Both WPO and EPO to remain in negative phase this week providing a nice high latitude block to the Westerlies……Energy and cold air now pooling up over the mid latitudes of the Mid Pacific…..Upper Jet to make a Run for the West Coast later this week…..
Monday February 2, 2015
Posted at 9:49 am by Howard
Spoke with the King WX Dweeb T. Cylke this afternoon. He gave me some kind words of advice. Never trust a warm storm of subtropical origin such as this one, in trying to predict snow levels. Why? Because of Micro Physical processes that can allow snow to fall at unusually low levels. This morning’s WX discussion from WSFO forecaster Wallman mentioned that there is an isothermal between 10K and 6500. ISO thermal layers can allow snow to fall to much lower elevations as the temperature in this case could become trapped near freezing through the layer. This would have the result of allowing wet snowflakes to fall to much lower elevation then expected.
The point is “All bet off on the snow level”…….Just know that it will be rising and falling a lot this weekend….
Additionally, I am “Out Voted” on the term Pineapple Express. Although “I do not agree” that this particular event is the colloquially known pattern of the Pineapple Express, in other words this particular version of an AR. Two noted and respectable Meteorologists disagree…..So I yield……;-)
Wednesday AM Update:
Some positive information coming out from the CRFC this morning. It appears that most of the precipitation over this region will be occurring Friday night into Saturday during a colder period of time. The SL is usually about 500 feet lower at night and the cool sector is in with the first wave Saturday. So we should get a nice shot of snowfall on Mammoth Mt Friday Night into Saturday afternoon. The snow level looks low enough for some 2 to 5 inches of accumulation in town near and above 8000 feet with last night’s guidance. There looks to be a break Saturday night through Sunday afternoon with only light showers in the forecast. That is certainly good news as the Freezing level goes up Saturday night and especially into Sunday to 10,500 feet. But little precipitation is expected. The next wave moves in Sunday evening and between the evening and midnight the freezing level is at or little above 10,000. So rain is likely Sunday night in town until midnight. The snow level is above 8500 to about 9K with rapidly lowering snow levels after midnight and into Monday AM. I expect 3 to 6 inches in town by Monday Noon at the Village by this 2nd wave. Mammoth Mt will have 1 to 2 feet of sierra cement above 9,000ft. by Monday Noon storm total. All in time for the Presidents Holiday weekend!!!!!
We ridge up again later next week as the high latitude block retrogrades and weakens. However, during weeks 3 ands 4 according to the CFSv2 Weekly Climate Anomalies, high latitude blocking returns to both the EPO and WPO region as they turn negative of sign. Thus more undercutting of the East Asian Jet is expected along with its extension to the west coast. At the moment, total precipitation for the month of February is expected to be 125% of normal. This is considering this weekends storm as well as the storms expected during the 2nd half of February. Based upon the same models temperature anomalies, it has been indicated that the last week of February will be below normal in temperature. That below normal temperature anomaly is expected to extend into the first 10 days of March. At the moment, March is expected to be 160% of normal precip wise.
It is interesting to note that during that 1st ten-day period, the emphases in the model as far as precip shows that a higher percentage of normal is expected from the sierra crest to the Nevada border. May the model be suggesting a Tonopah Low during the 1st 10 days of March? The Model continues wet through the 20th with rising temps between the 10th and the 20th. Please keep in mind that this is not a forecast. It is an outlook. There is a difference!
Tuesday AM Update:
The town is buzzing with weather rumors so I’ll give you all the straight scoop! First of all this not a Pineapple Connection or Pineapple Express. Those are specific patterns that combine specific anomalies across the northern pacific. You may very well read or hear about this being a pineapple express. However that term does not apply here. However, this is an “AR” event, or formally an atmospheric river event. Here is the difference, all pineapple expresses are AR events, however, not all AR events are Pineapple Expresses.
I can go into and explain the pattern of a Pineapple Express, but I will save that for another time.
An “AR” event is one in which contains specific criteria of PWAT for its terminology. PWAT or Precipitable Water is simply the depth of water in a column of the atmosphere, if all the water in that column were precipitated as rain. It is a factor in how much precipitation is expected within a time frame of a storm. The “AR” is a stretch of moisture that extends some distance off the west coast, and in this example, that contains at least the criteria of an AR via PWAT.
Tuesday AM Update:
CRFC came out this morning with a whopping 3.37 inches of water between this Friday and Monday AM. Keep in mind that this moisture is still coming through the west coast ridge so it is warm. Nevertheless, it is expected to reach the Sierra and slightly beyond. The Desert areas for the most part will be shadowed out like Nevada and Bishop. But at least it is something that will insure much better ski conditions for Mammoth Mt for the Presidents holiday. Snow levels will be high throughout the storms…But will vary.
