STATUS: Down

The pattern of a ridge in the west and a trough in the east continues today, with a major winter weather event in store for the Northeast.  This pattern is associated with cool, stable weather in Alabama, so VORTEX-SE is still down.

However, we still see signs of a pattern change beginning toward this coming weekend.  It looks like this pattern change will involve the western ridge building east across the southern US. This means that the winds aloft will be weakening, and the atmosphere warming.  It also means that Gulf moisture will start to creep northward.  This low-level moisture is a key ingredient for severe weather, but the weakening upper winds reduce the chance of severe weather because the shear is reduced.

It is fairly likely that the pattern that follows will feature stronger flow aloft and the continued presence of low-level moisture, and thus CAPE.  So the VORTEX-SE scientists will resume their daily weather discussions via the internet tomorrow, watching for the development of potentially research-worthy weather up to seven days away.

STATUS: Down

The SPC Reports page shows a number of wind damage reports across the northern 2/3 of Alabama from last night.  A more concentrated band occurred across Tennessee, with a couple of tornado reports embedded in this activity (mainly in southwest Missouri).  I have also received a message that the NWS Huntsville has identified EF1 tornado damage in southern Tennessee.  This event is remarkable because it appears that there was no surface-based CAPE  (a measure of updraft thermal energy) present in that area.  This is interesting because, as VORTEX-SE progresses, we are increasingly wondering about the role of CAPE in general, and about the role of subtle details of the wind profile and temperature structure in the lowest few thousand feet (or less) of the atmosphere.  A major future science thrust of VORTEX-SE, should the program continue, will be to find out what the atmosphere is doing, in these very difficult-to-forecast “low-CAPE” events, that is supporting tornadoes.

We are in one of those bleak forecast periods when storm researchers wonder if there is any hope for data collection.  But the atmosphere has a way of transitioning  to new patterns without giving a lot of advance notice!  Right now, it looks like a week to ten days of the current pattern with a western ridge favoring cool, dry, storm-free weather across our research domain.

I will probably not be able to blog on Saturday 11 March, but hope to start again on Sunday.

STATUS: Down

Today gives a nice illustration of the difficulty we face in VORTEX-SE in designating our IOPs (Intensive Observing Periods).

There will likely be an event tonight that includes the passage of storms with rotating updrafts.  The probabilities are much higher in the northwest part of AL where low-level moisture is much more likely to return in sufficient quantities.  Further east, storm outflow should become progressively colder owing to drier low-level air (and more evaporation), and the storm rotation will have decreasing probability of being associated with tornadoes.

But, in VORTEX-SE the size of the grants doesn’t really allow a lot of the scientists to be positioned in northern Alabama for a full two months.  Instead, they must travel on short notice, collect observations, and then return to their home bases.  Because of the time involved in arranging and conducting the travel, we must decide four days (three days makes things uncomfortably tight) before an event that we will conduct an IOP.  This time, there wasn’t a clear enough signal of tornado potential four days in advance for us to pull the trigger.  We only have funds for about four IOPs, so we look a lot at probabilities of certain atmospheric conditions being met, including CAPE (for updraft thermal energy) and shear (for updraft rotation and tornado potential).  This time, the probabilities were much too low to make it reasonable to use one out of our four IOPs.

You might think it’s impossible to make four-day tornado forecasts… you would be mostly right.  But we are not really forecasting tornadoes, but rather the large-scale change in conditions, often associated with a passing atmospheric wave, that would lead to thunderstorms with tornado potential.  That’s a much easier forecast problem… most of these waves are fairly well depicted in our numerical models out to about 6-7 days.

Nevertheless, VORTEX-SE supports certain “always-on” observations.  In the meteorology realm, these include a nice array of instruments, fixed and mobile, operated by the University of Alabama-Huntsville, the CLAMPS atmospheric profiler from NSSL, and the Stesonet array of surface stations that Texas Tech deployed last week across northern Alabama.  Certain other research programs in VORTEX-SE, involving damage and debris studies, treefall analysis, and analysis of forecasts and human response, are also rather independent of our IOPs and ready to go into action if a tornado does occur outside of an IOP (time or region).

Looking down the road… no big change from yesterday’s blog post.  The overall weather pattern should be cool and dry for a while, and we are casting a wary eye toward the Pacific and a possible jet stream approaching North America in about a week.

Status: DOWN

This is the first official day of the VORTEX-SE 2017 Field Campaign.

The weather pattern is not supportive of tornadic storms in the near future, so our status is DOWN.

