Dry air within an Atlantic subtropical ridge

November 16th, 2018 |

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

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

GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed a large region of very dry air within a subtropical ridge over the central North Atlantic Ocean on 16 November 2018. Infrared brightness temperatures were unusually warm (brighter yellow to red enhancement) on all 3 Water Vapor bands, especially along the western edge of the dry air.

A GOES-16 Upper-level Water Vapor image at 1700 UTC (below) showed a swath of NUCAPS sounding availability close to that time. The swath passed directly over the driest air within the subtropical ridge.

GOES-16 Upper-level (6.2 µm) Water Vapor image at 1700 UTC, with a swath of NUCAPS sounding availability [click to enlarge]

GOES-16 Upper-level Water Vapor image at 1700 UTC, with a swath of NUCAPS sounding availability [click to enlarge]

One of the green (high-quality) NUCAPS soundings within the arc of driest air (below) revealed a remarkably dry profile above the trade wind inversion — dewpoint values were -50ºC and colder within the 500-620 hPa layer, and dewpoint depressions were about 50ºC near the 550 hPa level.

NUCAPS sounding profile within the driest air [click to enlarge]

NUCAPS sounding profile within the driest air [click to enlarge]

Even though the middle to upper tropozphere was quite dry, note that the Total Precipitale Water (TPW) value calculated from the NUCAPS profile was 0.73 inch — there was still abundant tropical moisture within the marine boundary layer of the warm central Atlantic. The GOES-16 TPW product (below) showed minimum values of 0.6-0.8 inch in the region of driest air on the Water Vapor imagery (1800 UTC comparison). In contrast, TPW values over a large portion of the Lower 48 states were 0.6 inch or less, even in regions that appeared to be “moist” on the Water Vapor imagery.

GOES-16 Upper-level Water Vapor + Total Precipitable Water [click to play animation | MP4]

GOES-16 Upper-level Water Vapor + Total Precipitable Water [click to play animation | MP4]

Atmospheric River brings precipitation to south-central Alaska

November 12th, 2018 |

Blended Total Precipitable Water product [click to play animation | MP4]

Blended Total Precipitable Water product, with Upper Air sites plotted in white [click to play animation | MP4]

The NESDIS Blended Total Precipitable Water (TPW) product (above) showed an atmospheric river that was transporting moisture northward from the tropics to south-central Alaska during 11 November – 12 November 2018. TPW values were in excess of 2.0 inches near the leading edge of the moisture plume early in the period.

The corresponding Percent of Normal Blended Total Precipitable Water product (below) indicated that these values of TPW were at or above 200 percent of normal (yellow).

Percent of Normal Blended Total Precipitable Water product, with Upper Air sites plotted in red [click to play animation | MP4]

Percent of Normal Blended Total Precipitable Water product, with Upper Air sites plotted in red [click to play animation | MP4]

Using the MIMIC Multi-layer TPW site, you can see how TPW is partitioned within various layers of the atmosphere (below). This TPW product uses microwave data from POES, Metop NOAA-20 and Suomi NPP satellites (description). It’s important to keep in mind that the location and continuity of a plume of TPW (such as an atmospheric river) might not always exactly agree what is seen on geostationary satellite Water Vapor imagery, since water vapor spectral bands usually sense radiation being emitted from levels above where the bulk of TPW is normally found (as discussed here).

MIMIC Multi-layer Total Precipitable Water product [click to play animation | MP4]

MIMIC Multi-layer Total Precipitable Water product on 12 November [click to play animation | MP4]

Anchorage, Alaska rawinsonde data (below) showed that TPW values reached a maximum of 0.73 inch at 00 UTC on 12 September.

Sequence of Anchorage, Alaska rawinsonde data from 00 UTC on 11 November to 00 UTC on 13 November [click to enlarge]

Anchorage, Alaska rawinsonde data from 00 UTC on 11 November to 00 UTC on 13 November [click to enlarge]

The arrival of this moisture produced heavy rainfall and mixed winter precipitation across the region — Portage Glacier (about 50 miles southeast of Anchorage) received 9.99 inches of rainfall in 48 hours, and Anchorage set a new daily precipitation record on 11 November with 0.89″ (which included 1.0 inch of new snow). A summary of temperature and precipitation reports can be seen here.

A comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November (below) revealed widespread layered clouds across most of south-central Alaska.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November [click to enlarge]

Woolsey Fire in southern California

November 9th, 2018 |

GOES-16 “Red” Visible (0.64 µm, left) and Shortwave Infrared (3.9 µm, right) images [click to play MP4 animation]

GOES-16 “Red” Visible (0.64 µm, left) and Shortwave Infrared (3.9 µm, right) images [click to play MP4 animation]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (above) showed the thick smoke and hot thermal signature of the Woolsey Fire in southern California on 09 November 2018. On this day it exhibited extreme fire behavior, with the large thermal anomaly or fire “hot spot” (red enhancement) moving rapidly southwestward and reaching the coast (Wildfire Today). The fires were driven by hot, dry Santa Ana winds, which arrived at Camarillo KCMA around 19 UTC (11 AM local time) and reached the coast at Point Mugu Naval Air Station KNTD around 22 UTC (2 PM local time).

A longer animation of GOES-16 Shortwave Infrared imagery (below) begins at 2115 UTC (1:15 PM local time) on 08 November — when a Mesoscale Sector was first positioned over California — and ends 52.5 hours later at 0149 UTC on 11 November (5:49 PM local time on 10 November). The first Ventura County fire to show a pronounced thermal signature was the Hill Fire; the earliest appearance of Woolsey Fire pixels that were hot enough to be color-enhanced (yellow) was at 2254 UTC (30 minutes after the reported start time of 2224 UTC). The area of hottest (red) pixels then began to increase in coverage and spread toward the southwest after about 06 UTC on 09 November (10 PM local time on 08 November), when Santa Ana winds began to increase at higher elevations several miles inland. As was seen in the Visible / Shortwave Infrared animation above, the morning period from 15-19 UTC (7-11 AM local time) on 09 November was when the fire moved very quickly toward the California coast and the beaches of Malibu. After sunset on 09 November, the area and intensity of hot red/yellow pixels began to decrease, and after 10 UTC (2 AM local time) on 10 November only darker black fire pixels persisted. During the day on 10 November, color-enhanced hot fire pixels were again evident from 1726-2353 UTC (9:26 AM to 3:53 PM local time). Note that at 19 UTC the marine layer began to move inland, with the dewpoint jumping to 46ºF at KNTO and to 33ºF at KCMA an hour later — the fire responded to this influx of moist air by beginning to die down.

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

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

A nighttime comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Shortwave Infrared (3.74 µm) images at 0923 UTC (1:23 AM local time) on 10 November (below) showed a marked reduction in coverage and intensity of hot pixels compared to 15 hours earlier.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Shortwave Infrared (3.74 µm) images at 0923 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Shortwave Infrared (3.74 µm) images at 0923 UTC [click to enlarge]

The smoke was very dense as it moved out over the adjacent offshore waters of the Pacific Ocean on 09 November, as seen in a sequence of MODIS and VIIRS Visible images (below).

MODIS and VIIRS Visible images [click to enlarge]

MODIS and VIIRS Visible images [click to enlarge]

VIIRS True Color Red-Green-Blue (RGB) images from Suomi NPP at 2104 UTC and NOAA-20 at 2154 UTC on 09 November (below) also depicted the optically-thick nature of the smoke.

Suomi NPP VIIRS True Color image at 2104 UTC [click to enlarge]

Suomi NPP VIIRS True Color RGB image at 2104 UTC [click to enlarge]

NOAA-20 VIIRS True Color image at 2154 UTC [click to enlarge]

NOAA-20 VIIRS True Color RGB image at 2154 UTC [click to enlarge]

The smoke was so thick that Suomi NPP VIIRS Aerosol Optical Depth values exceeded 1.0 (below) —  this is likely due to the VIIRS Cloud Mask product (a component of the AOD algorithm)  falsely flagging the thick center portion of the smoke as “cloud”.

