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

A large outbreak of blowing dust developed in the wake of a cold frontal passage across parts of New Mexico, Texas, and Oklahoma on 22 January 2012. At Lubbock, Texas winds gusted to 60 mph, and surface visibility was reduced to 0.5 mile. The strongest wind gust was 77 mph, farther to the north in the Texas panhandle region (NWS Lubbock summary). Early in the day, the consolidation of numerous smaller blowing dust plumes into a single large blowing dust “cloud” could be seen on 1-km resolution GOES-15 (GOES-West) 0.63 µm visible channel images (above; click image to play animation).

Later in the day, due to a more favorable forward scattering angle, the areal extent of the airborne blowing dust could be better seen on 1-km resolution 0.63 µm visible channel images from the GOES-13 (GOES-East) satellite (below; click image to play animation). The leading edge of the primary large dust plume began to move northeastward over Oklahoma, while a number of smaller dust plumes could be seen moving southeastward across the Oklahoma and Texas panhandle regions behind a secondary cold front. Note that the GOES-13 satellite had been placed into Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-10 minutes.

GOES-13 0.63 µm visible channel 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, viewed using Google Earth) displayed even greater detail in the structure of the blowig dust plume at 20:02 UTC.

Aqua MODIS true color Red/Green/Blue (RGB) image (displayed using Google Earth)

There was also a bit of smoke mixed in with the blowing dust, due to a few small wildfires that were burning across the region. Three small wildfire “hot spots” (dark black to yellow pixels) could be seen on an AWIPS image of 1-km resolution MODIS 3.7 µm shortwave IR data at 20:00 UTC (below).

MODIS 3.7 µm shortwave IR image

Over southern Oklahoma at 21:23 UTC a pilot reported that at an altitude of 9000 feet the flight level visibility was zero due to blowing dust (below).

GOES-13 0.63 µm visible channel image + Aircraft pilot report

GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 µm water vapor channel images (click image to play animation)

Strong winds aloft associated with a cyclonically-curved jet streak over the Northern Rocky Mountains were responsible for a number of mountain waves and lee “banner clouds” over parts of Wyoming and Montana on 25 December – 26 December 2011. A side-by-side comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 µm water vapor channel images (above; click image to play animation) revealed some interesting differences in the appearance of these mountain waves. Note that the images are displayed in the native projection of their respective satellites.

A comparison of the GOES-15 and GOES-13 imager 6.5 µm water vapor channel weighting functions (below) showed that the satellite viewing angles (or satellite zenith angles) were very close — 56.41 degrees for GOES-15, and 59.95 degrees for GOES-13 — and the weighting function profiles were nearly identical. However, the fact that GOES-15 was viewing the region from the west allowed it to better resolve the warm/dry signatures (yellow color enhancement) of the most pronounced sinking regions associated with some of the stronger mountain waves. These warm/dry subsidence signatures were possibly masked by the high-altitude lee banner clouds when viewed from the east with GOES-13.

GOES-15 vs GOES-13 water vapor channel weighting function profiles

At 00:40 UTC there was one pilot report of brief moderate turbulence at an altitude of 37,000 feet near the Wind River Range in west-central Wyoming (below). Only a lee banner cloud was evident on the GOES water vapor imagery at that particular time, but a few hours later the warm/dry signature of strong mountain wave subsidence started to become more distinct over that location.

GOES-13 6.5 µm water vapor channel image + pilot report of turbulence

Had higher spatial resolution water vapor imagery been available closer to the 00:40 UTC time of the turbulence encounter, perhaps a more distinct mountain wave signature might have been apparent. For example, a comparison of 1-km resolution MODIS 6.7 µm and 4-km resolution GOES-13 6.5 µm water vapor images at 05:01 UTC (below) demonstrated the advantage of improved spatial resolution water vapor imagery for identifying subtle mountain wave signatures across the region.

