Radar Composite over Midwest (click image to play animation)

Satellite and especially radar revealed the tell-tale signs of an undular bore over southern Wisconsin on the morning of 26 August. The parallel lines of enhanced radar return, above, suggest that the outflow from the convective complex over northern Wisconsin organized into a bore, in part because the atmosphere over Wisconsin (as sampled, for example, by the 1200 UTC Green Bay Sounding) included a stable layer. The wind at Madison’s Truax Airport shifted to northeast at 1453 UTC as the bore moved overhead. This is typical. Winds are parallel to the bore motion and perpendicular to the linear bore feature. What did the visible imagery show?

GOES-14 was in SRSO-R mode over the midwest on 26 August, providing one-minute imagery. As shown below, an abundance of cirrus obscured information from the lower cloud deck throughout the early part of the morning. However, parallel lines of low clouds do occur, marking the edge of the bore, later in the loop (after 1600 UTC northwest of Madison). The GOES-14 animation also shows the transformation of the atmosphere from convectively unstable at the beginning, with transverse bands in the cirrus outflow suggestive of turbulence, to an atmosphere with mid-level cumuliform clouds (over northwest Wisconsin) in the wake of a departing Mesoscale system. Finally, the Mesoscale system exits the state as cirrus continues to erode. Low- and mid-level clouds have dissipated. As the lower atmosphere destabilizes due to diurnal heating, the bore must dissipate, as it requires a stable layer to propagate.

GOES-14 0.63 µm visible channel images (click image to play large animation)

(Click here for a QuickTime movie of the animation above. It has a much smaller file size).

GOES-13 imagery of the same event shows the general evolution of the atmosphere, but the temporal resolution is very coarse, with half-hourly imagery between 1445 UTC and 1545 UTC due to a Full-disk scan and subsequent housekeeping. This is a period during which GOES-14 shows considerable weakening of the convective complex. The coarse time steps also make it difficult to infer the presence of a bore.

GOES-13 0.63 µm visible channel images (click image to play animation)

Landsat-8 imagery (below) shows that the parallel lines of clouds persisted past 1642 UTC. Note that the Landsat-8 imagery is also available through the SSEC Web Map Server: Link.

Landsat-8 0.56 µm visible channel image

GOES-13 10.7 µm IR channel images (click image to play animation)

Regarding the aforementioned transverse bands in the cirrus outflow, there were a few pilot reports of turbulence that appeared to be associated with these cloud features as they were dissipating over northern Lower Michigan and adjacent portions of Lake Michigan and Lake Huron. AWIPS images of GOES-13 10.7 µm IR channel data (above; click image to play animation) and GOES-13 6.5 µm water vapor channel data (below; click image to play animation) showed the location of pilot reports of turbulence.

Most notable was the report of Severe turbulence at an altitude of 39,000 feet over northeastern Lower Michigan at 19:20 UTC (which the pilot reported as a “mountain wave”). Farther to the southeast, there was a report of Moderate turbulence at 19:00 UTC as the aircraft was descending from 40,000 to 32,000 feet. By these later times, the transverse banding signature was becoming difficult to identify on the 4-km resolution GOES-13 IR and water vapor imagery. However, the transverse banding signature was a bit more evident on a 1-km resolution POES AVHRR 12.0 µm IR image at 18:08 UTC (around the time of a report of light to moderate Clear Air Turbulence at an altitude of 35,000 feet).

GOES-13 6.5 µm water vapor channel images (click image to play animation)

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Suomi NPP VIIRS “Fog/stratus product” and Day/Night Band images

A comparison of AWIPS images of Suomi NPP VIIRS IR brightness temperature difference (BTD) “Fog/stratus product” and 0.7 um Day/Night Band images (above) revealed the formation of nocturnal river valley fog across parts of southwestern Wisconsin and the adjacent Upper Mississippi River Valley region at 08:00 UTC or 3:00 AM local time on 23 August 2013. Overlays of METAR surface reports and cloud ceiling/surface visibility indicated that the fog was restricting visibilities to 1/4 mile at a few locations.

A comparison of the 375-meter resolution (projected onto a 1-km AWIPS grid) VIIRS BTD “Fog/stratus product” image with the corresponding 4-km resolution GOES-13 BTD Fog/stratus product (below) demonstrated the advantage of better spatial resolution for detecting these fine-scale river valley fog features.

Suomi NPP VIIRS and GOES-13 IR brightness temperature difference “Fog/stratus product” images

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Suomi NPP VIIRS 3.74 µm shortwave IR and 0.7 µm Day/Night Band images

A night-time (10:01 UTC or 3:01 AM local time) comparison of AWIPS images of Suomi NPP VIIRS 3.74 µm shortwave IR and 0.7 µm Day/Night Band data (above) showed signatures of the Rim Fire which had been burning since 17 August near Yosemite National Park in California. On the shortwave IR image, numerous “hot spots” (black to yellow to red enhancement) revealed the location of larger, hotter fires that were burning along the periphery of the large burn scar. The Day/Night Band image showed (1) a bright white glow over the area of active fires, and (2) light gray signatures of the primary middle to upper altitude smoke plume that was moving northward, in addition to an area of lower altitude smoke that was moving westward toward lower elevations. Due to ample illumination from a 98% full waning gibbous Moon phase, the “visible image at night” capability of the Day/Night Band proved to be useful for identifying the location of the smoke plumes.

