GOES waver vapor imagery + PV1.5 pressure + 500 hPa geopotential height

A strong potential vorticity (PV) anomaly was propagating southeastward just off the California coast on 09 February 2010 — and this feature had a striking presentation on AWIPS images of GOES-11 water vapor channel data (above), with a pronounced arc of very dry air (yellow color enhancement) seen around the periphery of the circulation. According to the CRAS model fields, the tropopause (taken to be the pressure of the PV1.5 surface) was being brought downward as low as the 600 hPa pressure level within the core of the PV anomaly.

Images of the GOES-11 sounder Total Column Ozone derived product (below) depicted ozone values as high as 430 Dobson Units (red color enhancement) in the vicinity of the PV anomaly, supporting the idea that the tropopause height was very depressed within the circulation feature.

GOES sounder Total Column Ozone + PV1.5 pressure + 500 hPa geoptential height

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GOES-11 Sounder and Imager water vapor channel images

A 4-panel comparison of the three water vapor channels on the GOES-11 Sounder (6.5 µm, 7.0 µm, and 7.4 µm) and the GOES-11 Imager 6.7 µm water vapor channel (above) showed that the dry air signature was even quite evident on the Sounder 6.5 µm channel (darker blue color enhancement, upper left panels) — this particular water vapor channel weighting function normally peaks quite high in the atmosphere (around 325 hPa), where these types of water vapor gradients and signatures are usually not as well-defined.

However, due to the dry air within the middle to upper troposphere associated with the PV anomaly, the weighting functions of all 4 of the GOES-11 water vapor channels (calculated using rawinsonde data from Vandenberg Air Force Base) peaked at altitudes that were quite a bit lower compared to the more “normal” conditions that would be seen in a US Standard Atmosphere or USSA environment (below). Convection moving onshore across southern California that day was responsible for at least one sighting of a waterspout in the San Diego area, and inland precipitation amounts of 1.0 to 1.5 inch were widespread.

GOES-11 sounder and imager water vapor weighting functions (Vandenberg vs USSA)

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GOES-11/GOES-12 water vapor composite images

The Winter of 2009/2010 has brought a number of significant snowfall events to parts of the US East Coast — and another powerful storm affected that region on 05 February – 06 February 2010. The highest storm total snowfall reported was 40.0 inches at Colesville in Maryland. Washington Dulles International Airport received 32.4 inches of snow (their largest 2-day snowfall on record), and Baltimore-Washington International Airport received 24.8 inches of snow (their second-largest 2-day snowfall on record). So far, this is Philadelphia’s 2nd-snowiest winter on record (56.3 inches) and Washington DC’s 3rd-snowiest winter on record (44.9 inches).

AWIPS images of 3-hourly composites of the GOES-11 and GOES-12 water vapor channel data (above) showed a strong disturbance originating over the Pacific Ocean that was progressing eastward across the southwestern US and northern Mexico during the days leading up to the storm. There was also evidence of a plume of subtropical moisture seen on the water vapor imagery.

The presence of this moisture plume was confirmed on MIMIC Total Precipitable Water (TPW) images (below), which revealed a clear linkage to the rich moisture source within the Inter-Tropical Convergence Zone (ITCZ) over the eastern equatorial Pacific Ocean. MIMIC TPW values were in the 50-60 mm (2.0 – 2.4 inch) range within this moisture plume as it was being drawn northeastward across the Gulf of Mexico — and the Blended Total Precipitable Water product showed a large area of TPW values exceeding 200% of normal from the Gulf of Mexico to the mid-Atlantic states.

MIMIC Total Precipitable Water

4-km resolution GOES-12 water vapor images with an overlay of cloud-to-ground lightning strikes (below) showed 3 important phases of the storm: (1) a expansive area of cold cloud tops associated with the initial round of heavy snowfall later in the day on 05 February; (2) the penetration of a broad dry slot, which helped to release convective instability along it’s leading edge that led to periods of thunder and lightning (especially during the 08-10 UTC time period), and (3) a well-defined deformation zone where additional snowfall banding developed during the final hours of the storm.

GOES-12 6.5 µm water vapor images + cloud-to-ground ligtning strikes

A series of 1-km resolution AVHRR Cloud Top Temperature product images and MODIS 11.0 µm IR images (below) showed greater detail of some of the banding structures during different phases of the storm.

