Pyrocumulonimbus cloud in Bolivia

August 18th, 2019 |

GOES-16

GOES-16 “Red” Visible (0.64 µm, top), Shortwave Infrared (3.9 µm, middle) and “Clean” Infrared Window (10.35 µm, bottom) images [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the formation of a pyrocumulonimbus (pyroCb) cloud over far southeastern Bolivia on 18 August 2019. The small anvil cloud briefly surpassed the -40ºC pyroCb threshold from 1800-1820 UTC, attaining a minimum cloud-top infrared brightness temperature of -45.2ºC along the Bolivia/Paraguay border at 1800 UTC. This pyroCb formed over the hottest southern portion of an elongated fire line, as seen in the Shortwave Infrared imagery.

A 1.5-day animation of GOES-16 Shortwave Infrared images (from 12 UTC on 17 August to 2350 UTC on 18 August) revealed the rapid southeastward run of the fire to the Bolivia/Paraguay border on 17 August, followed by the eastward expansion of the fire line on 18 August (below).

GOES-16 Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

GOES-16 Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

A toggle between Suomi NPP VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images as viewed using RealEarth (below) showed the large and dense smoke plume streaming southeastward, with the small pyroCb along the Bolivia/Paraguay border at 1745 UTC — the brighter white tops of the pyrocumulus and pyrocumulonimbus clouds reached higher altitudes than the tan-colored smoke plume. The coldest cloud-top infrared brightness temperature was about -55ºC (orange enhancement), which corresponded to an altitude around 9 km according to rawinsonde data from Corumbá, Bolivia.

Suomi NPP VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images [click to enlarge]


Strong northerly to northwesterly surface winds were blowing across the region, in advance of an approaching cold front (surface analyses) — at Robore, Bolivia (located just north-northwest of the fires), winds were gusting to 25-28 knots during much of the day (below).

Time series of surface report data from Robore, Bolivia [click to enlarge]

Time series of surface report data from Robore, Bolivia [click to enlarge]

This is likely the second confirmed case of a South American pyroCb (the first being on 29 January 2018) — in addition, it’s the second pyroCb documented in the tropics and the first pyroCb documented during a winter season. Thanks to Mike Fromm (NRL) for bringing this case to our attention!

Using NUCAPS soundings to nowcast convective evolution

August 15th, 2019 |

GOES-16 Visible (Band 2, 0.64 µm) Imagery, 1721 – 1946 UTC on 15 August 2019. NUCAPS Sounding Points — from 1926 UTC — are present over the image at 1946 UTC (Click to animate)

GOES-16 Visible Imagery, above (Click to animate), shows shower/thundershower development over eastern Oklahoma moving into Arkansas. At the end of the animation, 1946 UTC, NUCAPS Sounding profiles from 1926 UTC are shown, and they’re shown below too.

GOES-16 Visible (Band 2, 0.64 µm) Imagery, 1946 UTC on 15 August 2019. (Click to enlarge)

The time 1946 UTC is about the earliest you could hope to have NUCAPS profiles in an AWIPS system — and only if you had access to a Direct Broadcast antenna. The more conventional method of data delivery, the SBN, means NUCAPS will be available about an hour after they are taken, so by 2036 UTC. The visible imagery at 2036 UTC is shown below.

GOES-16 Visible (Band 2, 0.64 µm) Imagery, 1946 UTC on 15 August 2019. (Click to enlarge)

At 2036 UTC, which time is about when in the forecast office the NUCAPS soundings would become available, would you expect the convection in western Arkansas to move southward, or eastward, based solely on Satellite imagery? How could you use NUCAPS profiles to gain confidence in this prediction? Visible imagery alone suggests a moisture boundary; the southern quarter of Arkansas shows markedly less cumulus cloudiness. The animation shows motion mostly to the east, with higher clouds moving more west-northwesterly. The GOES-16 Baseline Total Precipitable Water product, below, shows a maximum in TPW over central Arkansas, with values around 1.5″;  values are around 1.3″ in southern Arkansas, and around 1.2-1.3″ in northwest Arkansas.  A corridor of moisture is indicated.

GOES-16 Baseline Level 2 Total Precipitable Water at 1946 UTC; Visible imagery is shown in cloudy regions. (Click to enlarge)

Baseline Total Precipitable Water, above, part of a suite of products that emerge from Legacy Profiles, is heavily constrained by model fields, however;  the image above could simply show the GFS solution.  In contrast, NUCAPS observations are almost wholly independent of models.  What do NUCAPS profiles show? The animation below steps through vertical profiles east and south of the developing convection.

