1-minute Mesoscale Domain Sector GOES-18 (GOES-West) “Red” Visible (0.64 µm) images (above) showed the development of thunderstorms across much of the eastern portion of Interior Alaska on 24 July 2023. The large satellite viewing angle — which is 73.5 degrees for Fairbanks (station identifier PAFA) — provided an oblique perspective that nicely displayed the vertical buildup of towering cumulus as well as the formation of thunderstorm anvils.

In the corresponding 1-minute GOES-18 “Clean” Infrared Window (10.3 µm) images (below), the coldest thunderstorm tops exhibited infrared brightness temperatures around -60ºC (darker shades of red).

When viewing satellite imagery at high latitudes, it is important to keep parallax in mind — so for the thunderstorms that produced wind damage east-southeast and southeast of Fairbanks at 0315 UTC and 0330 UTC, their cloud tops (at an average altitude around 30000 ft) were actually displayed about 32 km (20 miles) to the north-northwest of their true location over the surface (above).

The parallax displacement was apparent in a closer view of 1-minue GOES-18 Visible and Infrared images, centered near Fairbanks, with plots of Severe Thunderstorm Warning polygons (below). 

Pulses of overshooting tops were evident with many of these thunderstorms, such as one seen just northeast of Eielson Air Force Base (PAEI) in a toggle between GOES-18 Visible and Infrared images at 0244 UTC (below) — which was about 30 minutes prior to the first report of damaging winds 15 miles ESE of Fairbanks.

For the overshooting top northeast of PAEI at 0244 UTC, cursor-sampled values of GOES-18 infrared (10.3 µm) brightness temperature, Cloud Top Temperature and Cloud Top Height were -61.85ºC, -63.93ºC and 38669.15 feet, respectively (above) — which, according to a plot of 0000 UTC rawinsonde data from Fairbanks (below), represented an altitude just above the Equilibrium Level (EL) of a Most Unstable (MU) air parcel.

These thunderstorms occurred on a day that Fairbanks set a new daily record high temperature of 90ºF — and a Cooperative Observer in the Fairbanks area reported a high temperature of 92ºF (Regional Temperarture and Precipitation).

Fairbanks officially hit 90°F on Monday. The last time that the Fairbanks airport officially hit 90 degrees before Monday was back in June of 2017. We also broke a daily high temperature record for 7/24. #akwx pic.twitter.com/MWH7c3KXxq

— NWS Fairbanks (@NWSFairbanks) July 25, 2023

The 92F observation from the Ester 5 NE Cooperative station (northwest part of Fairbanks) is the warmest reading in Alaska in 2023.

— Brian Brettschneider (@Climatologist49) July 25, 2023

View only this post Read Less

The Joint Typhoon Warning Center (JTWC) website has for more than a day been tracking invest number 91W, shown above. The feature is circled in yellow, meaning development is unlikely in the next 24 hours. What satellite data might be used to make that determination?

MIMIC Total Precipitable water fields, for the 24 hours ending at 1600 UTC on 24 July 2023, below, show an area rich in tropical moisture, and a broad, diffuse, cyclonic circulation is present between 140 and 150^o E, an between the Equator and 10^oN. In other words, there is plenty of moisture here and one can therefore infer a lack of dry air to impede convection. Are there observations to support the presence of a cyclonic circulation? Motion in the MIMIC fields is a by-product of advection of MIRS Total Precipitable Water fields (computed from individual data swaths from low-earth-orbit — LEO — satellites) by the GFS model (see this training on MIMIC).

Advanced Scatterometer (ASCAT) data from Metop-C and Metop-B (from this NOAA/NESDIS/STAR website), below, shows a cyclonic circulation with southwest winds between 2^o and 6^o N, and southeast winds from 6^oN to 10^oN, around near 147^o E at around 0000 UTC on 24 July 2023. The 1200 UTC imagery, below, doesn’t quite show a circulation in the same region, but it’s hard to tell how well it might have been sampled.

Tropical Cyclones typically form in regions of low shear. Estimates of shear are available at the SSEC/CIMSS Tropical Website (direct link), as are convergence/vorticity analyses, shown in a toggle below. For the region between 0 and 10^oN, 140 to 150 ^oE, there is low-level vorticity (not as concentrated as in the region of Typoon Doksuri, of course) near a narrow ribbon of low shear values (larger shear values are Equatorward of the vorticity center). Low-level convergence and upper-level divergence in the region are weak and do not appear to be linked however.

Himawari-9 Upper-level and lower-level Water Vapor imagery, below (Band 10, 7.34 µm, on the left and Band 8, 6.24 µm, on the right) from 1000 to 1500 UTC shows widespread convection in the square bordered by 140 and 150 oE and 0 and 10oN. No widespread dry air is present. Much of the convection is south and east of the vorticity center.

Future information on this invest (and on Typhoon Doksuri) can be viewed at the webpages of the Joint Typhoon Warning Center. The RSMC at Tokyo also has information on Western Pacific tropical cyclones. Forecasts are for 91W to move between Yap and Guam in the next days. The information presented here might help the reader decide for themselves whether or not the Invest will develop further.

View only this post Read Less

The image above shows International Space Station orbital paths over the western Pacific Ocean on 24 July 2023, computed from the TLE files and displayed using McIDAS. Note the orbital path at 1600 UTC that moves from mainland China southeastward over Taiwan and then to Indonesia. This is in close proximity to Typhoon Doksuri at that time. LIS lightning observations along this path, from 1602 to 1607 UTC, are shown below. Lightning strikes are detected within the outer rainbands of the typhoon, but no observations occur near the eyewall.

View only this post Read Less

GOES-18 (GOES-West) SO2 RGB and Ash RGB images (above) showed the northeastward drift of a volcanic cloud produced by an eruption of Mount Shishaldin that began shortly before 0730 UTC on 23 July 2023. The initial (higher-altitude) portion of the volcanic cloud likely contained moderate concentrations of SO2 (denoted by brighter shades of yellow in the SO2 RGB images) — while the trailing (lower-altitude) portion of the volcanic cloud likely contained concentrations of ash (shades of pink in the Ash RGB images). The ash signature dissipated after about 4 hours, while the SO2 signature persisted for the duration of the 11.5-hour animation.

A toggle between the SO2 RGB and Ash RGB images at 1000 UTC is shown below.

A pilot report issued at 0727 UTC (below) indicated that volcanic ash (VA) was rising to altitudes of 30000 feet (FL300).

===== 24 July Update =====

A longer animation of GOES-18 SO2 RGB images (above) showed the distinct SO2 signature (brighter shades of yellow) from the Shishaldin eruption, as it rotated counterclockwise within the circulation of a slow-moving middle tropospheric low in the Bering Sea — moving over far southwest Alaska and St. Lawrence Island on 23 July, and eventually becoming stretched into a long/narrow filament over far eastern Russia on 24 July.

View only this post Read Less