MODIS 0.65 µm visible image + MODIS Sea Surface Temperature product + NAM surface winds

AWIPS images of the MODIS 0.65 µm visible channel data (above) revealed a few dark features within the otherwise bright sun glint region just off the coast of Florida and Georgia on 05 May 2010. The corresponding MODIS Sea Surface Temperature (SST) product indicated that SST values were also quite warm within these dark visible image features (SST values as high as 79ºF, darker red colors) — in fact, just as warm as those seen a bit farther to the east within the Gulf Stream. In contrast, to the north of the dark/warm features, the MODIS SST values were only around 69-70ºF (yellow to green colors).

This type of visible image “dark signature” over water illuminated by sun glint has been observed before — for example, over Lake Michigan — and is recognized as a signature of regions of very light or calm winds. The surface wind field from the NAM20 model (cyan wind barbs) did show a west-to-east oriented axis of calm winds just to the south of the dark/warm signature noted on the MODIS imagery. In this case, the MODIS imagery could have been used to identify the slight southward bias of the NAM20 model wind fields at that time.

MODIS 0.65 µm visible image + NAM surface winds + HPC surface frontal analysis

The Hydometeorological Prediction Center (HPC) surface frontal analysis for 15 UTC is overlaid on the MODIS visible image (above). Judging from the location of the dark features on the visible image, it would appear the the weak cold front had not yet advanced as far southeastward as the area of light/calm winds seen just after 16 UTC .

MODIS true color image (visualized using Google Earth)

A closer view using a 250-meter resolution MODIS true color Red/Green/Blue (RGB) image — created using MODIS bands 1/4/3 as the R/G/B channels — acquired from the SSEC MODIS Today site (above, visualized using Google Earth) is annotated to point out the subtle yet potentially important clues as to the exact location of the leading edge of the cold frontal boundary at the time of the Terra satellite overpass (approximately 16:18 UTC). This example also suggests that frontal boundaries do not necessarily resemble the nice smoothly-drawn features we see on weather maps, but instead can be complex in their shape due to various interactions with terrain, coastlines, etc.

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MODIS true color and false color RGB images

A comparison of the 18:50 UTC 250-meter resolution Aqua MODIS true color Red/Green/Blue (RGB) image — created using MODIS bands 1/4/3 as the R/G/B channels — and the corresponding false color RGB image — created using MODIS bands 7/2/1 as the R/G/B channels — acquired on 04 May 2010 from the SSEC MODIS Today site (above) showed the oil slick from the Deepwater Horizon oil rig explosion and collapse in the northern Gulf of Mexico 14 days earlier. Due to prolonged wind and wave action, the shape and size of the oil slick signature appeared to have changed and spread out in terms of areal coverage (compared to that seen for several days following the accident).

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Terra MODIS and Aqua MODIS true color RGB images

We received an email from Ron Miller at the National Weather Service forecast office at Spokane, Washington asking if there was any good MODIS imagery of the major dust storm that they had in their area on 03 May 2010. There most certainly was: the 250-meter resolution Terra MODIS (19:39 UTC or 12:39 pm local time) and Aqua MODIS (21:21 UTC or 2:21 pm local time) true color images (created using MODIS bands 1/4/3 as the R/G/B channels) from the SSEC MODIS Today site (above) revealed a very large and distinctive plume of blowing dust (light brown color) streaming eastward across eastern Washington state into Idaho. Winds at higher elevations gusted as high as 80 mph — and surface visibility was restricted to below 1/4 mile at times. For more details on the event, see the Damaging Wind Storm summary on the NWS Spokane website.

There were a number of traffic accidents reported across the area due to the strong winds and reduced visibility; the MODIS true color images visualized using Google Earth (below) showed that a significant portion of Interstate 90 was affected by the blowing dust plume. In addition, note that the thick dust plume appeared to be having an impact on cumulus cloud development, by reducing the amount of surface heating to initiate updrafts.

MODIS true color images (visualized using Google Earth)

NOAA/NESDIS/ASPB and CIMSS staff produce real-time volcanic ash retrieval products — and this thick blowing dust plume actually triggered an automated alert for volcanic ash over eastern Washington. Though the retrievals were performed using an ash microphysical model, the results for this blowing dust plume can be of some utility — for example, the maximum height of he dust feature was given as 3.9 km, which could be useful to aviation concerns.

