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KEY MESSAGES

* Dry conditions persist through the rest of today with gusty winds this afternoon. * The next impactful storm arrives tonight bringing gusty to strong winds with rain and high elevation mountain snow through Wednesday. Flooding potential persists with this weak atmospheric river event, but flooding confidence remains low.

* Warmer and drier conditions return late this week into the weekend. Although, there are hints of a weak system this weekend into early next week.

DISCUSSION

Dry conditions continue going into the evening with temperatures steadily climbing. However, chances for precipitation will begin to creep into the Sierra and NE CA tonight (increasing around midnight) as the next system approaches with winds gradually increasing late afternoon and this evening. Forecast guidance depicts an Eastern Pacific low splitting into a closed low that moves more into the Pacific and a shortwave trough that will pass through the PacNW on Tuesday into Wednesday. With this happening above, moisture from a weak atmospheric river will be pulled into the area. Tuesday still looks to be the peak day for precipitation with the Sierra and NE CA seeing a 65-85% chance, the Sierra Front seeing a 35-45% chance, and the NV Basin and Range seeing around a 10-20% chance of isolated showers. Precipitation chances gradually lessen going into Wednesday with the last of the showers ending in the Sierra around late Wednesday afternoon.

As for what to expect for actual precipitation: snow levels will raise to above 9-10 kft resulting in most of the area seeing a p- type of rain with snow showers limited to the those elevations elevations and above particularly in the Eastern Sierra in Mono County. Forecast snowfall accumulations in the higher elevations of Mono County still look to be 1 to 4 inches with 10-30% chance of over 4 inches of snow in the Eastern Sierra crest by Wednesday night. The character of the snow will be very wet with snow-to- liquid ratios of around 2-6:1. Snow levels do come down to 7.5-9 kft by Wednesday evening, so there is a chance snow may mix into the lingering showers on Wednesday.

For the majority of the region seeing rain: the higher QPF amounts will stay west of the CA/NV border through this system. The Sierra crest has the highest QPF amounts ranging between 1.5-2.5 inches with a 15-35% chance of greater than 2 inches. The other portions of the CA mountains from western Lassen County down to Mono County will see around 0.5-1 inch of QPF with the lower elevations of the Tahoe Basin seeing up to 1.5 inches. As spillover is expected to be limited, the Sierra Front areas have around 0.1-0.3 inches of QPF in the forecast by Wednesday night while the NV Basin and Range could see up to around 0.1 inches. Localized flooding and ponding in the region may be a possible during this time. Please refer to the Hydrology section for more info on this.

Another concern with this system is the strong winds that it will bring to the region. The Sierra crest and the highest peaks expect to experience gusts over 100 mph with areas along US-395 and those at Lake Tahoe level will see gusts up to around 35-45 mph. A Lake Wind Advisory has been issued for Lake Tahoe beginning tonight lasting into Wednesday. Western NV wind-prone areas look to have a 40-70% probability chance of gusts over 40 mph. Winds then will gradually decrease on Wednesday as the system moves out with an upper ridge moving over the area.

Drier and warmer conditions are expected from Thursday into the weekend. Long term guidance shows another potential system to begin March with signs of a trough moving into the area, but there's good uncertainty in timing and details this far out. -078

AVIATION

VFR conditions expect to persist through this evening. The next system looks to move into the region from the west late tonight allowing for areas of MVFR to IFR conditions with mountain obscurations to become likely. Sierra terminals begin to experience rain shower chances generally after 23/06Z though KTVL may see vicinity showers a few hours before. Ahead of the system, KMEV=KTRK-KTVL winds increase with southerly gusts around 20 kts around 23/02Z. LLWS and turbulence returns after 23/00-03Z due to FL100 winds increasing to 40-55 kts and then up to 60-65 kts around 23/09-10Z. -078

AVALANCHE

No snow is forecasted for today with partly to mostly cloudy skies.

The next storm arrives tonight and peaks on Tuesday with more rain and high mountain snow above 9 to 10 kft, as well as gusty winds up to 90-110 mph at the highest peaks.

Snow levels come down on Wednesday afternoon to 7.5-9 kft for the Tahoe Basin, and for Mono county on Wednesday evening, when precipitation chances taper off. However, there may be some lingering low shower chances going into early Thursday.

Liquid amounts continue to fluctuate with this weak AR event. In the latest NBM probabilities, there is a 15-35% chance of 2+ inches of liquid at the Sierra crest from the Tahoe Basin northward between tonight and Wednesday evening with the Eastern Sierra having a <10% chance. Current storm totals haven't changed much from the previous forecast: around 1.5-2.5" in the Sierra crest around the Tahoe Basin, 1-1.5" below the crest. For Mono County, 1-2" near the crest from Mono Lake and northwards, and 0.5-1.5" south of Mono Lake near the crest. Below 8 kft in Mono County, 0.5-1.0" of liquid is forecast.

SLRs will be 2-6:1 above 9-10 kft with snow accumulations of 1-6" with isolated higher accumulations from Mono Lake southwards.

Ridgetop winds decrease on Wednesday to 50 to 80 mph.

-HC/078

HYDROLOGY

Rain at all but the highest elevations during the weak atmospheric river will lead to rises on rivers and streams throughout the area.

The now expansive low elevation shallow snowpack (below about 5500 feet), will contribute additional runoff as it melts with warm temperatures, rain, and high winds. The deeper and colder high elevation snowpack (above about 7000 feet) is expected to retain most of the rainfall, but warm significantly during the event. How the now significant mid elevations snowpack responds to the rain is an area of greater uncertainty.

The greatest flooding concerns is for mountain urban areas where deep snow large plow berms may block drainage systems and funnel runoff into unexpected areas.

Flooding from rivers and streams is not currently expected, but minor flooding is possible along if rainfall exceeds expectations. Current forecasts show about about a 5% chance of minor flooding along the Susan River near Susanville and the West Fork of the Carson river into Carson Valley, and very low, but non zero chances along the Middle fork of the Feather near Portola.

Elevated flows are expected to continue through the week as warm temperatures will impact the recently ripened snowpack.

The River Forecast Center will be extending hours will add a third evening forecast on Tuesday for river points where flooding is possible. Check for updated river forecasts at: www.cnrfc.noaa.gov

-TB

REV Watches/Warnings/Advisories

NV...Lake Wind Advisory from 7 PM this evening to 7 PM PST Wednesday NVZ002.

CA...Lake Wind Advisory from 7 PM this evening to 7 PM PST Wednesday CAZ072.