Ice eddies in the Gulf of Saint Lawrence

March 6th, 2012 |

We received the following in an email from John Goff, lead forecaster at the Burlington, Vermont National Weather Service office:

“Couldn’t help but notice the apparent large ice eddies up in the Gulf of Saint Lawrence this afternoon (3/6) per the TERRA MODIS noon overpass (250m res). I thought that initially these were eddy/small-scale cloud vortices we sometimes see up there, but upon looping the GOES visible imagery on my AWIPS workstation it’s fairly obvious these are not clouds, but ice structures.”

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

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

Thanks John for the heads-up on this very interesting example! McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation) showed the development and motion of the ice eddies on 06 March 2012. Note how many of the ice floe structures began to move toward the northeast by the end of the day, due to increasing southwesterly surface winds across the region.

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel data and the corresponding MODIS false-color Red/Green/Blue (RGB) image (below) demonstrated the value of using RGB imagery to aid in the discrimination between snow/ice (which appeared as varying shades of red in the false-color RGB image) and supercooled water droplet clouds (which appeared as the brighter white to cyan features on the RGB image).

MODIS 0.65 µm visible channel image + MODIS false-color Red/Green/Blue (RGB) image

MODIS 0.65 µm visible channel image + MODIS false-color Red/Green/Blue (RGB) image

An AWIPS image of the 1-km resolution POES AVHRR Sea Surface Temperature (SST) product at 18:55 UTC (below) indicated that SST values over the open waters were in the 30-31º F range (blue color enhancement), while the ice features exhibited colder values in the 23-25º F range (violet color enhancement).

POES AVHRR Sea Surface Temperature product

POES AVHRR Sea Surface Temperature product

Finally, a comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) showed a closer view of the ice eddies, and again demonstrated the value of using various RGB image combinations to discriminate between snow/ice (cyan in the false-color image) and supercooled water droplet low cloud features (white on the true-color image).

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

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

CIMSS participation in GOES-R Proving Ground activities includes making a variety of POES AVHRR and MODIS images and products available for National Weather Service forecast offices to add to their local AWIPS workstations. Currently there are 51 NWS offices receiving MODIS imagery and products from CIMSS.

Heavy rainfall in Hawaii

March 6th, 2012 |
GOES-15 10.7 µm IR channel images (click image to play animation)

GOES-15 10.7 µm IR channel images (click image to play animation)

McIDAS images of GOES-15 10.7 µm IR channel data (above; click image to play animation) showed the cold cloud tops (some -60º C and colder, red color enhancement) associated with numerous large thunderstorms that moved across the northern Hawaiian Islands of Kauai and Oahu during the 04 March – 06 March 2012 period. Storm total rainfall amounts were as high as 35.97 inches at Hanalei on Kauai, and 15.64 inches at Punaluu Stream on Oahu. Lihue on Kauai set a new daily record rainfall amount with 8.64 inches falling on 05 March.

As one of the largest thunderstorm complexes was approaching the island of Kauai from the southwest around 03 UTC on 06 March (5 pm local time on 05 March), a comparison of a 1-km resolution NOAA-15 AVHRR 10.8 µm IR channel image to the corresponding 4-km resolution GOES-15 10.7 µm IR channel image (below) demonstrated the advantage of higher spatial resolution for identifying the location of colder cloud top IR brightness temperatures associated with convective overshooting tops. Southwest of Kauai the coldest IR temperature on the AVHRR image was -70º C, compared to -62º C on the GOES-15 image.

NOAA-15 AVHRR 10.8 µm IR image + GOES-15 10.7 µm IR image

NOAA-15 AVHRR 10.8 µm IR image + GOES-15 10.7 µm IR image

AWIPS images of the MIMIC Total Precipitable Water product with overlays of surface analyses (below; longer animation) showed that deep moisture was pooling along a stationary frontal boundary / wind shear axis that was situated between the islands of Kauai and Oahu. (Note to NWS forecast offices: MIMIC TPW is available in AWIPS, via LDM subscription)

MIMIC Total Precipitable Water product + Surface analyses

MIMIC Total Precipitable Water product + Surface analyses

GOES-15 6.5 µm water vapor channel images with water vapor Atmospheric Motion Vector (AMV) winds from the CIMSS Tropical Cyclones site (above) showed that a well-defined trough of low pressure was located to the northwest of the Hawaiian Islands during the 05 March – 06 March period.

