As pattern transition nears….Brutal Cold Still a Possibility before year end……Northwest slider to bring light snowfall Wednesday…..Dweebs watching “week two period” for Model Consensus….Still the possibility of a storm….A cold one….Or a wet one!

Monday PM:

Just a quick comment or two;

The new 12Z GFS run is still keeping the short, medium and long-range dry.  However, the ECMWF continues to develop a pattern involving a block in the WPO and EPO region that is remarkable. So, I will begin to write about it and explain somewhat, the pattern that is evolving in the ECMWF.

All Global Model simulations show over the western hemisphere, a highly amplified long wave pattern with a ridge along 125west that is importing Arctic air into the nations mid-section. However for week 2, the Euro and now the Canadian Ensemble controls are latching on to something very interesting. On Christmas day, the Euro is developing a cold polar vortex near 75N/150E.  It is feeding Arctic Air into another Trof that it is phased along 50 North and between 120E and 140E. That Western Pacific cold trough builds a ridge along 165E that will bubble up over the Bering Sea and couples with another Blocking High over the EPO region (AK) on the 27th. From the Western Pacific east to the Eastern Pacific, the westerly’s have nowhere to go but underneath the block that forms to the north.  Todays ECMWF model simulations show short wave trajectories down through Western Canada tapping (CPK) Continental Polar Air with Cyclogenesis off the Northern CA coast next Wednesday night the 27th. There is a series of these lows that spin-up into the new year.   This would be a cold snowy pattern with Powdery type snow.

For those that are up here over the New Year weekend prior to New Years day, you plan ahead by asking your boss if you could stay a few more days in Mammoth…..Just in case we have one of those “Platinum Powder” events….:-)

 

Remember this is in the outlook period, and subject to change.  But the notion of issuing a platinum powder watch Christmas Day for later next week is exciting!

 

Monday AM:

We have about two weeks left in the year and this is what I see in the models and teleconnections as well as in ENSO and tropical Forcing:

I.

  1. The EURO and GFS are miles apart in their week two outlooks.   The Euro came in wet last night with a good sized storm the end of the year.  There is support for this in their ensembles. This is a good point to consider.
  2. The GFS is dry as a bone in their week two outlook. For you hobbyist’s, if you relying on week two GFS guidance, you have missed the boat. It may be worth it to you to pony up the bucks and buy a subscription to the ECMWF.

II.

Our La Nina has most likely peaked. Watching the SOI, (Southern Oscillation Index), the Index has been moderately to strongly negative the past 8 days and so a strong weakening of positive surface pressure difference between Tahiti and Darwin is occurring. This means that La Nina has possibly peaked and that SST waters are going to moderate warmer, or at the least the negative SSTAs over the ENSO region would be trending neutral in the coming months. Note;  “This may allow the MJO to become stronger further east” and force an extension of the East Asian Jet into the west coast under an Alaskan block at some point.  MJO’s eastward extension is easier when the SSTA’s are not so cold from the dateline east. At the moment, it is the LA Nina’s “base state” that is “inhibiting” the MJO to hold together longer further east. Never the Less, the Negative values of the SOI is saying that the forces of La Nina are on the wane.  I would imagine that there is an air-sea Coupled Kelvin Wave that is involved with all this.

 

Short Term:

The long stretch of very warm air aloft to the degree it has been, is over for the foreseeable future. We have enough retrogression in the west coast ridge to allow shots of cold to periodically bring cooling to our region. Of significance, is a short wave in the form of a NW slider coming south Tuesday night and Wednesday. Although this is still a relatively dry pattern, we could get 3 to 6 inches of cold dry powder from it by Thursday AM.  Beyond that time frame, both EC and GFS has the Arctic opening up for the Midwest and East with very cold Arctic Air invading the CONUS.

The narrow but highly amped upper ridge is forecasted to be at 130W which keeps us cool but dry.

If we believe the ECMWF, serious retrogression develops week two as we head through the Yule Season as a serious cold and wet storm is at hand for year end…… Looking at the MJO RIMM phase space with some incursions by some of the models to phase space 8 and then 1, I’d give it a 60% chance at this time, considering that the GFS has nothing but ridge at 500MB week two forecast outlook.

 

More Later:>>>>>>>>>>>>>>>>>>>>>:-)

 

 

 

 

 

 

Just a short update:

the eastern Sierra will have moderating temperatures early next week before a Northwest slider brings Wind, Cold and Light snowfall.  Snow to water ratios could be higher than normal. For the time being the Dweebs are looking at about 3 to 6 inches Wednesday.  Will fine tune in a day or two. Pattern transition still having it difficulty with GFS showing cold scenario for Christmas eve and the Euro’s cold outbreak more toward the end of the year.  We are talking about modified Arctic air in late December so it will be cold.   However, some ensemble members in both the GFS and EURO are showing undercutting of the westerlies and a wetter system. Another week is need to iron out the differences…I would prefer the wet scenario over the cold one….

