VORTEX-SE In the Field

Teams are mostly in place and waiting for storms.  The deployment plan looks like this:

The domain shown here is northwest Alabama and far southern Tennessee and NE Mississippi.  Huntsville AL is in the middle-right part of the figure.  A few showers linger to the south and east of the domain, but the weather is currently tranquil across the study area.  In this graphic, the two lines crossing near Florence AL are a north-south array of sounding systems that will launch soundings about once per hour from five sites, and an east-west array of three systems.  This should help us study the rapid return of warm, humid air from the south as the current convective system departs.  There are four overlapping circles within which we will have dual-Doppler coverage.  The smaller two areas in the west part of the domain are covered by a combination of the UAH MAX X-band mobile dual-polarization radar, and the Purdue/UMASS XPOL radar.  Their “baseline” is the short line segment extending from the WNW to the ESE in the northwest part of the domain.  The two larger areas in the east part are covered by the combination of MAX and UAH ARMOR C-band radar, with a nearly east-west baseline illustrated.

The surface observations that are seen in this figure are the Texas Tech “Stesonet”… 16 sticknet instruments deployed in a mesonet that is collecting data 24/7 throughout our 2-month campaign.  An additional set of Sticknets is in a mobile vehicle that is now sitting out toward the MS border, awaiting a clearer idea of where the most significant storms will pass.  Similarly, the deployable disdrometer instruments from Purdue are sitting stationary and awaiting storms.

The MAX radar began collecting data about 20 min ago, and the Purdue/UMASS radar will commence data collection shortly.

This experiment has been designed around the general idea that an old outflow boundary from this morning’s convection will possibly lift northeast toward, or even across, the domain during the afternoon, with an attendant increase in low-level shear and possibly convective initiation.  Later, toward sunset or shortly thereafter, storms are expected to move eastward into the domain.  The structure of this system remains to be seen… it could be anything from supercells to a QLCS (quasi-linear convective system), to a band with embedded supercell structures.

The investigators are currently meeting to develop today’s science plan.  Because of the typical constraints of observing in this region (fast storm motion, limited radar deployment sites, etc.) it won’t be possible to adjust the radar deployment when we see the storms approach or develop.  Some of the more nimble assets, such as sticknets, disdrometers, etc. will likely be held near the center of the deployment domain and try to deploy ahead of the most interesting activity when it develops.  There will be another status post shortly describing the overall weather scenario and the deployment plan.

Scientist currently meeting at the SWIRLL facility at UAH

STATUS: IOP

The observations in this IOP will commence Thursday morning immediately after the passage of an expected round of morning convection.  This morning round is expected to be marginally severe at most, owing to a complete lack of low-level CAPE.  Thereafter, the atmosphere is expected to destabilize rapidly, with moderate low-level shear and strong deep shear supportive of supercells.  Afternoon supercells are possible in the VORTEX-SE domain, especially after 2 PM.  Severe storm activity is expected to increase in the evening as low-level flow accelerates and CAPE is maintained, and persist through part or much of the night.  The main window for VORTEX-SE observations is expected to be 2 PM – 2 AM for storm studies, and earlier (perhaps 10 AM to 10 PM) for environment evolution studies.  The likely focus will be NW AL, centered toward the Courtland/Florence region.

A morning science planning meeting, and short briefing, will be held at UAH SWIRLL at 9 AM.  Deployments will occur sometime after that planning meeting.  All participants are encouraged to get as much rest as possible on Wed night because of the expected long duration and nighttime observations.

Media: try to attend the 9 AM planning meeting where you can meet and discuss your opportunities with the scientists.

Beyond this IOP… we did not discuss the long range in today’s briefing, but will resume that discussion at a future briefing.  Be aware that we are likely to have another “hard down” period with no briefings for a few days after this IOP unless the weather dictates otherwise.  Watch this blog for later information.

STATUS: IOP

This IOP will commence at the earliest on Wednesday night, but more likely on Thursday morning.  The science planning meeting will be scheduled during the Wed 30 March daily briefing, and might occur on Wed evening, but more likely on Thur morning.

The overall scenario is one of several rounds of convection between Thur morning and late night/early morning Friday.  The first round should be “elevated” with the primary threat being heavy rain.  There may be another round or two during the day on Thursday, based on recent experience.  Several models are showing a buildup of surface-based CAPE Thursday afternoon, with varying degrees of low-level shear, and strong deep shear.  Finally, a cold front passes on Thursday night with an additional round of convection.

There is much uncertainty in this forecast, almost all related to the effects of hard-to-forecast convection on the state of the atmosphere.  The PIs had a long discussion about this uncertainty, and whether this IOP should be terminated.  However, we have a general philosophy that once an IOP is declared, we will terminate it only if there are obvious reasons that it will be a null event.  Without this approach, traveling investigators would likely be in the frequent situation of starting travel and then returning home, canceling reservations, etc.

After this IOP, current forecast model runs indicate a generally quiet and dry pattern for the first ~10 days of April.

STATUS: IOP

We have decided to have an IOP on Thur Mar 31.  Based on current guidance, operations would commence around sunrise.

The system we are watching is forecast to have two phases… an early phase on Thur morning with very strong low-level shear but surface-based CAPE likely not present (but with considerable rain and thunderstorms feeding on potentially buoyant air aloft), and an afternoon-evening phase with a buildup of surface-based CAPE to > 1000 J/kg, but a steadily weakening low-level wind profile.  These model details are uncertain, so the investigators have opted to declare an IOP.  There is a chance that if the forecast becomes negative tomorrow, the IOP will be canceled at the 1 PM briefing.

Beyond this week’s event, there are no signs of significant severe weather potential in the first third of April.

Status: DOWN

VORTEX-SE is down until Mon 28 March.  Mid-day briefings will resume on that date.

Hope is fading, as the large MCS in southern AL has prevented the forecasted return of CAPE.  Instead of ~1000 J/kg as forecasted earlier today, and 1000-1500 J/kg in yesterday’s forecast, we ended up with (wait for it….)  35 J/kg.  And now shear is decreasing rapidly in the wake of the earlier system… with 850 mb (~ 1 km) flow of around 35-40 kt, whereas two hours ago it was 50-55 kt.

The echoes that grew rapidly at the time of the last update were quite shallow… less than 15,000 ft deep.

Unless conditions become more favorable quite soon, we are likely to call it quits.

Hours of waiting, but we are seeing echoes develop rapidly in a confluence zone in NW AL down to eastern MS.  Dewpoints have risen to the low-mid 60’s in the vicinity of this zone.  So we are watching this closely as it approaches our larger dual-Doppler lobes.

We are watching a weak circulation moving through our high-resolution northern Dual-Doppler lobe, associated with a break in the line.  The circulation extends from the surface to the upper parts of these cells.  The cells are producing little lightning.  The best activity with this line has occurred in a small area of locally larger surface-based CAPE of less than one county in size.  Late grab from SASSI:

A couple of lines of showers have passed through, and the atmosphere has stayed stable.  However, very recent surface observations indicate that we may be getting close to having surface-based CAPE.  This means that a parcel of air rising from the ground will begin ascending buoyantly fairly close to the ground.  Our soundings show that the shear from 0-500 m above the ground is about 45 kt which should be supportive of low-level rotation.

The next line of storms is just moving into far NW AL.  Part of this line exhibited some broad rotation recently.

It seems that we may be about to have a transition to more interesting convection with the development of small amounts of surface-based CAPE.

Here’s a recent radar and satellite image from the College of DuPage site: