tyweather wrote: ↑Fri Mar 13, 2026 2:09 pm
• The initial round of precipitation is expected to begin later Sunday and continue into Wednesday AM. The forecast has trended markedly wetter compared to yesterday’s and most likely 3-day totals are now moderate to very heavy 75-200 mm for the South Coast, and 20-70 mm for the Columbia, northern Kootenays and higher elevations of southern Williston. Confidence is medium for this outcome. A lower likelihood wet scenario brings up to 250 mm to the wettest South Coast sites.
• A second round of precipitation is expected after what may be a short pause later Wednesday and continue into early Friday, an additional moderate to borderline heavy 30-70 mm could fall during this period on the South Coast, with 5-30 mm in the Columbia/Kootenay. Confidence for this period is lower than for the first half of the week, and the forecast could trend wetter.
• Most likely 5-day totals Sunday to Thursday are in the range of 125-275 mm for the South Coast and 30-90 mm for the Columbia extending into northern Kootenays and southern Williston. The Lower Mainland basins are most likely to receive the highest totals.
• A lower-likelihood wet scenario brings heavy to borderline extreme 150-350 mm to the South Coast, with 50-150 mm in the Columbia, northern Kootenays and Southern Williston over five days.
• During the most intense phase of the AR, Monday to Wednesday, short-period rainfall rates could reach heavy to very heavy 7-15 mm/h at times on the South Coast.
• Freezing levels over much of BC are forecast to climb to 2000-2500 m on Monday and then remain elevated into Friday, with the potential of climbing toward 3000 m locally on the South Coast, supporting rain from the lowlands into the alpine. Antecedent conditions have been wet but cool, with much fresh snowpack addition. Fresh snow is more prone to melting than the older snowpack, and points to the potential for significant snowmelt contribution, especially on the South Coast.
• The forecast atmospheric river has some similarities to the 13-15 Nov 2021 event, though currently is not forecast to produce 48-hour precipitation totals as extreme, perhaps closer to 2/3 of the 2021 event. 5-day totals may approach the levels of 2021. For duration, the infamous “week of rain” in January 2005, a 4- to 5-day event, had a substantial rain-on-snow component and produced significant impacts.