 

Stay tuned…..

 

Dr Howard and the Dweebs……………..:-)

Temperature Inversion Peaks today into Friday AM along with warmest temps in this pattern Today and Friday…..Upper west coast ridge really flattens Friday night into Saturday for much cooler temps aloft……Major Change in location of Long Wave Trof may bring Brutal Cold to the Eastern Sierra before Christmas….

December 15th:

The general trend of the models are to weaken the west coast ridge in the coming days and bring cooling and wind to the upper elevations. Although the upper ridge does strengthen early next week. It will not be to the point where it has been as there is another shot of cooling coming Mid Week. The big changes from the past few days in the outlook deal with the Christmas weekend where an inside slider type system affects the far west along with a closed low off the coast of Baja. This continues the dry pattern for the Central Sierra now until after Christmas. Of other concern, is  another opportunity later next week for another very significant Santa Ana wind event for Southern CA.

In general, the models are not handling the transitional pattern change that is upcoming very well at all.  The global models are continuing to flip-flop on the important details. They are not in sync with each other as well. Thus at the moment, long-range confidence in any specific solution is very low. The most that can be said is that it will be cooler in the coming days, breezy or windy at the upper elevations with a few period’s of light snow showers.

 

The Dweeber……………………….:-)

 

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The Dweebs are beginning to see a trend in the Models that may bring a very Cold, “Even for December” air mass to the Eastern Sierra. This is proposed now for the weekend prior to Christmas Day..  In an earlier Discussion’s back in November, I wrote about the possibility of a major cold wave this  December for the Eastern Sierra with “CPK”  “Continental Polar” backing up from Canada, southwestward over the Eastern Sierra.  I reasoned this because of the proposed developing Meridianial  flow in the upper jet, usually associated with La Nina in combination with the negative phase of the QBO.  Over the past few days, the ECMWF has been becoming more consistent with the retrogression of the Eastern pacific ridge,  (due to the MJO going from Phase 7 to Phase 8).  The EC has the formation of a highly amplified upper ridge, currently along the California Coast backing up to about 140 West. The location of this highly amplified ridge is critical to the short wave track and cold 500mb-1000mb thickness pool over the far west.  If the upper ridge axis is a little too east, the track become a bit more east and we miss the exceptional cold over the far west. The GFS model has this ridge axis about 137 west….Too far east at the moment.  So confidence is based upon the Ecmwf being the best model at distance.  The Dweebs will follow the trend, as the trend is our friend…:-)

The bench mark for cold here in the Eastern Sierra over the past 40 years occurred 19 years ago, over the 19th, 20th and 21st.  The Morning of the 20th was the coldest aloft and Dec, 21 and 22nd over the valleys. However, surface antecedent conditions were different then, than they are today.  In the December 20th, Scenario, there was snow cover to lower elevations over Eastern CA, east and north over much of Nevada.  So there was a feed back system or at the least, less potential modification to the on coming frigid air mass.

According to the GFS Reanalysis 500MB charts as well as 500-1000mb thickness, from December 12z 19th, 1990 event, GFS 500MB heights were 513dm along the OR/WA border. The 00z 20 GFS had 515dm at the corners of CA, NV, OR.   By 12Z on the 20th, 500MB Heights were 518mb, so you can seen, there was very little modification that occurred on upper low pressure systems track SE.  According to the 500mb-1000mb thicknesses the morning of the 20th, the thicknesses were indicated to be about 516 just on the west side of the crest near Mammoth Mt.  I recall the thicknesses of 511 near Mammoth AP on the Nested Grid model (NGM). The high temperature that day was 6 degrees and the low at my home, then on Ridgecrest Dr was -12F. I did go down to the Forest Service recording site, east of the corner of Old Mammoth Rd and Main Street later that night of the 20th. I Peered into the instrument shelter, and it showed   -23F below 0.   This is the coldest temp I have experienced in nearly 40 years, living up here. It gave me a new meaning of cold.  The days that followed, were highlighted by frozen pipes all over town as well as all over the Eastern Sierra. When the weather warmed up, flooding from broken pipes were common.  PS. Even Bishop CA got down to -8 a few mornings after and Bridgeport was colder than -30F as I recall. PPS; it was the coldest Night of Lights, then at the Main Lodge, before it was moved to Canyon Lodge. (Fireworks show)

Although it is very early in the forecast game, the forecast progs are not as cold with this system as the Dec, 1990 pattern “at this time”…  Nevertheless, any extended period of below freezing temps, day and night for 5 to 7 days can create a big problem in town.

