Day 197′s post (2 days ago) displayed the severe thunderstorm outlook from the Storm Prediction Center (SPC) valid on Friday. So what happened on Friday? Well, as you can see, there was quite a bit of severe weather across the northern plains.
Poor Internet connectivity continues, so once again another short — yet informative — post.
The Storm Prediction Center (SPC) is forecasting a moderate risk of severe thunderstorms across a portion of Minnesota tomorrow. People across the northern plains should review their severe weather preparedness plans and be prepared to enact them tomorrow.
Author’s Note: It was only after writing tonight’s post that I learned about Tropical Depression #2. I’m sure I’ll be blogging about that tomorrow.
As I was preparing to head home this afternoon, I received an email from the Storm Prediction Center’s (SPC) Warning Coordination Meteorologist (WCM), Greg Carbin. He had created a cursory overview of June 2010′s severe thunderstorm and tornado warnings. In my conversations with Greg this week, he informed me that Monday (5 July 2010) was the first day the SPC had not issued a watch since 15 May 2010. That means the entire month of June had at least 1 severe thunderstorm or tornado watch issued per day. That’s very impressive!
All severe thunderstorm warnings issued during the month of June are plotted above. The darker the shading of blue, the more times a given area was under a severe thunderstorm warning. It is quite apparent that the central plains east into Ohio had a very active month, with numerous severe thunderstorm warnings issued for most areas. There are several states in this swath that were almost entirely covered by severe thunderstorm warnings.
All tornado warnings issued during June are plotted below. Once again, the darker shading indicates the more times a given area was under a tornado warning. The same area from central plains east toward Ohio stands out once again. However, in this plot the northern Minnesota and eastern North Dakota areas also stand out. Most of these warnings were issued on 17 June 2010, when a very large tornado outbreak unfolded across the northern United States.
As a plug, I should point out that these images were created using the Python programming language – a favorite of mine! If there is the slightest of chances that you might need to learn to program at some point in your career (note: this includes ALL METEOROLOGY STUDENTS, undergraduate and graduate alike) this is one language that you need to have under your belt. It’s very easy to learn and very powerful!
VORTEX II was once again forced to call a down day because the atmosphere just wasn’t willing to cooperate. Fortunately for the crew, tomorrow appears to hold more promise for thunderstorms in their general area.
So, with all these down days recently, I wondered how the 2010 tornado season has compared to the tornado seasons of years past. I’ve previously mentioned that 2010 has been a below normal year for tornadoes through the first three months of the year. Now that another (almost) 2 months have passed, and VORTEX II has begun, where do things stand now?
In the image above (which I’ve described previously here), the average over the last five years is marked in grey, and actual events for this year are plotted in red. As you can see, we are still nearly 200 tornadoes below the average over the last five years. This is not a good sign for the VORTEX II crew. Here’s to hoping the next few days and weeks are better for researchers.
As I’ve been alluding to for several days, the stage is being set for a significant severe weather outbreak on Monday. In fact, the VORTEX II crew called off any operations today, Day 9, so that they could travel to be in position for operations tomorrow.
Although it is becoming increasingly apparent that a significant severe weather outbreak will unfold tomorrow, the exact location of the worst weather is not entirely obvious. It is true that a very powerful mid-level trough will be racing through the plains at the same time warm, moist air will be drawn northward, and hot, dry air will be surging eastward from the west. But it isn’t apparent where the intersection of all these ingredients will occur.
Below are forecast soundings from a couple of sites throughout the southern plains taken from four different numerical models that were initialized and run this morning. A sounding is essentially a vertical snapshot of the atmosphere’s temperature, moisture, and wind profiles. They allow meteorologists to assess the atmosphere’s potential for producing a wide variety of phenomena ranging from ice storms to wind storms to severe thunderstorms and tornadoes. Temperature and moisture profiles are plotted on a Skew-T (named because the temperature lines are “skewed” at angles), whereas the wind profile is typically displayed using a hodograph.
