The March 2 Severe Weather Outbreak

On Wednesday, February 29th, I trained three HPC forecasters on using the GOES-Sounder RGB Airmass product in operations with model overlays to identify model weaknesses/strengths. The forecasters seemed to grasp this method of training well and one of them included it in the HPC Map Discussion on Friday to show just how well the PV anomaly showed up in this product when compared to conventional water vapor imagery. Below are some sample images as the event unfolded in the Tennessee and Ohio Valleys.

The GOES-Sounder RGB Airmass product valid at 21z on 03/02/12.

Figure 1: The above image shows the severe event unfolding in the Ohio Valley around 21z on 03/02/12. The red circle highlights the tail end of a squall line with discrete cells on the southwest flank. The red circle highlights drying behind the frontal band, but no stratospheric air is evident in this image. The yellow circles highlight three PV anomalies evidenced with the pinks of the dry stratospheric air acting as a tracer.

The MODIS (Aqua) RGB Airmass product valid at 1910z on 03/02/12.

Figure 2: This MODIS (Aqua) RGB Airmass image is two hours earlier (1910z on 03/02/12) and shows greater detail in regards to the drying behind the frontal band. This dry air looks to be part of a larger dry punch that originates from lower in the atmosphere, but may also contain some dry stratospheric air (highlighted in the larger red area). Note the extra dry surge that precedes the frontal band (smaller red area) that was associated with earlier supercells that caused significant tornado damage in parts of southern TN and northern AL. Although we only get a few MODIS passes a day, this product is definitely showing much more detail than the GOES-Sounder product.

The GOES-13 water vapor image valid at 2115z on 03/02/12.

Figure 3: This final image shows the GOES-13 water vapor image at 2115z on 03/02/12 with the CIMSS water vapor table. The red circle highlights the drier air behind the frontal band, indicating drying around 400 mb, which could have aided in the discrete appearance of the southern supercells along with the excellent environmental instability and shear. The yellow circle highlights the earlier disturbance that initiated the supercells in northern AL and southern TN. Although you can identify the drying, it is hard to decipher the origin of that drying from water vapor imagery alone.

This is only one case of how the airmass products could provide additional information to forecasters in identifying subtle features within the synoptic flow. I hope to collect more cases like this to give HPC forecasters and SAB analysts more confidence in isolating a particular region that would be at high risk for heavy rainfall. This could also prove useful to SPC forecasters for identifying heightened risk areas for severe weather.

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