GOES-11 (GOES-West) visible channel images (above) displayed an unusually large area of open-cell cumulus clouds across the North Pacific Ocean on 20 January 2010. This type of open-cell mesoscale convective cloud pattern is a signature of strong instability (via boundary layer cold air advection over relatively warmer waters) in an environment of cyclonic flow. These cloud patterns tend to be fairly shallow, as indicated by their relatively warm appearance on IR imagery (below) — and the presence of open cell convection usually indicates that winds within the marine boundary layer are greater than about 25 knots.

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On the following day (21 January 2010), the cold front marking the leading edge of the cold air advection had moved south of 20º N latitude — and GOES-11 visible images (above) showed the formation of a large area of closed-cell stratocumulus clouds to the northeast of the Hawaiian Islands. This type of closed-cell convection often forms in regions of anticyclonic flow, as confirmed by the GFS360 surface wind field (below) — and stronger subsidence causes the cumulus cloud features to flatten out and form stratocumulus clouds beneath the subsidence inversion. Also note the “barrier effect” of the Hawaiian Islands on the marine boundary layer stratocumulus, as well as the formation of lee cloud lines downwind of the islands.

As a deep cyclone approached the California coast on 21 January, a number of all-time minimum pressure records were set across the state. A MODIS false color Red/Green/Blue (RGB) image (below) shows the extensive cloudiness associated with this storm; on this RBG image supercooled clouds appear as white features, while glaciated clouds take on more of a lighter pink color. Snow cover shows up as darker pink areas (such as those over northern Nevada and southern Oregon/Idaho).

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McIDAS images of the 4-km resolution GOES-11 10.7 µm IR channel data (above) showed the development of convection that moved onshore across southern California during the afternoon hours on 19 January 2010. Of particular interest is the strong convective cluster that developed just offshore over the Santa Catalina and San Clemente Island area — the GOES-11 IR brightness temperatures of this feature cooled to -53º C (darker orange color enhancement) as it was moving inland around 20:46 UTC (12:46 pm local time).

A closer view using AWIPS images of the GOES-11 IR channel with overlays of surface METAR reports and cloud-to-ground lightning strikes (below) revealed that this convective cell with the coldest cloud tops exhibited a number of lightning strikes (as many as 31 for the 15-minute period ending at 21:30 UTC). These storms were developing in the vicinity of a surface wave that had formed along a strong cold frontal boundary — and according to SPC Storm Reports (overlaid on a MODIS 11.0 µm IR image) there were two reports of a tornado in the Huntington Beach area and a number of high wind gusts (including 93 mph at Newport Beach, and 92 mph at Huntington Beach) as the severe thunderstorm moved onshore. For radar images and additional information, see the WeatherMatrix blog.

The 1-km resolution POES AVHRR Cloud Top Temperature (CTT) product (above) indicated that the coldest CTT value with this storm was -56º C, with the Cloud Top Height product (below) showing the maximum cloud tops at a height of 14 km.

A MODIS 6.7 µm water vapor image with an overlay of CRAS model Level of Maximum Wind isotachs (below) showed that southern California was located beneath the left exit region of a strong upper level jet stream, which likely contributed to strong deep layer wind shear and ageostrophic forcing to aid in the development of the severe thunderstorms.

A sequence of water vapor images from 15 January to 19 January (below) showed that this particular storm was one of a series of strong disturbances that was moving across the Pacific Ocean along a very strong zonal (west to east) jet stream.

On 18 January, The GFS360 model Level of Maximum Wind isotach field indicated that winds just exceeded 200 knots within the core of the jet stream; however, GOES-11 satellite-derived water vapor winds (below) suggested that speeds were as high as 239 knots along the jet stream axis.

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An AWIPS image of the 1-km resolution POES AVHRR 11.0-3.7 µm “fog/stratus product” (above) revealed a very interesting banded structure in the fog and stratus features (yellow to red color enhancement) that covered a large part of the western Great Lakes region at 07:49 UTC on 16 January 2010. With stagnant high pressure in place and light winds over much of the area, there was little boundary layer mixing to mitigate the formation and persistence of the low clouds that were trapped under a very strong low-level temperature inversion (Rawinsonde data: Davenport IA | Lincoln IL | Wilmington OH; NAM12 Line A-A’ west-to-east cross section).

An animation of the 4-km resolution GOES-12 11.0-3.9 µm fog/stratus product (below) suggested that there might be a thin veil of high-altitude cirrus clouds (which show up as darker black features) drifting over the banded portion of the fog and stratus — the presence of overlying high clouds could have been contributing to the unusual appearance of those low cloud features on the fog/stratus product imagery.

To further explore whether or not there were indeed cirrus clouds overhead that might be masking the low-altitude fog/stratus signal and creating the false appearance of banding as seen on the fog/stratus product, let’s examine a few additional satellite images. The POES AVHRR 10.8 µm IR image (below) did show some thin filaments that exhibited slightly colder IR brightness temperatures, but most were warmer than -20º C — much warmer than would be expected of typical cirrus clouds. However, with very thin cirrus features, a significant amount of thermal energy reaches the satellite IR detectors from the warmer surfaces below; this then leads to IR brightness temperatures values that are much warmer than those of the actual cirrus clouds themselves.

Multi-spectral POES AVHRR derived products such as Cloud Type, Cloud Top Temperature, and Cloud Top Height (below) did a better job at identifying more of the thin features as Cirrus (orange color enhancement on the Cloud Type product) — with cloud top temperatures of -30º C to -40º C and cloud top heights of 7-8 km — but some of the thinnest cirrus filaments were still flagged as supercooled water droplet clouds (cyan color enhancement on the Cloud Type product).

In this case, perhaps the best satellite product to confirm the presence of thin cirrus filaments aloft was the 1-km resolution MODIS 6.7 µm water vapor channel (below). Since the weighting function of such a water vapor channel normally peaks at higher altitudes in the middle troposphere, it is generally immune to the effects of warm surface radiation that can sometimes plague proper cirrus cloud classification using conventional IR imagery alone.

As it turns out, a broad region of high-altitude “transverse banding” had formed from the southern Great Lakes to the mid-Atlantic region — this banding was generally located along the axis of a strong (120 to 130 knot) anticyclonically-curved jet stream axis, as confirmed by an overlay of CRAS model Level of Maximum Wind isotachs (below).

This transverse banding is a satellite signature that indicates a potential for high-altitude turbulence — and there were a few pilot reports of moderate turbulence over the area during the 02-11 UTC time period, shown overlaid on 4-km resolution GOES-12 6.5 µm water vapor images (below).

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McIDAS images of GOES-12 and GOES-14 visible channel data (above) showed that large chunks of ice (known as “ice fields”) were drifting north-northeastward across the western portion of Lake Erie on 14 January 2010. Southerly to southwesterly winds were beginning to increase on that day, helping to move the ice features across the surface of the lake.

AWIPS images of MODIS false-color Red/Green/Blue (RGB) composites (below) confirmed that these were indeed ice features — snow and ice appear darker red on this false color imagery, in contrast to supercooled water droplet clouds which appear as brighter shades of cyan to white. Surface METAR reports plotted on the imagery indicated that wind speeds were generally in the 10-20 knot range. This example offers a glimpse at the type of RGB image capability that should be available with the upcoming AWIPS II software.

A closer look using 250-meter resolution MODIS true color images from the SSEC MODIS Today site (below) revealed how far the ice fields drifted between the 16:58 UTC overpass of the Terra satellite and the 18:42 UTC overpass of the Aqua satellite.

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