GOES-18 (GOES-West) Air Mass RGB images (above) showed the progression of a strong cold front — associated with a deepening Alberta Clipper type of midlatitude cyclone — which produced strong winds across parts of central/eastern Montana and western North Dakota / South Dakota during the afternoon and evening hours on 17 October 2023. Notable METAR site peak wind gusts included 61 knots (70 mph) at Jordan MT (KJDN) and Buffalo SD (K2WX), and 60 knots (69 mph) at Dickinson, ND (KDIK); in addition, a mesonet station at Beach ND recorded a peak wind gust of 66 knots (76 mph).

It's getting windy out west. Showers are bringing down gusty winds from above the surface. Froid, Beach, Sentinal Butte and Beach have all had gusts above 60 mph in last hour. Beach "winning" with 76 mph gust. @NWSBismarck has just issued a High Wind Warning for the area. #ndwx pic.twitter.com/NMhZ511hMh

— NDAWN (@NDAWNmesonet) October 17, 2023

The brighter shades of orange-red in the Air Mass RGB imagery highlighted dry, ozone-rich air indicative of the lower tropopause associated with this disturbance. Contours of the “dynamic tropopause” — taken to be the pressure of the RAP40 model PV1.5 surface — portrayed the tropopause extending down to the 650 hPa pressure level over far northeastern Montana (above). A SW-to-NE oriented cross section from western Montana to the US/Canada border (below) also showed the pronounced lowering of stratospheric values of Potential Vorticity (greater than 1.5 PVU) over northeastern Montana.

2 examples of GOES-18 Mid-level Water Vapor (6.9 µm) imagery with plots of associated Derived Motion Winds (above) showed speeds greater than 50 knots. A plot of rawinsonde data from Glasgow, Montana at 0000 UTC on 18 October (below) depicted steep mid-level (7.3 C/km) and boundary layer (near dry adiabatic) temperature lapse rates, which were aiding the downward transport of momentum (strong winds) from the middle troposphere to the surface. The aforementioned low tropopause was also evident in the temperature profile, near 370 hPa (which had descended dramatically since 1200 UTC) — with very dry air above 500 hPa.

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GOES-R Satellites (GOES-16 as GOES-East and GOES-18 as GOES-West) provide single-channel observations, such as the clean window infrared image above that can be used to identify features. In the example above, a mid-level cloud deck stretches southeastward from the Samoan islands that surround 170^oW Longitude. Higher clouds with with embedded convection are apparent in the northeastern quadrant of the animation, with a noticeable convective feature forming from 1000 to 1100 UTC. A useful Level 2 product to include in a Clean Window infrared image is the Total Precipitable Water: this is a clear-sky only product and thus gives information where the Band 13 image is returning surface information. The animation below has TPW underlain under the Band 13 image and the default AWIPS enhancement for TPW has been altered: the driest value is 0.5 (inches) rather than 0.0. The TPW distribution allows a viewer to note that the cloud band to the southeast of the Samoan Islands is aligned with a moisture gradient. That deep convective complex is developing near the southern gradient of that deepest moisture. The driest atmosphere is south of 20^oS in the image below.

Derived Motion Wind vectors are another Level 2 product, and they can be plotted as a function of pressure, as shown below. This added information provides useful context to the infrared imagery. At lower levels (surface-900 mb), cloud motion is brisk and from the east and southeast at 20-25 knots. From 775-900 mb, motion is more easterly; derived vectors have appeared on top of the cloud band that stretches southeastward from the Samoan islands. The convection that develops between 1000 and 1100 UTC is within a region of cyclonic winds. Between 600-775 mb, winds are more westerly, and the convection that is developing between 1000 and 1100 UTC is within a region of diffluence associated with anticyclonic motion. Winds from 450-600 mb also show diffluence in the region where convection developed.

The animation below shows the derived winds all plotted on top of each other. AWIPS will also plot vectors such that the wind barb color is a function of wind speed. Low-level winds at this time are mostly derived from the 3.9 µm imagery. High-level winds are derived from Water Vapor channels and from 11.2 µm imagery.

