Marine Weather and Tide Forecast for Portola, CA

DISCUSSION

* High pressure ridge remains in control through late Thursday with a very dry airmass in place. Our afternoon sounding on the 21st showed just 0.06" of precipitable water - a record low for the date. We'll continue with dry weather and low humidities. We can also expect morning inversions to return with poor dispersion. Morning low temperatures will be seasonal with above seasonal high temperatures in the low to mid 50s in western NV and mid 40s to near 50 degrees for our eastern Sierra communities.

* On Friday a trough will drop into the northern Great Basin. Then by the weekend, a closed low pressure breaks off from the main flow and digs into California. This low continues its track into the southwest US by the start of next week. One thing to note with this pattern evolution, is that the model ensembles are still having trouble in exactly how and where the aforementioned closed low tracks. Some are quicker and further east while others form a deeper, slower low over CA. Lots of uncertainty in this pattern, which is not uncommon with closed lows.

* What does this mean for our forecast? Given the synoptic cooling, there is higher confidence in below average temperatures throughout the region. But how below average depends on the upper low track. Another wildcard - where it snows, lows and highs will be much lower. For precipitation, models still are consistent in snowfall for the Sierra, especially in the Tahoe Basin south through Mono County. There is far less certainty for any precipitation for northeast CA.
Models still show a formation of a deformation zone in western NV. At this time it favors areas along and south of US-50. But again, the position of this zone may not be fully recognized until Thursday or Friday. Winds become breezy during this time frame, but so far nothing jumps out as significant. But, that too will change! Ensembles in the long term start to show ridging returning to the western US next week, with seasonal temperatures. McKellar

AVIATION

VFR conditions prevail through Friday with generally light winds.
Valley inversions will produce areas of haze with minor reductions in slantwise visibility each day mainly from 15-21Z around KRNO.
MJD/McKellar

REV Watches/Warnings/Advisories
NV...None.
CA...None.