STATUS: IOP in progress

As of 2 PM CT, the NOAA P-3 aircraft is in the air.

Today’s situation seems to pick up where the last two seasons left off: very difficult to forecast the potential for tornadic storms in the Southeast, even a few hours in advance. For several days, the models had been painting a pretty consistent picture of the highest potential for research-worthy storms across N LA. Last night, the convection-allowing guidance such as the HRRR and the NAM-Nest (NAM-3km) jumped to a consistent idea of very little convection across N LA, but a band of storms with rotating updrafts moving across central AR this evening, and heading SE toward central MS tonight. This pretty much is smack dab in between our two subdomains (near Monroe, LA and Huntsville, AL).

Of course the P-3 can cover a lot of ground quickly, but the challenges of planning those missions is huge. They can only carry a certain amount of fuel, and obviously they have to spend a certain amount of time on the ground between missions. So the P-3 scientists have to decide today what they plan on doing tomorrow. And since there are targetable storms possible tomorrow in southern AL and GA, they opted to go ahead and fly at 2 PM today on an 8 hour mission, and have scheduled a mission for tomorrow as well.

As I write, the interesting storms are forming in eastern OK, and we will watch them closely to see if 1) they develop southeastward into AR early enough for the P-3 to study them, and 2) if they are showing signs of developing down toward the Monroe area where our ground-based radars are waiting.

This spring, we are taking a breather from the style of experiments we conducted in 2016 and 2017. This is intended to give researchers some time to study data we have already collected, and to use new insights to improve our scientific questions and use of resources in future years.

However, the NOAA P-3 Hurricane Hunter aircraft will be used in VORTEX-SE this spring. This aircraft has a Doppler radar with a pair of antennas in the tail so that we can do analysis of the precipitation and winds in Southeast storms. One antenna looks slightly forward of the aircraft and the other slightly rearward. As the plane flies by a storm, along-beam velocities measured in these two separate “look angles” can be combined to give us the complete velocity at millions of points.

We have a huge challenge in VORTEX-SE owing to the terrain and vegetation to produce the kinds of mobile radar analyses that have been obtained comparatively routinely in the Great Plains. Until we can tackle this problem, we will not be able to do the sorts of detailed storm studies that can tell us how a particular tornado formed, and how the parent storm might have behaved differently than the fairly well-understood Great Plains cousins. So in addition to the NOAA P-3, we will be deploying three-radar networks consisting of University of Oklahoma SMART-Radars (dual-polarization mobile C-band radars) and either the U. Alabama-Huntsville C-band dual-polarization Doppler radar at Huntsville (known as ARMOR), or the U. Louisiana-Monroe S-band dual-polarization Doppler radar at Monroe. We want to know if such deployments of combined surface/airborne Doppler radars can be used to produce higher quality storm airflow analyses than other combinations of radars, and whether/not we can do a better job piecing together the airflow patterns in the crucial near-ground layer that is so important to tornado formation and longevity. Then, using this assessment, we can more effectively plan future observations to address VORTEX-SE science questions.

STATUS: IOP

We just finished a fairly lively discussion of the system that is approaching for early Monday.  It highlighted a lot of the issues we deal with in VORTEX-SE.

Of course, the first thing we try to assess is tornado potential, because if there isn’t at least some potential, there’s not much point to operating.  It looks like there will be very favorable hodographs in our domain on Monday.  The question is: will there be CAPE?  It almost certainly will be low CAPE (< 500 J/kg).  There was a lot of debate about whether potentially buoyant air would move this far north ahead of the early-Monday system, and debate about whether the air mass could recover after this first round and give a second round of storms later in the day.  I think it’s a reasonable hypothesis that tornadoes can occur in nearly zero CAPE as long as the updraft, augmented by the upward forcing associated with very strong environmental wind shear, can extend near the ground.

So after a round of discussion, the researchers generally felt that this is a system we need to look at.

One of the most important items of discussion was a comment made by one of our researchers to the effect of: “Isn’t this exactly what VORTEX-SE is about?  The more uncertain situations, and the low-CAPE high-shear situations?”  In a broad sense, these are exactly the situations we need to target.  The obvious tornado situations are not a big problem in the Southeast… they are well-handled.  So as discouraging as busted deployments can be, and as much as everyone would like to observe a tornadic storm, VORTEX-SE has an overriding obligation to develop knowledge to reduce the uncertainty in situations just like the one we are facing Monday.