Suomi NPP VIIRS True Color RGB and Aerosol Optical Depth [click to enlarge]

Suomi NPP VIIRS True Color RGB and Aerosol Optical Depth [click to enlarge]

===== 11 November Update =====

GOES-16

GOES-16 “Red” Visible (0.64 µm, left) and Shortwave Infrared (3.9 µm, right) images [click to play MP4 animation]

Santa Ana winds began to increase again on 11 November — 1-minute GOES-16 Visible and Shortwave Infrared images (above) showed the development of new smoke plumes and hot thermal signatures around the periphery of the ongoing Woolsey Fire. As of 1812 UTC (10:12 AM local time), the fire had burned 83,275 acres and was listed as 10% contained.

The new smoke plumes (as well as residual smoke from previous days of burning) could be seen on VIIRS True Color RGB imagery from Suomi NPP at 2029 UTC and NOAA-20 at 2114 UTC (below). The entire image swaths as captured and processed by the Direct Broadcast ground station at CIMSS/SSEC can be seen here and here.

Suomi NPP VIIRS True Color RGB image at 2029 UTC [click to enlarge]

Suomi NPP VIIRS True Color RGB image at 2029 UTC [click to enlarge]

NOAA-20 VIIRS True Color RGB image at 2114 UTC [click to enlarge]

NOAA-20 VIIRS True Color RGB image at 2114 UTC [click to enlarge]

Lake-enhanced snow along the south shore of Lake Superior

November 9th, 2018 |

GOES-16

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

NWS Duluth requested a GOES-16 (GOES-East) Mesoscale Domain Sector to monitor the potential for lake-enhanced snowfall along the south shore of Lake Superior on 09 November 2018 — and 1-minute “Red” Visible (0.64 µm) images (above) showed the cyclonic flow around abroad area of low pressure over the Great Lakes (surface analyses), along with the formation of convective elements within the northeasterly flow over western Lake Superior.

A closer look at GOES-16 Visible imagery (below) showed that as the convection moved inland over north-central Wisconsin and far western Upper Michigan, moderate snow developed at Ashland WI and heavy snow was reported at Ironwood MI beginning around 2030 UTC. GOES-16 GLM Flash data did not indicate any lightning associated with the lake-enhanced convection. Hourly surface wind barbs are also plotted; 10-minute wind data for Buoys ROAM4 and DISW3 are available here and here — northerly wind gusts at Buoy ROAM4 reached 25.2 m/s (49 knots) at 2257 UTC and 21.1 m/s (41 knots) at Buoy DISW3 at 2048 and 2202 UTC.

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

GOES-16 “Red” Visible (0.64 µm) images, with hourly surface weather type plotted in yellow and wind barbs (knots) plotted in cyan [click to play MP4 animation]

A sequence of Suomi NPP and NOAA-20 VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images (below) showed a more detailed view of the convection that developed over western Lake Superior (in response to instability from cold air moving over relatively warm water — the temperature difference between cold air aloft at 850 hPa and the lake surface was on the order of 15-20º C).  Snowfall rates were also locally enhanced by lifting when northerly/northwesterly surface winds off the lake interacted with the topography of the Gogebic Range in Wisconsin and Michigan (where elevations rise to 1800 feet).

Suomi NPP and NOAA-20 VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images, with Topography [click to enlarge]

Suomi NPP and NOAA-20 VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images, with Topography [click to enlarge]

A comparison of Snow Depth at 12 UTC on 09 and 10 November, plus 24-hour Total Snowfall ending at 12 UTC on 10 November from NOHRSC (below) showed accumulations of 14 inches at two sites in north-central Wisconsin; other snowfall amounts included 8.6 inches at Bayfield WI and 14.6 inches at Ironwood MI.

Snow Depth at 12 UTC on 09 and 10 November, plus 24-hour snow accumulation ending at 12 UTC on 10 November [click to enlarge]

Snow Depth at 12 UTC on 09 and 10 November, plus 24-hour Total Snowfall ending at 12 UTC on 10 November [click to enlarge]

Animations of radar reflectivity over the Upper Midwest and Wisconsin are available here and here (courtesy of Pete Pokrandt, UW-AOS).