Later that day during the afternoon hours the Rim Fire exhibited very active growth, nearly doubling in size to over 105,000 acres (Wildfire Today | InciWeb). A comparison of 250-meter resolution MODIS true-color and false-color images from the SSEC MODIS Today site (below) showed the large and very dense smoke plume at 18:42 UTC (11:42 AM local time).

MODIS true-color and false-color Red/Green/Blue (RGB) images

The GOES-14 satellite had been placed into Super Rapid Scan Operations for GOES-R (SRSO-R) mode, providing images at 1-minute intervals during the entire day. A sequence of these GOES-14 SRSO-R 0.63 µm visible channel images (below; click image to play animation) showed that the initial northward motion of the smoke plume began to transition to a more northeasterly motion after about 17 UTC. This was due to a shift in the winds aloft as a semi-stationary cut-off low just west of the coast of California began to move northward during the day.

GOES-14 0.63 µm visible channel images (click image to play animation)

The  change in the winds aloft which allowed the smoke plume to begin drifting more toward the northeast prompted the National Weather Service forecast office at Reno, Nevada to amend their forecasts for some areas to include smoke and haze (complete AFD):

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
207 PM PDT THU AUG 22 2013

ONLY MINOR CHANGES MADE TO ONGOING FORECAST WITH THE GREATEST CHANGE TO ADD SMOKE AND HAZE DUE TO MULTIPLE ONGOING WILDFIRES, THE GREATEST CONTRIBUTOR BEING THE RIM FIRE JUST WEST OF YOSEMITE. THE UPPER LEVEL LOW WHICH HAS BROUGHT US PLENTY OF THUNDERSTORMS THE PAST FEW DAYS IS BEGINNING TO LIFT NORTH WITH A DRIER  SOUTHWEST FLOW RESULTING ACROSS NORTHEAST CALIFORNIA AND NORTHWEST NEVADA.

Surface visibilities at locations such as South Lake Tahoe were reduced as low as 1.25 miles once the smoke plume began to move over that area.

===== 23 August Update =====

Night-time Suomi NPP VIIRS 3.7 µm shortwave IR images on 21, 22, and 23 August

Suomi NPP VIIRS 3.74 µm shortwave IR images on 3 consecutive nights (21, 22, and 23 August) showed the rapid increase in size of the Rim Fire (above).

Another example of smoke from the Rim Fire being detected during the night-time hours can be seen at 09:43 UTC or 2:43 AM local time on 23 August (below). The VIIRS 0.7 µm Day/Night Band image revealed a number of discrete plumes of smoke streaming northward, then northeastward toward the Lake Tahoe area. At South Lake Tahoe the surface visibility at the time of the image was 2 miles, but it decreased to 1/2 mile four hours later.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 3.74 µm IR channel images

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GOES-14 0.63 µm visible channel images (click image to play animation)

A cold front moving through Wisconsin triggered severe convection (SPC storm reports) on 21 August 2013. GOES-14 SRSO-R data gives a compelling look at the convective development at 1-minute intervals. Because of the satellite position, the rear inflow into the convection near Rice Lake, WI, is very apparent.

It is useful to compare the SRSO-R views of the convection from GOES-14 (30-second imagery will be available with GOES-R) to the routine scanning strategy used by GOES-13. That comparison is shown below. Routine scanning is unable to capture the very dynamic nature of rapidly evolving convection.

GOES-14 (left, SRSO-R) and GOES-13 (right) 0.63 µm visible channel images (click image to play animation)

Even Rapid Scan Operations (RSO) imagery (GOES-13 was in RSO during this event) can also miss important details, especially at times when GOES-East is doing a full-disk scan (at 20:45 UTC, for example) and no imagery is available for 30 minutes. The loop below compares SRSO views of this system (top) to RSO (middle) to standard 15-minute scanning (bottom). GOES-R will have the capability simultaneously to scan globally and in designated mesoscale sectors.

GOES-14 (SRSO-R, top; RSO, middle; standard, bottom) 0.63 µm visible channel images (click image to play animation)

GOES-13 Sounder DPI values of Lifted Index (click image to play animation)

GOES-13 sounder Derived Product Imagery (DPI) of the Lifted Index (above, available at this site) and Convective Available Potential Energy (below) readily shows the unstable airmass supporting the convection.

GOES-13 sounder Convective Available Potential Energy (CAPE) product (click image to play animation)

Total Precipitable Water (available at this site), below, shows moisture pooling along the approaching front.

GOES-13 Sounder DPI values of Total Precipitable Water

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