Upper Midwest snowstorm

November 13th, 2010 |
GOES-13 6.5 µm "water vapor channel" images + cloud-to-ground lightning strikes

GOES-13 6.5 µm "water vapor channel" images + cloud-to-ground lightning strikes

A major winter storm impacted parts of the Upper Midwest region on 13 November 2010, producing snowfall amounts as high as 14 inches at Emmetsburg, Iowa, 12.0 inches at Maple Grove, Minnesota (NWS MPX story), and 11.0 inches at Hawthorne, Wisconsin (NWS DLH story).

AWIPS images of 4-km resolution GOES-13 6.5 µm “water vapor channel” data (above) revealed a pronounced middle-tropospheric dry slot wrapping into the eastern sector of the storm. Thundersnow was reported at a few locations — note that there were a few cloud-to-ground lightning strikes showing up near the leading edge of the dry slot (over western Iowa after 05:15 UTC, and then over southern Minnesota after 12:15 UTC).

The corresponding 4-km resolution GOES-13 10.7 µm “IR window channel” images (below) showed that the cloud top IR brightness temperatures were not particularly cold across the areas that received the heavy snow (generally in the -30 to -40º C range, dark blue to green color enhancement), though there were bands exhibiting much colder cloud tops (colder than -60º C, red color enhancement) farther to the east within the warm conveyor belt of the storm.

GOES-13 10.7 µm "IR window channel" images + cloud-to-ground lightning strikes

GOES-13 10.7 µm "IR window channel" images + cloud-to-ground lightning strikes

A more detailed view of the storm’s cloud structures could be seen by examining a series of 1-km resolution MODIS 11.0 µm and POES AVHRR 10.8 µm “IR window channel” images (below). An overlay of the 12 UTC HPC-analyzed surface fronts and surface pressure on the 11:16 UTC POES AVHRR IR image showed that the center of the storm system was located over central Iowa at that time.

MODIS 11.0 µm and POES AVHRR 10.8 µm "IR window channel" images

MODIS 11.0 µm and POES AVHRR 10.8 µm "IR window channel" images

A 1-km resolution MODIS false-color Red/Green/Blue (RGB) image (below) showed the beginning portion of the heavy snow swath, which was stretching from southeastern Nebraska (where as much as 4.0 inches was reported at Gretna) into southwestern Iowa as the main cloud deck associated with the storm system began clear out over that region. In this false-color RGB image (created using the MODIS 0.65 µm “visible channel” image as the Red, and the MODIS 2.1 µm “snow/ice channel” image as the Green and Blue components), the deeper snow cover shows up as the darker red features.

MODIS false-color Red/Green/Blue (RGB) image

MODIS false-color Red/Green/Blue (RGB) image

========== 15 NOVEMBER UPDATE ==========

There was enough of a break in the clouds on 15 November to get a nice view of the southern portion of the swath of snow cover that stretched from Iowa into southern Minnesota — on the comparison of MODIS false-color RGB images at 17:35 UTC and 19:17 UTC  (below), the snow cover again appears as the darker red feature (in contrast to the brighter supercooled water droplet clouds, and the lighter pink ice crystal clouds).

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

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

Long, narrow swath of snow cover across Wyoming, Montana, and North Dakota

November 11th, 2010 |
MODIS 0.65 µm "visible" channel and MODIS 2.1 µm "snow/ice" channel images

MODIS 0.65 µm "visible" channel and MODIS 2.1 µm "snow/ice" channel images

AWIPS images of MODIS 0.65 µm “visible channel” and 2.1 µm “snow/ice channel” data (above) revealed a long, narrow band of snow cover oriented from south to north across far northeastern Wyoming, far eastern Montana, and far western North Dakota at 19:42 UTC (12:42 pm local time) on 11 November 2010.   Both snow cover and clouds appear as brighter white features on the visible image, but the near-IR snow/ice channel image helps to discriminate between snow cover and clouds (since snow and ice are strong absorbers at the 2.1 µm wavelength,  they appear very dark on that particular image).    NOHRSC snow depth data indicated that as much as 5-6 inches of snow remained on the ground that morning, which explains the strong  signal on the MODIS snow/ice channel image.  According to National Weather Service local storm reports, total snowfall amounts during the preceding 24 hours in that particular area were as high as 17 inches at Hulett, Wyoming and 12 inches at Carlyle, Montana.

On a MODIS false-color Red/Green/Blue (RGB) image using the visible and snow/ice images (below), snow cover appears as varying shades of red, while water droplet clouds appear as brighter white features. Note the lack of first-order stations reporting snow depth within the area of the heavy snow swath — this highlights the value of using high spatial resolution satellite imagery for helping to determine the areal coverage of the snow on the ground.

MODIS false color Red/Green/Blue (RGB) image

MODIS false color Red/Green/Blue (RGB) image

The MODIS Land Surface Temperature (LST) product (below) indicated that LST values were being held in the mid 20s to low 30s F (violet to blue colors) within the snow band, while LST values across the adjacent bare ground areas were rising in the upper 40s to low 50s F (cyan to green colors). However, there was not quite that large of a contrast in instrument shelter air temperatures across that area.