In the beginning on Friday, as moisture increases, there will be a cooling effect due to the drier air and low dew point. As the air mass juice’s up, the snow level will rise. And, depending how saturated the air mass becomes locally, and where the freezing level is, will govern the snow level. By the fact that CRFC is painting over 3 inches of water, it appears that the air mass will become very saturated at times. So there maybe times that it will rain all the way to the top and times when it will snow down 7K or 8K. Typically, the snow level in a normal storm is 1,000 to 1500 feet below the freezing level. However, when the air is totally saturated, it can equal the Freezing Level. So variable amounts of moisture, (RH at the 700MB), relative to the freezing level will for the most part determine the snow level. The good news is the on Saturday when the freezing level is really high, the QPF that day is low.
Here are the freezing levels for Yosemite by 6 hour increments expected Friday through Monday AM. Courtesy of CRFC-You make the call! 😉 10.4 = 10,400ft etc
Friday>>> Sat>>> Sun>>>> Mon 10.4/ 10.0/ 9.8/ 9.5/ 10.3/ 11.1/ 11.9/ 11.1/ 10.9/ 10.2/ 9.9/ 8.8 10am 4pm 10pm 4am 10am 4pm 10pm 4am 10am 4pm 10pm 4am
So the best chance of lower elevation snows would be early Saturday AM around 4:00am and again especially (Sunday Night into Monday AM)
We could see between 1 and 2 feet above 10K by Monday AM
As highlighted above, the WPO (Western Pacific Oscillation) and EPO Eastern Pacific Oscillation are now both in the Negative mode, providing a block over the high Latts between the Gulf of AK and Eastern Siberia. This in effect forces Upper Jet energy to “Under Cut” this block. This favors an “AR” event for Northern CA northward. Additionally, this is well supported by the MJO as it moves into phase 8 next weekend. The block is “retrogressive” and so heights will again begin to fall in the EPO area then WPO area leading to the strengthening of the West Coast ridge week 2.
While the eastern pacific/far western ridge continues to reign over the Golden State, there is now hope for heavy precipitation for at least Northern CA; The Wine Country Northward. For the Sierra, the story is the same temperatures wise as this pattern also keeps heights in the mean, very high over most of the state. This spells out for the most part, high elevation snow as 500MB heights in the mean remain well above 570DM over Mammoth Lakes. Considerations for the snow level are; the time of day, IE the timing of the waves either day or night. (SL) +/-500 feet. How saturated the air mass is over Mammoth. A fully saturated air mass can keep the snow level very close to the freezing level barring any mico-physical processes. Where as usually the snow level can range from for 1000ft to 1500 feet below the freezing level. Although it is possible there may be a few waves that lower the snow level + or – of 8000 feet. The freezing level is expected to range up and down of 700MB (10K ft) next weekend. So the snow level will probably average about 9,000 feet next weekend. Latest CRFC shows the freezing level coming down Friday Night about Midnight to 9400. That could drop the snow level to between 8K to 85K. May be a few inches piling up just above the Village by Saturday AM. Beyond that wave that finishes through Saturday, the 12Z ECMWF has another large plume of moisture at 700mb moving in Sunday about 12:00 Noon into Monday. I am not sure what to make of it as the GFS does not show it at all…..
So the ridge is not going away anytime soon, it is just being forced to flatten and shift a bit east as a result of the Strong Upper Jet. At this time, the Southern 3rd of the state looks to stay out of the precipitation. Although it is a bit early to forecast amounts of snowfall, best guesses for this time frame is that Mammoth Mt could pick up a good foot of heavy wet snow next weekend at and above 10K Ft. with 6 inches or so at the Main Lodge Friday/Night. The Dweebs will fine tune later this week. No doubt amounts will range up and down depending upon which model you look at. The following week looks dry up to the 15th but there is still that question about the ECMWF for Sunday afternoon into Monday.
As mentioned in the last discussion, precipitation is expected to come back to the high county along with much cooler temperatures later in the month of February and into March. Although there is no real defined period of time that it will begin with any confidence, the last week of February looks to me to be of best interest…..
Update: 5:10PM Monday:
New 02z run ECMWF EPS Weeklies shows a change beginning “the end” of the 3rd week of February. It shows retrogression of the Eastern Pacific High and a cold pattern setting up over the far-west the last week of February.
Will update later this week………………………….
Dr Howard and the Dweebs…………………………:-)