GOES-15 6.5 µm water vapor images + water vapor atmospheric motion vector winds

GOES-15 6.5 µm water vapor images + water vapor atmospheric motion vector winds

Upper-tropospheric divergence derived from these satellite AMVs (below) revealed a trend of increasing divergence aloft over the northern Hawaiian Islands as the trough approached.

GOES-15 6.5 µm water vapor images + satellite wind derived upper-level divergence

GOES-15 6.5 µm water vapor images + satellite wind derived upper-level divergence

Juxtaposed beneath the strong upper-tropospheric divergence was strong lower-tropospheric convergence in the vicinity of the stationary front / wind shear axis, as seen in GOES-15 10.7 µm IR images with contours of IR satellite wind derived 850-925 hPa convergence (below). This created a favorable environment for upward vertical motion, with plenty of deep moisture to fuel the development of the strong thunderstorms.

GOES-15 10.7 µm IR images + satellite wind derived lower-level convergence

GOES-15 10.7 µm IR images + satellite wind derived lower-level convergence

Tehuano wind event following the 02 March 2012 severe weather outbreak

March 4th, 2012 |
METAR surface reports + tropical surface analyses + ASCAT scatterometer winds

METAR surface reports + tropical surface analyses + ASCAT scatterometer winds

The powerful mid-latitude cyclone that was responsible for the widespread outbreak of severe weather across parts of the eastern US on 02 March 2012 spawned a southward surge of cold air (OPC surface analyses) that traversed the Gulf of Mexico, crossed the mountainous terrain of far southern Mexico, and emerged across the Pacific Ocean as a strong gap wind event known as a Tehuano wind. AWIPS images showing METAR surface reports, Tropical surface analyses, and a pass of ASCAT scatterometer surface winds (above) showed that there was blowing sand reported at Veracruz (station identifier MMVR), with wind gusts to 45 knos at Minatitlan (station identifier MMMT) and 35 knots at Ixtepec (station identifier MMIT).

McIDAS images of GOES-13 0.63 µm visible channel data from 04 March 2012 (below; click image to play animation) showed the cloud arc that marked the leading edge of the Tehuano wind, and also showed the hazy signature of blowing dust that was being lofted southward across the Pacific coast and over the waters of the Gulf of Tehuantepec (hence the name “Tehuantepecer“ given to this type of strong wind event).

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

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

A similar Tehuano wind event was seen on 08 March 2008.

02 March 2012 Severe Weather Outbreak

March 2nd, 2012 |
POES AVHRR 10.8 µm IR image + total cumulative hail, wind, and tornado reports

POES AVHRR 10.8 µm IR image + total cumulative hail, wind, and tornado reports

One of the largest severe weather outbreaks on record for the month of March occurred from the Ohio River Valley to the Gulf Coast states on 02 March 2012. This outbreak produced dozens of tornadoes, more than 400 hail reports (as large as 4.25 inches in diameter in Kentucky), and over 200 reports of severe damaging winds (SPC storm reports) — and was responsible for more than 30 fatalities. Focusing on one of the hardest-hit regions (from southern Indiana into Kentucky), a composite of the total cumulative SPC hail, severe damaging wind gust, and tornado reports are overlaid on an AWIPS image of 1-km resolution POES AVHRR 10.8 µm IR data (above).

4-km resolution GOES-13 10.7 µm IR images with overlays of corresponding SPC storm reports (below; click image to play animation) showed that during the 16:25 to 23:45 UTC period a number of cold overshooting cloud tops (IR brightness temperatures as cold as -70º C, darker black color enhancement, at 19:45 UTC), enhanced-V signatures, and cold-warm thermal couplets could be seen. For the large supercell thunderstorm that produced the tornado/tornadoes that did EF4 damage in Henryville in far southern Indiana after about 20:11 UTC, we can see that it exhibited fairly well-defined enhanced-V and/or cold/warm thermal couplet cloud top sinatures as it moved eastward across southern Indiana during the hour or two leading up to the tornadoes. Henryville is located approximately halfway between Seymour, Indiana (station identifier KSER) and Louisville, Kentucky (station identifier KSDF).