MODIS Land Surface Temperature product + surface METAR reports

MODIS Land Surface Temperature product + surface METAR reports

35-year anniversary of the sinking of the Edmund Fitzgerald

November 10th, 2010 |
48-hour simulated IR satellite imagery from the CRAS model (9-11 Nov 1975)

48-hour simulated IR satellite imagery from the CRAS model (9-11 Nov 1975)

Today marks the 35-year anniversary of the powerful Great Lakes storm that was responsible for the sinking of the SS Edmund Fitzgerald (on 10 November 1975). Since the first operational geostationary weather satellites (SMS-1 and SMS-2) were relatively new back in 1975, the CIMSS Regional Assimilation System (CRAS) model was utilized to generate synthetic IR satellite images to provide an idea of what the satellite imagery might have looked like for this intense storm (CRAS model surface winds). A 48-hour sequence of synthetic IR images (above) shows the evolution of the model-derived cloud features at 1-hour intervals.

As part of the CIMSS involvement in GOES-R Proving Ground activities, CRAS synthetic forecast satellite imagery (IR and Water Vapor channels, below) is currently being made available in an AWIPS format for interested NWS forecast offices to add to their local AWIPS workstations (via LDM subscription). For more information, see the CRAS Imagery in D-2D site. VISIT training is also available on the topic.

CRAS forecast IR imagery in AWIPS

CRAS forecast IR imagery in AWIPS

CRAS forecast water vapor imagery in AWIPS

CRAS forecast water vapor imagery in AWIPS

Patch of thin cirrus and contrails over Arkansas and Tennessee

November 8th, 2010 |
GOES-13 0.63 µm "visible channel" image

GOES-13 0.63 µm "visible channel" image

A quick look at a 1-km resolution GOES-13 0.63 µm visible channel image (above) would suggest that it was a cloud-free day across Arkansas, Tennessee, and the surrounding region on 08 November 2010.

However, a comparison of AWIPS images of the 1-km resolution MODIS 0.65 µm “visible channel” , the MODIS 11.0 µm “IR window” channel, and the 1.3 µm “cirrus detection” channel (below) revealed that there was a patch of thin cirrus clouds and contrails over much of Arkansas and Tennessee. As with the GOES-13 visible channel, there was no indication of any cloud features on the MODIS visible image. On the MODIS IR image, there was a signature of some sort of cloud features over that region, but the IR brightness temperatures were quite warm (mostly above 0º C), which would be much too warm for cirrus clouds. However, the MODIS cirrus detection channel did a very good job at highlighting the patch of very thin clouds. This is due to the fact that the near-IR 1.3 µm channel is very effective for detecting features that are good scatterers of light (such as ice crystals, volcanic ash, airborne dust, etc).

MODIS 0.65 µm "visible", 11.0 µm "IR window", and 1.3 µm "Cirrus detection" images

MODIS 0.65 µm "visible", 11.0 µm "IR window", and 1.3 µm "Cirrus detection" images

Rather surprising, however, was the fact that this patch of cirrus clouds and contrails existed within a region that appeared to be a fairly dry area (indicated by the lighter blue to yellow color enhancement) on the MODIS 6.7 µm “water vapor” image (below). The pronounced dryness of the middle to upper troposphere was quite evident of the Little Rock, Arkansas rawinsonde data.

MODIS 6.7 µm "water vapor channel" image

MODIS 6.7 µm "water vapor channel" image

A false color Red/Green/Blue (RGB) POES AVHRR composite image (below) did show a subtle hint of some brighter cloud features against the green to brown background of the land surface, but again not to the extent of what was seen on the MODIS cirrus detection channel image.

POES AVHRR false color Red/Green/Blue (RGB) image

POES AVHRR false color Red/Green/Blue (RGB) image

If we examine the 1-km resolution POES AVHRR Cloud Top Temperature (CTT) product (below), we do begin to see features that exhibited CTT values of -50º C and colder (yellow color enhancement), which is more representative of what you would expect for cirrus cloud features.

POES AVHRR Cloud Top Temperature product

POES AVHRR Cloud Top Temperature product

In addition, the 1-km resolution POES AVHRR Cloud Top Height (CTH) product (below) showed features with CTH values of 10-11 km (cyan color enhancement), which are also more representative of the altitude where cirrus cloud features would usually  be located. These altitudes also matched the Cloud Top Temperature values around -50º C on the rawinsonde data from Little Rock, Arkansas and Nashville, Tennessee.

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Top Height product

Given that these cloud features were obviously quite thin, the 1-km resolution POES AVHRR Cloud Optical Depth product (below) showed correspondingly low values.

POES AVHRR Cloud Optical Depth product

POES AVHRR Cloud Optical Depth product

Another way to distinguish ice clouds from water droplet clouds is examine the 1-km resolution POES AVHRR Cloud Particle Effective Radius product (below). Ice crystals are typically much larger (in this case, at least 30-40 micrometers in diameter) than water droplets (usually around 20 micrometers or less in diameter).

POES AVHRR Cloud Particle Effective Radius product

POES AVHRR Cloud Particle Effective Radius product

Because of the very thin nature of these cirrus and contrail features, the 1-km resolution POES AVHRR Cloud Tye product (below) did seem to struggle in assigning the correct type to the features — although many were correctly identified as Cirrus (orange color enhancement).

POES AVHRR Cloud Type product

POES AVHRR Cloud Type product