The image above is taken from the 12 UTC (7 AM CDT) run of the North American Model (NAM). It is the sounding and hodograph for Norman, OK at 01 UTC Tuesday (8 PM CDT Monday). The image below is taken from the same model run but is valid an hour earlier for Wichita, KS. Without going into a lot of interpretation (if enough people request it, I’ll do a future blog post or two about interpreting soundings and hodographs), both of these images are representative of what would be expected in a significant severe weather outbreak. These images alone would argue that the chance of significant severe weather would be quite high in central Oklahoma and southern Kansas.
But, it can’t be that simple, right?
The image above is once again valid for Norman, OK at 01 UTC Tuesday (8 PM CDT Monday), the difference is that it comes from the 15 UTC (10 AM CDT) run of the North American Model with the Kain-Fristch convective scheme (NAMKF). The image below is taken an hour earlier from Wichita, KS. Notice anything different about these two images and the two images above?
Although the hodographs (wind fields) still look conducive to severe thunderstorm development, the thermal and moisture profiles do not. In these runs the instability is considerably lacking and the moisture appears to have dried out. This would indicate that central Oklahoma and southern Kansas would not be in the axis of greatest threat for a severe weather outbreak tomorrow. So where did it go?
This would indicate that central Oklahoma and southern Kansas would not be in the axis of greatest threat for a severe weather outbreak tomorrow. So where did it go?
If we take a look (above) at the same kind of plot a farther east of the I35 corridor, in this case, Tulsa, OK, we can once again find temperature, moisture, and wind profiles that look similar to the first two I showed. This would seem to argue for the severe weather threat to be centered more in the northeast Oklahoma area than the I35 corridor in central Oklahoma and southern Kansas.
So which is it? Maybe looking at another model will help us determine where the highest risk will be…
These images are taken from today’s 12 UTC run of the Global Forecast System (GFS) model. The image above is valid for Norman, OK at 00 UTC Tuesday (7 PM CDT Monday) and the image below is valid at the same time for Wichita, KS.
Although not as impressive as the NAM forecast for Norman, OK that I posted initially, the GFS forecast for Norman is certainly indicative of a significant severe weather potential. Wichita, KS, on the other hand, still has very good wind profiles, but doesn’t have the temperature and moisture profile to support a widespread significant severe weather outbreak.
What about Tulsa, OK?
The forecast (below; valid at the same time as Norman, OK and Wichita, KS) for Tulsa, OK isn’t as impressive as Norman’s, but is a lot better than Wichita’s.
This set of temperature, moisture, and wind profiles would argue for a severe weather threat centered in central Oklahoma, extending northeastward through Tulsa, OK and not much in the way for south central Kansas.
Anything else to look at? You bet! Below is a set of forecast soundings from a model with a grid-spacing of 4 kilometers. This model doesn’t have to parameterize convection as it is capable of generating thunderstorms in the model natively. What does this model forecast?
Once again, this model was initialized at 12 UTC (7 AM CDT) and the plots are valid for 00 UTC Tuesday (7 PM CDT Monday). The image above is for Norman, OK and the image below is for Wichita, KS. Norman’s sounding is once again indicative of a potential major event whereas Wichita’s is considerably more marginal.
Examining the sounding for Tulsa, OK (below) indicates that severe thunderstorms would be possible, but the threat for tornadoes might not be as high as the other models would indicate.
So what does all this mean? Well, for one, all these plots did was show whether the temperature, moisture, and wind profiles would be sufficient for severe weather. I didn’t even discuss whether or not a thunderstorm would develop in an environment characterized by one of these soundings. In general, the farther north you go tomorrow (based on the domain laid out in the post of central OK, southern KS, and northeast OK) the better your chance of seeing a thunderstorm. Thus, while the environment may be supportive of a major tornado in central Oklahoma, we aren’t guaranteed that a thunderstorm will develop.
Keeping all this in mind, what would you forecast if you were working tonight at the Storm Prediction Center? What would you forecast if you were working on the VORTEX II project? In both cases your forecast will put into motion various plans that affect a lot of people and millions of dollars worth of equipment. Do you err on the side of caution and over warn with your forecast, knowing it’s better to be safe than sorry? Or do you take a chance by making a more specific forecast, trying to save some people money and stress, and risk being wrong?