The pronounced shift in wind direction with height is also apparent from the 1200 UTC 17 October 2023 Rawinsonde from Pago Pago, below (from this link).

The persistent winds have raised seas around American Samoa. The buoy at Aunu’u below shows seas climbing to above 10 feet before sunrise American Samoa Time on the 17th. One other recent change that has happened is the cessation of the very long-period southerly swell that had persisted for several days through yesterday.

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In this environment with persistent winds, Tutuila experienced rain activity that was unforecast by numerical models. Night Microphysics RGB imagery, below, from the CSPP Geosphere site, show the evolution of cloud lines from light violet to violet with a reddish tint as clouds grow in height and start to precipitate.

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Two other GOES-18 Level 2 derived products that helped to further characterize the rain-producing cloud lines were Cloud Top Height (above) and Cloud Top Phase (below). As cloud-top heights increased and reached colder temperatures, their cloud-top phase changed from water (cyan) to supercooled (light green) then to mixed supercooled/ice (darker green). Note that not all of the hourly METAR surface reports were plotted by AWIPS: at 0820 UTC and 0850 UTC, heavy rain reduced the surface visibility to 1.0 and 0.5 mile, respectively, at Pago Pago International Airport on Tutuila Island, American Samoa (plot | text).

Cursor sampling of GOES-18 Cloud Top Phase, Cloud Top Height and Cloud Top Temperature at 1130 UTC — when the maximum height of the cloud line in the vicinity of Tutuila was 22036 ft — is shown below.

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MIMIC Total Precipitable Water fields, above, (archived here), show the motion of Typhoon Bolaven as it evolved from a strong typhoon west of 150^o E Longitude on 10 October to a potent extratropical cyclone approaching 150^oW Longitude on 16 October 2023, at which later time a long filament of tropical moisture continued to accompany the system. True Color imagery from the CSPP Geosphere site, below, shows the elongated system with the cold front stretching to the west-southwest.

MIMIC TPW fields over the eastern Pacific at 1800 UTC on 16 October, below, show two different moist airstream; one is affecting the Pacific Northwest of the USA (and southwestern Canada) at 1800 UTC. The moisture with the remains of Bolaven is approaching from the west. The GFS model initialized on 1200 UTC on 16 October suggests the next 72 hours will be wet along Coastal British Columbia with widespread rainfalls of 4-6″ (link, from this site) .

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GOES-18 Air Mass RGB images from 14-16 October (above) showed the period during which Typhoon Bolaven made its extratropical transition to a Hurricane Force Low on 14 October and then to an expansive Storm Force Low on 16 October (surface analyses from OPC). The brighter shades of orange-red in the RGB imagery depicted a Potential Vorticity anomaly associated with this strong storm system. 

At 2100 UTC on 16 October, a cross section of AK-NAM40 model Potential Vorticity and Wind Speed along Line J-J’ (below) highlighted a well-defined tropopause fold, descending into the middle troposphere below the core of a 130-140 knot jet stream (the jet axis was situated along the southern periphery of the storm).

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The storm has generated a particularly large wind field, as shown below (from this website). Between 0650 and 0834 UTC, when Metop-B (twice) overflew the area, the Advanced Scatterometer detected a very large region of 30-35 knot winds (red in the enhancement), with peak winds near 45 knots near 40^oN, 153^oW.

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10-minute Full Disk GOES-16 (GOES-East) CIMSS Natural True Color RGB images created using Geo2Grid (above) showed the 2023 Annular Solar Eclipse shadow as it progressed southeastward from the Pacific Northwest to Brazil on 14 October 2023.

GOES-16 Near-Infrared “Vegetation” (0.86 µm) images — in the native projection of the GOES-16 satellite (below) — provided another view of the eclipse shadow path.

A staggered set of three Mesoscale Domain Sectors from GOES-18 (GOES-West) provided 1-minute imagery of the eclipse shadow progression (below).

GOES-16 SUVI Fe171 images from the SSEC Geostationary Satellite Imagery site (below) showed the Moon’s silhouette as it passed in front of the Sun during the eclipse period.

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