Ramblings of a Graduate Student

Those of us involved in VORTEX 2 often joked about how the atmosphere would produce out ideal storm the day after the project ended. Well, we were right.

Tonight in South Dakota, a complex of supercells has developed and is nearly stationary. These supercell thunderstorms have produced what appear to be large tornadoes one right after the other. A chaser in the area has reported seeing at least 13 tornadoes today, 3 of them very large, and up-to 5 at the same time. That is just amazing. The towns of Dupree, SD and Green Grass, SD appear to be the two areas that have experienced the worst weather so far this evening, with Dupree, SD experiencing the worst. The town had numerous tornadoes develop in and around the area, prolonged period of 70-80 mph winds, and frequent bursts of very large hail. I’d be very surprised to hear there is a single building in Dupree, SD that has not been damaged.

The image above depicts what appears to be a tornado moving through the southern portion of Green Grass, SD. Tomorrow, I’ll be interested to hear what kind of damage reports come from this part of the country. This is certainly a very rare, very high impact event. The exact kind of data VORTEX 2 was looking for…

Originally I planned to blog tonight about VORTEX 2′s deployment and successful intercept of a supercell and tornado in northeast Colorado. (Ironically, this successful intercept occurred near Last Chance, Colorado!). However, details of how successful the deployment was are still a little sparse. I do know that the tornado was observed by many pieces of the armada, however it will be a few days before we know just how good the data collection actually was. The armada went a long way today – starting in Chadron, Nebraska and going as far south as several miles south of Last Chance, Colorado – so I’m extremely happy for them.

Since I don’t have any good images of the VORTEX 2 deployment, I thought I’d display a meteogram from Beaver, Oklahoma. A meteogram displays a time series of meteorological data for a given station for multiple fields. This meteogram displays temperature (red) and dewpoint (green) in the top panel; sustained wind speed (dark blue), maximum wind gust (light blue), and wind direction (diamonds) in the second panel; surface pressure (brown) in the third panel; accumulated rainful (light green) in the fourth panel; and incoming solar radiation (orange) and approximate maximum possible incoming radiation (grey) in the bottom panel.

This meteogram is special in that it captured a rare atmospheric phenomenon known as a heat burst. In a heat burst the temperature increases rapidly, the air becomes really dry (dewpoint falls), wind speed quickly increases, and often times the pressure changes. All of this occurred at Beaver, OK this evening when an apparent heat burst affected the area. Oklahoma is very lucky to have the Oklahoma Mesonet so that we can record such awesome atmospheric phenomena!

The VORTEX 2 armada once again intercepted a tornado from a storm moving into, through, and then out of Goshen county, Wyoming. For those of you who don’t remember, this is the county where VORTEX 2 intercepted it’s first (and only) tornado of 2009. I don’t have all the details of the deployment because it was very late, and the armada is still traveling, but what I do know was the several members of the armada saw at least a brief touchdown on the east side of Scottsbluff, Nebraska. The Doppler On Wheels (DOW) trucks were able to collect data on the tornado, and actually saw what appears to have been an additional tornado. Granted, no one “saw” this tornado, we’re just inferring it’s presence from the radar data. Hopefully I’ll have more information in the next few days.

As exciting as this intercept was, the image tonight is of a storm just east of the storm(s) the armada targeted. The above radar image was taken shortly before 10 PM CDT (03 UTC) and clearly shows a very strong supercell thunderstorm (complete with “hook”) beginning to wrap up. It’s a shame this storm didn’t develop earlier in the evening (before dark) so that VORTEX 2 could have targeted it. I can only imagine the dataset a storm like this would provide! Oh well. There is always tomorrow…

For day 23 of VORTEX II operations the armada targeted west central Kansas. The day started in North Platte, Nebraska, took them as far south as Garden City, KS, and will end with them located farther north. (Check back tomorrow for the actual location.)

The armada had a difficult day with storms developing rapidly, in several locations, and moving north-northwest at high speeds. The storm motion made deployment opportunities difficult and the fact there were numerous storms to choose from (and watch out for) made data collection extremely challenging – but a challenge the armada was up to. The storm V2 targeted is circled in orange (below) and had a tornado warning on it at one point. The storm’s rotation looked fairly good on radar and spotters reported brief funnel clouds, but it never produced a tornado.

Ironically, one of the sounding units (circled in yellow) was in position to observe the storm VORTEX II targeted as well as the storm immediately to the north. The northern storm (circled in red), actually went on to produce a tornado. Because Kansas is so flat, the sounding unit was able to observe the tornado from over 15 miles away! Amazing!

This wasn’t the only tornado of the day in Kansas. In fact, it was just getting started at this point. As the armada was heading back to their hotel because of darkness, strong rotation developed to the northwest of Goodland, Kansas.

The radar images above and below (same image, just annotated below) capture the tornado (area circled in yellow) and a developing tornado (area circled in orange). The radar is sampling the tornado (yellow circle) at a height of 300 feet above the ground. In other words, the velocities being displayed in this image are what the radar believes the wind speeds are of air moving toward the radar (greens and blues) or away from the radar (reds and oranges). Whenver these colors are immediately next to each other it means that the wind is either rotating, coming together (convergence), or going apart (divergence). In the examples above, the air is rotating, and quite rapidly. (I’ll do a post on radar analysis in the near future to explain how to tell if the air is converging, diverging, or rotating.) The values of the winds in this post are approximately 70 knots away from the radar and 40 knots toward.