MODIS 6.7 µm and GOES-13 6.5 µm water vapor channel images

GOES-15 6.5 µm water vapor channel images (click image to play animation)

McIDAS images of 4-km resolution GOES-15 6.5 µm water vapor channel data (above; click image to play animation) showed an intense upper level shortwave trough of low pressure moving northeastward across southcentral and eastern Alaska on 18 December 2011. Strong southerly flow associated with this system brought unseasonably warm air into the region, with Anchorage (station identifier PANC) reaching a daily maximum temperature of 45º F (one degree F shy of their record high for the date), and Big Delta (station identifier PABI) tied their daily record high of 37º F. Strong winds were also experienced with this disturbance, with surface winds gusting in excess of 100 mph in southcentral Alaska. It is also interesting to note the development of a small westward-propagating “wave feature” at the end of the water vapor animation near Tanana (station identifier PATA).

Over eastern Alaska the water vapor images also showed a large orographic “banner cloud” that formed downwind of the high terrain of the Alaska Range. A closer look at this banner cloud feature can be seen using an AWIPS image of 1-km resolution MODIS 11.0 µm IR channel data with an overlay of GFS model 500 hPa winds (below). The coldest MODIS IR brightness temperatures along the leading edge of the banner cloud were -65º C, which was just a few degrees colder than the tropopause temperature on the 12:00 UTC Anchorage rawinsonde data. The winds aloft then turned anticyclonically, carrying some of the banner cloud materail eastward into the Yukon Territory of Canada.

MODIS 11.0 µm IR image + GFS 500 hPa winds

The corresponding 1-km resolution MODIS Cloud Type product (below) indicated that much of this banner cloud was of the “opaque ice” category (yellow color enhancement).

MODIS Cloud Type product

The 1-km resolution POES AVHRR Cloud Top Height product (below) indicated that the highest portions of the banner cloud feature were in the 10-11 km range.

POES AVHRR Cloud Top Height product

As an interesting aside, a Boeing 747 flying just off the coast of Alaska encountered severe turbulence at a flight level of 35,000 feet — the captain of the aircraft “said this was the first time he has ever reported severe turbulence” (below).

POES AVHRR 12.0 µm IR image with pilot reports of turbulence

Note on the GOES-15 water vapor images shown above that this area was near the leading edge of an advancing dry slot — and 1-km resolution GOES-15 0.63 µm visible channel images (below) depicted a few cloud features resembling banded convective cells along the trailing edge of the cloudiness just ahead of the dry slot. These convective bands (or the strong deformation axis seen developing on the water vapor imagery) may have been responsible for producing high-altitude turbulence across that region.

GOES-15 0.63 µm visible channel images

GOES-15 3.9 µm shortwave IR images (click image to play animation)

The 2000-acre “Caughlin Fire” started burning around 08:45 UTC (1:45 am local time) in the hilly terrain near Reno, Nevada, and soon grew out of control due to strong winds gusting as high as 74 mph. McIDAS images of GOES-15 3.9 µm shortwave IR data (above) showed the “hot spot” (black to yellow to red enhanced pixels) associated with the fire. At least 30 homes were destroyed, with many more damaged by the fire. Thousands of residents were evacuated.

Evidence of the strong winds across the region could be seen on an AWIPS image of MODIS 6.7 µm water vapor channel data (below), with a number of very pronounced mountain waves showing up on the image. These mountain waves persisted for several hours, and were responsible for pilot reports of severe turbulence, wind shear, and 50-knot crosswinds during descent to final approach into the Reno airport. The highest wind gust reported at the Reno airport was 44 mph, and surface visibility was also reduced to 6 miles at the airport due to smoke.

MODIS 6.7 µm water vapor channel image

GOES-11, GOES-13, GOES-15, and MODIS water vapor channel images

A comparison of 8-km resolution GOES-11 6.7 µm water vapor channel, 4-km resolution GOES-13 and GOES-15 6.5 µm water vapor channel, and 1-km resolution Aqua MODIS 6.7 µm water vapor channel images (above) demonstrated how differences in satellite viewing angle as well as differences in satellite sensor spatial resolution have an impact in being able to resolve the structure and areal coverage of small-scale features such as the mountain waves that existed across much of southeastern Colorado and northeastern New Mexico around 19:45 UTC on 12 November 2011.

