GOES-13 fog/stratus product (click image to play animation)

AWIPS images of the 4-km resolution GOES-13 10.7 µm – 3.9 µm “fog/stratus product” (above; click image to play animation) showed a large area of fog and/or stratus (yellow to orange color enhancement) that was increasing in areal coverage during the pre-dawn hours on 06 February 2012. Although the fog/stratus product is useful for locating the presence and temporal trends of such features, it does not offer any reliable indication of whether it is fog on the ground or stratus cloud aloft.

One product that attempts to give the forecaster some quantitative information is the GOES Low CLoud Base (LCB) prodcut (below; click image to play animation), which attempts to blend surface observations with satellite data to indicate whether the cloud base is above or below the threshold of 1000 feet.

GOES-13 Low Cloud Base product (click image o play animation)

With 1-km resolution data, the MODIS instrument aboard the polar-orbiting Terra and Aqua satellites offers a similar “fog/stratus product” (below) that provides better clarity, especially regarding the exact location of the edges of the fog and/or stratus.

MODIS fog/stratus product images

In this particular case, a number of locations beneath the western and southern edge of the fog/stratus feature were expereincing freezing fog (below) and visibilities of 1/4 mile or less, which was creating hazardous road conditions and prompting the issuance of Freezing Fog Advisories.

MODIS fog/stratus product with METAR surface reports

As part of CIMSS participation in GOES-R Proving Ground activities, products are being developed which can provide more quantitative information about such parameters as Fog Depth and the Probability of Marginal Visual Flight Rules (MVFR) or Instrument Flight Rules (IFR) conditions (below). In this case, across the southwestern part of Iowa (where widespread freezing fog was being reported), the fog depth was as high as 1400-1500 feet, with probabilities of MVFR and IFR conditions as high as 75-90% and 60-75%, respectively.

MODIS Fog Depth, MVFR Probability, and IFR Probability products

Shortly after sunrise, it is interesting to note that a comparison of 1-km resolution POES AVHRR 0.63 µm visible channel, 3.74 µm “shortwave IR” channel, and 10.8 µm channel “IR window” channel images (below) revealed that part of the swath of fresh snow cover (as deep as 4-6 inches) across western Iowa could be seen through the translucent western edge of the fog/stratus deck that was beginning to burn off during the morning hours. The fog/stratus deck appears warmer (darker gray enhancement) om the 3.74 µm image, due to the sensitivity of that channel to the reflection of solar radiation off the tops of supercooled water droplet clouds.

Farther to the south, note the presence of narrow fingers of valley fog in the Ozark Mountains and surrounding regions in Oklahoma, Arkansas, and Missouri.

POES AVHRR 0.63 µm visible, 3.74 µm "shortwave IR", and 10.8 µm "IR window" images

GOES-15 0.63 µm visible channel images (click image to play animation)

Strong northeasterly winds created large plumes of blowing dust across parts of the Baja California region of Mexico on 27 November 2011. GOES-15 0.63 µm visible channel images (above; click image to play animation) showed the development of one blowing dust plume originating near the west coast of mainland Mexico, with another more broad plume fanning out from the Baja California peninsula.

GOES-15 will be replacing GOES-11 as the operational GOES-West satellite on 06 December 2011 — and one of the benefits is improved Image Navigation and Registration (INR), which leads to less image-to-image “wobble” when viewing an animation. The improved GOES-15 INR is quite evident when compared to GOES-11 for this blowing dust case (below; click image to play animation).

GOES-11 0.65 µm and GOES-15 0.63 µm visible images (click image to play animation)

A 250-meter resolution MODIS true color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below) revealed more complex details about the structure of the blowing dust features.

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

AWIPS images of GOES-11 0.65 µm visible channel data with an overlay of MADIS 1-hour interval satellite winds (below) indicated that the airborne dust feature was moving southwestward at speeds of 15-20 knots.