The orange circle has a much weaker circulation, but it is one nonetheless. In the images that followed (not displayed here), the tornado (yellow circle) weakened and the developing tornado (orange circle) took over. This is known as a “tornado cycle”, or “cycle” for short. The thunderstorm that produces these “cyclic tornadoes” is known as a “cyclic supercell”.

I should add that the forecasters at the National Weather Service office in Goodland, KS were able to see these tornadoes from their office. They were also able to see a tornado on the southwest side of the city a little bit earlier!

Well, it’s over.  VORTEX II has ended for 2009.  (It actually ended on 13 June 2009, but due to an incredibly hectic last few days, I was unable to blog about it until now.)

VORTEX II 2009 intercepted only one tornado this year, but a lot of good data was collected on non-tornadic thunderstorms.  These “null” datasets (ones without tornadoes) are just as important as tornadic datasets in that it allows researchers to develop numerical prediction models that have to produce tornadoes when the atmosphere would produce tornadoes, and not produce tornadoes when the atmosphere wouldn’t produce tornadoes.  I know this sounds pretty basic and trivial, but it is a crucial distinction to make.  At this time most of our numerical models of supercell thunderstorms result in tornadoes.  However, an overwhelming majority of supercell thunderstorms do not produce tornadoes.  However, it would be nice if next year we can get more tornadic datasets.

In other news, the night of 12 June (34th day of VORTEX II) will be one I won’t forget anytime soon.  An EF1 tornado struck Norman, OK less than 1.5 miles from where I live.  This tornado developed from a thunderstorm that was approximately 30 minutes old, which is extremely fast for a thunderstorm to produce tornadoes.  Furthermore, this tornado struck the “meteorology Mecca” and the sirens did not sound until 10 minutes after the tornado lifted.  Needless to say there is quite a controversy brewing in Norman.  The text of the Public Information Statement about the damage survey is below.

000
NOUS44 KOUN 131717
PNSOUN

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE NORMAN OK
1217 PM CDT SAT JUN 13 2009

...TORNADO IN NORMAN FRIDAY EVENING...

METEOROLOGISTS FROM THE NATIONAL WEATHER SERVICE FORECAST OFFICE IN
NORMAN CONDUCTED A SURVEY OF DAMAGE THAT OCCURRED IN NORMAN ON
FRIDAY EVENING. THE SURVEY DOCUMENTED THAT A WEAK TORNADO OCCURRED
AROUND 1030 PM ON FRIDAY JUNE 12 ALONG A 2 MILE PATH EXTENDING FROM
NEAR SOUTHEAST 24TH AVENUE AND ALAMEDA STREET TO SOUTHEAST 48TH
STREET AND LINDSEY STREET. CURRENT INDICATIONS ARE THAT THE TORNADO
WILL BE RATED A LOW-END EF1 TORNADO. ALL OF THIS INFORMATION IS
PRELIMINARY AND SUBJECT TO CHANGE AS THE INVESTIGATION CONTINUES.

THIS IS THE FIRST TORNADO TO OCCUR WITHIN THE CITY LIMITS OF NORMAN
SINCE MARCH 13 1990 WHEN TWO TORNADOES OCCURRED IN NORMAN. ON THAT
DAY...AN F2 TORNADO DEVELOPED 1 MILE WEST OF CRINER IN MCCLAIN
COUNTY AND CAUSED DAMAGE IN NOBLE BEFORE DISSIPATING WITHIN THE
SOUTHEASTERN PORTION OF NORMAN AT A POINT 5 MILES NORTHEAST OF
NOBLE. A SECOND TORNADO /AN F1/ MADE A 5 MILE PATH THROUGH EAST
NORMAN NEAR AND NORTH OF LAKE THUNDERBIRD.

AN EF0 TORNADO ON MAY 7 2008 OCCURRED JUST SOUTH OF THE NORMAN CITY
LIMITS MOVING FROM JUST SOUTHEAST OF GOLDSBY TO NEAR 36TH AVENUE
SOUTHEAST AND POST OAK ROAD.

$$

SPEHEGER/SMITH/ANDRA

The armada drove a long way last night to reach their hotels in Kearney, NE because they believed the best target for supercells and / or tornadoes today would be in southeast Nebraska and southwest Iowa.  However, during the morning briefing, the talk transitioned to heading back west and playing possible storms in western Nebraska.  The thought was that while the better tornado potential might exhist in Iowa, the road network and terrain made deployments difficult and the better chances of catching a workable storm were out west.

Without going into too many details, the armada intercepted a tornado warned thunderstorm that briefly appeared like it might produce a tornado, but never did.  This makes today a first for VORTEX II…consecutive days with a tornado warned thunderstorm!  This storm was moving quickly so the armada only got one chance at a deployment on it.  When it moved past, they targeted a new storm to the southwest of the old storm.  They armada hustled into place south of North Platte and got in position to watch the storm completely collapse.

There weren’t really any other targetable storms, and the armada was closing in on nightfall, so operations were ended around 8:21 PM CDT.

Tomorrow looks like a potentially tornadic day across places in the plains.  Hopefully, if a tornado does occur, the VORTEX II armada is on it.

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.