A series of powerful storms affected the southwestern US during the 18-23 January 2010 period, which resulted in record rainfall and snowfall in parts of northern Arizona. Flagstaff recorded 54.2 inches of snow, which was their 2nd largest storm total snowfall on record. A 250-meter resolution MODIS true color image from the SSEC MODIS Today site (above) showed the coverage of snow across the higher elevations of northern Arizona on 25 January 2010.

On the following day, a comparison of AWIPS images of the MODIS visible channel and a false-color Red/Green/Blue (RGB) image (below) shows that most of the bright features seen on the visible were snow cover (which shows up as darker pink features on the false color image).

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A cyclone off the mid-Atlantic coast was quickly transitioning to the occluded stage on the morning of 22 January 2010 (above). As the cyclone (in its mature stage) was just beginning to move out over the offshore waters of the Atlantic Ocean, winds gusted to 51 knots at buoy 41025 (Diamond Shoals NC) around 07 UTC and 37 knots at buoy 44014 (64 miles east of Virginia Beach VA) around 11 UTC.

The evolution of a classic “dry swirl” signature was seen on AWIPS images of the 4-km resolution GOES-12 6.5 µm water vapor channel (below) — this dry swirl water vapor signature is a tell-tale sign that a cyclone has reached occlusion (and is often seen with systems over the open oceans).

The appearance of an subtle elongated filament structure on the water vapor imagery (exiting the Georgia / South Carolina coast after about 10 UTC, to the southwest of the occluding cyclone) suggested the presence of a northeastward-propagating jet streak. A plot of 1-hourly MADIS satellite-derived water vapor atmospheric motion vectors (below) revealed one target with a velocity of 151 knots in the general vicinity of the thin filament signature — this wind speed was significantly higher than the 100-110 knots that was initialized by the GFS40 model over that particular area.

McIDAS images of the 1-km resolution GOES-12 visible channel data (below) showed finer details in the low-level cloud structure, as well as the formation of convective bursts near the circulation center toward the end of the animation.

A comparison of 1-km resolution NOAA-17 AVHRR visible channel and 10.8 µm IR channel images at 14:10 UTC (below) showed the cloud structures around the time that the dry swirl signature was becoming more well-defined on the GOES-12 water vapor imagery.

The AVHRR Cloud Top Temperature (CTT) product (below) indicated that CTT values were as cold as -70º C (black color enhancement) prior to the cyclone transitioning to the occluded stage.

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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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