GOES-11 0.65 µm visible images + MADIS satellite winds

A comparison of 1-km resolution MODIS 0.65 µm visible channel, 3.7 µm “shortwave IR” channel, and 11.0 µm “IR window” channel images (below) showed that (1) the thickest portions of the blowing dust plumes appeared several degrees warmer (darker black enhancement) on the shortwave IR channel image, due to reflection of incoming solar radiation off the small airborne dust particles, and (2) swaths of land which had significant amounts of blowing dust overhead exhibited a slightly cooler (lighter gray enhancement) signaure on the IR window channel image, since the dust was reducing the amount of solar radiation reaching the surface.

MODIS 0.65 µm visible, 3.7 µm "shortwave IR", and 11.0 µm "IR window" images

In fact, the corresponding 1-km resolution MODIS Land Surface Temperature (LST) product (below) displayed LST values in the 80s F in areas beneath the blowing dust plumes, in contrast to LST values in the 90s to around 100º F over adjacent areas.

MODIS 0.65 µm visible channel + MODIS Land Surface Temperature product

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

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

A comparison of an AWIPS image of 1-km resolution MODIS 0.65 µm visible channel data with the corresponding MODIS false color Red/Green/Blue (RGB) image created using the 2.1 µm “snow/ice channel” (above) showed that snow cover was beginning to increase in areal extent across parts of the north-central US on 20 November 2011. This example also demonstrates the utility of RGB imagery for helping to discriminate between snow cover (which shows up as shades of red on the RGB image) and supercooled water droplet clouds (which show up as varying shades of white). Snow depths at the time included 11 inches at Mount Rushmore, South Dakota, 10 inches at Rice, Minnesota and 5 inches at Minot, North Dakota.

MODIS false color RGB images created using data from consecutive overpasses of the Terra (17:22 UTC) and Aqua (19:03 UTC) satellites (below) also show the movement of the low cloud features during that period.

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

As pointed out in the NWS Minneapolis Area Forecast Discussion, the swath of fresh snow cover would have an impact on daily high and low temperatures at locations where the snow was deepest. An AWIPS image of the 1-km resolution MODIS Land Surface Temperature (LST) product (below) revealed that LST values were in the 0º F to +10º F range (cyan to blue color enhancement) over the areas with snow cover, in contrast to LST values in the 30s F (green color enhancement) over adjacent areas with bare ground.

MODIS Land Surface Temperature product

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

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

The first major winter storm of the season to affect the central Rocky Mountains region produced up to 19.9 inches of snowfall across parts of Colorado on 26 October 2011. On the following day, 250-meter resolution Terra MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed a nice view of the resulting snow cover across northeastern Colorado (the snow cover was cyan-colored in the false color RGB image, with cloud features appearing as shades of white). The morning snow depths included 10 inches at Boulder and Greeley, with reports of 12 inches on the ground at a number of higher elevation stations.

A corresponding AWIPS image comparison of 1-km resolution MODIS 0.65 µm visible channel data and a false color RGB image created using the 2.1 µm “snow/ice channel” (below) further demonstrated the utility of using RGB imagery to discriminate between snow cover (which appeared red in this second RGB image) and cloud features (which again appeared as lighter shades of white).

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

===============================================

18:13 UTC and 19:53 UTC MODIS false color RGB images

Some of the snow cover began to melt during the day across eastern Colorado, as could be seen in a comparison of the 18:13 UTC (12:13 PM local time) and 19:53 UTC (1:53 PM local time) MODIS false color RGB images (above). GOES-15 0.63 µm visible channel images at 15 minute intervals (below; click image to play animation) more clearly showed the temporal evolution of the melting snow cover.

GOES-15 0.63 µm visible channel images (click image to play animation)

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

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

A significant rain and snow event occurred across parts of southeastern Wyoming and western Nebraska on 08 October 2011 (see NWS Cheyenne story) — snowfall amounts as high as 12.0 inches were reported near Cheyenne , Wyoming with 2.73 inches of rain reported farther to the northeast near Crawford in western Nebraska. Two days later (on 10 October 2011), a large patch of low-elevation snow cover could still be seen in far southeastern Wyoming  on a 250-meter resolution MODIS true color Red/Green/Blue (RGB) image  from the SSEC MODIS Today site (above, viewed using Google Earth).

