A strong and extensive upper-level jet brought widespread weather impacts to the United States in mid-December 2019. Water vapor imagery from GOES-West on 12 Dec showed the jet extending from north of Hawaii to the US Rockies (Fig 1). The feature is identified in water vapor imagery by the sharp poleward transition from cooler to warmer brightness temperatures, along with localized fast moving moisture/cloud features. The more significant vorticity maxima/shortwaves are diagnosed in the water vapor imagery as well.

Airmass RGB imagery makes clearer the transition from a warmer/more moist airmass south of the jet (greens) to the cooler/drier airmass to the north (Fig 2). Shades of red near the jet and shortwaves are also apparent, indicating the descent of drier, higher PV air.

By 13 Dec, the jet exit region had dug into the southern US, helping to deepen a trough (Fig 3). The jet exit region, trough and associated deepening surface low would continue east and develop into a nor’easter as it progressed up the east coast. The far southeast US was highlighted in a Slight Risk for Severe by the SPC on the 13th in association with the deepening trough/jet. Further west, the jet core remained over the US Rockies, with GOES-East Derived Winds product indicating speeds as high as 180 knots around 300 mb! The strong jet was driving elevated amounts of pacific moisture into the western US. As a result of the enhanced moisture content and strong orographic forcing, heavy snow was ongoing across much of the Rockies, resulting in numerous winter weather highlights. Across the Colorado Rockies, several feet of snow was forecast to fall by the end of the weekend.

The Airmass RGB product on the 13th continued to depict the contrast between the two airmass poleward across the jet (Fig 4).

The operational Blended TPW product, which blends moisture information from multiple instruments, clearly shows the plume of moisture associated with the pacific jet driving east across the eastern pacific and western US (Fig 5). TPW values were indicated to be well above normal, (200% of normal in many areas; Fig 6). The prolonged period of such anomalously high TPW values lends confidence to significant snow potential over high elevations where orographics are favorable.

Analysis of the Layer PW product shows that the lengthy plume of moisture extended vertically from the surface to the upper levels (Fig 7).

Bill Line, NESDIS