Storm-force low in the central Atlantic Ocean

January 29th, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

The compact circulation of an occluded surface low over the central Atlantic Ocean could be seen on GOES-16 (GOES-East) “Red” Visible (0.64 µm) images on 29 January 2018 (above); surface analyses indicated that the system was producing Storm Force (48-55 knot) winds.

This surface low was located beneath a larger upper-level low, as seen on GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (below). Very dry air (yellow to red enhancement) was evident just to the south and southwest of the storm.

GOES-16 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm) images [click to play MP4 animation]

GOES-16 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) images [click to play MP4 animation]

Hourly images of a (preliminary, non-operational) GOES-16 Deep-Layer Wind Shear product (calculated using Low-level and Mid-upper level GOES-16 Derived Motion Winds) are shown below — they revealed that the surface low was protected within the favorable low-shear environment of the upper low circulation, with more unfavorable high values of shear immediately surrounding it.

GOES-16 Deep-layer Wind Shear products [click to play animation]

GOES-16 Deep-layer Wind Shear products [click to play animation]

Pyrocumulonimbus cloud in Argentina

January 29th, 2018 |

GOES-16 Visible (0.64 µm, top), Shortwave Infrared (3.9 µm, center) and Infrared Window (10.3 µm) images [click to play animation]

GOES-16 Visible (0.64 µm, top), Shortwave Infrared (3.9 µm, center) and Infrared Window (10.3 µm, bottom) images [click to play animation]

A large cluster of fires burning in central Argentina became hot enough to generate a brief pyrocumulonimbus (pyroCb) cloud on 29 January 2018; according to media reports, on that day there were winds of 55 km/hour (34 mph) and temperatures of 37 ºC (98.6 ºF) in the vicinity of these La Pampa province fires. GOES-16 (GOES-East) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.3 µm) images (above; also available as an MP4 animation) showed the smoke plumes, fire thermal anomalies or “hot spots” (red pixels) and the cold cloud-top infrared brightness temperatures, respectively. The minimum 10.3 µm temperature was -32.6 ºC at 1745 UTC. Note the relatively warm (darker gray) appearance on the 3.9 µm image — this is a characteristic signature of pyroCb clouds tops, driven by the aerosol-induced shift toward smaller ice particles (which act as more efficient reflectors of incoming solar radiation).

An Aqua MODIS True-color Red-Green-Blue (RGB) image viewed using RealEarth (below) showed the dense lower-tropospheric smoke drifting southward and southeastward from the fire source region, as well as the narrow upper-tropospheric anvil of the pyroCb cloud. Suomi NPP VIIRS fire detection locations are plotted as red dots on the final zoomed-in image. The actual time of the Aqua satellite pass over Argentina was 1812 UTC.

Aqua MODIS True-color RGB image, with Suomi NPP VIIRS fire detection locations [click to enlarge]

Aqua MODIS True-color RGB image, with Suomi NPP VIIRS fire detection locations [click to enlarge]

According to Worldview the coldest MODIS Infrared Window (11.0 µm) cloud-top  brightness temperature was -41.2 ºC, thus surpassing the -40 ºC threshold that is generally accepted to classify it as a pyroCb. This is believed to be the first confirmed pyroCb event in South America.

Approximately 120 km north-northeast of the pyroCb cloud, rawinsonde data from Santa Rosa, Argentina (below) indicated that the -41 ºC cloud-top temperature corresponded to altitudes in the 10.8 to 11.6 km range. The air was very dry at that level in the upper troposphere, contributing to the rapid dissipation of the pyroCb cloud material as seen in GOES-16 imagery.

Plots of rawinsonde data from Santa Rosa, Argentina [click to enlarge]

Plots of rawinsonde data from Santa Rosa, Argentina [click to enlarge]

48-hour HYSPLIT forward trajectories originating from the center of the pyroCb cloud at altitudes of 7, 9 and 11 km (below) suggested that a rapid transport of smoke over the adjacent offshore waters of the Atlantic Ocean was likely at those levels.

HYSPLIT forward trajectories originating at altitudes of 7, 9 and 11 km [click to enlarge]

HYSPLIT forward trajectories originating at altitudes of 7, 9 and 11 km [click to enlarge]

On 30 January, Suomi NPP OMPS Aerosol Index values (below; courtesy of Colin Seftor, SSAI at NASA Goddard) were as high as 4.3 over the South Atlantic (at 41.81º South latitude, 53.22º West longitude, 17:31:34 UTC) — consistent with the HYSPLIT transport originating at 7 km.

Suomi NPP OMPS Aerosol Index on 30 January [click to enlarge]

Suomi NPP OMPS Aerosol Index on 30 January [click to enlarge]

Additional Suomi NPP VIIRS True-color and OMPS Aerosol Index images can be found on the OMPS Blog.

