Smoke and Fog in the VIIRS Day/Night Band

July 2nd, 2015
Suomi NPP VIIRS 0.70 µm visible Day/Night Band and 11.45 µm - 3.74 µm Brightness Temperature Difference images, and Ceilings and Visibilities, ~0800 UTC (click to enlarge)

Suomi NPP VIIRS 0.70 µm visible Day/Night Band and 11.45 µm – 3.74 µm IR Brightness Temperature Difference images, and Ceilings and Visibilities, ~0800 UTC (click to enlarge)

July’s first Full Moon occurred at 0219 UTC on 2 July (a second full moon occurs later this month on 31 July). Strong illumination from the moon showed river valley fog in several tributaries of the Mississippi River (for example, the Wisconsin River in southwest Wisconsin; the Upper Iowa River in Iowa) across the Upper Midwest. The Suomi NPP VIIRS Day/Night Band also shows a plume of Canadian wildfire smoke aloft, stretching from central Iowa northwestward to western Minnesota. This smoke (visible on 1 July in Aqua true-color imagery from the MODIS Today site) is not apparent in the IR Brightness Temperature Difference field, although the river valley fog certainly is. Smoke is transparent to most infrared channels and detection at night is very difficult if visible information such as that provided by the Day/Night Band is not present.

The VIIRS Day/Night Band also enabled detection of the dense plume of Canadian wildfire smoke as it moved off the US East Coast and over the adjacent offshore waters of the western Atlantic Ocean at 0614 UTC  (below). Again, note that the smoke aloft does not exhibit a signature on the corresponding VIIRS Infrared imagery.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm Infrared images (click to enlarge)

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm Infrared images (click to enlarge)

Why 1-minute data matters: Beavertails

June 4th, 2015
GOES-14 Visible (0.6263 µm) Imagery, 04 June 2015.  1-minute imagery on the left, 5-minute imagery on the right (click to play animation)

GOES-14 Visible (0.6263 µm) Imagery, 04 June 2015. 1-minute imagery on the left, 5-minute imagery on the right (click to play animation)

Beavertails are ephemeral cloud features that form in the inflow of supercell thunderstorms. They are horizontally long and roughly parallel to the inflow warm front. Its appearance (and presence) is affected by and influences inflow into the storm, and by inference, it affects radar returns. That is — a change in the Beavertail cloud can precede a change in radar. Accurate detection of this cloud type, then, aids the understanding of evolving storm morphology. The animation above shows a severe convective system over southeastern Wyoming, viewed at 1-minute intervals (Left) and at 5-minute intervals. Beavertails that form persist for about 30 minutes, so 5-minute imagery will resolve them; however, the resolution of the 1-minute data is far better to monitor the small changes in size and shape that are related to storm inflow.

Do beavertail changes affect the radar? The animation below shows the ProbSevere product readout from 2000-2220 UTC (Courtesy John Cintineo, CIMSS) (Click here for a slow animation). (Click here for an animation (from 1918-2058 UTC) that includes warning polygons). The increases and decreases in the MRMS MESH appear unrelated to the formation/decay of the various beavertails.

NOAA/CIMSS ProbSevere Product, 2000-2020 UTC on 4 June 2015 (click to animate)

NOAA/CIMSS ProbSevere Product, 2000-2020 UTC on 4 June 2015 (click to play animation)

This storm was captured by different chasers. This YouTube video from Scott Longmore shows the evolution of the convective system from the ground. Hat/tip to Jennifer Laflin, NWS EAX and Chad Gravelle, OPG, for alerting us to this case.

Why 1-minute data matters: Orphan Anvils

June 4th, 2015
GOES-14 Visible (0.6263 µm) Imagery, 11 May 2014.  An orphan anvil is indicated (click to play animation)

GOES-14 Visible (0.6263 µm) Imagery, 11 May 2014. An orphan anvil is indicated (click to play animation)

‘Orphan anvils’ typically will develop before and just as a cap that prevents convective development breaks down. They can therefore be a precursor to strong thunderstorm development. The animation above shows an orphan anvil just before strong convection (Storm Reports) develops over south-central Nebraska. The anvil development is obvious in the 1-minute animation, above. (Click here for an un-annotated, smooth animation). This anvil was mentioned in the SPC Day-1 Convective Outlook updated at 2000 UTC (the 1-minute imagery is called 1km in that outlook).

The animation below compares 1-minute (top), 5-minute (middle) and present 15-minute GOES (bottom) time-steps over northwest Kansas on June 4 2015. It is a straightforward matter to notice the orphan anvils in the 1-minute imagery; it is far more challenging when using the 5-minute time-step and it’s nearly impossible with present-day 15-minute GOES time-steps. In this case, the cap was not broken. (Hat tips to Bill Line, SPC and Chad Gravelle, OPG, for these cases; Click here for additional comments and here for additional information on SRSO-R Operations).

GOES-14 Visible (0.6263 µm) Imagery, 4 June 2015, with 1-minute time-steps (top), 5-minute time-steps (middle) and routine 15-minute GOES time-steps (bottom) (click to play animation)

GOES-14 Visible (0.6263 µm) Imagery, 4 June 2015, with 1-minute time-steps (top), 5-minute time-steps (middle) and routine 15-minute GOES time-steps (bottom) (click to play animation)

Mesoscale Convective Vortex (MCV) in southern California

July 20th, 2013
Suomi NPP VIIRS 0,7 µm Day/Night Band and 11.45 µm IR channel images

Suomi NPP VIIRS 0,7 µm Day/Night Band and 11.45 µm IR channel images

A comparison of AWIPS images of Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel data (above) showed a large mesoscale convective system in southwestern Arizona at 08:40 UTC or 2:40 am local time on 20 July 2013. With ample illumination from the Moon (which was in the Waxing Gibbous phase, at 96% of full), the “visible image at night” capability of the VIIRS Day/Night Band image allowed shadowing from overshooting thunderstorm tops to be clearly seen; the coldest cloud-top IR brightness temperature of the overshooting tops was -83º C (violet color enhancement). In addition, numerous cloud-to-ground lightning strikes were associated with the MCS at that time. A few hours earlier, this storm had produced reports of wind damage in the Phoenix area just after 05 UTC (SPC Storm Reports).

With the arrival of daylight, McIDAS images of GOES-15 (GOES-West) 0.63 µm visible channel data (below; click image to play animation) revealed the emergence of a well-defined and relatively compact Mesoscale Convective Vortex (MCV) that continued to move westward across southern California during the day. The MCV also played a role in helping to iniitate additional convection in areas such as the San Bernadino Mountains of southern California.

GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (click image to play animation)

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 20:05 UTC (below) showed that the clouds associated with the MCV were primarily low to mid-level clouds, which exhibited IR brightness temperatures that were generally warmer than -20º C.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

For aditional information on MCVs, see the VISIT lesson “Mesoscale Convective Vortices“. For additional information on VIIRS imagery, see the VISIT lesson “VIIRS Satellite Imagery in AWIPS“.