Widespread gusty winds and blowing dust developed across portions of Nevada during the late afternoon/evening of 28 June 2020 in association with a potent upper low and related cold front. GOES-West upper level water vapor imagery with RAP 500 mb analysis contoured depicts the evolution of the compact upper low sagging southeast across the Pacific Northwest, forcing frontal boundaries south across Nevada (Fig 1).
At 2212 UTC, the NWS Reno, NV AFD included the following text: “The winds are kicking up dust off the Carson Sink in eastern Churchill County as evidenced by the GOES-17 dust satellite imagery. While cloud cover is blocking the evidence of dust from the playa farther north, dust can be seen coming off the Black Rock/Smoke Creek deserts from the Fox Mountain ALERT cam. So far evidence of major reductions in visibility are scant given the lack of visibility sensors in the dust plume areas.”
Both GOES-East and GOES-West captured the development and evolution of blowing dust plumes and wildfire hot spots across Nevada during the day. First analyzing 0.64 um VIS, blowing dust is most apparent extending south out from under the broad cloud shield over central Nevada (Fig 2 and 3). Another source of obvious blowing dust develops slightly further south near the southwest NV/CA border. Finally, a smoke plume becomes apparent in southern Nevada toward the end of the period. Blowing dust and smoke is most obvious in the VIS near sunset and in the GOES-East imagery where/when forward scattering becomes greatest. Similar to the 6/25 event, it is important for forecasters in the western 1/3 of the US to keep in mind they have two sources for 5-min imagery (GOES East and West), and the ideal source may vary from event to event.
10.3 minus 12.3 um Split Window Difference imagery with a linear gray colorscale and IRW overlay for coldest BTs (clouds) captured the blowing dust as the darkest grays to black in the scene (Fig 4 and 5). Additional plumes become more easily detectable than in the VIS alone, including in far southern Nevada near the beginning of the period, and smaller more subtle plumes in far east-central Nevada and southwest Utah during the middle of the period.
10.3 minus 11.2 um Split IRW Difference imagery captured the blowing dust similarly to the SWD using similar color tables (Fig 6 and 7).
Given the dry and windy conditions, conditions were ripe for the development of wildfires as well. Viewing 3.9 um imagery during the same period, several wildfire hot spots appear during the day as relatively dark gray flickering pixels (Fig 8 and 9). This linear grayscale colortable applied to 3.9 um imagery remains the authors recommended method for wildfire hot spot detection. The range is set as -40C (white) to 110C (black). Hot Spots appear as relatively dark gray and flickering pixels, and is consistent across all seasons and locations.
One can combine the SWD, IRW, and SWIR channels to create an RGB that combines dust plume detection with wildfire hot spot detection (Fig 10 and 11). In this RGB, dust plumes are vivid green, wildfires are red, bare ground is shades of dark red/green/cyan (depending on sfc temp), thick clouds are vivd blue to cyan, thin cirrus clouds are very dark blue to black, low stratus clouds are a medium green, and bodies of water are a dull cyan. Dense smoke plumes may also appear as dark green-to-cyan. In the RGB animation, the dust plumes contrast well against the background surface and above clouds. The primary dust plumes referenced earlier are obvious, with the additional smaller plumes very apparent as well. Wildfire hot spots, small and large, also pop against the bright background. Cloud classification also remains possible.
Features identified in the Dust Fire RGB are noted in Fig 12.
NOAA-20 and SNPP passes provided high resolution VIIRS imagery over the location of blowing dust and wildfires during the early afternoon. The same Dust Fire RGB is applied to the VIIRS imagery, which allows for a more detailed (spatially) look at the blowing dust underneath the clouds and it’s evolution over the 42 minute period, as well as developing active wildfires to the southeast (Fig 13 and 14). Animation here.
Finally, 1-minute GOES-West satellite imagery was available over the region courtesy of SPC for: “SPC Critical Fire Weather in CA/NV/UT/AZ” (Fig 15).
The “Dust Fire RGB” is available in AWIPS upon request (contact bill.line).
Bill Line, CIRA and NESDIS
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