There were a number of pilot reports of moderate to severe turbulence aloft across the region – and at the surface, wind gusts as high as 115 mph were reported. As can be seen in a comparison of 1-km resolution MODIS 0.65 µm visible channel and MODIS 6.7 µm water vapor channel images (below), many of the mountain waves were located in cloud-free areas — this highlights the value of water vapor channel imagery for identifying such regions of potential aircraft turbulence.

MODIS 0.65 µm visible channel + MODIS 6.7 µm water vapor channel images

GOES-15 6.5 µm water vapor images (click image to play animation)

McIDAS images of GOES-15 6.5 µm water vapor channel data (above; click image to play animation) showed the changing signature of a persistent upper level cut-off low lingering over the north-central US during the 23 September – 27 September 2011 period. As the system lingered over the region, it produced widespread wind gusts in the 30-40 mph range (with a peak wind gust of 46 mph at Green Bay, Wisconsin), and rainfall totals of 4-5 inches at some locations in northern Illinois.

AWIPS images of the hourly GOES sounder Total Column Ozone product on 25 September - 26 September (below; click image to play animation) revealed a distinct elevated ozone signature (300-400 Dobson Units, green to red color enhancement), which indicated that the height of the tropopause was lower in the vicinity of the cut-off low.

GOES sounder Total Column Ozone product (click image to play animation)

One notable impact associated with this cut-off low included thunderstorms along the Lake Michigan shoreline that produced a number of waterspouts that were seen from Milwaukee to Chicago. A comparison of MODIS 0.65 µm visible channel and 11.0 µm IR window channel image at 17:28 UTC (12:28 pm local time) on 24 September (below) showed one of the storms that exhibited cloud top IR brightness temperatures colder than -40ºC (blue color enhancement), along with a number of cloud to ground lightning strikes as it moved inland.

MODIS 0.65 µm visible channel and 11.0 µm IR window channel images

Another impact of this cut-off low included a number of pilot reports of light to moderate turbulence over the central and southern Great Plains region. A well-defined bloom of cirrus clouds developed within a zone of high 400-200 hPa layer wind shear, as seen on 4-km resolution GOES-13 6.5 µm water vapor channel images with overlays of CRAS model fields (below; click image to play animation).

GOES-13 6.5 µm water vapor images + turbulence reports + CRAS layer winds and shear (click image to play animation)

Better detail of the banded structure of the cirrus cloud features within the high-shear deformation zone can be seen on a 1-km resolution MODIS 6.7 µm water vapor image (below). Note the pilot report of light to moderate turbulence during the entire flight from Denver (DEN) to Kansas City (MCI).

MODIS 6.7 µm water vapor image + pilot reports of turbulence

A sequence of 1-km resolution MODIS 6.7 µm water vapor channel images on 26 September (below) showed some very intricate dry air and moisture structures within the cut-off low during that particular day.

MODIS 6.7 µm water vapor channel images

In a comparison of MODIS 0.65 µm visible channel and MODIS 6.7 µm water vapor channel images (below), note how much more structure is seen in the water vapor image — even in areas that are cloud-free in the visible image. This allows a number of water vapor features and gradients to be tracked using 3 consecutive GOES water vapor images, to produce MADIS high-altitude atmospheric motion vectors (AMVs) that can provide important wind direction and wind speed data. An AMV with a wind speed of 130 knots (at 300 hPa) was seen in the dry slot over southern Missouri.

MODIS 0.65 µm visible image + MODIS 6.7 µm water vapor image + MADIS satellite winds

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.

