Archive for March, 2013
Friday March 29, 2013
Posted at 9:43 am by Howard
Saturday AM Update:
Last weekend update…….
Precipitation to begin by late this afternoon or evening……
Latest AMSU CIRC TPW still shows about an inch of TPW wrapped into a band ahead of the cut-off low. There is a richer pool of PW off the Northern Baja coast which will most likely not be a factor.
Snow levels will begin very high…8500 to 9,000 today then lower late tonight into Sunday. By Sunday, the SL should be at or below 8000 then 7500 by the afternoon., then 6500 ft by Sunday night. On Monday, the SL will rise to 7000 feet.
2 to 4 inches of snow is certainly possible now in town at 8000ft. As mentioned yesterday, the storm is more spring like and accordingly, there could be some thunder. Additionally, snowfalls below the shafts in convective cells would favor even lower snow levels, temporarily.
Updated QPF from CRFC this morning showed about .8 over Yosemite. The EC has about 1.25 of an inch west of the crest by Monday evening. In that the upper jet (shown with the 12z GFS at 300mb), comes in over Santa Barbara., Mammoth is in the favorable front left exit region of the upper jet, tonight into Sunday night. Additionally, a good part of the Precip in the storm will occur during the warm sector…..Snow to water ratios will be low accordingly. Estimates are between 5 to 7 at the main lodge and 7 to 10 inches for the upper mountain by Monday evening.
Next Update Tuesday……
Next storm Thursday and again next weekend……………….:-)
Dr. Howard and the Dweebs………………………….:-)
Latest AMSU CIRC TPW shows about an inch of TPW wrapped into the cut off so far. Further entrainment is possible later today and tonight as a combination of the slow movement of the upper cut off and the Subtropical Jet get closer.
Today’s weather will be partly cloudy with a few isolated showers this afternoon. As the cut off moves towards the coast then onshore, showers will increase Saturday/Ngt. The Snow level will be high….above 8500 until the cool part of the system comes inland Sunday. 500mb-1000mb thickness lowers to near 546DM briefly, so we may have a snow level by Monday AM at 6500ft. Snowfall in town maybe a trace to a inch or two Sunday night into Monday AM. Snow fall amounts over the crest will be 6 to 12 inches by Monday evening. This system will weaken rapidly as it moves inland because it is cut off from the westerlies supply of cold air. It is only coming in because of an upstream kicker ridge. The higher Sun angle of late March and early April will keep a convective component to the system. So Thunder snow is possible Sunday afternoon. Showers will continue Monday and diminish Monday evening. There will be a break mid week before the next storm moves in beginning Thursday.
The ECMWF model’s total Precip for the Sierra Crest near Mammoth Mt, from the 00z Friday Run shows that over the next 10 days between 3 and 4 inches of QPF.
Meanwhile…..the latest DWP Snow Survey data shows the water content of the Snow Pack at Mammoth Pass less then 50% of normal, Similar to where we were last year this time.
Upper Flow Has Now Backed to the West With Upper Flow Becoming More SW with Time……Moisture Associated with The Subtropical Jet training from the Hawaiian Islands…..Subtropical Jet to Couple with Closed Low Late in the week for the possibility of some good precipitation Over Parts of the Sierra….The Demise of the Greenland Block is at Hand……Good Riddance!
Tuesday March 26, 2013
Posted at 8:37 am by Howard
A quick look at the common teleconnections…the NAO and AO are expected to remain weakly negative the next two weeks. I think that “weakly” is the key here.
The system coming into Ca Saturday night through Monday looks wet with good diffluence and upper divergence as the nose of a 100knot jet effects the Southern Sierra with Mammoth Mt to the north near the Front left exit region, (divergence aloft). Active anti-cyclonically curved subtropical jet is pumping a lot of moisture from near the Hawaiian Islands NE into the subtropics. CIRA Blended TPW loop shows that as much as 1.25in TPW streaming from that region. So there is plenty of subtropical moisture that potentially could to be drawn into the closed low. Its slow movement will allow time for it to gather up “its cookies” by entrainment, Friday into Saturday before landfall. Although this is a very mild system with the snow level about 8000ft, it will have a convective nature to it which would allow for snowfalls within convective cells below the projected snow-level…..Thundersnow may shake up the Easter Bunny a bit Sunday. Additionally, this may also prove out to be a system that produces cold core funnels over a part of the Great Valley of Ca, especially if its timing is right during the afternoon Sunday. As mentioned before, the SPC Mesoscale Analysis Pages will be a useful tool this weekend.
Yes……Good Riddance to that awful block! Although the Weather Weenies across the Eastern US have loved every minute of it…..that Block has been a problem for most of California.