Another possibility; It is possible that this cold upper low digs west off shore. Unless that happens off the Northern CA coast, A major storm would be likely well to the south of us.

 

 

Peak of warm up in process with Thursday into Friday AM with highest Freezing levels…..Upper West Coast Ridge will begin discontinuous retrogression next week with some interesting possibilities over the next few weeks…..

For the Eastern Sierra, this pattern is still dry for the remaining time of this week, however, there will still be reasons to watch the skies over the next few nights.  The Gemini meteors will be flying tonight through Friday night with the peak of the meteor shower Wednesday night into early Thursday morning.  I guess if there is any consolation about this dry spell, it will be a spectacular night time display with up to 120 meteors per hour possible. This will be the best display of the year as the Summertime Presides meteor shower was hampered by a bright moon. The weather under the mega ridge will be cloudless. Calm winds and temperatures while still cold in the upper elevations, will be seasonably mild for this time of the year. This will make for very good viewing conditions. Constellation Gemini rises during the evening hours in the NE and is high in the sky at 2:00AM Thursday. Meteors will begin flying Wednesday mid-evening from the NE and then in all direction once Gemini is high in the sky at 2:00AM in all directions.  A small crescent moon will begin rising at 3:35AM.

 

The upper ridge remains in control……The Forecast still includes a warm up through Thursday and possibly Friday. Highs in the upper 50s Thursday and Friday with lows in the 20s to low 30s in the village.  WInds in town will be calm at least through Friday afternoon.

Here is the latest thinking from the Dweebs today Tuesday;

I listened in on the weekly discussion from the CPC.  The discussion mainly deals with tropical forcing which in many cases can be the tail that wags the dog.  The MJO is currently active, moving from phase 6 into Phase 7 and increasing in strength.  Phases 6-7 is the western pacific phase. When the MJO is strong in this area, it is usually associated with a strong +PNA pattern in the far west which we are now experiencing. The CPC prefers the ECMWF version of the RIMM (Phase Space) showing phase 7 to be the dominant mode for the next 5 to 7 days. Thereafter, the MJO progresses to phase 8 which moves the upper divergent and convective envelope out of the western pacific to near the dateline. This is almost always associated with retrogression of the long wave pattern for the west coast in the winter. IE the backward or westward redevelopment of the west coast ridge.  However, with the MJO forecasted to fall apart quickly as it moves through phase 8 toward phase space 1, (Possibly due to the anomalous cold waters of La Nina), most likely, we will not experience what would often take place thereafter. IE, the strong undercutting of the westerlies into the west coast. (That would be a wet pattern) An MJO strong through phase 8 usually results is an extension of the East Asian jet stream to the California coast. The CPC today indicated that this tropical convection is forecasted to be suppressed near the Dateline and in effect,  weakens the MJO…..”thus no gas to put the peddled to the metal”. (the latter are my words)

More comments……..

Most likely, we will be teased the next few weeks with some undercutting possibilities. Is undercutting of the westerlies possible? sure, but not probable.  The fact that only a few of the ensemble members shows that undercutting is testament to that possibility.

So, what is the more likely pattern that may emerge? As you all know, I am just a hobbyist. I love the science and all outcomes. Because I know that every outcome works out exactly the way it was supposed to…..Not necessary they way anyone forecasts it to!  😉

Here are my thoughts this evening….

  1. We are going a bit deeper into La Nina the next four weeks…..
  2. La Nina usually is usually highlighted by a -PNA pattern (long wave trof in the west) Occasional Arctic Outbreaks spilling westward.  (So far that has not happened)
  3. As far as weather pattern change, there is going to be retrogression…..No doubt about it!  The question is, how far west will it take place and how amplified will it be.  If a highly amplified pattern with a track down the west coast develops,, I am not all that concerned about any closed low diving so far south it misses California all together. Sea Surface temperatures anomalies have increased along the west coast and especially Southern CA due to the absence of storms this season. So the subtropical High (Hadley Cell) should be stronger further north.
  4. What the ECMWF ensembles are hinting about now is a system with “Arctic Air” plunging SW off the BC coast, spinning up then picking up some moisture from a weak undercutting. The issue is, the moisture tap is pretty much over by the time the front gets south of Northern CA. However, a cold storm for California around the 23rd of December, or any storm with Arctic Air in December is going to be a memorable cold system for Mammoth.
  5. The GFS ensembles actually has a similar pattern with the same cold Arctic Trof digging out of British Colombia. However, instead of the system coupling with moisture west and under a blocking high, this storm is just out right cold with limited moisture as the long wave sets up over the far west, more in line with what one would expect from a La Nina year.
  6. Remember, this is well over a week away and so there is plenty of time to watch and learn!
  7. The screaming message here is that we are going to get a transition and it looks cold for at least part of it.

 

Dr Howard and the Dweebs…………………………:-)