GOES-13 10.7 µm IR images + Severe storm reports (click image to play animation)

GOES-13 10.7 µm IR images + Severe storm reports (click image to play animation)

About an hour prior to the Henryville tornado, a comparison of 1-km resolution MODIS 0.65 µm visible channel and 11.0 µm IR channel images at 19:10 UTC (below) displayed a large thunderstorm over far southern Indiana, with overshooting top shadows seen on the visible image and an enhanced-V with a distinct cold/warm thermal couplet cloud top signature on the IR image.

MODIS 0.65 µm visible chaneel + 11.0 µm IR channel images

MODIS 0.65 µm visible chaneel + 11.0 µm IR channel images

In a comparison of the 19:10 UTC 1-km resolution MODIS 11.0 µm IR image with the correspondng 4-km resolution GOES-13 10.7 µm IR image (below), the advantage of improved spatial resolution is immediately obvious in terms of being able to identify storm-top severe storm signatures such as the enhanced-V or the cold/warm thermal couplet (Note: the spatial resolution of IR imagery on the next-generation ABI instrument on GOES-R will be 2 km). The coldest cloud-top IR brightness temperature on the MODIS image was -76º C, compared to -67º C on the GOES-13 image. Also evident is the northwestward “parallax shift” on the GOES-13 IR image, due to the large viewing angle from that particular geostationary satellite located over the Equator at 75º West longitude; a more accurate placement of the storm top features is seen using imagery from polar-orbiting satellites that fly more directly overhead.

1-km MODIS 11.0 µm IR image + 4-km GOES-13 10.7 µm IR image

1-km MODIS 11.0 µm IR image + 4-km GOES-13 10.7 µm IR image

A similar comparison between the 19:44 UTC 1-km resolution POES AVHRR 10.8 µm IR image with the corresponding 4-km resolution GOES-13 10.7 µm IR image (below) again demonstrated the easier identification of important storm-top signatures with improved spatial resolution data. These images were about 20-30 minutes before the Henryville and Marysville tornadoes in far southern Indiana.

1-km POES AVHRR 10.8 µm IR image + 4-km GOES-13 10.7 µm IR image

1-km POES AVHRR 10.8 µm IR image + 4-km GOES-13 10.7 µm IR image

Many of the supercell thunderstorms exhibited unusally fast forward motion speeds (as fast as 70-80 mph), due to the approach of a strong 140-knot core upper-level jet streak. A 1-km resolution MODIS 6.7 µm water vapor channel image with an overlay of NAM maximum wind speeds is shown below — strong divergence aloft within the left exit region of this upper-level jet streak helped to promote an environment supportive of strong vertical ascent.

MODIS 6.7 µm water vapor channel image + NAM maximum wind speeds

MODIS 6.7 µm water vapor channel image + NAM maximum wind speeds

From a larger synoptic-scale point of view, 10-km resolution GOES-13 sounder Lifted Index (LI) derived product imagery (below; click image to play animation) did begin to show a trend of destabilization early in the day within the warm sector of the mid-latitude cyclone, before extensive cloud cover prevented the subsequent retrieval of GOES sounder-based products.

GOES-13 sounder Lifted Index derived product imagery (click image to play animation)

GOES-13 sounder Lifted Index derived product imagery (click image to play animation)

Blended Total Precipitable Water product (click image to play animation)

Blended Total Precipitable Water product (click image to play animation)

In terms of moisture, the Blended Total Precipitable Water product (above; click image to play animation) showed that TPW values in excess of 25 mm (or 1.0 inch) were being drawn northward within the warm sector of the cyclone. These TPW values were near or even in excess of 200 percent above normal for many areas for this early in the season (below; click image to play animation).

Percent of Normal Blended Total Precipitable Water (click image to play animation)

Percent of Normal Blended Total Precipitable Water (click image to play animation)

———————————- 10 March Update ——————————

Before (01 March) and after (10 March) MODIS true-color RGB images

Before (01 March) and after (10 March) MODIS true-color RGB images

A comparison of before (01 March 2012) and after (10 March 2012) 250-meter resolution MODIS true-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) revealed the southwest-to-northeast oriented tornado damage path from the Henryville, Indiana EF4 tornado.