Carson City area weather: Atmospheric River taking shape with potential flooding
Submitted by Jeff Munson on Mon, 03/06/2023 - 1:46pm
UPDATE: With constant snow storms pummeling Lake Tahoe and Sierra, this week is looking like less accumulation with periods of snow through Wednesday, and a couple inches possible in the lower valleys. Those hoping for dry weather will be disappointed considering the forecast later in the week.
The National Weather Service says models are showing a high probability of a warm, Atmospheric River, also known as a Pineapple Express, reaching the region by Thursday.
This warmer system would leave most snow in the 7,500-8,000 foot elevation more than around lake level, with chances of rain at lower elevations including South Lake Tahoe, said Justin Collins, forecaster/meteorologist with NWS Reno.
As the system gets closer exact details will become more evident.
For now, considering possible scenarios, a warm Atmospheric River in the higher elevations should raise red flags because of the potential for flooding, not only for the Lake Tahoe Basin, but also for lower valleys and surrounding foothills around the 5,000 foot level and above, which already have several feet of snow on them.
NWS forecasters are keeping a close eye and monitoring the situation.
"At this time flooding is looking like a concern. The potential is certainly there," said National Weather Service Meteorologist Tyler Salas on Monday afternoon.
As to certainty, a lot is up in the air to make a determination he added.
"We don't want to alarm people but they should keep it in the back of their mind, and just like any storm preparation, make sure you are well prepared."
For now, here's the latest National Weather Service discussion. this is as of Monday afternoon and reflects more of any potential of rain concerns.
Thursday-Saturday Atmospheric River:
All the ingredients (and 90% of the ensemble solutions) are coming together for a wet and warm atmospheric river impacting the region starting late Thursday into the weekend. Let's break down the corresponding impacts below:
WIND:
Current ensembles show increasing confidence that the crests of the Sierra will see very strong wind gusts (80-100+ mph) from Thursday afternoon through at least Saturday night. There is still more uncertainty to exactly how strong winds will be in western Nevada.
RAIN/SNOW:
Let us first break down the ensembles anomalies. It's worth noting the PWAT's and IVT in our area are well above the 99th percentile, showing an immense amount of moisture moving into the area. In fact, this is an impressive amount of atmospheric moisture for mid-January, let alone early March. Instead of focusing on exact amounts (since those will definitely change closer to the event), let's take a look at the probabilities. As of now, the Tahoe Basin and higher elevations of the Sierra show a very high probability (>90%) for at least 1"; 70-80% chance of 2", and even 60% chance for 3" of QPF along the crests. Western NV (excluding the inner basins) and northeast CA have a high 90% probability for at least 0.25" of QPF, and a 40-50% chance for at least 0.5" of QPF.
The EFI and blended guidance is showing an increase in temperatures, with high temperatures returning to average and low temperatures becoming above average. Thus, snow levels are currently trending higher. They will start off low on Thursday, eventually increasing to between 7,000-9,000 feet by Friday morning. There is a 10% chance that snow levels could exceed 9,000 feet. Above the snowline, snow will once again be measured in feet. There is a high likelihood of at least 8" along the crests in Lake Tahoe, but only a 40-50% chance of 12" of snow or more.
Snow amounts will be higher in Mono County, especially above 8,000-9,000 feet where there is a 100%+ chance for 12 inches and a 60% chance for at least 24" of snow.
After this Atmospheric River event, the larger scale pattern remains conducive for additional bouts of rain, snow, and wind into next week. The details will emerge as we get closer, but just stay prepared and tuned into the forecast.
Check back for updates.
