UW Overshooting Top Algorithm Hits Storm Prior to Springfield, MA Tornado

Yesterday, 1 June 2011, climatologically rare tornadoes hit New England. The University of Wisconsin Overshooting Top algorithm identified an overshooting top with a severe thunderstorm at 2002 UTC 1 June 2011, just west of Springfield, MA (right). The overshooting top magnitude is filled atop the GOES visible imagery. The overshooting top identification occurred 28 minutes ahead of the first tornado report in Westfield, MA at 2030 UTC (a western suburb of Springfield).

UW Nearcast Product and Developing Convection

The GOES Sounder Nearcasting product is being used today on the EFP CI-desk to identify possible forcing mechanisms for the deep convection. In the image below the nearcasting theta-e difference is shown, valid 1700 UTC 01 June 2011. Strong convection has been ongoing and continually developing in eastern to north-central Kansas along the minimum (maximum instability) and northeastward toward the strong gradient in the nearcasting theta-e difference. It was noted this gradient is also coincident with a strong dewpoint gradient at 850 hPa. It is believed southerly flow across this gradient is helping force the convection. Further east across the Mid Atlantic region, convection was developing largely in the minimum of the theta-e difference, with a strong gradient to the west as low-level moisture decreases behind the front. It has also been noted there are many other areas of strong potential instability indicated by the nearcasting product, however there is not deep convection associated with many of these areas. One hypothesis is there needs to be not only instability present, but also a forcing mechanism. Possible forcing mechanisms maybe inferred by a strong gradient in the instability indicated by the nearcasting product, suggestion strong temperature and/or moisture advection.

NSSL-WRF Simulated ABI Imagery and CI forecast

This morning on the EFP CI-desk, the simulated ABI imagery from the NSSL-WRF provided guidance on location and timing of initial CI location for many of the forecasters. As can be seen in the image below, there was a tight cluster of forecasted first CI location points over the higher terrain of northern New Mexico. The simulated ABI band 13 image valid at 1900 UTC shows newly developing convention over northern New Mexico. A few other forecasters favored convective initiation along the moisture gradient in the lower troposphere in eastern Kansas. (Ongoing storms northwest of Salina, Kansas were excluded from the forecast area.)

UW CTC Highlights Most Rapid Development of Convective Line

The UW Cloud-Top Cooling (CTC) rate cannot only be used to nowcast convection initiation, but also highlight the most rapid vertical growth along a line of developing convective clouds. Below is the GOES visible imagery/UW CTC valid at 1732 UTC 31 May 2011 and base radar reflectivity at the same time. The entire line of towering cumulus over central Michigan looks similar on visible imagery, but the UW CTC highlights (green circle) the most rapidly growing and hence precipitating portion of the line (also green circle).

Simulated ABI Radiances Compared to GOES Observations

This week there is no EWP running so all support is geared towards the EFP. Early Tuesday on the CI desk of EFP, the NSSL-WRF simulated ABI radiances were compared to the current GOES observations for judging the timing/placement of the upper level vorticity maxima/upper level dry intrusion over the Central US, as well as impact of cloud cover on convective intiation forecasts over the western Great Lakes.

Below are the 15 UTC simulated ABI brightness temperatures (top) and observed GOES brightness temperatures (bottom). The consensus of the forecasters on the CI desk was the NSSL-WRF had excellent placement of the upper level vorticity as depicted by the water vapor channels. On the other hand, the NSSL-WRF struggled to capture the intensity and magnitude of a band of clouds and decaying convection over the Upper Mississippi Valley/western Great Lakes. The images below show the GOES observed clouds are much more expansive and have colder brightness temperatures than the simulated ABI clouds from the NSSL-WRF. Discussion is ongoing on how these clouds will impact convective initiation timing and location later today.







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