A Transition in the Weather Pattern from Warm to Cold this Week is Certain….Light snowfall looks likely….Cool Breezy Weather is Expected Next Week….Then March Roars in Like a Lion…..
Thursday February 19, 2015
Posted at 9:32 am by Howard
Monday AM Update: 7:25 AM
8 Inches of fresh dry powder here near the Village at Mammoth and still falling…..
Upper cut-off low is still wobbling around and over Central CA today. So there could be a little more snowfall depending upon where the snow bands set up. Another trace to as much as an inch or two is possible over Southern Mono Country up until this evening…..The low gets the boot out tonight from another approaching short wave……The next upstream system for Wednesday afternoon is pretty weak. It looks to be mostly clouds and breeze. The following short wave will bring the potential for more snowfall later Friday into the weekend. Amounts will be dependent upon how far west the up-stream ridge builds… See discussion below…………….
Sunday Night: 10:00PM
5 inches of snow at the 8200 foot level just west of the Village at Mammoth…..Still snowing lightly….
Few comments about the pattern in the future…
The storm track next weekend is still a bit east for a good heavy snowfall producer. The GFS has the upper ridge retrograded to about 145W and the ECMWF has it closer to 140W. A sharp ridge at 140W is an inside slider pattern and 145west puts the upper jet far enough off shore for some over water trajectory and a better chance of some moderate snowfall. The 00z 23rd ECMWF retrogrades the upper ridge to 145W for the subsequent short wave for the following Monday/Tuesday. Overall, the trend looks good for the month of March.
The Dweebs expects more retrogression with time through the month of March due more as a result of the climatic effect of the transition of winter into Spring. Thus the effects of the warm version of the PDO begins to lose its grip on the west coast as the CONUS begins to warm up over time. The Dweebs would be very surprised if Mammoth Mtn did not get at least one good storm cycle type dump in March of several feet. Weeks one and two calls for discontinuous retrogression of the eastern pacific ridge through the period. The inter-seasonal model, CFSv2 still shows the possibility of an anomalous period of wet in March, beginning about Mid Month…
Some light to occasionally moderate snowfall has fallen this morning and is continuing into this afternoon…. I have about 2 to 3 inches on the deck at a temperature of 24 degrees. “Nice and light” The Dweebs did not put out a Platinum Powder alert yesterday and no alert was put out this morning as the criteria of a foot or better at 15:1 is not expected. Nevertheless those that are skiing or boarding over the Upper Mtn will be enjoying some very nice, light, dry powder! 🙂
Looking at the 12Z NAM model this AM, the 700mb RH, wind and OMEGA parameters showed the deformation axis to the south of Mammoth…..this afternoon and evening. Thus the focus as mentioned yesterday still appears to be mostly to the south of Mammoth for the most generous QPF.
Amounts in general still look good in the 4 to 8 inch range over all by morning. The highest amounts would be over the higher terrain and boosted a bit due to the Snow to Water Ratio. The storm track for the up coming week looks like it will be down over the interior of the west coast. Although there may be some over water trajectory to boost amounts next weekend, no long fetch or subtropical entrainment is expected. The ECMWF continues to show it cold with either Interior west coast or inside slider type short waves in this pattern. The pattern will remain progressive and so no Tonopah Lows or Great Basin cut offs are expected at this time. Later in the week there is a stronger short wave with an upper jet that will likely bring some significant wind to the region, just prior to the weekend.
The 12z NAM Model is pretty dry over Fresno and Reno with this system. However, this looks more to be an Eastern Sierra to the crest type storm with upper divergence over the sierra 1st Saturday night, then as the upper low develops Sunday afternoon into Monday AM, a deformation zone sets up over the central sierra and shifts south through Mammoth down into the northern part of the southern sierra. There will be a upslope component to this system as well for the Central Sierra. Again although the NAM model is pretty dry, the system has a lot of cold air to work with and so dynamically the feeling is that it will be strong enough for general amounts of a quarter to one half an inch over and along the eastern slopes of the Central Sierra with the possibility of some localized areas of up to an inch of water. The period of the heaviest snowfall will be between Sunday Night and Monday AM. So at least 3 to 6 inches of snow along the eastern slopes is reasonable. However, where the exact location of the deformation zone sets up could allow for up to a foot+ in some areas.
According to HPC , there will be areas over the northern part of the Southern Sierra that may get up to an inch+ of Water Eq. Considering the snow to water ratio which will be much higher with this colder system, amounts of a foot+ in some favored areas of the eastern slopes would not be surprising. The exact location of those areas look a little south of Mammoth. Where a combination of deformation, (surface convergence), combined with the most favored areas of “Upslope from ENE flow” could result in snowfall total amounts of 12 inches plus of light fluffy snow by Monday afternoon. Although those highest amounts may include, Mammoth Mtn, it is not certain…..
