Carson City area weather: Storm system arrives, 1.5 to 3 inches of valley rain possible

UPDATE: The National Weather Service in Reno issued a Flood Warning on Sunday afternoon for western Carson City, Douglas County, northern Lyon County, Storey County, southern Washoe County, western Churchill County, southwestern Pershing County in Nevada and Alpine, El Dorado, Placer, Nevada, Plumas and Sierra county in northern California.

Flooding is ongoing or expected in the the warned area. Between 1 and 4 inches of rain have fallen. Mudflows, rock falls and rises in creeks and streams are occurring in several locations with further impacts likely, according to the National Weather Service. There is also high likelihood for standing water on roadways. Go here to read the full warning.
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Discussed and forecast over several days, a strong atmospheric river weather system has arrived to the Sierra, Lake Tahoe and western Nevada regions, prompting a number of National Weather Service watches and warnings, especially for areas hit hard by wildfires earlier this year that are now threatened with flooding and debris flows.

A Flood Watch continues through Monday morning for portions of east central California and western Nevada, including the Reno area, Carson City, Lake Tahoe, and Carson Valley in Douglas County. Heavy rainfall from the weather system will continue through tonight, according to the weather service.

Total rainfall of 1.5 to 3 inches for Western Nevada cities, 3 to 4 inches for foothill areas, and 4 to 6 inches for the Tahoe Basin, Truckee and Markleeville areas, forecasters say.

Debris flows, ash flows, rock falls, and tree falls are likely, especially on or near burn scars and steep terrain. This includes the Caldor, Tamarack, and Numbers Fires. Significant rises on rivers, small creeks and streams are expected. Equipment in and near river and creek channels should be moved to safety. Rock falls in canyons and ponding of water on roads will create hazardous driving conditions. This can especially be an issue on. Interstate 80 between Reno and Truckee, according to the NWS.

A High Wind Warning has been canceled.

For the Lake Tahoe area, a Winter Storm Warning is in effect from 5 p.m. Sunday to 11 p.m. Monday for areas above 7,000 feet.

Heavy wet snow expected above 7000 feet. Total snow accumulations of 4-8 inches for Donner Pass and Echo Summit, 3-5 inches for Spooner Summit, 12-18 inches for Mt Rose Summit, with multiple feet of snow for higher mountains. Communities around Truckee and the Tahoe Basin are likely to only get an inch or two, with mainly rain falling, however there is a 30 percent chance of 6 inches of snow if snow levels fall faster than forecast.

The heaviest snowfall rates of 1-2 inches per hour possible at pass elevations between 8 p.m. Sunday and 4 a.m. Monday.

Travel could be very difficult. The hazardous conditions could impact the morning or evening commute. Very strong winds could cause extensive tree damage. Winds will gust to 50 mph across the Truckee and Tahoe Basin areas, with ridges gusting well over 100 mph. This will result in extremely rough water on Lake Tahoe.

The weather services advises motorists to avoid travel if possible, warning they could be stuck in their vehicle for many hours. If you must travel, prepare for long delays and carry an emergency kit with extra food, water and clothing. If you stay home, have a backup plan in case of power outages.

The latest road conditions can be fond at NVroads.com or calling 511.

The following is the National Weather Service forecast discussion from early Sunday morning regarding the storm.

A strong atmospheric river will bring a deluge of rain, heavy mountain snow, and gusty, potentially damaging, winds to the region. Flooding is a concern, particularly near recent burn scars. Some lingering showers possible through Tuesday as the upper trough continues its exit from the region. High pressure builds over the West Coast the later half of next week.

TIMING and HOURLY RAINFALL RATES:
The main precipitation for the northern Sierra occurring now and continuing into the afternoon. The highest risk and impacts associated with flash flooding and debris flows over the Dixie Fire burn scar should extend through this morning and afternoon(6AM to 7PM). Hourly precipitation rates could range from 0.25 to 0.50 for many areas across the northern Sierra and nearby high-risk burn scars. Areas to the west could see hourly totals up to 0.75.

The nearly lateral conduit of moderate to heavy precipitation will shift south and focus of the Lake Tahoe Basin and Reno area later this morning (10AM-12PM) and continue through the afternoon into the evening (5PM-8PM). Hourly precipitation rates for the Lake Tahoe Basin will hover around 0.25 per hour with higher mountain elevations seeing a range between 0.30 to 0.50. Reno and surrounding areas could see hourly rates varying from 0.10 to 0.25 along higher foothill areas.