===== 01 February Update =====

This analysis of CALIPSO CALIOP data (courtesy of Mike Fromm, NRL) suggests that the upper-tropospheric smoke from this pyroCb event was transported as far as the eastern South Atlantic Ocean by 02 UTC on 01 February, having ascended to altitudes in the 9-10 km range.

Tornado near Eureka, California

January 25th, 2018 |


A waterspout moved inland near the NWS Eureka forecast office during the late afternoon hours on 25 January 2018. The brief tornado caused some EF-0 damage (interestingly, it was the only report of severe weather in the US that day, and the first tornado in the Eureka forecast area since 1998).

A comparison of GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (below) showed the line of convection as it moved across the area (Eureka and the location of the 0040-0041 UTC tornado are a few miles south-southwest of the airport KACV) — the coldest cloud-top infrared brightness temperatures on the 0037 UTC and 0042 UTC GOES-16 images were -30.7ºC (dark blue color enhancement). Note: there were no western US images available from GOES-15 (GOES-West) between 0030 and 0100 UTC, due to a routine “New Day Schedule Transition” and a 0051 UTC Southern Hemisphere scan.

GOES-16

GOES-16 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.3 µm, right) images, with plots of hourly surface reports [click to play animation]

There was an overpass of the NOAA-19 satellite about 2 hours prior to the Eureka tornado, at 2251 UTC. If we compare the NOAA-19 Visible (0.63 µm) image to the corresponding GOES-16 Visible (0.64 µm) image (below), a parallax shift to the west is evident with GOES-16 (which was scanning that same scene only 24 seconds later than NOAA-19: 22:52:23 UTC vs 22:51:59 UTC).

NOAA-19 and GOES-16 Visible images at 2252 UTC, with plots of 23 UTC surface reports [click to enlarge]

NOAA-19 and GOES-16 Visible images at 2252 UTC, with plots of 23 UTC surface reports [click to enlarge]

In the corresponding Infrared Window images from NOAA-19 (10.8 µm) and GOES-16 (10.3 µm) (below), the parallax shift was also apparent — and the coldest cloud-top infrared brightness temperatures associated with the convection just northwest of KACV were -36.2ºC and -35.2ºC, respectively. Given the very high viewing angle for GOES-16 (about 67 degrees over Eureka), the qualitative and quantitative satellite presentation compared quite favorably to that seen from the more direct overpass of NOAA-19.

NOAA-19 and GOES-16 Infrared Window images at 2252 UTC, with plots of 23 UTC surface reports [click to enlarge]

NOAA-19 and GOES-16 Infrared Window images at 2252 UTC, with plots of 23 UTC surface reports [click to enlarge]

As mentioned in the afternoon Area Forecast Discussion, offshore Sea Surface Temperature (SST) values were in the 50-55ºF range; this was also seen in a comparison of the nighttime and daytime MODIS SST product (below). With the presence of cold air aloft and relatively warm water at the surface, the lower troposphere was unstable enough to support the development and growth of showers and thunderstorms.

MODIS Sea Surface Temperature product [click to enlarge]

MODIS Sea Surface Temperature product [click to enlarge]

Mid-latitude cyclone in the central US

January 22nd, 2018 |

GOES-16 Water Vapor (6.9 µm) images, with hourly precipitation type plotted in yellow [click to play MP4 animation]

5-minute GOES-16 Water Vapor (6.9 µm) images, with hourly precipitation type plotted in yellow [click to play MP4 animation]

A large mid-latitude cyclone intensified over the central US on 22 January 2018, producing a wide variety of weather — in the cold sector, heavy snow and blizzard conditions across the Plains and Upper Midwest (WPC storm summary), and in the warm sector, severe weather (tornadoes, large hail and damaging winds: SPC storm reports) from Mississippi to Illinois, Indiana, and Ohio. GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) images (above) showed the large size of the storm circulation, which included a well-defined Warm Conveyor Belt (WCB) and a Trough of Warm Air Aloft (TROWAL) as identified here. More information on conveyor belts and TROWALs is available here.

A GOES-16 Mesoscale Sector provided 1-minute imagery over the Upper Midwest — “Red” Visible (0.64 µm) images (below) revealed some of the convective elements surrounding the surface low as it reached its occluded stage over Iowa. A small cluster of thunderstorms also developed over central Illinois around 19 UTC, producing 1.0-inch diameter hail.

GOES-16 Visible (0.64 µm) images, with hourly precipitation type plotted in yellow [click to play MP4 animation]

1-minute GOES-16 Visible (0.64 µm) images, with hourly precipitation type plotted in yellow [click to play MP4 animation]

Taking a  closer look at the eastern portion of the previous satellite scene, there was an overlap between the M1 and M2 Mesoscale Sectors — this allowed for images at 30-second intervals (below).

30-second GOES-16 Visible (0.64 µm) images, with hourly precipitation type plotted in yellow [click to play MP4 animation]

30-second GOES-16 Visible (0.64 µm) images, with hourly precipitation type plotted in yellow [click to play MP4 animation]