Ramblings of a Graduate Student

Tonight a mid-level low continues to aid development of showers and thunderstorms across northern Texas. Additionally, a second mid-level low spins across the central Gulf of Mexico. Both of these lows are tropical in origin, which decreases the large-scale threat of severe thunderstorms across the aforementioned areas. (This is for reasons I won’t explain tonight – sorry!)

Across the northern United States and southern Canada, a mid-latitude cyclone is moving eastward. Severe weather has occurred and is continuing to occur across portions of the western Great Lakes in association with the passage of cold front. Tonight’s image depicts the showers and thunderstorms developing along the cold front. Thunderstorms that develop into long lines like this are often referred to as “squall-lines“. Strong winds are typically found along the leading edge of the squall-line, followed by intense rain. Squall-lines are a form of Mesoscale Convective Systems or MCS.

Well, I’ve made it to day 200; that’s 200 consecutive days of blogging. I should get a gold star or a cookie or something, right?!?

Anyways, a relatively quiet weather pattern persists across the United States tonight. A large, subtropical ridge is located across the southern United States, helping to keep the heat locked in place across the southern half of the US. To the north of this ridge, mid-level flow is a bit stronger on the periphery of the ridge. Embedded within this stronger flow, several minor shortwave troughs are racing through the flow, helping to initiate daily bouts of convection acorss Nebraska and Iowa. This convection then develops into an MCS overnight and pushes eastward and/or southward during the subsequent day.

However, I wanted to turn attention toward the tropics. A large upper-level trough is moving through the Gulf of Mexico currently; it looks like a giant “6″ in the water vapor image above. This upper-level trough is increasing shear throughout the Gulf of Mexico, which will help inhibit any tropical storm development in the near term.

Turning attention toward the Puerto Rico area, a large area of tropical showers and thunderstorms are ongoing just north of the island. The National Hurricane Center (NHC) currently gives this tropical wave a 20% chance of developing into a tropical depression/storm during the next 48 hours. This is partly the result of strong shear co-located with the tropical wave, owing to the mid-level low currently located just to the north and east of the tropical wave. Model forecasts show the shear weakening atop the tropical wave in the coming days, which will give the tropical wave a chance to develop into a tropical depression/storm, just about the time the wave moves into the Gulf of Mexico. It’s still a long ways off, but certainly is of more concern than anything else over the last week or two.

This is becoming a reoccurring theme of late. Thunderstorms develop in the afternoon across eastern Colorado, eastern Wyoming, northern Kansas, or Nebraska. These thunderstorms then merge into a large complex that persists throughout the overnight hours. These repeat MCS in the same areas are what lead to long term flooding problems. It is only a matter of time, should this continue, before we start hearing about flooding problems across the central United States… Will this be a repeat of 1993? Only time will tell…

Tonight’s post won’t be long as the title conveys it all…

However, I do want to say that this MCS developed out of what appears to have been a fairly substantial tornado outbreak. My thoughts and prayers are with the residents of the northern plains this night.

I awoke this morning thinking that VORTEX 2 would take a down day or do some light traveling in preparation for tomorrow. I figured that they must be extremely tired from the day-after-day grind. Boy was I mistaken! The principal investigators decided to head west, across the entire state of Nebraska, and target storms coming out of Wyoming. I have to tip my hat to their dedication!

This dedication paid off with two deployments on two separate tornado warned thunderstorms. Although neither storm appears to have produced a tornado, they did drop extremely large hail! I heard at least one report from a probe of numerous vehicles with all the windows smashed out from hail. As was mentioned to me, “hail + high wind + glass = $$$”. How strong was the wind? At least one probe measured a 72 miles per hour wind gust. Just east of this report, the National Weather Service had a report of 80 miles per hour wind gusts. As I mentioned, these storms meant business.