As the broad shaft of heavier precipitation continues to trek south of the Lake Tahoe Basin, the Caldor and Tamarack burn scar could see hourly rain rates ranging 0.25 to 0.50 (12PM-8PM). Areas south along the Sierra Front into Mono County will see similar hourly rate that should continue till 12 noon Monday.

LIQUID EQUIVALENT PRECIP TOTALS:

The highest anticipated liquid precip totals remain mostly unchanged with the Sierra Crest potential maintaining its lead at 6-10 inches. The Lake Tahoe Basin could have 3 to 6 inches of rain with northeast CA and the Eastern Sierra in Mono County accumulating 2-4 of liquid equivalent precipitation. Along areas of the Sierra Front in far western Nevada liquid totals could still range 0.75 to over 3 for some areas. The west central Nevada Basin and Range will follow on with a steady range between 0.25 to over an inch for some areas.

The greatest variation in upper/lower end QPF ranges lie in areas near and east of US-395. This is likely due to shadowing in higher resolution models and an uptick in wind speeds. A lot of these high res models do tend to overshadow in the lee of the Sierra and in this case, the synoptic set up and intense IVT would lead me to favor the wetter scenarios with precipitation extending Just keep in mind, there is a 20% chance for the drier scenarios to come to fruition.

If we are in the 50th-75th percentile range of the QPF guidance, 2-day precipitation records (for the month of October) are possible. Example, the current forecast of ~5" of liquid in Tahoe City is the second highest 2-day October total in 112 year climate history (5.72" is the current record). For Reno, the current forecast of near 2 inches of rain would be a 2-day record for October, with the current record 1.67 inches.

STRONG WINDS:

The HREF ensemble remains very strong with peak wind speeds for Sunday. Hi-Res CAM and NBM guidance showing general agreement with this impending forecast. Ensemble meteograms show the gusts still trending only slightly upwards with a narrowing spread of upper end numbers. 60+ mph wind gusts still appear in only a far minority of ensemble solutions. There is plenty of wind energy aloft and little is going to impede higher wind gusts mixing down to the surface.

The higher wind gusts that do mix in with the more intense precipitation rates may reduce the potential for more damaging gusts. Therefore, there is little need to make any changes to Wind Warnings in effect in the main areas of concern along the western NV Sierra Front and Eastern Sierra areas. We are still looking for gusts easily exceeding 100 mph across ridgelines. These winds will bring periods of travel and recreation concerns along with very bumpy flights for aviators.

FLOODING CONCERNS CONTINUE:

Despite the copious amounts of rain, the dry soils and large amount of available storage in reservoirs will likely mitigate widespread flood risks. That being said, recent ensemble scenarios from the CNRFC indicate low end probabilities (10% chance) for more significant river rises, possibly even near or above monitor stage, with a 5% chance of exceeding flood stage in some locations. Keep in mind, this is likely worst case scenario, but it still bears watching. Smaller creeks and streams and urban/poor drainage flooding is certainly possible as well.

The greatest threat will be the recent burn scars — really any major burns in the past couple of years in the Sierra and/or western Nevada foothills. This will be the first real test for several burns, including but not limited to: Caldor East, Tamarack, Slink, and Numbers. Dixie East, Beckwourth, Sheep, and Walker saw minor impacts from the rain yesterday and now have saturated soils, so this could further exacerbate things there. Higher resolution model guidance is indicating rainfall rates possible exceeding 0.5"/hour at times in northeast California and the Sierra from early Sunday morning through Sunday evening. Mud/debris flows or rock/tree falls are all on the table, so pay extra attention if you are near a burn scar.

SNOW ACCUMULATIONS:

Snow levels will start rather high, around 9,000-10,000 feet, but will fall late Sunday into Monday. The question at this point is how fast will they fall. It looks like Sierra passes above 8000 feet will start to see impacts Sunday night, with those closer to 7,000 feet before sunrise Monday. Snow levels will crash to around 5500-6000 feet by Monday night, but the bulk of the precipitation will have already fallen by this point. Snow totals for the high Sierra (above 8,500-9,000 feet) could reach 2-4+ feet, with the character being heavy and wet. Communities in the Tahoe Basin and those along US-395 in the Eastern Sierra are likely to only see 1-5 inches, but if snow levels fall faster, those totals could easily increase markedly.

Check the latest forecast at weather.gov/Reno and check road conditions with Caltrans and NDOT. For Carson City area updates see CarsonWeather.com.