An upper-level closed low and associated deepening surface low pressure system brought snowfall from New Mexico to the UP of Michigan and severe weather to the ArkLaTex region on 21 January 2018. Additionally, strong surface winds associated with the storm system caused a blowing dust event across west Texas. GOES-16 provided valuable information to forecasters across the middle of the US in forecasting and analyzing this event.
The 10.3 – 12.3 um “split window difference” provide a great method for detecting and tracking dust. Recall, this blog has discussed using this channel difference in the past for detecting low-level moisture gradients from the clear sky. Negative values of this difference will highlight lofted dust as well. Figure 1 shows the situation across the southern Plains by combining the split window difference (gray/brown scale) for non-cloudy skies with the IR Window channel(bright colors) for clouds. The dust appears as brown, and can be seen spreading from west Texas into southwest Oklahoma as it wraps around the deepening low. The shades of gray are mainly clear skies. To the north, snow-producing clouds are detected from Oklahoma through Nebraska into Iowa. To the east, convection is developing within a Tornado Watch. Additionally, low-level GOES-16 derived winds (white barbs) indicate wind speeds over 40 knots at the top of the dust layer.
Taking a closer look at the convection over Oklahoma and Texas using GOES-16 5-min VIS/IR sandwich combo, storm growth was not all that explosive in an environment characterized by meager instability and high shear (Fig 2). Blowing dust is also observed in the 0.5 km visible imagery making its way into Oklahoma.
GOES-16 Derived Motion winds can be combined with surface obs to determine deep layer bulk shear values (Fig 3). In this northeast Texas example shortly before storms developed, surface winds of 23 knots from 190 degrees and GOES-16 400-500 mb winds of 78 knots from 214 degrees meant ~0-6 km shear values of 58 knots! Similar values were computed from elsewhere in the region.
On 22 Jan, the winter storm continued to advance northeast into the upper midwest, producing heavy snow and blizzard conditions along its path. The GOES-16 day cloud phase distinction RGB allows one to easily differentiate the fresh snow (already melting) from clouds containing ice from clouds containing mostly water from bare ground (Fig. 4 and 5).
– Bill Line, NWS