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]

Flooding in North Dakota, Minnesota and South Dakota

April 22nd, 2019 |

Landsat-8 False Color RGB image and GOES-16 Flood Detection product [click to enlarge]

Google Maps background, Landsat-8 False Color RGB image and GOES-16 ABI Flood Detection product [click to enlarge]

Comparison of a Landsat-8 False Color Red-Green-Blue (RGB) image with the corresponding GOES-16 ABI Flood Detection product as viewed using RealEarth (above) showed the extent of flooding along the Red River of the North (which forms the border of North Dakota and Minnesota, and flows northward into Manitoba) on 22 April 2019. The Red River flooding was a result of a relatively rapid Spring snow melt — a significant Winter snow cover across eastern North Dakota and northwestern Minnesota reached a peak in early March.

The Flood Detection product — originally developed for use with Suomi NPP VIIRS data, but adapted for use with GOES-16 ABI data — provides an estimate of land fractions with flooding water (green to yellow to red shades) along with regions of ice, snow cover, cloud and shadows. In the example above, much of Devils Lake in the southwest portion of the satellite scene was classified as ice (cyan), as the melting of winter ice was still in progress.

A closer view of the Landsat-8 False Color Red-Green-Blue (RGB) image and the corresponding GOES-16 ABI Flood Detection product for a portion of the Red River is shown below — the level of the Red River at Oslo, Minnesota was over 37 feet (hydrograph), at which point ND State Highway 54 has water over the road, MN State Highway 1 overtops and water affects the Canadian Pacific railroad tracks west of Oslo.

Google Maps background, Landsat-8 False Color RGB image and GOES-16 Flood Detection product [click to enlarge]

Google Maps background, Landsat-8 False Color RGB image and GOES-16 ABI Flood Detection product [click to enlarge]

Farther to the south, Landsat-8 False Color Red-Green-Blue (RGB) imagery along with the corresponding Suomi NPP VIIRS and GOES-16 ABI Flood Detection products over part of the James River (and upstream reservoirs) in northeastern South Dakota is shown below. Note that the higher spatial resolution of the VIIRS product (375 meters) indicated higher fractions of land with flooding water — up to 90% (red) compared to 60% (orange) with the ABI product.

Google Maps background, Landsat-8 False Color RGB image,and Suomi NPP VIIRS + GOES-16 Flood Detection products [click to enlarge]

Google Maps background, Landsat-8 False Color RGB image, and Suomi NPP VIIRS + GOES-16 Flood Detection products [click to enlarge]

Unusually dry air over the Upper Midwest

April 20th, 2019 |

GOES-16 Low-level (7.3 µm, left) and Mid-level (6.9 µm, right) Water Vapor images [click to play animation | MP4]

GOES-16 Low-level (7.3 µm, left) and Mid-level (6.9 µm, right) Water Vapor images, with hourly plots of surface reports [click to play animation | MP4]

GOES-16 (GOES-East) Low-level (7.3 µm) and Mid-level (6.9 µm) Water Vapor images (above) revealed a southwest-to-northeast oriented band of anomalously-dry air along the northwest periphery of a slow-moving low pressure center over the eastern US on 20 April 2019. The hourly dew point dropped to 10ºF at Chicago O’Hare, with a Relative Humidity value of 12% — a new record low value for Chicago. In addition, the dew point dropped to 6ºF at the Chicago Midway and Chicago Executive airports. With this dry air in place, note that the coastline of a portion of southern Lake Michigan could be seen in the 7.3 µm (and to a lesser extent, the 6.9 µm) Water Vapor images.

AWIPS examples of the GOES-16 Low-level and Mid-level Water Vapor imagery are shown below.

GOES-16 Low-level (7.3 µm) and Mid-level (6.9 µm) Water Vapor images [click to play animation | MP4]

GOES-16 Low-level (7.3 µm) and Mid-level (6.9 µm) Water Vapor images [click to play animation | MP4]

A larger-scale view of the GOES-16 Low-level Water Vapor (7.3 µm) image at 1201 UTC (below) showed that the Gaylord, Michigan (KAPX) and Lincoln, Illinois (KILX) rawinsonde sites were located within the elongated zone of dry air.

GOES-16 Low-level Water Vapor (7.3 µm) image, with plots of rawinsonde sites [click to enlarge]

GOES-16 Low-level Water Vapor (7.3 µm) image at 1201 UTC, with plots of rawinsonde sites [click to enlarge]

Plots of GOES-16 Water Vapor weighting functions for Gaylord, Michigan (KAPX) and Lincoln, Illinois (KILX) at 12 UTC (below) showed significant contributions from Band 10 (7.3 µm, violet) radiation originating at the surface — this allowed the thermal signature of the outline of Lake Michigan to be easily seen in the 7.3 µm Water Vapor imagery. Although the contribution of Band 9 (6.9 µm, blue) radiation originating near the surface was small, it was still enough to enable a brief and subtle coastal signature to be seen in the 6.9 µm images.

GOES-16 Water Vapor weighting functions for Gaylord, Michigan and Lincoln, Illinois at 12 UTC [click to enlarge]

GOES-16 Water Vapor weighting functions for Gaylord, Michigan (KAPX) and Lincoln, Illinois (KILX)  at 12 UTC [click to enlarge]

Plots of Total Precipitable Water sounding climatology for Gaylord, Michigan (KAPX) and Lincoln, Illinois (KILX), with record minimum values for 20 April at 12 UTC highlighted within a red box (below) showed that the 0.10″ at KAPX and the 0.12″ at KILX set new records for that date/time.

Plots of Total Precipitable Water sounding climatology for Gaylord, Michigan (KAPX) and Lincoln, Illinois (KILX), with record minimum values for 20 April at 12 UTC highlighted within a red box [click to enlarge]

Plots of Total Precipitable Water sounding climatology for Gaylord, Michigan (KAPX) and Lincoln, Illinois (KILX), with record minimum values for 20 April at 12 UTC highlighted within a red box [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]