Marine Weather and Tide Forecast for Truckee, CA

DISCUSSION

The persistent blocking pattern that produced valley inversions and areas of freezing for more than a week is finally expected to weaken this weekend. Current coverage of freezing fog/stratus remains mainly limited to the Honey Lake basin of southeast Lassen County including Susanville, with a few patches of fog/stratus into the northwest NV deserts and around Pyramid Lake. Based on trends of recent days, the fog should ease around Susanville between daybreak and mid-morning, but could linger along US-395 between Doyle and Janesville through late morning.

By this afternoon, a weak trough brushing across far northern CA/NV will flatten the ridge and weaken the inversion. Although surface winds aren't expected to increase very much, the cooling air above the surface along with swaths of mid-high level cloud cover are more likely to scour out most of the fog/stratus around the Honey Lake basin. Otherwise, we are expecting a milder day with temperatures pushing into the mid-upper 50s for the urban areas of far western NV, and into the Tahoe area/Alpine County communities.

Precipitation is not anticipated with this weekend's system, except for a 15% chance of a few very light showers (less than 0.05") near the OR border this evening. The second stage of this weekend's trough passage will occur with a shallow dry cold front dropping in from the north late Sunday/Sunday night. This will further help scour out any leftover inversions that didn't get fully cleared out today, as winds shift more to the north.

The main effects of this front will be a notable cooling with highs on Monday only in the lower-mid 40s, with areas north of I-80 struggling to reach 40. Also, northeast-east ridge top winds will strengthen Monday-Monday night with potential for gusts of 50+ mph. A shortwave ridge then returns Monday night-Tuesday and may re-introduce inversion conditions and patchy freezing fog again around Honey Lake, although this isn't likely to be as strong or persistent compared to recent days.

By mid-late next week, weak shortwave passages will help re-open the storm door which has been largely shut since Thanksgiving.
While light showers could return late Wednesday into Thursday, the medium range ensemble guidance is trending toward a wetter outcome from late Friday into next weekend. While there remains some variance with the storm track and timing, a larger percentage (60-70%) of the cluster guidance is projecting decent moisture (greater than 1" liquid for the Sierra) with potential snowfall of 1 foot or more in higher elevations, and chances are increasing for the first meaningful snowfall (6+ inches) of this season down to the Tahoe basin as well. Some of the more aggressive outcomes bring potential for 3-4" liquid (2 or more feet of snow) near the crest and pull in enough cold air for snow levels dropping to many western NV valleys by next Saturday. The signal for a more active pattern in mid-December has been present for a while, but these stronger/wetter storm scenarios are a more recent trend that bears watching as we get closer to next weekend. MJD

AVIATION

Valley inversions again this morning will keep haze with minor reductions in slantwise visibility around the far western NV terminals. These inversions are expected to weaken as the weekend progresses, with haze gradually diminishing. VFR conditions with generally light winds will prevail through early next week, although increasing NE-E FL100/ridge top winds will produce increased turbulence near/west of the Sierra crest from late Sunday night through Monday night.

Low clouds, freezing fog and IFR/LIFR conditions will continue to linger around the Honey Lake basin and Susanville Airport (KSVE)
through this morning, with some improvement likely later today and less potential for fog returning to KSVE tonight. MJD

REV Watches/Warnings/Advisories
NV...Freezing Fog Advisory until 10 AM PST this morning NVZ004-005.

CA...Freezing Fog Advisory until 10 AM PST this morning CAZ071.