NOAA-18 AVHRR volcanic ash retrieval products

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GOES-13 10.7 µm IR images

During 01 May – 02 May 2010 the 2-day total precipitation at Nashville, Tennessee was 13.57 inches — by far the wettest 2-day period on record for that location (the old record was 6.68 inches on 13-14 September 1979, in association with Hurricane Fredrick). With 7.25 inches falling on 02 May (5.57 inches of that in just 6 hours!), this also set a record for the wettest calendar day on record. And, remarkably, only 2 days into the month May 2010 is already the wettest May on record for Nashville. An animation of 24-hour observed precipitation can be seen here.

AWIPS images of 4-km resolution GOES-13  10.7 µm IR channel data (above) showed several rounds of deep convection moving northeastward across the region during the period, with some cells exhibiting IR cloud top brightness temperatures as cold as -74º C. This convection was developing along and ahead of a slow-moving cold frontal boundary.

Images of 1-km resolution MODIS  11.0 µm IR data (below) revealed even colder cloud top IR brightness temperature values of -82º C with some of the stronger convection developing over far western Tennessee. The 1-km resolution AVHRR Cloud Top Temperature (CTT) product also indicated CTT values as low as -80º C for some of the stronger thunderstorms.

MODIS 11.0 µm IR image

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Blended Total Precipitable Water (TPW) product

However, more important than the cold convective cloud top temperatures was the plume of rich moisture that was feeding northward across the Gulf of Mexico and into the Tennessee Valley. The Blended Total Precipitable Water (TPW) product (above) showed that TPW values began to exceed 50 mm across the Lower Mississippi River Valley late in the day on 01 May, with TPW within the moisture plume reaching 75 mm over the Gulf of Mexico late in the day on 02 May. TPW values were greater than 200% of normal across most of the Mississippi and Tennessee Valleys, as well as within the northward-moving moisture plume.

With the greater areal coverage on AWIPS of the MIMIC TPW product (below), it could be seen that the plume of moisture moving meridionally (northward) across the Gulf of Mexico actually originated from the zonal band of deep moisture associated with the Inter-Tropical Convergence Zone (ITCZ) that was located between the Equator and 10º N latitude over the far eastern Pacific Ocean. MIMIC TPW values over the Gulf of Mexico became greater than 60 mm late in the day on 02 May; GOES-13 Sounder TPW values were also as high as 66 mm over the Gulf of Mexico on 02 May.

Incidentally, this case also serves as a great example of why you can’t always identify and track important TPW plumes on standard water vapor imagery — the water vapor channel is often sensing radiation from a layer that is above that of the bulk of the TPW plume (comparison of GOES water vapor image and MIMIC TPW image).

MIMIC Total Precipitable Water (TPW) product

Rawinsonde data from Nashville (below) generally revealed a very moist atmosphere throughout much of the troposphere during the period, with TPW values as high as 2.00 inches at 00 UTC on 02 May.

Nashville, Tennessee rawinsonde data

===== 03 MAY UPDATE =====

Before (29 April) and after (03 May) MODIS false color RGB images

A comparison of before (29 April 2010) and after (03 May 2010) 250-meter resolution MODIS  Red/Green/Blue (RGB) false color images (above) from the SSEC MODIS Today site shows dramatic changes in some of the smaller rivers across western and central Tennessee following the record-setting rainfall that occurred on 01-02 May. On the false color images (created using MODIS bands 7/2/1 as the R/G/B channels), water appears as darker shades of blue,  while dense vegetation appears as brighter shades of  green.

On the corresponding set of before/after MODIS true color images (created using MODIS bands 1/4/3 as the R/G/B channels), increased river water turbidity (varying shades of light brown) can be seen — a result of  high amounts of sediment transport (below).

Before (29 April) and after (03 May) MODIS true color RGB images

AWIPS images of the MODIS 0.645 µm visible channel and the 2.1 µm near-IR “snow/ice channel” data (below) demonstrate how the 2.1 µm imagery can be used to better identify flooded areas that do not show up as well on the visible channel imagery. Water (like snow and ice) is a strong absorber at the 2.1 µm wavelength, and thus appears very dark on the  “snow/ice” image.

MODIS 0.645 µm visible channel and 2.1 µm near-IR “snow/ice” channel images

CIMSS has been supplying a variety of MODIS images and products in AWIPS (some of which are displayed on this page) to a number of NWS forecast offices as a part of the GOES-R Proving Ground effort.

===== 05 MAY UPDATE =====

MODIS false color images from 03, 04, and 05 May 2010

A comparison of 250-meter resolution MODIS false color images from 03 May, 40 May, and 05 May 2010 (above) showed that while some of the smaller rivers and tributaries appeared to be receding somewhat, a number of the larger rivers did appear to remain swollen, with many areas still inundated with flood waters.

Related sites:

NWS Nashville precipitation total map
AccuWeather WeatherMatrix blog
Weather Underground blog

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