As an anomalously-strong upper-tropospheric jet streak was moving across the Mid-Atlantic region on 20 November 2022, GOES-16 (GOES-East) Upper-level Water Vapor (6.2 µm) images (above) displayed numerous 6.2 µm Derived Motion Wind (DMW) vectors having speeds of 190 knots and higher — with the jet streak axis passing just to the north of the Wallops, Virginia rawinsonde site (KWAL). Derived Motion Wind speeds as high as 201 knots and 202 knots were seen shortly before the launch of the 12 UTC Wallops sounding.

Plots of Wallops, Virginia rawinsonde data at 00 UTC and 12 UTC on 20 November (below) showed that the maximum wind speeds were at the 213 hPa level (187.8 knots) at 00 UTC and the 206 hPa level (189.8 knots) at 12 UTC.

A plot of 250 hPa wind speed climatology for the Wallops rawinsonde site (from SPC) includes the 12 UTC value on 20 November 2022 (shown by the black circle) — which indicated that the 183-knot value measured during that 12 UTC sounding ascent was the fastest 250 hPa wind speed for the month of November at that site.

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1-minute Mesoscale Domain Sector GOES-16 “Clean” Infrared Window (10.3 µm) images (above) include an overlay of GLM Flash Extent Density — which showed rapidly-cooling cloud-top infrared brightness temperatures (and intermittent lightning) over the eastern half of  Lake Erie, associated with the initial impulse of lake effect snow (LES) immediately downwind of the lake after sunset on 17 November 2022. Snowfall rates quickly ramped up to 3 inches per hour at Buffalo (station identifier KBUF), with lightning reported. Along the north shore of Lake Erie, about 20 miles west of Buffalo, a peak wind gust of 60 knots was recorded at Port Colborne, Ontario (station identifier CWPC) at 0211 UTC on 18 November.

In the wake of this initial impulse, a dominant LES band became established along the axis of Lake Erie, which persistent during the entire night and into the following morning — snowfall accumulations were as high as 36.0 inches by 1530 UTC (10:30 AM EST).

After sunrise on 18 November, 1-minute GOES-16 Day Cloud Phase Distinction RGB images (below) indicated that much of the dominant LES band had cloud tops of mixed phase (supercooled water droplet + ice crystal) or glaciated phase (shades of yellow to green). By 2100 UTC (4:00 PM EST) on 18 November, the highest snowfall accumulations had reached 54 inches at Orchard Park just south of Buffalo.

A toggle between Suomi-NPP VIIRS True Color RGB and False Color RGB images (below) depicted the broad LES band at 1828 UTC. The VIIRS data used to create these images were acquired and processed using the SSEC/CIMSS Direct Broadcast ground station.

The GOES-16 Cloud Top Phase derived product (below) confirmed the Mixed Phase nature (darker green) of much of the LES band.

After sunset on 18 November, GOES-16 Infrared images (below) showed that while the Lake Erie LES band was not as well-defined as earlier in the day, it still persisted (with isolated brief periods of lightning). By 0000 UTC on 19 November (7 PM EST on 18 November), snowfall accumulations had reached 66 inches at Orchard Park.

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Breaks in the cloud cover on the morning of 19 November provided a partial glimpse of the snow cover that resulted from this LES event — appearing as shades of red in the GOES-16 Day Snow-Fog RGB images, and shades of green in the Day Cloud Phase Distinction RGB images — which extended into the western Finger Lakes region of western New York. Snowfall accumulations were as high as 77.0 inches at Orchard Park.

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A list of storm total snowfall amounts from this multi-day (16-20 November) LES event is available here.

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The Gálvez-Davison index (GDI) is a useful derived product (available online here from NCEP) for predicting tropical convection in tradewind regimes. In general, the larger the GDI, the more likely that showers and thunderstorms will be present. The toggle above compares GDI with K-Index derived from NUCAPS data (the Sounding Availability plot shows in green where the NUCAPS retrieval completed successfully; i.e., where the data are considered most appropriate). There’s good spatial correlation between the GDI and the diagnosed stability.

The toggle below compares GDI from GFS to the GOES-17 K-index (a Level 2 GOES-R derived stability product computed in clear skies only) that is displayed on top of GOES-17 Band 13 Clean Window infrared (10.3 um) imagery. A corridor of lower stability is readily apparent in the K Index, stretching across the Samoan Islands. Relatively stable air overlays Fiji, and a large region of instability lies east of American Samoa. The GDI agrees very well with the K Index derived from the satellite data, and convection as diagnosed by the Band 13 imagery is limited to regions where GDI values are larger. It is a good practice is to compare the K Index and the GDI. If the K Index starts to diverge from the predicted GDI, it’s a good idea to ask why!

Thanks to Dora Meredith and Elinor Lutu-McMoore, WGO PPG, for their assistance with this blog post!

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RADARSAT-2 observations of SAR data near/around the island of Guam in the Marianas Islands continue in November (as previously discussed here, here and here). Overpasses on 15 November (above) and 17 November (below) contain features that deserve comment. For example, there is an obvious seam (and a less-obvious second seam) in the SAR wind analysis above. The “Beam Seams” arise because the 500-km wide scan for SAR winds is created from smaller individual beam positions.   Each beam position has its own set of adjustments applied during SAR image processing and sometimes there is slight disagreement from one beam to the next.   The image above has 3 subswaths – so 2 beam seams. The seams are also apparent in the normalized radar cross section (NRCS) image here.

Although SAR winds as displayed in AWIPS do not have a wind direction, a direction can be inferred from the ‘shadow’ of weaker winds in the lee of Guam. Imagery at this website does include the constraining GFS wind barbs (as shown here). Note that MetopB Advanced Scatterometer (ASCAT) winds show winds (from this site) in the 15-20 knot range in the region to the west of Guam, in agreement with the SAR observations.

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SAR winds on 17 November at 0830 UTC, shown below with Himawari-8 infrared imagery, show winds of similar strength to those on the 15th. (Click here to view the analysis with wind barbs, or the NRCS analysis, both from this site.) On this day, the Marianas Islands all have an apparent effect on the downstream winds (Click here to see the AWIPS image of SAR winds; here’s a similar example over the Caribbean). The wake from Rota, for example, extends all the way from Rota to the western edge of the SAR scan! The wake from Guam is being affected by convection, but it too can be followed to the western edge of the SAR domain. Islands in the Marianas have an effect on winds that stretches for 100s of kilometers on some days, such as the 17th, but not on others, such as the 15th. (Note also: very faint Beam Seams are detectable on the 17th).

This SAR scan includes the islands of Tinian and Saipan, as shown below. Are there still large ships near Saipan, as noted in this blog post where 5 are present? Per the SAR data below, perhaps only one! Also, the lighter winds downwind of both Saipan and Tinian are very apparent in the image below: winds of 20 knots on the windward side of the islands (green in the enhancement used) and 10 knots or less (blue and purple) on the leeward side.

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You can find information on RADARSAT-2 at this WMO link.

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