Orographically-trapped waves near Haida Gwaii

April 22nd, 2019 |

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with topography [click to play animation | MP4]

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with topography [click to play animation | MP4]

GOES-17 (GOES-West) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed orographically-trapped waves propagating westward against the ambient flow over the Haida Strait (between Haida Gwaii and British Columbia) in the wake of a cold frontal passage (surface analyses) on 22 April 2019. The waves initially formed downwind of the 2000-3000 foot terrain of Haida Gwaii, and moved eastward — but were then reflected back to the west by the higher 6000-8000 foot terrain farther inland over British Columbia.

Note that the wave signatures became more attenuated — especially over the southern portion of the Strait — as middle-tropospheric moisture began to overspread the area. This moisture at higher altitudes absorbed radiation being emitted from below, and re-radiated energy at the colder temperatures found within that layer of mid-level moisture.

A plot of GOES-17 Water Vapor weighting functions calculated using 00 UTC rawinsonde data from Annette Island, Alaska (below) showed significant contributions for Band 10 (7.3 µm, violet) and Band 9 (6.9 µm, blue) radiation coming from within the 700-850 hPa range, so it’s likely that many of the waves resided within that layer. Higher-altitude contributions from the 500-600 hPa layer were due to the aforementioned high-level moisture that later moved over the region.

GOES-17 Water Vapor weighting functions calculated from 12 UTC rawinsonde data at Annette Island, Alaska [click to enlarge]

GOES-17 Water Vapor weighting functions calculated from 00 UTC rawinsonde data at Annette Island, Alaska [click to enlarge]

In a toggle between Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 2137 UTC (below), cloud-top infrared brightness temperature of cloud features in the Haida Strait were generally in the -5 to -10ºC range, corresponding to altitudes of 4400-6400 feet (1.4-2.0 km, 850-780 hPa) on the 00 UTC Annette sounding. On 2140 UTC GOES-17 Water Vapor imagery, the waves were still apparent in the 7.3 µm image but were becoming less distinct in the 6.9 µm and 6.2 µm images due to the arrival of mid-tropospheric moisture.

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 2137 UTC [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 2137 UTC [click to enlarge]

Smoke in the Gulf of Mexico

April 18th, 2019 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with surface fronts plotted in cyan [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed some clearing of the dense pall of smoke across the far western Gulf of Mexico in the wake of a cold front that was moving southward/southeastward off the Texas coast on 18 April 2019. The parallel wave clouds of an undular bore were also evident ahead of the cold front from 13-16 UTC — the bore was also causing horizontal convective roll perturbations in the smoke about 20-40 miles ahead of the wave clouds (1506 UTC image).

The hazy signature of smoke was better defined in GOES-16 True Color Red-Green-Blue (RGB) images from the AOS site (below). This smoke was the result of widespread annual Springtime agricultural burning across southern Mexico, Guatemala, Belize and Honduras. Toward the end of the day, additional small plumes of smoke and blowing dust could  be seen moving back across the Gulf of Mexico into the “cleaner” air behind the cold front.

GOES-16 True Color RGB images [click to play animation | MP4]

GOES-16 True Color RGB images [click to play animation | MP4]

Thermal anomalies or “hot spots” (yellow to red pixels) associated with the larger fires in Mexico, Guatemala, Belize and Honduras could be seen in GOES-16 Shortwave Infrared (3.9 µm) images (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 map of fires detected by Suomi NPP VIIRS on the previous day is shown below, as viewed using RealEarth.

Fires detected by Suomi NPP VIIRS on 17 April [click to enlarge]

Fires detected by Suomi NPP VIIRS on 17 April [click to enlarge]

Mesoscale disturbance over northern Alaska

April 17th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm) and Low-level Water Vapor (7.3 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and Low-level Water Vapor (7.3 µm) images (above) showed a mesoscale disturbance that was moving northward over the eastern Brooks Range in far northeastern Alaska on 17 April 2019. The curved configuration of the associated cloud structure suggested that a closed circulation center was present (or had just recently developed) — while surface analyses showed an area of low pressure much farther to the south along the Alaska/Yukon border, there were no features moving northward across the region shown in the GOES-17 imagery.

Light to moderate snow was reported at Arctic Village as this mesoscale disturbance moved over the area (below).

Time series of surface weather observation data from Arctic Village [click to enlarge]

Time series of surface weather observations from Arctic Village [click to enlarge]

375-meter resolution Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2131 and 2313 UTC (below) provided a more detailed view of this feature, in which the clouds exhibited an appearance suggestive of embedded convection. Cloud-top infrared brightness temperatures were as cold as -50ºC just southwest of Arctic Village on the 2313 UTC image — this corresponded to an altitude of 8.5 km on the 00 UTC Fairbanks rawinsonde data.