The GL Block ( Strong positive height anomaly over Greenland west to the Davis Straits…Baffin Bay) has pretty much put the kabash for storms effecting California since the 1st of the year with the PNA teleconnection fairly neutral to positive most of the time. Now the GL Block is breaking down and the east will get more Spring and the West, hopefully some Winter during early Spring!!!! Although The first system is nothing to write home about, its a start. There looks to be more behind it through the middle of April. A new but temporary block is expected to set up near AK…splitting the jet with a lower/mid Latitude storm track into California. This looks to possibly develop further the first week of April in the the following week. The Dweebs hope that there will be enough energy left in the Arctic to play catch up for California!
Otherwise what we have now is a weak subtropical connection from Hawaii with a weak subtropical jet NE into Central California this week. Some shower action mostly initiated by orographics is possible as the air mass juices up this week. By the time we get to Thursday, a short wave gets the squeeze SE into the remaining Eastern Pac blocked up pattern for a cut-off or closed low that will effect the central and northern Ca this weekend. This is a mild storm for the high country. Snow levels will respond accordingly. Saturday night through Monday appear to be the most effected time period as the upper low ejects through Central California. The EC and the GFS are now pretty similar on all this.
Longer Range…the ECMWF has another storm later next week…..That system should have an easier time getting in here as the AK block is stronger. Looks like mother nature is trying to relight the candle…….at least for a week or two.
Upper Ridge Builds Onshore Tonight then Progresses East……Westerly Flow Develops Tuesday…..Next Storm’s a Creeper with Easter Weekend in Jeopardy…..
Sunday March 24, 2013
Posted at 12:06 pm by Howard
Quick Sunday Afternoon Update: 12:30pm
New 12Z ECMWF has the upper cut off drifting north to a position west of Monterrey by Sunday Am (130W-36N). By Monday a kicker trof descends out of the Gulf of AK and nudges to the upper cut NNNE to a point about 128W-39N by Monday AM. This is quite the change from earlier runs! Thereafter, the kicker Trof drives the upper cut off down our throat late Monday afternoon into Tuesday morning as it opens into a sharp tight dynamic system. The Dweebs like deece’…..:-) Well see how the models handle all this in coming days……..lots of time for things to change either way…..
It was a beautiful end to a Winter that was over-all pretty good to the locals in town. Much less was spent on snow removal by the HOA’s . The private guys with contracts did well again like last year, while the hourlies did not. Sorry Guys……
This is the first weekend of Spring…and now forecasters have to treat their forecasts differently with the addition of the higher sun angle. Daytime convection must be considered in every forecast now during active patterns, especially with cold air aloft systems on a synoptic scale, (within 620Mi). Thunderstorms will highlight some of these systems with closed lows that favor good upper level Diffluent/Divergent features. Here is a good link http://www.spc.noaa.gov/exper/mesoanalysis/ to use this Spring during active patterns.
This leads the Dweebs to chat about the next system that looks like quite the creeper. This mornings GFS showed an incipient wave located 350 miles west of the dateline at daybreak. The front aligned north south over the dateline. The wave is expected to travel east to a point some 1600 mi north of the Hawaiian islands by Tuesday night. Thereafter, it splits off from the westerlies as it heads SE toward the Eastern Pacific. This is due to the persistence of blocking in the eastern pacific that has been there most of the Winter in various degrees. Today’s 12z deterministic GFS has it east of 140W and south of 40N Daybreak Thursday while it spins up to occlusion…then true closed low fashion, with REX design. The 12Z Sunday 24th GFS run had the upper closed low drifting east to a point some 400Mi west of Santa Barbara by Saturday Daybreak.
For the Central Sierra it is important to add the convective component to the possible scenarios which will be dependent upon the placement of the upper low on a synoptic scale. Closed or cut offs which are common now this time of the year, and their placement is difficult within 72 hours, let alone a week away. Additionally, today’s 12z GFS also showed a subtropical jet that develops along 20N and lifts NE underneath the California low Friday. It appears to “couple” with the systems upper jet as well to add more moisture to the mix. So there is the potential for some heavy snowfall some where between the Southern Sierra north to the Central Sierra. Lets hope the system gets positioned just right for Mammoth Mtn!
In the meantime, nothing much is going to happen the next few days. The Clouds will increase Tuesday into Tuesday night with a passing wave to our north. The wave will kick up the wind here locally, but the “system is pretty wimpy”. There will not be much of any cooling either except for the effects of less sunshine. The aforementioned storm will begin to advect in moisture as early as Thursday and so showers could begin anytime then on……………….
Longer Range: There does appear to be another system headed from the NNW/SSE into California the following Tuesday, but this could be an inside slider…..too soon to tell.
Next Update Mid Week………………………….>>>>>
PS. Hats off to Geoffrey McQuilkin of the Mono Lake Commitee for his assistance on getting Mammoth Weather’s data system back on line…..
Dr Howard and the Dweebs……………………….:-)