GOES-13 Visible with Airplane Positions

Turbulence associated with a developing line of convection over the Atlantic Ocean east of Florida was severe enough on August 9th to cause five injuries on a Miami-to-Washington DC flight and force an unscheduled landing of the 737-800 aircraft in Charleston, SC. The GOES-13 image, above, shows the path that the aircraft took through a line of developing convection east of Florida (Click here for a flash-based animation). The time that the satellite was scanning the region east of Florida was between 1935 and 1936 UTC (the nominal time of the image, 1932 UTC, refers to the first line scanned in by GOES-13; it takes almost 5 minutes to completely scan North America. See this NESDIS website for the normal scanning schedule).

Animations of visible imagery, 10.7-micrometer infrared imagery, and 6.5-micrometer infrared imagery (the so-called ‘water vapor channel’) all show a similar evolution, namely strong thunderstorms at the coast of Florida at the start of the loop followed by the development of a line of thunderstorms northeastward. It is through this developing line that the airline penetrated. (The flight path is here).

GOES Satellite data are routinely monitored to detect both the initiation of convection, and the presence of Overshooting Tops and Thermal couplets, the latter two features being well-correlated with severe weather and turbulence. Detection suffers, however, because of the relatively poor spatial and temporal resolution afforded by routine GOES scanning. What was detected on this day?

Overshooting tops were detected over the Florida peninsula at 1715 UTC and at 1732 UTC. The top at 1732 UTC is quite apparent in both the visible and infrared loops. Overshooting tops were not detected in the area again before the turbulence event, but their detection prior to the event suggests an airmass with the potential for strong convective development.

Convective Initiation (CI) was flagged along the southwest-to-northeast line of developing convection at 1832 UTC and 1845 UTC, roughly an hour before the turbulence event. (See this link for all Blog Posts on Convective Initiation). Note that the CI detection in this case — occurring — means that glaciation of the clouds has started. CI is drawing the eye to the convective towers that are growing most rapidly; therefore, their tops cool most quickly. It is to these growing cells that a forecaster must pay attention, particularly when they appear in an environment that will sustain overshooting tops.

(Here is an article on this flight from The Aviation Herald).

GOES-13 10.7 µm IR images (click image to play animation)

AWIPS images of GOES-13 10.7 µm IR data (above; click image to play animation) showed the progression of two long-lived Mesoscale Convective Systems (or “derechos”) on 11 July 2011 — one moving southeastward from the Dakotas and Minnesota, and another moving northeastward from Nebraska. These two MCS features were responsible for a large number of severe weather reports (SPC: 10 July reports | 11 July reports).

Note the elongated band of cirrus that developed  behind the departing MCS feature, curving across parts of Iowa, Nebraska, Kansas, and Colorado toward the end of the IR image animation above — this striated cloud band marked the location of a well-defined deformation zone. Areas of light to moderate turbulence aloft are often present in association with such deformation zones, as was seen by the number of pilot reports overlaid on a GOES-13 6.5 µm water vapor channel image at 17:45 UTC (below).

GOES-13 6.5 µm water vapor channel image + pilot reports of turbulence

The GOES-13 sounder Total Precipitable Water (TPW) derived product (below; click image to play animation) showed that abundant moisture (TPW values of 50-60 mm or 2.0 to 2.4 inches, violet color enhancement) was in place ahead of the storms as they moved rapidly eastward.

GOES-13 sounder Total Precipitable Water product (click to play animation)

A closer view of GOES-13 10.7 µm IR images with overlays of the Automated Overshooting Top Detection product (below; click image to play animation) revealed a number of overshooting tops, with the minimum cloud top IR brightness temperature of -81ºC occurring over eastern Iowa at 09:45 UTC. The overshooting tops were very evident after sunrise on GOES 0.63 µm visible channel imagery, as they cast shadows upon the thunderstorm anvil tops below (11:45 UTC visible image + overshooting top detection product comparison).