NUCAPS profiles from the ~1900 UTC overpass at points plotted over the 1946 UTC GOES-16 Band 2 Visible (0.64 µm) image (Click to enlarge)

AWIPS will soon (planned for shortly after Labor Day at the time of this post) include horizontal fields of information derived from NUCAPS vertical profiles. The images below show values computed within the NSharp AWIPS software for a variety of fields: Total Precipitable Water, MU Lifted Index, MU CAPE, MU CINH. All fields suggest that convection more likely to build eastward than to expand southward.

NUCAPS Sounding Points and derived quantities, as indicated, at 1926 UTC 15 August 2019; NUCAPS data are plotted over the 1946 UTC GOES-16 ABI Band 2 Visible 0.64 µm image. (Click to enlarge)

Convection did not move southward; motion and development was to the east. The timing of NUCAPS profiles means that they give a good estimate of atmospheric thermodynamics in mid-afternoon, a key time for assessing convective development.

GOES-16 Visible (Band 2, 0.64 µm) Imagery, 1721 UTC on 15 August 2019 to 0001 UTC on 16 August 2019 (Click to animate).

NUCAPS Soundings surrounding an isolated Thundershower

August 14th, 2019 |

GOES-16 ABI Band 2 (0.64 µm) at 1946 UTC on 14 August 2019 (Click to enlarge)

The GOES-16 Visible (0.64 µm) image above shows a weak thunderstorm over southeastern Oklahoma surrounding an decaying outflow boundary.  (Click here to see an animation of the visible imagery). The convection did not look particularly robust, but it did produce lightning that was detected by the Geostationary Lightning Mapper (GLM), as shown below.

GOES-16 ABI Band 2 (0.64 µm) and GLM observations of Flash Extent Density at 1946 UTC on 14 August 2019

Lightning requires charge separation in a cloud; typically lightning occurs after the cloud top glaciates. During daytime, glaciation can be detected with ABI Band 5, at 1.61 µm, the so-called Snow/Ice band. The toggle below shows the visible, snow/ice band, and the Baseline Cloud Phase product. Glaciation is indicated.

GOES-16 ABI Band 2 (0.64 µm), Band 5 (1.61 µm) and Baseline Cloud Phase at 1946 UTC on 14 August 2019

This case is interesting because NOAA-20 overflew the convection, and soundings were produced around the convection, as shown below.

GOES-16 ABI Band 2 (0.64 µm) at 1946 UTC on 14 August 2019 along with NUCAPS Sounding Points at 1945 UTC

The animation below steps north-south through seven profiles that surround the weak convection. Note that a profile near the convection has thermodynamic parameters more favorable for convection than at the other profiles.  For example, NUCAPS profiles show the convection at the northern edge of a precipitable water gradient, and also in a local minimum of inhibition.    Although the convection has initiated here, the fields do suggest that NUCAPS can be used to monitor thermodynamics at small scales before initiation.

NUCAPS Soundings at various points north, south and within convection at 1946 UTC on 14 August 2019 (Click to enlarge) Thermodynamic variables from the sounding are noted.

Horizontal gridded information derived from NUCAPS data will be in AWIPS shortly.  See this post from Emily Berndt at SPoRT!

GOES-16 ABI Derived Products such as Cloud-top Phase in AWIPS

August 14th, 2019 |
AWIPS

AWIPS image of the Contiguous US domain showing the ABI 3.9 µm (on the left portion of the image and the ABI 1.6 µm (on the right portion of the image). The readout of the Level 2 cloud-top phase is also displayed.

The above animation shows the ABI 3.9 µm band for regions of less solar illumination and the ABI 1.6 µm “snow/ice” band for regions more fully illuminated. Also shown is a readout of the GOES-16 cloud-type phase product for a point in eastern Texas. Note how the estimates range for this location from clear sky, liquid water, mixed phase and super-cooled droplets. This shows one example of how to use imagery in conjunction with derived products. These images where generated in AWIPS using a procedure.

Cloud-top phase can be found in RealEarth (search on ‘phase’), GEOCAT (direct link to cloud-top type), and the GOES-R cloud page. An archive of netCDF are held in NOAA’s CLASS.

There are many “Level 2” or derived products generated from the ABI radiances. These include, but are not limited to: cloud proprieties, atmospheric motion, fire, stability, sea and land surface temperatures. More information on these products can be found on the Algorithm Working Group web page, product quality web page or these links.

AWIPS image

AWIPS image of the Contiguous US domain showing the ABI 3.9 µm (on the left portion of the image and the ABI 1.6 µm (on the right portion of the image). The readout of the Level 2 cloud-top phase is also displayed.