All large scale features still preforming well as forecasted, with upper pattern morphing toward a temporary REX block near the dateline Sunday afternoon. This is always good for the generation  of tropical and subtropical moisture for storms to feed upon at a later time.

 The eastern pacific upper ridge continues to progress into California as it becomes squashed over the area Saturday. On a smaller scale…..heights increase over Mammoth this weekend as  a short wave moves through the pacific northwest. This has the effect of increasing winds at 700mb and so it will be quite breezy over the upper elevation Saturday and at the same time, temperatures will actually be warmer.  By Sunday afternoon…the ridge axis shifts east into the Great Basin and the door opens to high level subtropical moisture along with stronger gusts over the Sierra Crest. The new 12z Friday GFS has a lot of upper level moisture advection at 700mb (rh) rushing in during the afternoon Sunday….so it is possible that although Sunday morning may be mostly sunny……then by the afternoon cloudy. 700mb winds will continue to increase Sunday PM.

Synoptic scale timing: 

Just using the new deterministic 12z Friday GFS for timing. 700MB (rh) has slug of mid level (50%) moisture into the Sierra after midnight Sunday night increasing to 70% by Monday mid morning then up to 90%  by late afternoon Monday. Initially, this is moisture advection without any dynamics from the subtropical 1st short wave.  Nevertheless, orographically induced light precipitation is possible as early as Monday morning with the chances increasing during the afternoon.  The actual energy and dynamic lift from this 1st subtropical short wave comes through during the early morning hours Tuesday. Thereafter….a larger scale Trof deepens with a vigorous cold front coming through Wednesday afternoon with heavy snowfall both frontal and pre-frontal. Snow levels may drop to 3500 feet by Wednesday night.  700mb winds natural to the Sierra may keep orographically induced snowshowers  going up to about 9 to 10z (UTC) Thursday am.  It is still too early to really predict how much snow we may get. However, the Dweebs have a 1st call of 2.5 feet over Mammoth Mt. by ooz Thursday…..just a guess at this time.

Longer Range: 

The longer range models still has the long wave ridge in the mean back between Hawaii and the dateline which is good. However, the GFS is beginning to display typical characteristics of Spring with an incipient trend of cut off lows during week 2. Once we get to March which typically begins cut off low season, week 2 reliability begins to diminish.  Additionally…looking at the fantasy charts of the GFS, the energy coming off Asia and Japan becomes split.  This often times creates a split flow pattern for the west coast. Of course, where the split occurs is what is important.

Although March is typically a very wet month on the average, this is an La Nina year. La Nina winters are usually more intense but shorter precip seasons. It may be that Cut-Off low season will begin earlier this year?

Future timing of “significant energy” through west coast “week 2”.

1. Night of Friday the 18th

2. Thursday morning the 24th

Dr Howard and the Dweebs…………………………….:-)

Reference Glossary of Weather Terms
Disclaimer: I have been a hobbyist meteorologist for over 30 years here in the Mammoth area and I do this for my personal enjoyment. The National Weather Service saves lives every day . . . I do not. When making important planning decisions please use information provided by the National Weather Service as they are the most knowledgeable and accurate information source available today.