Southern Georgia: West Mims Fire

As the spring season accelerates into summer, it is that time of year again for fires to occur all around the United States. A large fire that is a-brewing is the West Mims Fire located in southern Georgia, embedded in the Okefenokee National Wildlife Refuge. As of 11 May 2017, the fire, initially started by lightning, has burnt over 140,000 acres and is still raging on. To add insult to injury, southern Georgia has not received much precipitation over the past few months where the Okefenokee National Wildlife Refuge is currently in a D3, Extreme Drought as of 9 may 2017. A category D3 Extreme Drought is classified as an area that is susceptible to the listed impacts: major crop losses and potential widespread water shortages or restrictions, according to the US Drought Monitor. The latest updates of the West Mims Fire can be seen via the InciWeb link.

Here are the latest Day/Night Band (DNB) (0.7 um) and Imagery Band (I-4) (3.74um) animations from the Visible Infrared Imaging Radiometer Suite (VIIRS) on-board the Suomi-National Polar-orbiting Partnership satellite. For reference, the DNB utilizes a sun/moon reflectance model that illuminates atmospheric features, senses emitted lights, and assists in cloud monitoring the nighttime, while the I-4 band shows the locations of the hottest wildfires, known as ‘hotspots‘. The DNB is at 750 meter resolution while the I-4 band is at 375 meter spatial resolution. The animations are from 5-12 May 2017.

DNB Animation 

Animation highlights the evolution of the wildfires in southern Georgia denoted by the large white circle. Some of the features that are seen are the emitted city lights and the emitted lights from the fires, corresponding smoke, clouds and one can infer the location of the burn scar extent. Additionally, in the top-right hand corner shows the moon percent visibility and the moon elevation angle. A high moon percent visibility and a positive moon elevation angle imply the moon is above the horizon and adequate moonlight is present to see the atmospheric features via satellite.

DNB_animation

Imagery Band (I-4 ) Animation

Over the same domain, the IR animation shows the brightness temperatures of the fires from a range of 180-400 degrees Kelvin (K), where yellow and red colors imply the hottest parts of the fires. In contrast, the white, grey and black colors imply cold low-to-high clouds in the area. The evolution of the fire can be seen at a high spatial resolution at 375 meters.

IR_animation

Posted in Fire Weather, POES, Satellites | Leave a comment

Tropical Cyclone Donna

Have you ever been to the Solomon Islands or the Republic of Vanuatu? They are both remote islands located in the southwestern Pacific Ocean, relatively close in proximity to Australia and Papau New Guinea. There is a tropical cyclone that is a-brewing in this area of the world….her name is tropical cyclone ‘Donna’. As of Friday morning, 5 May 2017, Donna is a Category 2 hurricane and is expected to reach a Category 3 on the Saffir-Simpson Scale.

Donna is unique in that it is considered an ‘out of season’ tropical cyclone where tropical cyclones are normally produced between the months of November and May in the Southern Hemisphere. Flooding, high winds and heavy rains are expected for islands that are in the path of Donna; a tropical cyclone warning has been issued for the effected areas.

To track and monitor Donna, a forecaster or user can utilize the Day/Night Band (DNB) which is a sensor, and is one of 22 channels on the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument which is on-board the Suomi-National Polar-orbiting Partnership (S-NPP) satellite. The DNB uses a sun/moon reflectance model that illuminates atmospheric features, senses emitted natural and anthropogenic lights, and assists with cloud monitoring during the night-time hours; consider it as a night-time visible channel. A DNB image of tropical cyclone Donna, provided from the CIRA TC Real-Time web-page at 1432Z, 5 May 2017, is seen below.

2017SH18_SRSNPPDV_201705051432

Users can see the high-resolution (750-meters) and the detailed cloud structures that the DNB provides during the night-time as Donna moves through the area. Users can also assess the magnitude of Donna, inferring how many islands are or will be impacted by the storm.

For more updates and current status on Tropical Cyclone Donna click the following link.

Posted in Miscellaneous, POES, Satellites, Tropical Cyclones | Leave a comment

16 April 2017: 1.37 micron band (“Cirrus band”) features other than cirrus clouds

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.  Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

By Dan Bikos, Louie Grasso, and Ed Szoke

For this blog entry, we are going to focus in on the state of Durango in Mexico during the mid-day hours of 16 April 2017.  Conditions during that time were warm and very dry:

TPW_metars

The sky cover was mostly clear throughout the period of interest (mid-day hours):

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/mexico/B02&loop_speed_ms=80

A topographic map of the region reveals that the elevation (given below in thousands of feet) is quite high:

terrain

 

If we analyze the GOES-16 1.38 micron (“Cirrus band”):

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/mexico/B04_default&loop_speed_ms=80

There are features that are moving that are approximately oriented southwest-northeast (ignoring the cirrus clouds later in the loop in the northern regions and also the low-level cumulus to the south).  These features are not clouds since we did not see them in the visible channel shown above.

Let’s look at the GOES-16 7.34 micron (“low-level water vapor”) band:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/mexico/B10&loop_speed_ms=80

Features similar to those that were observed in the 1.38 micron band appear at 7.34 microns.  The 1.38 micron band can be displayed with a different color table to increase the contrast, thus bringing more clarity to the features that we observe:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/mexico/B04_enh&loop_speed_ms=80

Recall at this wavelength, 1.38 microns, water vapor is the primary absorber.  If there is sufficient moisture to absorb incoming radiation, cirrus clouds show up rather clearly due to the large contrast between bright cirrus clouds and a dark background, hence the band being named the “Cirrus band”.  In the case discussed here, moisture is limited, particularly at higher elevations where we see the southwest-northeast oriented banded  features.  In fact, here is a comparison of the corresponding features at 1.38 and 7.34 micron band.

annotated1

We note that each feature labeled above has the following characteristics:

1) 1.38 micron band darker corresponds to 7.34 micron band cooler brightness temperature and

2) 1.38 micron band lighter corresponds to 7.34 micron band warmer brightness temperature.