GOES-13 10.7 µm IR images + Overshooting Top Detection (click to play animation)

A set of three comparisons of 1-km resolution POES AVHRR 10.8 µm IR images with their corresponding 4-km resolution GOES-13 10.7 µm IR images (below) demonstrated the value of improved spatial resolution for more accurate detection of the location and magnitude of the coldest cloud tops on severe thunderstorms. On the 08:22 UTC, 08:47 UTC, and 11:37 UTC POES AVHRR images, the coldest cloud top IR brightness temperatures were -84ºC, -90ºC, and -85ºC, respectively (the coldest GOES-13 IR brightness temperatures were -78ºC for all three of those times). Note that the apparent northwestward displacement of cloud features on the GOES-13 images is a result of parallax error due to the large viewing angle from the geostationary satellite.

1-km resolution POES AVHRR 10.8 µm IR and 4-km resolution GOES-13 10.7 µm IR images

1-km resolution POES AVHRR 10.8 µm IR and 4-km resolution GOES-13 10.7 µm IR images

1-km resolution POES AVHRR 10.8 µm IR and 4-km resolution GOES-13 10.7 µm IR images

Very strong surface winds were observed along and in the wake of the well-defined bow echo seen on radar — peak wind gusts included 74 mph at Dubuque, Iowa, 75 mph at Chicago Midway Airport, and 85 mph at Michigan City, Indiana. These strong winds created a seiche across southern Lake Michigan (Seiche Warning | NWS Chicago event summary), with oscillations in water levels seen at Calumet Harbor, Illinois, Milwaukee, Wisconsin, and Holland, Michigan.

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

AWIPS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed that 17 May 2011 was a generally cloud-free day over the state of Wisconsin.

However, the GOES-13 6.5 µm “water vapor channel” images (below; click image to play animation) displayed a series of well-defined “dry cyclonic swirls” aloft that were propagating southwestward. Due to the dry air associated with these features, the weighting function of the GOES-13 imager water vapor channel was shifted downward, sampling a layer that peaked near 500 hPa. GOES imager and sounder weighting functions for a particular rawinsonde location are available here.

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

A comparison of the 1-km resolution MODIS 6.7 µm water vapor image with the corresponding 4-km resolution GOES-13 6.5 µm water vapor image (below) demonstrated the advantage of improved spatial resolution for displaying the edges and gradients associated with such features. The effect of parallax (due to the large viewing angle of the geostationary satellite positioned at the Equator) acted to shift the location of the GOES-13 features slightly to the northwest compared to the image from the polar-orbiting satellite that carries the MODIS instrument.

MODIS 6.7 µm water vapor image + GOES-13 6.5 µm water vapor image

Hourly images of the GOES-13 sounder Total Column Ozone product (below; click image to play animation) revealed that ozone levels were quite high (over 400 Dobson Units, darker red color enhancement) within the large “dry swirl” feature that was moving over Wisconsin — this suggests that the dry vortex features seen on the water vapor imagery were actually stratospheric intrusion vortices (since high ozone is a characteristic of stratospheric air).

GOES-13 sounder Total Column Ozone product (click image to play animation)

The Advanced Baseline Imager (ABI) instrument on the future GOES-R satellite will have an ozone channel, which will allow for this type of total column ozone product to be generated at higher spatial and temporal resolution that the current GOES Sounder instrument can provide.

A northwest-to-southeast oriented vertical cross section using RUC13 model fields (below) illustrated how low the tropopause (taken to be the height of the “PV1.5″ Potential Vorticity surface) had descended within the PV anomaly associated with the stratospheric intrusion vortex over Wisconsin at 16:00 UTC.

RUC-13 model northwest-to-southeast oriented vertical cross section

As is sometimes the case with these features, there were a few pilot reports of light to moderate turbulence around the periphery of the well-defined stratospheric intrusion vortex as it moved across the region (below; click image to play animation).

GOES-13 6.5 µm water vapor images + pilot reports of turbulence (click image to play animation)

CIMSS participation in GOES-R Proving Ground activities includes making products such as the GOES Sounder Total Column Ozone and MODIS imagery available for National Weather Service forecasters to add to their AWIPS workstations. The VISIT training lessons “Water Vapor Imagery and Potential Vorticity Analysis” and “MODIS Products in AWIPS” are available to help users understand the products and their applications to weather analysis and forecasting.