Persistent southerly to westerly flow over the Pacific Northwest has allowed a series of disturbances to produce rain each day so far this month in Seattle, including a record rainfall on December 7th (a day that was particularly dark, given the extensive clouds and the low sun angle: Link). (Update: Seattle also had record daily rainfall on 8 December.) The GOES-15 Water Vapor animation, above, from 0000 UTC on 6 December through 2100 UTC on 8 December (available here as an mp4 file) shows that series of impulses on the south side of a strong circulation in the Gulf of Alaska (Surface Analysis), and later scenes suggest a jet extending to the southwest. MIMIC Total Precipitable Water, below, for the 72 hours ending at 1700 UTC on 8 December, shows the signature of an atmospheric river moving moisture towards the Pacific Northwest coast, auguring rain. The broad southerly and southwesterly flow has meant above-normal temperatures as well (Seattle recorded a daily record high maximum — 60 F — on December 8).

The Aqua Satellite, carrying a MODIS (MODerate resolution Imaging Spectroradiometer) instrument, overflew the Pacific Northwest at about 2045 UTC on 8 December. The MODIS instrument senses radiation at 1.38 µm, a water vapor channel that is particularly sensitive to Cirrus Clouds (GOES-R will also detect radiation at this wavelength). The toggle below, between the 1.38 µm near-infrared and the 0.64 µm visible, shows that the storm in the Gulf of Alaska and the jet moving in from the southwest are prolific cirrus producers! Cirrus is present almost everywhere. The cirrus channel on MODIS is dark (that is, it is not detecting upper-level clouds that are inferred to be cirrus) only over the central Plains, over the Pacific Ocean west of California/Oregon and over parts of north-central Oregon and western Washington.

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Now that Himawari-8 is their operational geostationary satellite, the Japanese Meteorological Agency (JMA) decommissioned MTSAT-1R (which was relaying the direct broadcast of MTSAT-2 imagery) as of 0630 UTC on 04 December 2015. A comparison of the final 5 hours of available MTSAT-2 6.75 µm water vapor channel images with the coresponding 6.2 µm water vapor channel images from Himawari-8 (above) demonstrated the advantages of improvements in both spatial resolution (2-km with Himawari, vs 4-km with MTSAT) and temproal resolution (10-minute with Himawari, vs 30-minute with MTSAT) for resolving the signature of middle-tropospheric waves within a dry slot in the wake of an occluded storm-force low over the North Pacific Ocean (surface analyses).

In addition, there are 3 water vapor channels on the Himawari-8 AHI instrument – a comparison of these 3 water vapor bands (below) offers a closer look at the aforementioned waves within the dry slot. The weighting functions for each of the 3 water vapor bands (centred at 6.2 µm, 6.9 µm, and 7.3 µm) peak at progressivesly lower altitudes, providing different views of features within those particular atmospheric layers. The same color enhancement is applied to the 3 sets of water vapor images — note that warmer brightness temperatures (yellow to orange colors) dominate the 6.9 µm and 7.3 µm images (which are showing features at lower altitudes, where the atmosphere is warmer).

Similar improvements in spatial and temporal resolution will be seen with imagery from the upcoming GOES-R ABI, which will also feature 3 similar water vapor bands (weighting functions); however, the ABI will provide full-disk images every 5 minutes.

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A large and slow-moving occluded mid-latitude cyclone left a large swath of heavy snowfall across much of the north-central US during the 30 November – 02 December 2015 period. The GOES-13 water vapor (6.5 µm) images shown above (also available as a 62 Mbyte animated gif) revealed the unusually large size of the circulation associated with this storm system. Storm total snowfall amounts included 12.0 inches at Valentine, Nebraska, 11.0 inches at Chamberlain, South Dakota, 8.7 inches at Sibley, Iowa, and 7.2 inches at Madison, Minnesota. The 8.7 inches at Sioux Falls, South Dakota was a record daily snowfall accumulation for 30 November.

As the storm moved eastward over the Great Lakes region on 02 December, clouds cleared to reveal the large areal extent of the snow cover on Suomi NPP VIIRS true-color and false-color Red/Green/Blue (RGB) images (visualized using RealEarth) at 1948 UTC on 02 December (below). On the false-color image, snow cover (as well as lake ice) appears as shades of cyan, in contrast to supercooled water droplet clouds which are shades of white; glaciated (ice crystal) clouds also appear cyan. The deep snow cover, clear skies, and light winds aided strong radiational cooling during the following night, with minimum temperatures on the morning of 03 December as cold as -5º F at Brookings, South Dakota and -4º F at Sheldon, Iowa (KFSD RTP).

An alternative true-color vs false-color comparison (below) uses different spectral bands from the Aqua MODIS instrument — is this case, snow cover and lake ice appear as darker shades of red. The creation of these types of true-color and false-color RGB images will be possible using bands from the upcoming GOES-R ABI (scheduled to be launched in late 2016).

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The sequence of 5 daily Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images shown above are centered on Beijing in northeastern China — these images (viewed using RealEarth) showed the transition from the Beijing area being sunny and snow-covered on 26 November to enshrouded in dense smog on 30 November 2015. The smog exhibited a distinct gray-colored appearance, in contrast to the brighter white clouds and snow cover. Much of this smog was driven by the burning of coal, both on a local level and by regional power plants (as discussed in this Capital Weather Gang blog post).

The corresponding daily time series plots of surface weather data at Beijing Capital International Airport (below) revealed that the surface visibility remained below 1.0 statute miles for extended periods. Although not indicated on the 26 November plot, the surface visibility began at 19 statute miles on that day, before the wind speeds became 4 knots or less beginning at 10 UTC and the visibility eventually began to decrease.

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