Why?

In this relatively dry, higher elevation environment, the surface is not completely obscured by the intervening (and highly absorbing) atmospheric water vapor when viewed at 1.38 microns.  In this near-infrared band, regions that are darker correspond to more column-integrated water vapor (and a lower surface reflectance contribution), while regions that are brighter correspond to less column-integrated water vapor (and a  higher surface reflectance contribution).

The alignment of these features most likely associated with water vapor are oriented with the terrain:

annotated2

Note that the lower valleys at locations 5 and 6 can be seen as darker regions at 1.38 microns (recall, more water vapor is associated with darker regions at 1.38 microns).

Can we rule out that these features are associated with dust or smoke?  This will now be investigated.

The split window difference product (11.2 micron minus 12.3 micron band difference):

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/mexico/SWD&loop_speed_ms=80

would have negative values (brown in this color table) if lofted dust was present, since the values are positive, we can rule out lofted dust.

For assessing smoke, we look at the GOES-16 0.47 micron (“Blue”) visible band:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/mexico/B01_midday&loop_speed_ms=80

There are no obvious smoke plumes during this time period.  However, if we look later in the afternoon when fires tend to be more pronounced and show up more clearly due to  favorable scattering associated with the view angle:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/mexico/B01_later&loop_speed_ms=80

We do observe a few smoke plumes.  However, the orientation of the smoke plumes does not match with what we observed in the 1.38 or 7.34 micron bands and does not cover such a large area in bands that are oriented with the terrain.

In conclusion, the GOES-16 1.38 micron (“Cirrus”) band can observe features other than cirrus clouds and plumes of water vapor may be observed under specific circumstances.

Posted in GOES R | Comments Off

1-minute applications for severe thunderstorms from 15-16 April 2017

The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.  Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.

During the afternoon hours of 15 April, one of the GOES-16 mesoscale sectors captured severe thunderstorms in the Iowa / Nebraska region:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/15apr17/vis&loop_speed_ms=80

Often times we like to point out the use of 1-minute imagery for the evolution of severe thunderstorms.  However, the imagery also has utility to identify regions where the potential for thunderstorm development is suppressed which can be an important operational application.  In this particular case, notice the highlighted yellow regions at 2209 UTC:

annotated_20170415

Focus on those regions in the animation above.  Note that thunderstorm development is  suppressed in these regions.  The 1-minute imagery actually helps you identify these regions with more clarity than current GOES due to the increased temporal and spatial resolution.  We might not always be able to understand why suppression is occurring.  In this case, just considering the surface observations:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/15apr17/metars&loop_speed_ms=80   

for the southern region of interest, although there is cloud cover, the temperature and moisture does not appear unfavorable for thunderstorm development, however the imagery shows that any attempts at convective initiation are being suppressed by something in the environment.  Meanwhile, in the northern region of interest there is nothing apparent in the METARs that would suggest suppression, however GOES-16 imagery clearly indicates that something in the environment is unfavorable for convective development.  In operations, GOES-16 imagery could be integrated with model analyses, surface observations and other observational data to try to understand why the imagery shows what it does.

On the following day, another round of severe thunderstorms took place this time in Oklahoma and the Texas panhandle.  We’ll start with a loop of the IR band at 10.35 microns at 5 minute temporal resolution:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/ir&loop_speed_ms=80

We observe a number of thunderstorms across the scene;  the storm in southern Oklahoma has an enhanced-V signature as well as multiple gravity waves and is backbuilding southwestward for a while.  We see other thunderstorms in the scene as well, however lets focus in on the eastern Texas panhandle activity.  We see a westward moving boundary with low-clouds to its east and clear to the west.  The northern part of this boundary leads to a triple point with an outflow boundary oriented east-west.  It’s interesting to note that convective initiation occurs first south of the triple point and then later new convection develops at the triple point.  The initial storm that developed along the westward moving boundary south of the triple point develops an enhanced-V signature and in fact severe hail was observed with this storm.  Also note that this storm is moving southwestward in time as it backbuilds along the boundary against the mean west-southwest flow aloft shown in the 0000 UTC Amarillo, TX sounding:

AMA

 

Are there are any indications in the GOES-16 imagery to explain why the storm of interest along the boundary developed?

A 4 panel animation of the visible along with the 3 water vapor bands:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/4panel&loop_speed_ms=80

The visible band indicates what might be a gravity wave advancing east-southeast across the northeastern portion of the Texas panhandle (also shown in a subtle sense in the earlier IR loop).  The storm seems to initiate coincident with the passage of this feature across the boundary.  We include the 3 water vapor channels in an attempt to further identify this feature or any other feature that would not appear in the visible band.  The most obvious feature (at least in the mid-level WV band) appears later in the loop and is a north-south oriented brightness temperature gradient moving eastward, perhaps this is an approaching shortwave.  However, this comes after convective initiation for the storm noted above.  For this case, it’s difficult to definitely attribute convective initiation to any signature from the water vapor imagery, although a 4 panel like this may help in other cases.

Shortly thereafter, this region was in a mesoscale sector with 1-minute imagery, here is a loop with METARs included:

http://rammb.cira.colostate.edu/templates/loop_directory.asp?data_folder=training/visit/loops/16apr17/vis&loop_speed_ms=80

One point to note is that this was not a classic dryline with very dry westerlies behind it, rather the winds here are easterly and the moisture gradient is more subtle.  We do eventually see a storm initiate along the triple point discussed earlier north of the storm of interest.

Posted in Convection, GOES R, Hail, Severe Weather | Comments Off