On the afternoon of 03/31/17, severe thunderstorms, including a couple long-lived supercells, moved across the southeastern most part of Virginia leaving behind a path of hail, wind damage, and at least one tornado, with two more reported in northeast North Carolina. These storms developed in association with a mid-level trough and related surface cyclone and cold front.
The 10.3 µm “Clean” infrared channel on GOES-16 shows the large storm system transitioning to the East Coast with a dry slot that moves into eastern NC/VA quickly erupting into thunderstorms. Note how the cloud tops associated with the secondary band that develops in the afternoon quickly cool, then appear to jump to the Gulf Stream. This becomes a forecast challenge for the local National Weather Service offices as the storms transition from the land, to nearshore water, then to OPC’s offshore zones.
The 6.9 µm and 7.3 µm water vapor channels show the enhanced warming (drying) in the mid to low levels where the atmosphere becomes unstable in the presence of near-surface warming/moistening and strong forcing with the upper-low coming in from the west. The supercell ahead of the main forcing remains isolated until later in its lifecycle with the dry slot aiding in the instability.
Zooming in on the area of thunderstorm development in the 7.3 µm low-level water vapor channel (~700 mb), the region of enhanced mid/low-level drying/warming ahead of the cold front within which isolated thunderstorms developed is apparent. Behind the cold front, that region of the atmosphere is expectedly cooler. The 7.3 µm channel is new with the GOES-R series, and when combined with the higher spatial and temporal resolution, allows forecasters to track (for the first time) low/mid-level features such as elevated mixed layers and cold fronts aloft.
00Z Weighting functions (UW/CIMSS) from the GOES Sounder 7.4 µm channel (very similar to ABI 7.3 µm) at MHX (just south of strongest t-storms) confirms that the drying/warming we are seeing is centered around 700 mb.
Looking at 00z soundings for comparison, mid-level drying was indeed present above near surface warming/moistening ahead of the cold front in Morhead City, NC leading to an unstable atmosphere. Meanwhile behind the cold front at Roanoke, VA, the cooler surface and moistening aloft led to a significantly less unstable environment.
The 10.3 µm “Clean window” infrared channel overlaid with the 15-minute GLD-360 lightning density product produced at OPC, shows the rapid increase in lightning activity as the storms in the dry slot mature. This lightning density has proven quite useful to forecasters as a proxy to the Geostationary Lightning Mapper (GLM) that is located on GOES-16. The OPC forecasters can then use this information to characterize the thunderstorms as they move offshore into active shipping and fishing areas.
These storms developed within mesoscale domain sector (MDS) 1. This meant that 1-min imagery was available for this event even though no domain was requested, and because a domain was not requested elsewhere. The 1-minute, 0.5 km 0.64 µm “Red” visible imagery shows isolated supercell thunderstorms developing out ahead of the cold front in a warm, moist atmosphere. Additional development is noted along the cold front, which raced towards and caught up to the isolated thunderstorms by sun down.
The 1-minute 0.64 µm “Red” visible imagery with the 2-minute GLD-360 lightning density overlaid shows the uptick in lightning associated with the isolated supercell that moves through Chesapeake, VA and exits around Virginia Beach. Note the increased lightning intensity around the time of the tornado.
Forecasters are looking forward to using the GLM data with the imagery to help better forecast thunderstorm over land and especially over the oceans.
The preliminary storm surveys from the Wakefield, VA NWS Weather Forecast Office are included below for your convenience.
Thanks for reading!
Michael Folmer (CICS) and Bill Line (NWS)
“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”