Tropical Storm Bret

June 19th, 2017 |

GOES-16 “Veggie” Band (0.86 µm) animation of Tropical Storm Bret, 1545-2030 UTC on 19 June 2017 (Click to animate)

The fast-moving tropical system in the southern Caribbean Sea has developed a closed circulation and has been named Bret.  Tropical Storm Bret, shown above in an animation of GOES-16 Near-Infrared (0.86 µm) imagery that highlights land/water contrasts (the Orinoco River in Venezuela and Caribbean Islands — some with cloud streamers in their lee — north of Venezuela stand out clearly), is forecast to remain very close to the South American coastline.  Such proximity to land will likely hinder development. Further, wind shear in the atmosphere over the storm is predicted to increase.

Bret is embedded within a ribbon of very moist air (associated with the ITCZ) that stretches from Africa to the northwest Caribbean, as shown in the animation below (taken from this site) that shows morphed microwave observations of total precipitable water.

Microwave estimates of Total Precipitable Water for the 24 hours ending 1900 UTC on 19 June 2017 (Click to enlarge)

For more information on Bret, refer to the National Hurricane Center and the CIMSS Tropical Cyclones sites (where you can also follow the future of the system emerging into the Gulf of Mexico).

Scattering and Shadows

June 19th, 2017 |

GOES-16 Imagery over New England from 1022 through 1117 UTC on 19 June 2017. Blue Band (0.47 µm), upper left; Red Band (0.64 µm), upper right; ‘Veggie’ Band (0.86 µm), lower left; ‘Snow/Ice’ Band (1.61 µm), lower right. Click to enlarge.

GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing

The animation of GOES-16 imagery, above, showing, clockwise from upper left, the GOES-16 0.47 µm, 0.64 µm, 1.61 µm and 0.86 µm channels, shows lows clouds over southeast New England, with a few mid-level clouds aloft. The moving mid-level clouds are casting shadows on the lower clouds beneath. Note that the shadows appear darkest at the longest wavelength. This is shown in the AWIPS cursor readout below as well — for the point selected, the 1.61 µm reflectance is 5.4%, and it increases to 18.9% at 0.47 µm. Why does it change by wavelength?

AWIPS read-out of reflectance in a shadow east of Cape Cod. Note the reflectance increases as wavelength decreases. (Click to enlarge)

Rayleigh scattering in the atmosphere is a function of wavelength: scattering is more effective at shorter wavelengths. Thus, the atmosphere is scattering the greatest amount of 0.47 µm radiation (compared to the longer wavelengths shown here). Shadows are darker (there is less detected reflectance) at longer wavelengths because less longer-wavelength radiation is scattered towards the satellite sensor.

The tweet from the National Weather Service in Melbourne, below, shows another shadow scene with 0.86 µm imagery.


Deadly Fire in Portugal

June 18th, 2017 |

Suomi NPP VIIRS Day/Night Band Visible Imagery (0.70 µm) at 0240 UTC on 18 June 2017 (Click to enlarge)

(Images in this blog post were created by William Straka, SSEC. Thanks William!!)

Parts of Pedrogao Grande in central Portugal (northeast of Lisbon) burned over the weekend in a massive forest fire. At least 62 people were killed (News Link; Youtube Video 1, 2). Suomi NPP overflew the region shortly after the fire started, and annotated VIIRS (Visible Infrared Imaging Radiometer Suite) Day/Night Band imagery is shown above (Click here for an image without annotation).  The size of the bright light signature from the fire (overlain with thin clouds) rivals that of Lisbon.

Suomi NPP VIIRS Shortwave Infrared imagery ( 3.75 µm) at 0240 UTC on 18 June 2017 (Click to enlarge)

Shortwave Infrared channels on Suomi NPP also testify to the intensity of the fire. The 3.75 µm above (Click here for an image with no labels) shows a saturated pixel (exceeding 367 K) over the hottest part of the fire.  The 1.61 µm channel in the near infrared also had a strong signal.   The 4.05 µm imagery (Click here for an image without annotation) shown below had a maximum brightness temperature exceeding 550 K! (This channel was specifically designed for fire detection).

Suomi NPP VIIRS Shortwave Infrared Imagery (4.05 µm) at 0240 UTC on 18 June 2017 (Click to enlarge)

Meteosat-10 Severi Infrared Imagery (3.9 µm) from 0000 to 0400 UTC on 18 June 2017 (click to enlarge)

The SEVERI Instrument on Meteosat-10 also detected this fire, and because Meteosat is geostationary, it provided better temporal coverage vs. the single snapshot from Suomi NPP. The animation above shows considerable cloud cover over Portugal, but very warm pixels are present starting after 0145 UTC. The toggle below compares 3.9 µm SEVIRI at 0245 UTC with 3.75 µm Suomi NPP VIIRS at 0240 UTC. The better spatial resolution of the VIIRS instrument is apparent, as are much warmer temperatures as expected given the smaller pixel size on VIIRS.  Note also a slight parallax shift.

Shortwave Infrared Imagery (3.9 µm from Meteosat-10 SEVIRI at 0245 UTC and 3.75 µm from Suomi NPP VIIRS at 0240 UTC) over Portugal (Click to enlarge)


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Suomi NPP VIIRS Day/Night Band visible (0.70 µm) imagery at 0145 UTC on 19 June 2017 (Click to enlarge)

Data from the 0145 UTC 19 June overpass on Suomi NPP show that the fire continues, although with less intensity. The Day/Night Band (above) and the 3.75 µm Shortwave Infrared (below) show the fire locations.

Suomi NPP VIIRS Shortwave Infrared (3.75 µm) imagery at 0145 UTC on 19 June 2017 (Click to enlarge)

 

Large MCS affects Nebraska, Iowa, Kansas and Missouri

June 17th, 2017 |

GOES-16 Infrared Window (10.3 µm) images, with plots of SPC storm reports [click to play MP4 animation]

GOES-16 Infrared Window (10.3 µm) images, with plots of SPC storm reports [click to play MP4 animation]

** GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing **

A large Mesoscale Convective System (MCS)  developed over eastern Nebraska late in the day on 16 June 2017, which continued  to grow in size as it  propagated southeastward  and produced severe weather across western Iowa, northeastern Kansas  and northwestern Missouri during  the subsequent overnight hours (SPC storm reports). GOES-16 Infrared Window (10.3 µm) images (above) include plots of time-matched  SPC storm reports;  the report locations are parallax-corrected to match those of the cloud tops. The strong winds downed  numerous trees and power lines;  Kansas City Power & Light reported  that as many as 93,000 customers — more than 10 percent — were without power within the utility’s service area (which covers 46 counties in Kansas and Missouri).

In a comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at  0721 UTC or 2:21 am local time on 17 June (below), the Day/Night Band image showed a bright cluster of lightning streaks (cloud tops illuminated by intense lightning activity) straddling the Kansas/Missouri border. Note how the city lights of the Kansas City area were almost completely attenuated by the dense and vertically thick MCS core, while a diffuse signature of city lights was seen through the thin cirrus canopy around the edges of the storm. Packets of cloud-top gravity waves evident on both images, and the coldest cloud-top Infrared brightness temperatures were -85º  C (darker violet color enhancement), located in both Kansas and Missouri.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11..45 µm) images, with cumulative plots of SPC storm reports [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11..45 µm) images, with cumulative plots of SPC storm reports [click to enlarge]