And this mix of the role of uncertainty, biases, and recent experiences on decision making has to be pretty interesting to our Social and Behavioral Sciences researchers.  In a broad sense, our whole social sciences emphasis can be boiled down to how humans, from the forecaster all the way to members of the public, make decisions in the face of uncertainty.

STATUS: IOP

Teams are all deployed and operating across northwestern AL:

Those sideways ice cream cones are mobile radars.  The balloon symbols are mobile sounding teams.  In the eastern part of the domain you can see an aircraft symbol which is the NOAA P-3 hurricane hunter aircraft on the ground in HSV preparing for an afternoon mission.

We still have no clear idea where/when storms will form.  The numerical predictions paint a lot of scenarios, ranging from one to two rounds of storms, and just about anywhere across our domain. In general, conditions would support some rotating updrafts.  This is a fairly classic Southeast tornado forecast problem, with a relatively “uncapped” airmass and a lack of clear low-level features (fronts, etc.) to focus the location of the storms.  So we are collecting data that should help address this major problem.

STATUS: IOP Watch

Some of the researchers are gathering in Huntsville AL to participate in a Media Day tomorrow.  It will be fun to share some of the complexities, goals, and challenges of VORTEX-SE.

The Huntsville area is in SPC’s Slight Risk outlook tomorrow.  This situation still looks marginal for any tornado activity, but hail and damaging wind looks more likely.  Some of the researchers are going to check out their equipment, logistics, communications, etc. if storms move into the area tomorrow.

We are still watching the weekend.  Not much has changed in the forecast… it appears a strong upper wave and attendant cold front will move through the VORTEX-SE observing domain.  The resultant weather depends, as always, on a lot of details that won’t become apparent until late in the week, and maybe not even until we do the analyses of our data with 20/20 hindsight.  But as things stand now, an IOP is looking more likely every day.

And by late in the week, we will possibly be dealing with the idea that this first IOP could possibly involve two or more episodes of potentially tornadic weather.

The first Intensive Observing Period (IOP) of VORTEX-SE is completed.

Observations began in the early afternoon on Sunday, 13 March, with a sounding launch by NOAA’s ARL/ATDD from the SWIRLL facility at the University of Alabama in Huntsville (UAH).  UAH is hosting VORTEX-SE, and the Operations Center is at the SWIRLL.

Shortly after the midday briefing and weather discussion, the lead investigators in VORTEX-SE huddled to come up with the science plan for this episode.  The main weather feature of concern was a compact, fast-moving upper low pressure system moving out of southeast Oklahoma, expected to cross Arkansas and the Memphis, TN area during the nighttime and early morning hours.  We were fairly sure a system this intense would be associated with thunderstorms.  Much of the forecast guidance indicated that, in northern Alabama, there would be little or no surface-based CAPE (a measure of the energy available to produce buoyant, rising motion in air that is lifted from the ground feeding a thunderstorm updraft).  This doesn’t mean no storms… thunderstorms can be energized by air that originates somewhere above the ground… but tornadoes are unlikely when the surface-based CAPE is zero.  So our decision was to deploy as far west in northern Alabama as we could, hoping that the storms would still be somewhat energetic and perhaps there would be a little lingering surface-based CAPE before nighttime cooling removed it completely.  Where we can deploy is largely determined by where we can find suitable sites for mobile Doppler radars: because so many crucial processes in tornado formation happen near the ground, this requires a good radar view of the horizon without hills, trees, power lines, buildings, etc. obstructing the view.

Most of the research teams had found locations for their measurements by evening.  Sounding teams were arrayed along a line from Huntsville toward the west-northwest into northeastern Mississippi.  Mobile Doppler radars were arrayed in a triangle near Florence, AL, and other instruments joined them there, such as deployable disdrometers to measure raindrop sizes and numbers, and deployable “sticknets” to measure the temperature, humidity, pressure, and wind near the ground.

During the night, it became apparent from our soundings and the surface data that in fact the near-ground air had cooled under nearly clear skies, eliminating all surface-based CAPE.  Nevertheless, the band of thunderstorm activity continued to advance east across MS, and into AL around 2 AM.  With these storms, there was only very weak horizontal shear (change in wind from one area to another, about a mile apart, that might be a precursor to vortex formation) on a couple of occasions.  The storms were feeding off of air from well above the ground, and in this case no severe weather was reported at the ground.  By around 5 AM, the storms had weakened to showers and showed signs of departing the area to the north, and our observing operations were ended.

