Pacific Coast Bomb Cyclone (author: Gigi Pavur; date: 26 Nov. 2019)

Amongst preparations of turkey, cranberry sauce, and stuffing for Thanksgiving, West Coast residents in California and Oregon are also preparing for a potentially record-breaking winter cyclone. A powerful low pressure system, which is rapidly intensifying, is expected to make landfall near the border of Oregon and California during the afternoon of 26 November. With anticipated wind gusts up to 100 mph, this low-pressure system is expected to cause wind speeds comparable to a low-end Category 1 hurricane. Additionally, this system is predicted to cause up to 4 feet of snow in the Sierra Nevada and wave heights up to 37 feet along the coast.

Currently, the system’s central pressure values are predicted to drop 40 mb in 24 hours, which effortlessly surpasses the “bomb cyclone” requirements of a 24 mb decrease in pressure over 24 hours. In Fig. 1, a GIF of water vapor satellite imagery shows the variations of brightness temperature to the east and west of the low pressure system. To gain further insight into this pattern, it is helpful to use the Air Mass RGB satellite product. As shown in Fig. 2, dry upper level air with a cold air mass to the south, as well as high, thick clouds, contribute to the spiraling system. Fig. 3 shows a GFS model run of MSLP and 10m wind speed knots, which depicts the counter-clockwise wind barb orientations, which reflects the low pressure environment. Furthermore, if the central pressure decrease of 40 mb proves to be true, this could cause the region’s lowest pressure readings on record. The previous record was set in 2010, with a central pressure reading of 978 mb.

Figure 1: To view a GIF of water vapor satellite imagery of the low pressure system just off the western coast of the United States, please go to )


Figure 2: This Air Mass RGB satellite imagery shows the interactions of the dry upper level air (red), cold air mass (blue), and high, thick clouds (white) which spiral counter-clockwise at the bomb cyclone off the coast of California and Oregon.


Figure 3: This map from Tropical Tidbits shows a GFS model run of MSLP and 10m wind speeds. Here, the central pressure of the low system is predicted to be 971 mb.