The image above shows what has happened to the thunderstorms since VORTEX 2 ended operations for the evening. The multiple thunderstorms in the area have all grown together (this is known as “growing upscale”) and have become what meteorologists call a “Mesoscale Convective System”, or MCS for short. MCSs tend to last longer than an individual thunderstorm and can travel hundreds of miles fairly quickly, or they can remain nearly stationary. This was is moving at a decent clip to the south and east. It will be interesting to see how far south it makes it before dissipating. Will I wake up to rain in the morning? I’ll see in about 6 hours!

Not much time for a detailed blog tonight. However, I will say that VORTEX II had an unsuccessful chase day in eastern Nebraska. The original plan was to target eastern Nebraska, where it appeared the ingredients were coming together for potential supercells and tornadoes. Unfortunately, the armada was met with a rapidly developing Mesoscale Convective System, or MCS. A MCS is the term given to an organized area of thunderstorms that are working together on a scale larger than that of an individual thunderstorm, but smaller than that of a synoptic-scale cyclone. MCSs are responsible for a large portion of the rainfall across portions of the northern plains states during the warm season.

The image above depicts a classic MCS surging southeast across far eastern Missouri and western Illinois. This MCS originated in far eastern Nebraska and pushed through a large portion of Iowa during the evening hours. Assuming something drastic doesn’t occur, this MCS should continue on its southeastward trajectory and impact the St. Louis, MO area during the overnight hours.

As I mentioned in yesterday’s post, it finally happened.  The VORTEX II armada captured a tornado.  They started out the day in Sterling, KS and were faced with the decision of staying in the same general area / heading slightly SE or heading up NE of the Cheyenne ridge.  Field coordinator David Dowell and myself gave passionate arguments for targeting Wyoming which helped turn the tide…and this is what the armada did.

They started out by heading to Kimball, NE (which is in the far southwest county of the NE panhandle) and watched thunderstorms develop to their west.  As the thunderstorms moved closer to the armada, it became clear that the southern most storm had developed supercellular characteristics.  After a brief discussion, the armada decided to make this the target storm and they deployed on it.  As they approached the storm from the east, the National Weather Service office in Cheyenne, Wyoming issued a tornado warning on the storm.  While the storm was not producing a tornado at that precise moment, the storm certainly looked like it was getting ready to produce one.  The Weather Channel broke in to their regularly scheduled program began streaming live video of the supercell thunderstorm.

As the armada sent probes 1, 2, and 3 into the region of the thunderstorm that was about to produce the tornado, very large hail began to fall on the vehicles.  In fact, probes 1 and 3 received so much hail that the damage forced them to abandon all other missions for that day.  They were forced to stay behind the armdada and have their windows repaired.

While the probes were being pelted by hail greater than 4.50″  (softball size), the supercell began to develop a rapidly rotating wall cloud that went on to produce a tornado (carried live by the Weather Channel).  The storm was sampled from start to finish by the armada (and The Weather Channel).

Once the tornado dissipated, the armada tried to reposition themselves to try and observe any additional tornadoes that might develop.  This proved a difficult task due to the poor road network and storm motion.  Fortunately for the armada, the storm did not produce an additional tornado, so they didn’t miss one due to poor roads.

When operations where finally called off, the armada had a long drive back to their hotel (Kearney, NE).  To make matters worse, the storms they had been targetting all day had grown together and formed what is known as a Mesoscale Convective System (MCS; really just a really big cluster of thunderstorms interacting and aiding one another).  This MCS repeatedly had transient rotational signatures, extremely large hail, and damaging winds that tracked all along the roads the armada needed to travel in order to reach their hotel.  Because of this, I kept the VORTEX II Operations Center open until after 1 AM CDT.  I’m happy to report that every vehicle made it back safely…except probes 1 and 3 which were forced to stay in Cheyenne for repairs.

The tornado was preliminarily rated an EF-1 on the Enhanced Fujita scale.  For more information, including pictures of the tornado, please visit the NWS Weather Forecast Office in Cheyenne, WY

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