Was the mission a success?  I have some thoughts coming together that I will try to write down in a blog post in the “Perspectives” category soon.  We failed to observe any low-level vortices that could have developed into tornadoes, but I think we were successful in several ways.

First, one of the key aspects of VORTEX-SE is learning how to make observations to answer important tornado questions in the Southeast.  This is far from trivial.  We have no mobility in the traditional sense of storm chasing:  hills, trees, low clouds, sparse winding roads, rapid storm motion, storms at night, lack of deployment sites, and other factors make mobility nearly impossible.  So the challenge becomes how to forecast the probable weather with enough lead time to put together a scientifically useful observing network.  This means anticipating the structure, motion, and intensity of storms at least a few hours before they occur, instead of on the time scales of minutes that we became accustomed to in earlier tornado research programs.  In developing the network, important considerations are Doppler radar placement to allow for overlapping beams (giving us the ability to estimate 3D wind), and focusing the other observing systems within those multiple-radar networks.  In this first IOP, we were able to iron out the many of the wrinkles in deployment strategies, communication, and coordination.

Second, these “null cases” where we fail to observe tornadoes are important.  This is under-appreciated, even among many tornado researchers.  Thinking back across many years of storm chasing in the Plains, one of the toughest forecasts to make is when there is huge CAPE, but the warm, humid low-level air is trapped below a warm, stable layer of air aloft… the so-called “cap”.  We can compute a temperature called the “convective temperature” at which the air near the ground becomes warm enough to remove that stable layer, and convection ensues (it’s not that simple, but in broad terms the concept works pretty well).  So all this available energy can be associated with no deep cumulus clouds, or it can be associated with monster supercells, depending on a few degrees Fahrenheit difference in temperature near the ground.  Forecasting whether that “tipping point” occurs can be a big challenge with big consequences.  A similar situation exists in the Southeast: a few degrees difference in low-level temperature (and similarly, small changes in humidity) can mean the difference between no surface-based CAPE with small chances of vortex development near the ground, or “some” surface-based CAPE and much greater chances of vortex development.  To be clear, surface-based CAPE is just one number that we use to get a sense of low-level conditions; the intensification of a vortex near the ground is too complex to be understood using these simple parameters alone.  But no matter how one characterizes the near-ground conditions, it is likely that subtle differences can change the atmosphere from suppressing low-level vortex formation to favoring it.  In an ideal (lucky) IOP, we would observe a case where part of the domain had just-good-enough air for low-level spinups, and part of the area did not, and then we could compare the resulting weather in those two areas.  In the IOP we just finished, we were successful in sampling conditions that were slightly on the unfavorable side.

In VORTEX-SE we hope to make observations like these 4-5 times during March and April.  I hope we can observe a variety of regimes that have tornado potential during the remainder of our IOPs.

STATUS:  DOWN

VORTEX-SE is down today (Mon 14th) and tomorrow (Tue 15th).

There will be no briefing today as the forecast crew worked almost round-the-clock for the just-concluded IOP.  Briefings will resume at 1 PM Tuesday 14th.

IOP Watch

We are still watching the system that is about to dig into Mexico (with thickness < 540 dm well south in Mexico on the operational GFS this morning!).  It should lift northeast and weaken rapidly toward the end of the week.  At this time, it appears unlikely that this will allow for tornado-favoring wind profiles, but it’s too early to dismiss the threat completely.

Mid-month still looks more interesting.

NOAA has published a Federal Funding Opportunity announcement for VORTEX-SE in grants.gov.  To find the text of the announcement, follow these steps:

1.  At grants.gov, use the search feature to locate the announcement NOAA-OAR-OWAQ-2016-2004838

2.  Select the announcement package

3.  Click the “Package” tab, do the registration and press “Submit”

4.  On the resulting page, in the lower left, click the “Download instructions” button.

Status: IOP watch

We are monitoring the evolution of the forecast for a strong system coming onshore and progged to become a cutoff low in the vicinity of south TX.  An IOP decision will likely be made late this weekend.