MODIS 0.65 µm visible channel image + MODIS 2.1 µm "snow/ice channel" image

On a comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and MODIS 2.1 µm “snow/ice channel” data (above), snow cover (along with clouds) appears bright on the visible image, but snow appears very dark on the snow/ice image (since snow is a very strong absorber at that particular wavelength).

Another method to discriminate between clouds and snow cover is to use different MODIS images to create a 3-channel RGB false color image — snow cover appears darker red on such a false color image (below), which used MODIS channels 01/07/07 as the Red/Green/Blue components.

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

In far southeastern Wyoming, the areas that still had significant snow cover exhibited much colder MODIS Land Surface Temperature (LST) values (below), with LSTs ranging from the middle 30s F (darker green color enhancement) over deeper snow cover to the upper 60s to low 70s (darker orange color enhancement) over adjacent areas of bare ground.

MODIS Land Surface Temperature product

With the high October sun angle helping to produce warm temperatures (the daytime high at Cheyenne, Wyoming that day reached 59ºF or 15ºC) the patch of lower-elevation snow cover just to the north of Cheyenne began to melt during the day, as can be seen on an animation of GOES-15 0.63 µm visible channel images (below; click image to play animation).

GOES-15 0.63 µm visible channel images (click image to play animation)

============================

MODIS 11.0 µm IR image + topography

Another feature of interest on the satellite images was the formation of a  “cloud banner” or “cloud crest” just downwind of the ridge of higher terrain that ran northwest to southeast across the Wyoming/Colorado border region — this cold cloud feature could be seen on the 1-km resolution MODIS 11.0 µm IR image (above). The 4-km resolution MODIS Cloud Phase product (below) showed this to be an ice phase cloud feature (salmon color enhancement), with the 4-km resolution MODIS Cloud Top Temperature (CTT) product indicating CTT values as cold as -45ºC (darker blue color enhancement).

MODIS Cloud phase product + MODIS Cloud Top Tempeature product

The 1-km resolution MODIS 6.7 µm water vapor channel image (below) revealed a signature of mountain waves farther downwind of the cloud banner feature. A few hours later (at 23:58 UTC), there was a pilot report of light turbulence in that region at an altitude of 37,000 feet.

MODIS 6.7 µm water vapor channel image

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

MODIS and GOES-13 fog/stratus product images

Strong nocturnal radiational cooling beneath a large area of high pressure centered over the Ohio River Valley led to the formation of widespread areas of fog and stratus on 05 October 2011. AWIPS image comparisons of the 1-km resolution MODIS and the 4-km resolution GOES-13 fog/stratus products at 03:30 UTC or 11:30 pm local time (above) and 07:45 UTC  or 3:45 am local time (below) demonstrated the clear advantage of having improved spatial resolution to detect the more subtle features such as river valley fog.

MODIS and GOES-13 fog/stratus product images

To compliment the improved fog/stratus detection capabilities offered by higher spatial resolution, other products are being developed (as part of the CIMSS participation in GOES-R Proving Ground activities) that provide more quantitative information about areas of fog and/or low cloud: for example, Fog Depth, Marginal Visual Flight Rules (MVFR) Probability, and Instrument Flight Rules (IFR) Probability (below). In this case, the 07:45 UTC products indicated that the Fog Depth values were as high as 1231 feet (cyan color enhancement) over parts of northern West Virginia, where there were also MVFR Probabilities greater than 90% and IFR Probabilities greater than 75% (brighter red color enhancement).

GOES-13 fog/stratus product, Fog Depth, MVFR Probability, and IFR Probability

GOES-11 6.7 µm (left) and GOES-15 6.5 µm (right) water vapor channel images (click image to play animation)

McIDAS images of 8-km resolution GOES-11 6.7 µm and 4-km resolution GOES-15 6.5 µm water vapor channel data (above) demonstrated the advantage of improved spatial resolution for the detection of features and gradients in the water vapor imagery associated with a weak upper level low moving eastward across the southwestern US on 14 September 2010. GOES-15 is scheduled to replace GOES-11 as the operational GOES-West satellite in December 2011.

