February 15, 2024 – Overall active weather persists through the end of this week into early next week, with a few brief breaks in between systems. Periods of widespread Valley/foothills rain, mountain snow (heavy at times), and gusty winds are expected with each system. The strongest storm is expected early to mid next week, with heaviest rain and snowfall on Monday (Washington’s Birthday.)
Discussion
A fast moving system continues to bring scattered mountain snow showers this morning. Current radar shows heaviest showers over the northern Sierra, with snow levels around 4,500 feet. Caltrans continues to report widespread chain controls for many mountain roads. For current road conditions, go to quickmap.dot.ca.gov.
High resolution models show these showers diminishing through the morning, so the Winter Storm Warning for the northern Sierra and the mountains of western Plumas County/Lassen Park now will be ending at 10 am. Precipitation chances by this afternoon will be mainly limited to showers over higher terrain and the northern Sacramento Valley.
Some isolated heavier showers are possible over Shasta County late this afternoon and evening before the system exits the area entirely. Valley high temperatures will trend a little milder today, with some sun breaking through the clouds in the afternoon.
Moving toward the end of the week and into the weekend, ensemble guidance remains in good agreement on a ridge progressing across the region. This will bring dry weather during the day on Friday, along with a slight warm up back to near normal high temperatures. This period of calm will be relatively short lived, however, as a leading shortwave ahead of a deepening trough over the Pacific begins to impact interior NorCal on Saturday.
Another round of light to moderate Valley and foothills rain, moderate to occasionally heavy mountain snow, and gusty southerly winds is expected as a result. Heaviest precipitation is anticipated Saturday night.
Wind continues to trend a little stronger for the northern Sacramento Valley and adjacent foothills, peaking Saturday night. This does look to be less strong than the wind event in early February, but will continue to monitor forecast trends leading up to this event. There is a currently 30-50 percent probability of wind gusts to 40 mph or great for the northern Sacramento Valley, 45-76 percent for the adjacent foothills.
As for precipitation, overall forecast totals continue to be 0.5 to 1″ of rainfall possible through the Valley and foothills and up to 1 to 3″ of liquid equivalent possible across the northern Sierra and into northern Shasta County.
The trajectory of this shortwave looks less favorable for orographic enhancement of snowfall so as a result snowfall accumulations continue to look much lighter than compared to the midweek system. Latest NBM probabilities of exceeding 4″ of snowfall are in the 40 to 75% range above 6000 feet, with probabilities of exceeding 8″ in the 10 to 40% range, but generally confined to higher mountain peaks. Snow levels have trended a little higher for the event around 5,500 to 6,500 feet.
Moderate impacts are currently expected for this event, with travel delays and chain controls, especially during the heaviest snowfall Saturday night.
Sunday, there will be a brief period of shortwave ridging over us, before a large closed upper low off the CA coast brings yet another round of moderate to heavy rainfall, mountain snowfall, and gusty southerly winds at least through next Tuesday.
Lingering showers are expected in the foothills and mountains are through the morning Sunday. Latest guidance indicates a brief lull in the precipitation Sunday afternoon before the next low shifts inland bringing another wave of precipitation and gusty winds to the region overnight into Monday.
This will be the strongest of this set of storm, bringing more moderate to heavy rain to the region. High mountain snow spreads in Sunday night, with snow levels initially 6,500-7,000 feet.
Extended Discussion (Monday through Thursday)
The latest National Blend of Models (NBM) is showing a 45-75% probability of exceeding 1.00″ of rainfall in 48 hours for Monday- Tuesday across the Valley, with 30-60% probabilities of exceeding 3 inches in the mountains and foothills.
NBM 48-hr (Monday- Tuesday) snowfall probabilities of exceeding 18″ or more are 30-50% along the I-80 corridor, with probabilities of 40-80% south of Highway 50. Snow levels are forecast to be 5000-6000 feet.
Gusty southerly winds are possible as well, but confidence on how strong the winds will get is low at this point. Even so, the latest 24 hour max wind gust probabilities indicate 25-45% of wind gusts greater than 40 mph. Winds continue to look less significant than those observed on February 4th.
Beyond Tuesday, Cluster Analysis and Ensembles diverge a bit, but the mean indicates we will continue to be influenced by the closed low through at least mid week next week, before heights begin to increase, leaving drier and warming weather for Thursday.
Make sure to check road conditions frequently and check the forecast often for updates, especially if you have holiday travel plans. Forecast uncertainty persists regarding exact timing, precipitation amounts, and exact wind speeds so keep up to date with the latest forecast by checking our social media and website.