February 26, 2024 – A weak system today will bring some showers and mountain snow showers. Active pattern will return late week into next weekend bringing widespread precipitation, heavy mountain snow, gusty winds and even some low elevation snow accumulations. Following the cold system, expect abnormally cold temperatures, with Valley temperatures near freezing and morning frost.
Discussion today through Thursday
Through today, an inside-slider will move into the Great Basin and phase with an area of low pressure off the California coast and weaken as it continues to dig towards the southeast. The majority of precipitation is still forecast to fall across the Sierra, given the track and quick moving nature of the system. As such, Valley rainfall totals have continue to trend drier, with the majority of Sacramento Valley forecast to receive no measurable precipitation now.
Snow levels are forecast to be 5500-6000 feet ahead of the front, before lowering to around 4500-5000 feet tonight with the frontal passage. Latest hires has decreased by about half for snowfall totals from 12 hours ago. Confidence on the snowfall totals for today’s system is pretty low given the large spread in snowfall totals just within the hires models and based on the latest trends, now indicating anywhere from 0″-8″ is possible along the I-80 and Highway 50 corridors.
Breezy southerly winds will accompany this system as it moves through the region, with some wind gusts of 20-25 mph possible mainly Monday late morning- afternoon across the Valley.
As we move into Tuesday, dry northerly flow behind the front will bring some breezy north winds across the Sacramento Valley Tuesday morning through the afternoon. Strongest winds are forecast to be north of Sacramento along the I-5 corridor, where gusts to around 20-30 mph. Tuesday morning low temperatures will drop to near freezing across the northern Sacramento Valley, which will allow for patchy frost to develop. Afternoon high temperatures will climb into the upper 50s and low 60s for the Valley.
On Wednesday, an anomalously cold system approaches the area from the PacNW, beginning to bring some precipitation chances mainly for northern Sacramento Valley and the Southern Cascades by Wednesday evening/night.
As the trough continues to quickly dig into the area Wednesday night-Thursday, southerly to southwesterly winds will increase across the northwestern Sacramento Valley, Southern Cascades, and the Sierra bringing gusts to 35-55+mph.
By Thursday morning, precipitation will continue to spread south across northern CA, with significantly cold heights aloft and upslope enhancement across the Sierra, leading to impressive snow rates and accumulations in the mountains.
Snow levels will initially be around 5000-6000 feet Thursday, decreasing to 3000-5000 feet by Thursday night. Given how anomalously cold this system is, confidence in the snow level forecast is fairly low at this point, and snow levels may drop lower, creating more significant impacts for foothills.
Heaviest precipitation/snowfall is currently expected Thursday night- Friday. The time is NOW to prepare for this *significantly* impactful winter storm.
Extended Discussion (Friday through Monday)
Ensemble guidance is in good agreement on the deep, closed low off the coast of the Pacific Northwest continuing to deepen with a slight southward trajectory toward NorCal as it travels inland across the late week period into the weekend.
This will induce strong west-southwesterly flow aloft into interior NorCal, advecting a deep fetch of moisture into the region as well. With an influx of available moisture, strong lift associated with the approaching trough, and a flow pattern aloft favorable for strong orographic enhancement, widespread rain and mountain and foothills snowfall (heavy to very heavy at times) are expected with this system.
While Valley precipitation with moderate precipitation rates at times will be possible with this system, the bulk of the impacts are expected across the foothills and mountains.
Probabilities of exceeding 1″ of rain in the Valley through Sunday morning are in the 40 to 70% range (highest over the northern Sacramento Valley), with 2″ probabilities falling to 20 to 50%.
A slight (10 to 20%) chance of thunderstorms will also be possible Friday and Saturday afternoons, but will be highly conditional on seeing any breaks in cloud cover to allow for some weak instability to build.
Heaviest precipitation with this storm is expected over the foothills and mountains. Probabilities of liquid equivalent precipitation exceeding 2″ are in the 60 to 95% range, with probabilities of 40 to 80% for liquid equivalent precipitation exceeding 4″ over the Sierra and northern Shasta County.
While there is some inherent uncertainty regarding exactly how low snow levels will drop, a few pushes of colder air are expected throughout the lifespan of this storm.
Snow levels will initially be relatively high as the system approaches on Thursday, but will begin to rapidly fall off by Friday morning (3000 to 5000 feet), continue falling into Saturday morning (1500 to 3000 feet), and dropping even further by Sunday morning (potentially as low as 800 to 2000 feet) as the system wraps up.
Snowfall rates of 1 to 2+” at times will lead to periods of heavy to very heavy snowfall. As a result, significant snowfall totals are expected along the Sierra, with impactful accumulating snowfall likely into the foothills as well.
For reference, latest probabilities of exceeding 60″ of snowfall are in the 80 to 100% range above 5000 feet. This will result in near to impossible travel conditions from late week into the weekend.
Additionally, gusty south-southwesterly winds are anticipated with this storm as well. Strongest winds at this time are expected over the Sierra and across the northern and central Sacramento Valley and adjacent foothills locations. Currently, there are 60 to 90% probabilities of wind gusts exceeding 40 mph in these areas.
While additional showers may linger into Sunday, overall minor comparative impacts are expected with any residual precipitation. A period of relatively quieter and drier weather is then expected moving into early next week.
Although, with the introduction of the colder air mass to the region, early morning Valley low temperatures on Sunday and Monday look to drop into the low to mid 30s (coldest across the northern Sacramento Valley). This will result in at least some potential for Valley frost development.