Dr Howard and the Dweebs……………………….:-)
Want to know “one” reason why its been so dry with such a persistent ridge over the far west? Check this out. SEE: http://margaret.atmos.washington.edu/pdo/PDO.latest I challenge anyone to find a +PDO indice for the months of December of 2014 and January 2015 for the past 115 years as off the chart as it has been! Not since 1941 has the +PDO been so wacked out! All that unusually warm water along the west coast up into the Gulf of AK has “helped” support an unusually strong Eastern Pacific ridge off the west coast. This is not the only reason of our persistent drought. However, this is a big supporting player this year.
Here are some interesting items to ponder about.
1. According to the Jamstic, the AMO will crash this year and so the Atlantic will cool, especially over the western Atlantic north to the NW Atlantic. Odds are the +PDO will weaken at some point before the end of this year. The new ENSO outlook from Scripps shows El Nino taking another run for the tropics.
According to Scripps;
What might be more interesting to see is how well the model performs. The correlation in the model does quite well at a 6-month lead time over the tropical Pacific strip, and quite respectably at a 12-month lead time.
We’re in the 2nd half of February now. Typically, even during drought years, the weather tends to turn wetter in late February and especially March. The models all agree now that we will be much cooler this weekend into next week and beyond. But how about some snowfall?
Here is what the Dweebs See: All short-term models are in agreement in bringing a much cooler air mass arriving this weekend for the Great basin and Sierra. In fact I see High temps falling as much as 25 degree by Sunday over todays highs. Cooling is almost always associated with cold air advection and…….Wind! So it will be windy over the Sierra Crest Saturday, but breezy in town. Nothing out of the ordinary for the sierra crest like 60mph, w/gusts to 70+ mph on Saturday. The tend later next week is for colder weather with the chance of Snow.
What is happening is that the upper west coast ridge is sharpening and backing up to about 128 W, tapping some CPK Air (Continental Polar) which is typically dry. We have seen this pattern before this winter. This time the upper flow is backing up west, a little further north. The effects will be to spin up an upper jet to the south of us which will benefit extreme Southern CA, ENE to the South Central Rockies, via Northern AZ. LA and San Diego south to Rosareto, MX will get rain late this weekend into Monday.
Mammoth remains mostly in the convergent quad of the upper jet, both front and rear throughout the process. So cold showery weather is the most likely outcome for later in the weekend into Monday, as an upper low forms over the White MT’s of CA/NV Monday AM and shifts ESE over the following few days. The upper low does open up into a short wave Tuesday night over NW, AZ, as additional short wave action in the NW flow aloft, gives it the boot. As a note; although it is a long ways out, there looks to be an area of possible deformation, (surface convergence) forming Sunday night. Then some possible upslope over the Central Sierra that might enhance snowfall up to a few more inches…..or possibly more by Monday AM the 23rd. (well see how the models do later this week)….
A Dry NW Flow is expected next week prior to the last weekend in February, so the 60 degree high temps at the resort levels of late, and mid to high 70s in Bishop will definitely be gone from the Eastern Sierra and Mammoth Lakes forecasts. The American GFS model currently has the upper jet moving south through Mammoth the following Saturday AM with a nice storm accompanied by a long fetch of over-water trajectory, Saturday into Sunday. The ECMWF Control which I regards as the “Better Model for “Week Two”, is drier, as it takes the short waves inland to the north of us in a NW flow Aloft Pattern. This is still a cold pattern, but would be showery precip wise as well as windy, vs. a heavy snowfall pattern like the GFS shows. I should mention that the ECMWF ensemble is further west with the track, more of a blend between the two. So what we may end up with for the last weekend of February is a cold weekend, with moderate, beneficial snowfall, but not to the extent that the GFS is touting……
Additionally, I want to acknowledge that there are concerns about the fruit trees that are blooming in both the Owens Valley and even locations like the top of the grade at Sunny slopes. Unfortunately, the cold that I see in the future will be pretty intense as we transit from late February into March. I see plenty of hard freezes in early March….
If you remember last Fall, the buzz around town was that AU was having an incredible winter and that Mammoth Winters always follow what Australia does the winter before. As you can see by the results from the past year…there is no credible linkage between the two locations. So just because we or AU has a wet winter means nothing for the other location….otherwise it is just coincidence.
Dr Howard and the Dweebs…………………………………..:-)