AVHRR Cloud Top Temperature and MODIS 11.0 µm IR images

1-km resolution AVHRR visible images (below) displayed the cloud features as the surface low was rapidly deepening just offshore during the day on 06 February.

AVHRR 0.86 µm visible images + surface analyses

MetOp ASCAT scatterometer winds at 14:05 UTC on 06 February (below) indicated that surface winds were generally in the 30-40 knot range, which were in agreement with offshore buoys which were reporting wind gusts 31-43 knots at 15 UTC. The highest reported gust was 61 mph at Lewes, Delaware during the pre-dawn hours on 06 February.

AVHRR 0.86 µm visible image + ASCAT scatterometer winds

===== 07 FEBRUARY UPDATE =====

A comparison of a 1-km resolution MODIS visible channel image and a false-color Red/Green/Blue (RGB) image (below) shows the extent of the snow cover on the morning of 07 February. On the RGB image, snow appears as varying shades of red, in contrast to supercooled water droplet clouds (which appear as brighter features). Even after compaction of the heavy snowfall, there were still a number of sites reporting snow depths in excess of 30 inches that morning. Additional MODIS true color and false color imagery — at resolutions up to 250 meters — can be seen at the SSEC MODIS Today and the SSEC MODIS Direct Broadcast web sites.

MODIS visible + MODIS fasle-color Red/Green/Blue (RGB) image

MODIS true color images from the SSEC MODIS Today site can also be displayed using Google Earth (below). The location of 40.0 inch snowfall report (at Colesville, Maryland) is also noted on the image.

MODIS true color image (displayed using Google Earth)

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MODIS visible channel + MODIS Red/Green/Blue (RGB) false color images

A large winter storm spread heavy snowfall, sleet, and freezing rain from Texas and Oklahoma to the East Coast of the US during the 28-30 January 2010 period. AWIPS images of the MODIS visible channel and a MODIS false-color Red/Green/Blue (RGB) image using the visible and the 2.1 µm near-IR “snow/ice” channels (above) showed the resulting wide swath of snow cover across the Tennessee Valley and mid-Atlantic regions on 31 January 2010. This example also offers a glimpse at the type of RGB image capability that should be available with the upcoming AWIPS II software.

Snow cover (which appears as brighter white features on the visible image) is a strong absorber at the 2.1 µm wavelength — so it appears red on the false-color RGB image. However, ice is an even stronger absorber, so areas that received a significant accrual of ice (from freezing rain, freezing drizzle, and/or sleet) appeared as an even darker red band along the southern periphery of the broad area of snow cover — this darker red band was especially evident across parts of southern Tennessee, southern North Carolina, and extreme northern South Carolina. In contrast, supercooled water droplet clouds appear as brighter features on the RGB image.

A MODIS true color image from the SSEC MODIS Today site (below; viewed using Google Earth) showed the locations of some of the heaviest snowfall amounts in each state, as well as 2 locations that received the highest accruals of ice (0.75 inch at Wallace in North Carolina, and 0.5 inch at Franklin in Tennessee).

MODIS true color image (viewed using Google Earth)

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MODIS visible + MODIS Red/Green/Blue (RGB) image

A story on the National Weather Service Milwaukee/Sullivan website highlighted the appearance of ice on Lake Michigan on MODIS imagery on 28 January 2010. A comparison of AWIPS images of the 1-km resolution MODIS visible channel and a false color Red/Green/Blue (RGB) image (above) confirms that the brighter features seen on the visible image over the nearshore waters (from Milwaukee, Wisconsin to Chicago, Illinois to Gary, Indiana) were indeed lake ice (snow cover and ice appear as darker red features on the MODIS false color RGB image). This example offers a glimpse at the type of RGB image capability that should be available with the upcoming AWIPS II software.

A closer view using 250-meter resolution true color images from the SSEC MODIS Today site (below) revealed that the northwesterly surface winds were causing a small amount of motion of the ice field between the time of the Terra satellite overpass (17:11 UTC or 11:11 am local time) and the Aqua satellite overpass (18:54 UTC or 12:54 pm local time).

MODIS true color images

A comparison of the 18:54 UTC Aqua MODIS true color and false color images (below) again confirms that the features seen over the nearshore waters were indeed lake ice — snow cover and ice appear as cyan-colored features on this particular false color imagery.

MODIS true color and false color images

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