Potential HSLC severe event Thursday, March 24th, including VORTEX-SE deployment

A potent upper-level trough (Fig. 1) and associated surface cyclone (Fig. 2) moving through the eastern CONUS will bring a chance for severe high-shear, low-CAPE (HSLC) convection to portions of the Ohio and Tennessee Valleys on Thursday. This event is especially noteworthy because in addition to potentially affecting several collaborating CWAs, the VORTEX-SE project (including CSTAR students Jessica King and Keith Sherburn from NC State) will be operating in and near Huntsville, AL.

gfsUS_500_avort_036 (1)

Figure 1. 500 hPa absolute vorticity (1/s) and geopotential heights (m) for 0000 UTC 23 March 2016 GFS, valid 1200 UTC 24 March 2016. Credit College of DuPage.

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Figure 2. 2-m theta-E (K) and 10-m winds (kt) for 0000 UTC 23 March 2016 GFS, valid 1800 UTC 24 March 2016. Credit College of DuPage.

 

Several features of this setup are consistent with recent HSLC research of severe events. The narrow plume of low-level high theta-E air stretching from near the Gulf of Mexico northward through Tennessee (Fig. 2) is similar to that found in Jessica King’s high-resolution simulations and contributes to increased CAPE in this area, particularly in the NAM (Fig. 3). Additionally, forecast soundings suggest continuous advection of high theta-E in the low-levels throughout the event (not shown). Coupled with a rapid decrease in theta-E with height and favorable “ball cap”-shaped hodograph (both shown in Fig. 4), the thermodynamic and kinematic setup appear favorable for severe HSLC convection. Though best upper-level forcing for ascent is projected to lift northward away from the area of interest as the event goes on (note location of vorticity maximum in Fig. 5 compared to Fig. 1), other signs point to this being a severe event.

 

namSE_con_sbcape_039.gif

Figure 3. SBCAPE (contoured, J/kg), SBCIN (hatched, J/kg), and 10-m wind (kt) for 0600 UTC 23 March 2016 NAM, valid 2100 UTC 24 March 2016. Credit College of DuPage.

06_NAM_039_34.54,-86.81_severe_ml.png

Figure 4. 0600 UTC 23 March 2016 NAM forecast sounding for northern Alabama valid 2100 UTC 24 March 2016.

gfsUS_500_avort_042.gif

Figure 5. As in Fig. 1, but valid 1800 UTC 24 March 2016.

 

Convection-allowing NCAR ensembles suggest the possibility for rotating updrafts (Fig. 6) within a broken line of convection (Fig. 7). As noted, VORTEX-SE will be operating on this project with its multiple mobile sounding and radar teams, sticknet array, lightning mapping array, and disdrometers, in addition to other fixed instrumentation. More information on the project can be found here.

I plan to write a follow-up blog discussing VORTEX-SE operations during the event following its conclusion. However, this is an important and exciting step in our aims toward improving the understanding and forecasting of HSLC convection, as this (if it verifies) will be the most-sampled HSLC severe event in history.

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Figure 6. 0000 UTC 23 March 2016 NCAR ensemble paintball plot of hourly maximum 2-5 km updraft helicity > 50 m2/s2 valid 2000 UTC 24 March 2016.

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Figure 7. 0000 UTC 23 March 2016 NCAR ensemble paintball plot of 1-km AGL reflectivity > 40 dBZ valid 1900 UTC 24 March 2016.

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One Response to Potential HSLC severe event Thursday, March 24th, including VORTEX-SE deployment

  1. Jonathan Blaes @ WFO RAH says:

    Nice post Keith. Thanks for putting it together. Safe travels and good luck with the observations.

    It’ll be interesting to see what happens on the northern extent of the convective line in the true HSLC area in the western Ohio Valley.

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