Another Atmospheric River Pattern Plows into Western Canada and Washington

The Early Winter Cold Air Mass Source Region
11/22/2021, 11:48 am EST
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Fig. 1: NOAA/NWS weather watch, warning and advisory areas.

Discussion: Santa Ana wind gusting to 50-70 mph maintains a Red Flag Warning from Santa Barbara to San Diego in southern California until 6PM today (Fig. 1). The cause of the high wind event is return (easterly) flow around a high-pressure center cresting in the Great Basin. Across the top of the high-pressure cell a high wind zone associated with an “atmospheric river” is developing. The Canadian Operational model identifies a swath of heavy rain in the 5-day forecast extending from north of Hawaii into the Canadian West Coast and Washington (Fig. 2). The 5-day forecast indicates over 10 in. of rain in this zone with high spots approaching 20 in. Widespread flooding complicated by high wind strikes Washington (and northward)! An intense winter storm forms in East Mains tonight causing a snowstorm to develop today and last into tomorrow for northern New York and the northern half of New England into Quebec with widespread 5-15 in. snowfalls (Fig. 3) expected spawning Winter Weather Warnings. Another snowfall event brings 2-6 in. of snow to the Great Lakes region to Pennsylvania later this weekend (Fig. 4). The snows in the Northeast help to propel <32F risk into the Interior South States in the 5-day outlook (Fig. 5).

Fig. 2-3: CMC OP identifies an “atmospheric river” into the Canadian West Coast the next 5 days including Washington while GFS OP projects a snow storm for northern New England into the weekend.


Fig. 4-5: ECM 48-hour snowfall forecast ending 7AM EST Monday for the Great Lakes region and ECM risk of <32F day 1-5 forecast.

Fig. 6: U.S. gas population weight HDD forecast using all models and their consensus compared to 24 hours ago and the 30-year/10-year normal. The forecast is similar to 24 hours ago.

The consensus (of all models) U.S. gas population weight HDD forecast indicates a slightly warmer adjustment for the new week but colder adjustment for Dec. 3-9 (Fig. 6). Interestingly, the CMC ENS is very warm and the GFS OP is quite cold for Dec. 3-9 identifying low forecast confidence. The consensus forecast is near or slightly warmer than the 10-year normal through mid-December.