It’s a tough decision that meteorologists are faced with all the time. What is the best way to convey this kind of uncertainty? I’m interested in hearing your thoughts…
When it comes to forecasting, meteorologists try to use as many tools as available. Above is the output from the Map Analog Retrieval Systems (MARS) produced by the Storm Prediction Center. The idea is to take a given forecast field and compare it to the same field from the past. The top four analogs/matches are then examined for severe reports that occurred on the given analogs/matches. From these reports a probability of severe weather is created based solely off historical data. This is a form of pattern recognition…we’re just having computers find the pattern!
Above is the MARS output for Monday. In the upper right the analog is based on the forecast 500 millibar , the lower left is based on the 850 millibar analogs, the lower right is based on precipitable analogs, and the upper left is a combination of the other three. The 500 millibar and 850 millibar analogs have a similarity…8 May 2003. For those who don’t remember, there was a F4 that went through Moore, Oklahoma…Now, a lot can change between now and then, but Monday certainly has the potential to be a big severe weather day.
Below is some information regarding MARS.
1) MARS is a prefect prog approach. That prog happens to be a special version of the GFS ensemble mean. This is a version that is being tested here at SPC. The ensemble includes weighted time-lags from prior operational GFS, and GFS ensemble runs. There are 19 GFS members and MARS uses the overall mean for the height fields and the precipitable water field at each forecast hour. The ensemble mean can “wash out” significant features such as sharp troughs and ridges, especially at medium to extended ranges as the spread between the individual ensemble members increases. Verification statistics for the SPC Medium Range Ensemble forecasts are not yet available.
2) MARS uses the NCEP Reanalysis data with a rather course grid resolution of 2.5 degrees. This is far less detail than what is needed to discern the mesoscale features that play a huge role in severe weather. However, synoptically evident cases may be captured *if* the model forecast is correct.
3) Gridded severe weather output is based on arbitrary probability values ranging from 5% to 45%, with 15% roughly corresponding to a SLGT risk in past SPC Outlooks. We have not verified what a 15% contour means when generated on a MARS forecast map. If you look at the historical outbreaks using MARS you’ll see values of 25% inside areas that verified at over 45%. Is this a “good” or a “bad” forecast? We hope to have statistical verification after the 2005 severe weather season. In the meantime, use the link below for a graphical verification for the latest MARS forecasts.
4) Only 3 components go into the MARS scheme; 500 height gradient, 850 height gradient, and precipitable water. Obviously, many more ingredients that go into making a severe weather episode!
5) The MARS gridded severe weather output is based on the SPC rough logs from 1979 to 2004. There are huge problems with these logs including report inflation during the last 15 years. There may be incredibly good pattern matches from the earlier part of this period that may have very few reports associated with them. A poor match on a later date may contain 50-100 small hail events. Remember, “garbage in-garbage out”.
6) Again, be careful! Look at the date matches on the web page and make sure (if you can) that the pattern being forecast is similar to the analog pattern found by MARS. The RMS numbers help a little but investigation continues on ways to better define whether a match is “good” or “bad”. Right now, only the top 4 “matches”, or analogs are used. It’s entirely possible that some days will have 8 great analogs and other days may have none. On those bad days it is possible that a lot of unreliable severe weather data is being gridded anyway. Also, the RMS values usually decrease in the extended period as the GFS ensemble grid changes to a lower resolution.
Today was the first day of operations for VORTEX II (Day 6 overall). As you can probably surmise from the image above, they operated in northwest Kansas, on the far western edge of the Storm Prediction Center’s slight risk area today. Expectations were low for tornadoes, but the thought of practicing a storm intercept on an actual storm was too good to pass up.
The armada got what they were looking for…a severe thunderstorm. We also learned what bugs and kinks still need to be worked out before attempting a major intercept. It appears we’ll need to get these worked out quickly as next week has potential for severe significant severe weather days. I plan on discussing these potential operations days this coming weekend.