We had been watching the forecasts for a system that is expected to pass northern AL on Saturday (11th), but as time has passed, it has become apparent that this system will just lead to a cool, rainy day, with almost no potential for storms that meet our research needs.  One of our forecast models even shows the possibility of snow in Tennessee, perhaps reaching into the far northern fringes of Alabama.

After that, the overall trend is for fairly frequent passages of fronts leading to cool, dry weather.  This image shows the difference-from-normal of the conditions in the middle of the atmosphere (500 mb), forecast for five days from now.  It shows that it is more “troffy” in the northeast and eastern Canada, and more “ridgy” in the Great Basin, than normal.  Between these two areas, the jet stream air moves from northwest to southeast, driving the cool, dry air masses from the northern Plains and Canada toward the southeast US.  These two features are pretty persistent over the next week or so in the GFS forecast model.

There are hints in our best forecast tools that the pattern may become more active again in a week or ten days.  But even our best forecast tools have very little skill that far in the future.  So, stay tuned.

So now the forecast team will start looking further down the road.  When it looks like there may be targetable weather within seven days, we will switch the experiment status to “IOP WATCH”.  In VORTEX-SE, that simply means that the teams of scientists are collaborating on the forecast, and thinking about travel arrangements, logistics, and instrument status.  When our confidence becomes even higher that there will be weather suitable for our studies, we will switch to a status of “IOP”.  This means that teams from Texas Tech, Colorado State, Purdue, the University of Oklahoma, NSSL, the University of Massachusetts, and the NOAA Air Resources Lab in Tennessee will travel as quickly as possible to Northern Alabama to commence observations.  Because of all of the travel, and the limited research budgets, this decision is close to irrevocable.

It seems that this winter has featured higher humidities in the low levels of the atmosphere over the Gulf of Mexico than commonly observed.  I don’t have any analyses or numbers to back that up… just a subjective sense.  High dewpoints are a key ingredient in tornado potential.  So if this trend persists into the spring, we might expect a more active tornado season than typical.  Of course, high dewpoints, leading to greater updraft energy, are just one ingredient in the tornado recipe.  There are also certain important characteristics to the wind profile with height in the atmosphere, and of course there have to be lifting mechanisms to initiate the storms.

If I can carve out time, I will try to blog a time or two in the next couple of weeks about the progress of VORTEX-SE, and what we are trying to accomplish during this field campaign.

Erik

STATUS: Observations in progress

We are conducting a boundary layer heterogeneity experiment.  The convection forecast is extremely murky, and it would take some unforecastable accidents to yield a low-level flow structure supportive of tornadoes.  So we are going to focus on some remaining experiment objectives that have not been fully satisfied.

STATUS: Finished until tomorrow

We observed at least six supercells in the domain today, with reasonably good data collection on several.  One was tornado warned and appeared to be quite close to producing a tornado near Athens.

We are going to reconvene at 9 AM Sunday for a meeting at SWIRLL to plan our final (extra) day of observations.

Tornado sirens sounding in Huntsville.  Storm with intense rotation just west of here near Athens AL.  We have seen a number of circulations today, and are making some good observations.

STATUS: Operations in progress

We are expecting a convective system now in MS to move into AL early this afternoon.  The flow through the lower troposphere is stronger today than yesterday.  The low-level airmass is very inhomogeneous after yesterday’s storms, so it’s hard to anticipate where CAPE will be largest.  The highest dewpoints are to our SW in MS, and with the southwest flow, some of this air should move northward ahead of the incoming convection.

We are setting up one dual-Doppler baseline between ARMOR and Courtland, AL.  Later, we hope to add another mobile Doppler into the mix with a shorter baseline.  Disdrometer and sticknet deployment teams are heading west toward Florence/Muscle Shoals/Tuscumbia.  If interesting storms are targetable west of them, they will deploy.  Otherwise they will wait to deploy their sensors in the Dual-Doppler lobes.

STATUS: Operations today

HRRR guidance has been consistent during the last few hours.  The convective system currently in far western MS is expected to persist, and move into the V-SE domain around 3 PM.  Allowing for a ~2-h error, we might need to have in situ teams into the west end of the domain by 1 PM, and soundings even earlier.  So we will meet at 9 AM at SWIRLL.  This will be our only meeting… there will not be a prepared 1 PM weather briefing.

There will be an email and a status post around 12Z tomorrow/Sat morning, just in case we need to meet in the morning to plan the day’s operations.  Most likely the email will announce that we are waiting until 1 PM for the briefing/meeting, but there is a chance that an overnight MCS will persist and move into AL during the mid/late morning.