A series of potent mid-latitude cyclones brought an active period of weather to much of the US during the end of October. GOES Water Vapor imagery with GLM overlay captures the large scale features influencing the active period from the morning of Oct 24 through the morning of Oct 28 (Fig 1). The animation begins with the much discussed atmospheric river pushing across the west coast, characterized by relatively cool BTs in the water vapor imagery due to the presence of abundant atmospheric moisture and cloudiness.. The associated shortwave makes landfall on the US coast thereafter and advances across the southwest US, as drying/descending air coupled with cooling ascending air is diagnosed in the water vapor imagery with the amplifying trough. During the second half of the animation, this system continues east across the southern plains into the southeast, resulting in several rounds of severe weather. At the same time, another shortwave trough exits the midwest into the northeast, forcing the development of severe weather along its path. This system merges with another shortwave moving northeast along the east coast, developing into a strong nor’easter. The pulses of severe weather are apparent as increase in cloud cover (very cold BTs) and development of lightning (yellow-red overlay).
A GOES water vapor imagery analysis, typical of NWS forecasters, was presented by NWS AMA in their AM 26 Oct AFD ahead of expected severe weather forced by the approaching western US system: “The latest water vapor imagery reveals very dry subsiding air moving along the base of an upper level trough near the AZ/CA border. Lift associated with this system is now evident in east central AZ up across the Rocky Mountains. As this system advances east, strong jet level winds will move into the Panhandles, with some stacked jet alignment across the western zones this afternoon.”
A great water vapor analysis was presented by NWS ALY for the East Coast events during the morning of 26 Oct: “GOES 16 water vapor imagery shows the 3 upper-level features that will come together over the next several hours to produce a rapidly deepening coastal low. There is a southern stream shortwave off the East Coast, another shortwave currently over Virginia and North Carolina, and a remnant upper low over Michigan. What was initially the primary surface low weakened earlier tonight over Pennsylvania, and the new coastal low has developed in response to the southern stream disturbance off the Coast of the Carolinas and has already intensified to 995 mb. With this classic Miller Type B storm track, this coastal low is expected to continue to intensify as it moves northeastward during the day today.”
Focusing on 26 Oct, the western shortwave trough brought blowing dust and severe weather to the southern US plains. The split window difference (with IRW overlay for cold BTs), captured several plumes of blowing dust (low to neg SWD, or dark gray to black in this scale), including in southeast AZ, Chihuahuan Desert, and west Texas all within the strong/dry southwest flow (Fig 2). The SWD also reveals the presence of the dryline extending north across west TX through west Kansas (sudden transition from dark grey (dry) to light gray (moist), west to east). Convection initiates along this boundary toward the end of the animation.
Related to the blowing Dust, NWS EPZ wrote in their PM 26 Oct AFD: “Blowing dust still a concern, not many plumes visible from satellite though a few obs sites are reporting visby reductions. Willcox Playa [in southeast AZ] looks like it is starting to shed blowing dust off to the east across the Lordsburg area.”
The GOES TPW product also captures the deeper moisture gradient present along the N-S oriented dryline, along which convection subsequently develops (Fig 3).
Focusing on convective initiation along the dryline over the W OK/TX panhandle border, a 1-min GOES-East VIS/DCPD RGB side-by-side animation shows the value of the RGB (Fig 4). By 2222 UTC, the DCPD RGB begins to show glaciation within the cu field (transition from cyan to green to yellow), signification initiation is imminent. Meanwhile, in the VIS, one can diagnose vertical cloud growth and clumping of cu, but cannot classify glaciation. Note, the recipe for the DCPD RGB was modified slightly in this case, lowering the upper end of the VIS and Snow/Ice band components to account for the lower sun angle and resulting lower reflectance values.
Convection would go on to initiate, with the first lightning detected by GLM at 2248 UTC, and first convective warning at 2321 UTC (Fig 5).
An IR animation shows the evolution of convection, including severe storms, across Oklahoma through the evening (Fig 6). The GLM Flash points overlay (as opposed to the gridded overlay) allows one to view the IR image and GLM data within a single image without blocking the important cloud top information of the IR. The rapid dropoff of lightning activity toward the end of the animation is coincident with cloud top warming and weakening of the convective line.
The VIIRS DNB/NCC product captured active convection further south slightly after the animation above (Fig 7a and 7b). The two images provide a more detailed view of convection (visible imagery at night), and even captures a lightning flash, in the second image, associated with convection developing ahead of the main line in southern Texas.
Another line of severe storms developed across the southeast US on the 27th. GOES-East 1-min VIS and GLM flash points captured individual convective updrafts and potentially stronger storms embedded within the broader line of convection (Fig 8).
Bill Line, NESDIS and CIRA