Suomi NPP VIIRS Day/Night Band (0.7 µm) images at 2131 and 2313 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) images at 2131 and 2313 UTC [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images at 2131 and 2313 UTC [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images at 2131 and 2313 UTC [click to enlarge]

13-km NAM model fields (below) showed no clear signature of either a closed circulation or a discrete vorticity center — so satellite imagery was depicting the presence of an important feature that was not captured by numerical models. While the 18 UTC model run did show an area of light precipitation moving northward toward the region, the 00 UTC model run scaled back the areal coverage of this precipitation.

3-km NAM 500 hPa height, wind and absolute vorticity [click to enlarge]

3-km NAM 500 hPa height, wind and absolute vorticity [click to enlarge]

3-km NAM Mean Sea Level Pressure and 1-hour accumulated precipitation [click to enlarge]

3-km NAM Mean Sea Level Pressure and 1-hour accumulated precipitation [click to enlarge]

Severe weather outbreak across eastern Texas and the Deep South

April 13th, 2019 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with SPC storm reports plotted in red [click to play MP4 animation]

An outbreak of severe weather began in eastern Texas on the morning of 13 April 2019, where thunderstorms produced hail up to 3.0 inches in diameter, tornadoes and damaging winds (SPC storm reports). 1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images (above) showed the clusters of thunderstorms that developed as a surface low and associated frontal boundaries moved eastward (surface analyses). The corresponding GOES-16 “Clean” Infrared Window (10.3 µm) images (below) revealed numerous overshooting tops with infrared brightness temperatures as cold as -70 to -75ºC. In addition, the storm producing 3.0-inch hail and damaging winds at 1428 UTC exhibited an Above-Anvil Cirrus Plume (Visible/Infrared toggle).

GOES-16 "Clean" Infrared Window (10.3 µm) images, with SPC storm reports plotted in purple [click to play MP4 animation]

GOES-16 “Clean” Infrared Window (10.3 µm) images, with SPC storm reports plotted in purple [click to play MP4 animation]

A comparison of Terra MODIS Visible (0.65 µm) and Infrared Window (11.0 µm) images at 1650 UTC is shown below.

Terra MODIS Visible (0.65 µm) and Infrared Window (11.0 µm) images [click to enlarge]

Terra MODIS Visible (0.65 µm) and Infrared Window (11.0 µm) images [click to enlarge]

Later in the day, the thunderstorms continued to produce a variety of severe weather as they moved eastward across Louisiana and Mississippi, as shown by GOES-16 Visible and Infrared images (below).

GOES-16 "Red" Visible (0.64 µm) images, with SPC storm reports plotted in red [click to play MP4 animation]

GOES-16 “Red” Visible (0.64 µm) images, with SPC storm reports plotted in red [click to play MP4 animation]

GOES-16 "Clean" Infrared Window (10.3 µm) images, with SPC storm reports plotted in cyan [click to play MP4 animation]

GOES-16 “Clean” Infrared Window (10.3 µm) images, with SPC storm reports plotted in cyan [click to play MP4 animation]

After sunset, the thunderstorms continued to move eastward, spreading more serve weather across Mississippi into Alabama and far southern Tennessee (below).

GOES-16 "Clean" Infrared Window (10.3 µm) images, with SPC storm reports plotted in cyan [click to play MP4 animation]

GOES-16 “Clean” Infrared Window (10.3 µm) images, with SPC storm reports plotted in cyan [click to play MP4 animation]

VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP (below) provided additional views of the storms as they were moving across Mississippi and Alabama. Several bright lightning streaks were evident on the Day/Night Band images. Note: the NOAA-20 image (downloaded and processed from the Direct Broadcast ground station at CIMSS) is incorrectly labeled as Suomi NPP.

VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from Suomi NPP and NOAA-20 [click to enlarge]

VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 at 0645 UTC and Suomi NPP at 0734 UTC [click to enlarge]

On a NOAA-20 VIIRS Day/Night Band (0.7 µm) image at 0825 UTC (below), an impressively-long (~400 mile) dark “post-saturation recovery streak” extended southeastward from where the detector sensed an area of very intense/bright lightning activity northeast of Mobile, Alabama.

NOAA-20 VIIRS Day/Night Band (0.7 µm) image at 0825 UTC [click to enlarge]

NOAA-20 VIIRS Day/Night Band (0.7 µm) image at 0825 UTC [click to enlarge]