MODIS 0.65 µm visible channel images

AWIPS images of the 1-km resolution MODIS 0.65 µm visible channel data (above) showed a hint of a few aircraft contrails over the Southwestern US at 18:03 and 21:22 UTC on 16 March 2010. However, note that many more contrails were apparent on the corresponding MODIS 1.4 µm near-IR “cirrus detection channel” images (below). The ABI instrument on the upcoming GOES-R satellite will contain near-IR channels similar to this MODIS near-IR channel that will enable more accurate cirrus cloud and contrail detection.

MODIS 1.4 µm near-IR "cirrus detection channel" images

While none of these contrails appeared to be very cold on 1-km resolution MODIS 11.0 µm IR imagery (none were even near the -20º C IR brightness temperature threshold), the 1-km resolution AVHRR Cloud Top Temperature (CTT) product at 20:36 UTC (below) indicated that portions of a few of the contrails were exhibiting CTT values as cold as -30 to -40º C (darker blue color enhancement) — however, no single contrail appeared to be cold enough to have completely glaciated along it’s entire length.

AVHRR Cloud Top Temperature product

The 1-km resolution AVHRR Cloud Type Product (below) also indicated that the majority of these contrails were composed of supercooled water droplets (cyan color enhancement), although some portions of a few of the contrails were glaciating and being flagged as cirrus (orange color enhancement).

AVHRR Cloud Type Product

The 1-km resolution AVHRR Cloud Top Height (CTH) product (below) showed that segments of the highest contrails had CTH values around 9 km (blue color enhancement).

AVHRR Cloud Top Height product

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MODIS imagery from the Terra satellite clearly show the change in snowcover over the upper Midwest in the past week. The first image, from 6 March, shows widespread snowcover. The second image, from 15 March, shows widespread bare ground. The period from 9 March through 13 March was one of widespread low clouds, fog, and light rain that removed the cumulative effects of 3 months’ worth of snowstorms. Snowcover in Madison, for example, began on December 7th and remained for 93 days, until March 10th. That 93-day stretch was the 6th-longest such stretch of consecutive days with snowcover, tying with a streak in the winter of 1970-1971. The winter of 1978-1979 in Madison had the longest streak of consecutive days with snowcover: 118. (Link).

The imagery above were obtained from the WisconsinView website.

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MODIS Sea Surface Temperature product

AWIPS images of the 1-km resolution MODIS Sea Surface Temperature (SST) product (above) showed some intricate details in the SST structure of the warm Loop Current in the eastern Gulf of Mexico on 13 March 2010. Note the “swirl” of slightly cooler SST values (lighter orange colors) in the northern portion of the Loop Current.

A comparison of the MODIS SST product with the RTG_SST High Resolution model analysis (below) serves to illustrate how satellite data can add value in situations where even high-resolution models struggle to accurately depict some of the smaller-scale SST structures that were present in the Gulf of Mexico. For example, the RTG_SST_HR analysis placed the axis of warmest SST values over the eastern portion of the Loop Current, where MODIS SST values were in fact a few degrees F cooler than they were over the warmer western portion. The highest MODIS SST values in the western part of the Loop Current were around 80º F (darker red colors), which were about 4-5º F higher than what was indicated in that area by the RTG_SST_HR analysis.

MODIS SST product + RTG_SST Hi-Res SST model surface temperature

Three days earlier, AVHRR SST values in the southern portion of the Loop Current were as warm as 83º F (below) — however, brisk surface winds associated with the passage of a strong cold front helped to lower the SST values a bit, due to mixing and upwelling of slightly cooler water from below the surface.

AVHRR Sea Surface Temperature product

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After an unusually quiet February tornado-wise in the United States (only one tornado was reported, an EF-0 in California that lasted for 3 minutes late in the day on February 27th), two tornadoes touched down near sunset in western Oklahoma, near the town of Hammon. The above animation from NAWIPS shows 1-km GOES-12 visible imagery with superimposed contours of cloud-top cooling (and lightning strikes) from about 2000 UTC on 9 March to 0015 UTC on the 10th, shortly after tornado touchdown (the tornado location is indicated by the red triangle in the animation). The growing cell that will ultimately spawn the tornado is correctly identified. Such cloud-top cooling is computed routinely as part of a University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (CIMSS) project on convective initiation. The algorithm locks on to the convective cell that spawns the tornado, and not adjacent cells. The strongest cooling was associated with the storm that produced the tornado.

If the detected cloud-top cooling is co-located with changes in cloud phase (for example, from supercooled water droplets to ice crystals, or from all water droplets to supercooled water droplets) as inferred from GOES-12 radiances for different infrared channels, then convective initiation is deemed to be ongoing. In this animation of 11-micron cloud temperatures overlain with Convective Initiation, note the CI Likely at 2132 UTC along the Texas/Oklahoma border. Note that only the nascent cell that subsequently produces a tornado is identified, as only that cell contains the required strong cooling and the phase changes. That region of cloud top cooling and phase change then moves north-northeastward as the convective cell that spawned the tornado develops. Convective Initiation is no longer indicated, however, because the initiation stage of convection is over by 2200 UTC.

(Added: CNN has Andy Gabrielson’s too-close-for-comfort video).

(Added: Another video, from YouTube).

(One more Addition: Write up on the tornadic event from the Norman, OK office of the National Weather Service).

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