Inversions weakened over the past 24 hours and Mammoth AP Thursday morning which was -20F. This mornings over night low only was only +1F.  The strong upper ridge and surface high that kept the cold Arctic air from the previous storm trapped in the lower high elevation valleys this week is weakening…..

The next changes to our pattern:

1. Upper cut-off low off LA is currently ejecting through Southern Ca today bringing a few showers possible to the higher terrain.

2. A Northwest slider off the Southern BC coast is acting as the kicker. This system will develop quite an impressive upper jet the next 48 to 60 hours, after which couples with a mid latitude jet  into NW California  Saturday. No doubt there will be an increase of wind over the Sierra Crest later Saturday Afternoon with stronger winds Sunday into Sunday night.  The new 12z Friday GFS shows 300mb isotachs over NW Ca at about 70 knots which then increase to 110knots by 4:00am Sunday.

By late Sunday afternoon, the upper jet at 300MB is diagonally slicing through Central NV with a 135 knot upper Jet. This will keep the upper elevations of the sierra crest winds going….bring further cooling to our region and even the slight chance of some flurries or snow showers as the right rear entry region passes off to the southeast on Monday. Daytime highs for Monday in Mammoth will drop to the low to mid 20s.

3. In the systems wake…colder air will advect in. This will eventually be the lifting mechanism for several mid latitude short waves coming up from near Hawaii Tuesday….Wednesday….Thursday and Friday. These will be all warm advection precipitation producers. Will it be light or moderate in amounts?  Too so0n to tell. Warm  advection precip is some of the most difficult to forecast here in the Eastern Sierra as far as amounts. So for you snow plowers…..don’t take that trip to Mexico just yet. Your hall passes are canceled until we see if the  proposed “January Thaw” is going to be real or not!

4. The long range models are deepening the Hudson Bay Low in last nights 0000 UTC GFS  500mb Height/Anomaly Forecast 7 Day Mean, Centered Day 11 (10 days out). This looks like a January Thaw Pattern.  However, looking at the new 12z Friday deterministic run of the GFS , I have my doubts on how long any period of fair weather will last, as that key negative height anomaly (Hudson Bay Low) does not seem to like the Hudson Bay area very much this year. Thus, any strong loading of the +PNA will probably be short lived?

As usual…we’ll see how it all develops……………;-)

The Dweeber

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.