AWIPS images of the GOES-11 sounder Convective Available Potential Energy (CAPE) product (below) showed that the atmosphere was destabilizing in advance of the upper low, with CAPE values in the 1000-2000 J/kg range.

GOES-11 sounder Convective Available Potential Entegy (CAPE)

With the increasing instability and large scale lift ahead of the upper low, areas of thunderstorms developed over parts of Nevada, Arizona, and Utah, as seen on a MODIS 11.0 µm IR image with an overlay of cloud-to-ground lightning strikes (below). About an hour after the time of the MODIS image, one of these storms produced 1.0-inch diameter hail that covered the ground near Munds in northern Arizona (SPC storm reports).

MODIS 11.0 µm IR image + cloud-to-ground lightning strikes

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS and additional GOES Sounder images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

GOES Water Vapor Imagery and turbulence reports

Clear Air Turbulence can be a significant aircraft hazard, occasionally causing injuries and long delays. (See, for example, here and here for two recent examples. The second example resulted in a 6-hour delay (Link))

At the upper-tropospheric boundary between air masses, vertical shearing at the jet stream combined with the ageostrophic convergence of polar, subtropical and stratospheric air produces a region known for its potential for clear air turbulence called a “tropopause fold.” These features are evident in satellite-observed upper tropospheric water vapor by the large-scale spatial gradients in brightness temperature, which define boundaries between the air masses. The tropopause fold extends from this boundary to a limited distance into and underneath the wetter air mass.

Thus, water vapor imagery can be used to infer large changes in vertical motion that can herald the presence of turbulence in the atmosphere. For example, in the region of turbulence shown in the water vapor imagery above, the yellow enhancement — warm brightness temperatures — suggest water vapor concentrated lower in the atmosphere (subsidence); bluer enhancements — colder brightness temperatures — suggest water vapor that is concentrated higher in the atmosphere (rising motion).

The Tropopause Folding Turbulence Prediction (TFTP) product locates these regions in the atmosphere and identifies the sections most likely to produce turbulent flight conditions for aircraft. The upper-tropospheric water vapor channel of the GOES-R Advanced Baseline Imager (primary: channel 8, backup: channel 9) is the source for resolving gradients that reveal the horizontal distribution of tropopause folds. An ancillary numerical weather model constrains these features vertically in the atmosphere. The four key output products consist of two fields that define the lower and upper bounds of the turbulent volumes of air, and two fields that define the two flight directions that are the most susceptible to moderate or greater turbulence. For now, the GOES-East (or MODIS) water channels can be used as a proxy.

GOES Water Vapor Imagery and turbulence reports

The animated gif above shows the predicted tropopause fold (green), model results that show the tropopause (yellow, the 1-2 PV Unit surface) for a turbulence event that occurred in September 2011 (link). Note that the strongest turbulence (red airplane icon) occurred as the plane traversed the fold.

GOES-13 6.5 µm water vapor channel images (click image to play rocking animation)

The animation of water vapor imagery (above) centered on the time of the turbulence includes some key features. For example, the gradient in the water vapor field between the colder brightness temperatures over the Atlantic Ocean south of New England and the warmer brightness temperatures off the coast of New Jersey is tightening with time. There is also evidence of a jet feature propagating northeastward along the gradient from east of the mouth of Chesapeake Bay at the start of the loop to south of Long Island at the end of the loop. Both of these features are suggestive of an evolving tropopause fold.

MODIS true color and false color RGB images (11 September)

MODIS true color and false color RGB images (12 September)

250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed the very large pyrocumulus and smoke plume from the Pagami Creek wildfire that was burning in the Boundary Waters Canoe Area Wilderness region of northeastern Minnesota on 11 September 2011 and 12 September 2011. The wildfire “hot spot” appears as the large red-colored feature on the false color images.  Other options for viewing this MODIS imagery include the SSEC Web Mapping Service and WisconsinView sites: WMS MODIS image | WisconsinView: Terra and Aqua MODIS images. Additional information and photos are available from the Duluth National Weather Service.

