side of Cheyenne, WY.  The storm exhibited fairly decent low-level rotation but there were no reports of tornadoes.  Several members of the armada experienced golf ball sized hail, but as of this writing, there has not been any damage to the vehicles.

Currently, the armada is experiencing thunderstorms enroute to their hotel.  I’ll be sitting here watching their safety until they reach their destination or the storms have passed.