A multi-week “parade of storms” over the Pacific Ocean featuring a persistent atmospheric river pattern and numerous winter storms pounding the U.S. west coast has resulted in record snowpack in the Sierra Nevadas with water equivalency at 205% of normal for mid-January in the northern Sierras, 255% central, and 293% of normal for the southern Sierras. (Data relayed via NWS Sacramento from the California DWR) A break in the cloud cover on Tuesday January 17th enabled satellite views of the record snowpack and visual confirmation of the rising reservoirs.

Ground water is also replenishing making dents in the multi-year drought impacting the western United States.

Compare the weekly Drought Monitor maps (December 27th through January 17th) to see weekly improvements. Note how areas of Exceptional and Extreme drought conditions in California are eradicated during this time period.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) displayed the small eye-like feature associated with a warm seclusion that developed about 200 miles southeast of the New Jersey coast on 15 January 2023. Areas of deep convection around the periphery of the seclusion occasionally exhibited cloud-top infrared brightness temperatures around -50ºC.

During the preceding nighttime hours, a comparison of Suomi-NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images valid at 0718 UTC (below) provided a view of the cyclone as it was beginning to transition to its occluded phase — and the Sea Surface Temperature derived product indicated that water temperatures in the general vicinity were in the upper 60s to low 70s F (suggesting that the system was very near the axis of the Gulf Stream). One isolated bright lightning streak was seen in the Day/Night Band image, associated with a thunderstorm located near the warm front (which exhibited a cloud-top infrared brightness temperature of -56ºC).

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1-minute GOES-16 (GOES-East) Mesoscale Domain Sector “Red” Visible (0.64 µm) images (above) included time-matched (+/- 3 minutes) plots of SPC Storm Reports — which showed severe thunderstorms that moved east-northeastward across parts of the Deep South and Ohio Valley on 12 January 2023.

1-minute GOES-16 “Clean” Infrared Window (10.3 µm) images (below) indicated that the coldest pulsing overshooting tops associated many of the storms exhibited infrared brightness temperatures around -70ºC range (darker black enhancement). These thunderstorms produced numerous tornadoes (with multiple fatalities in Alabama and Georgia), hail up to 1.75 inches in diameter in Mississippi and Alabama, and damaging winds up to 67 mph in Alabama.

In a toggle between NOAA-20 (mislabeled as NPP) VIIRS Infrared Window (11.45 µm) and Near-Infrared (1.61 µm) images valid at 1843 UTC (below), the thunderstorm located over Autauga County, Alabama (where at least 7 fatalities occurred) appeared to exhibit a subtle Above-Anvil Cirrus Plume or AACP (reference | VISIT training) — along with a pronounced cold / warm (-71ºC / -50ºC) cloud-top infrared brightness temperature couplet. According to NWS Birmingham, this was the same tornado-producing thunderstorm that produced extensive damage in Selma (located just to the southwest, in adjacent Dallas County) about 30 minutes earlier.

A toggle between Infrared Window images from NOAA-20 VIIRS (11.45 µm) and GOES-16 ABI (10.3 µm) valid at 1843 UTC (below) revealed the parallax displacement of thunderstorm cloud-top features that is inherent in geostationary imagery (which is dependent on latitude, storm top height and the resulting satellite viewing angle). In this case, there was a north-northwestward parallax offset of about 4 miles (6.4 km) for the Autauga County AACP feature; according to 1200 UTC Birmingham rawinsonde data (source), the -71ºC overshooting top sensed by VIIRS was roughly equivalent to a Most Unstable air parcel altitude near 12.5 km. For a higher-altitude storm top of 15.2 km over Alabama, the GOES-16 parallax offset would be around 13.5 km.

In addition, the cold / warm storm-top thermal couplet sensed by GOES-16 was -65ºC / -55ºC; the multispectral Cloud Top Temperature derived product values were only about 0.7ºC colder.

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GOES-18 (GOES-West) Upper-level Water Vapor (6.2 µm), Mid-level Water Vapor (6.9 µm), Lower-level Water Vapor (7.3 µm) and “Clean” Infrared Window (10.3 µm) images (above) revealed the diurnal cycle of nighttime cooling and daytime warming at the summits of Mauna Kea and Mauna Loa on the Big Island of Hawai’i on 10 January 2023. In addition, a hot thermal signature (darker red to black pixels) was evident in the 10.3 µm imagery due to ongoing volcanic activity at Kilauea. This case is another example which helps to underscore the fact that Water Vapor spectral bands are essentially Infrared bands, which — in the absence of clouds — essentially sense the mean temperature of a layer (or layers) of moisture within the troposphere.

The presence of very dry air within most of the middle/upper troposphere over Hawai’i on 10 January had the effect of shifting the water vapor weighting functions to lower altitudes, as seen on plots for the 3 ABI Water Vapor bands calculated using 12 UTC rawinsonde data from Hilo PHTO (below). This allowed thermal radiation from the higher terrain to pass upward — with minimal attenuation — through what little high-altitude moisture was present and reach the 7.3 µm / 6.9 µm / 6.2 µm detectors on GOES-18.

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