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel, 3.7 µm shortwave IR channel, and 11.0 µm IR window channel data (below) revealed the very large fire “hot spot” on the shortwave IR image (red to yellow to black color enhancement) — and also note that the resulting pyrocumulus cloud just east of the fire hot spot exhibited a cloud top 11.0 µm IR window brightness temperature of -70º C (black color enhancement), which was just as cold as that associated with the thunderstorms farther to the north in Ontario, Canada!

MODIS 0.65 µm visible, 3.7 µm shortwave IR, and 11.0 µm IR images

AWIPS images of GOES-13 3.9 µm shortwave IR data (below) showed the diurnal changes to the size and intensity of the fire hot spot. Early in the animation during the overnight and morning hours, the hot spot was smaller and less intense as the wind speeds became very light– however, once strong southwesterly winds began to increase during the afternoon hours in advance of an approaching cold front, the hot spot was seen to dramatically increase in size as the fire quickly grew.

GOES-13 3.9 µm shortwave IR images (click image to play animation)

A comparison of the 4-km resolution GOES-13 3.9 µm and the 1-km resolution MODIS 3.7 µm shortwave IR images (below) demonstrated the advantage of better spatial resolution for more accurate location of the fire hot spot boundaries. In addition, the MODIS image revealed another small fire hot spot could be seen to the north, just across the Minnesota/Ontario border — this small fire was not seen on the GOES-13 image.

MODIS 3.7 µm and GOES-13 3.9 µm shortwave IR images

===== 13 September Update =====

A significant amount of smoke was transported southeastward across Wisconsin on 13 September 2011, as seen on GOES-13 0.63 µm visible channel images (below). The surface visibility was reduced to 2 miles at Milwaukee (station identifier KMKE), and 3 miles at Chicago O’Hare (station identifier KORD). Special Weather Statements were issued by the National Weather Service forecast offices at Milwaukee/Sullivan and Chicago/Romeoville to advise the public about the potential harmful effects of the smoke.

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

The smoke feature was even more apparent on the afternoon MODIS true color Red/Green/Blue (RGB) image (below), and this smoke produced an elevated signal on the MODIS Aerosol Optical Depth (AOD) product from the IDEA site.

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

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

Comparison of 8-day average MODIS SST (left) and 07 September MODIS SST (right)

A comparison of the MODIS 8-day average Sea Surface Temperature (SST) ending on 06 September 2011 (above, left) with the MODIS SST product on 07 September 2011 (above, right) revealed a dramatic cooling of the near-shore waters just off the east coastline of Lake Michigan. Persistent strong northerly daytime winds (gusting in the 20-30 mph range) induced an upwelling of colder water from below the surface, with 07 September values as cold as 6.8ºC (44ºF) at one location (Latitude/Longitude 43.63 North/81.96 West) — compared to the previous 8-day average SST of 22.8ºC (73ºF) at that same location. Unfortunately, the MODIS Cloud Mask that is applied to the SST product mistakenly identifies the strongest SST gradient as a cloud, and blanks out the SST product along the far western fringe of the ribbon of colder water.

AWIPS images of MODIS 0.65 µm visible channel and 11.0 µm IR channel data (below) showed greater detail in the ribbon of colder waters, with a series of eddies forming along the northern edge of the feature. Since no Cloud Mask is applied to the IR image, the full westward extent of the cold water feature can be seen.

MODIS 0.65 µm visible channel and 11.0 µm IR channel images

A sequence of four MODIS 11.0 µm IR images (below) shows the evolution of the eddy features along the western edge of the cold water. Note that the land surfaces exhibit cool IR brightness temperatures (blue to cyan color enhancement) on the first 2 night-time images (03:10 UTC and 07:21 UTC, or 10:10 pm and 2:21 am local time), but on the 2 daytime images (16:45 UTC and 18:27 UTC, or 11:45 am and 1:27 pm local time) urban areas and regions with less dense vegetation heat up and exhibit much warmer IR brightness temperatures (orange to red color enhancement). However, the Lake Michigan IR brightness temperatures generally remain constant during this time period.

MODIS 11.0 µm IR images

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS. In addition, the VISIT training lesson “MODIS Products in AWIPS” is available to help users understand these products and their applications to weather analysis and forecasting.