Temperatures over the Eastern Sierra definetly showing signs of becoming more variable as Poler Jet begins to flex its muscle over the higher Latts…..Fall like weather not that far off…..
Friday August 22, 2014
Posted at 7:47 am by Howard
A Northern Great Basin slider will bring the first shot of synoptic scale cooling to the Eastern Sierra as the stable weather pattern of July and early August give way to a strengthening Polar Jet in the more Northern Latts…..Fall like weather has set in over many areas north of 60 N. The weather over the eastern sierra the next 5 days will be highlighted by periods of warming and cooling. The timing of the 1st shot of cooling will be associated with the slider later today and tonight where winds will precede the cooling this afternoon and tonight. Highs today in Mammoth will cool to the low 70 with upper 60s possible for highs Saturday. Nighttime lows will drop to the 30s Saturday AM. The further outlook shows the Trof progressing east Sunday and in it wake, a subtropical high will build back into the high country rapidly Monday into Tuesday with an equally rapid warm-up Monday through Thursday. By mid week, high temps will be well into the mid to upper 70s especially by Thursday. No rain in the outlook through Thursday.
Will discuss the Labor Day holiday weekend outlook Sunday….
Upper Level Low of the Southern CA Coast to get the Boot Thursday as Larger Synoptic Scale Trof moves though the Pacific NW….Warmer Early Next Week….
Wednesday August 20, 2014
Posted at 8:50 am by Howard
An area of showers and thunderstorms developed yesterday afternoon and lasted into the evening hours over Mono County. Although Mammoth just picked up a few light showers, accumulating precipitation occurred to the NNW of Mammoth. Todays air mass shows a slight increase in Precipitable Water. However as the day goes by, the divergence/convergence couplets now in place will probably weaken. There is still a slight chance of TSRW’s this afternoon into the evening for Mono County.
The Upper Low currently off the coast of Santa Catalina Island will get the boot into AZ late Thursday as a larger synoptic scale trof moves through the pacific NW. This trof will bring a little cooling Friday into Saturday with wind the main feature Friday afternoon into the night. This appears to be the first quasi insider slider type system to bring wind and cooling associated with a 110knot upper NW jet that cuts through Northern CA and NW Nevada. I am sure that it will be one of many as we go into the cooler half of the year.
Winds will crank up Friday afternoon into the night with gusts 20 to 40 mph in Mammoth and over 50+mph over the Mammoth Crest Friday night. It will feel like Fall Friday PM into the night.
Pressures aloft begin to build from the SE early next week partially aided by the tropical storm moving NW up the coast of Baja next week. With higher heights over the state, warmer temps will follow early next week and into the last week of August. Although the models all deflect most of the TS moisture WNW of Central CA, it will have to be watched as we head into the Labor Day holiday weekend….. Remember, models are guidance…….Not a forecast…..
Dr Howard and the Dweebs…………………………………….:-)
Upper Level Low Spinning up off the Northern CA Coast may bring some showers to the high country Tuesday PM…..Otherwise partly cloudy at times but dry weather this week into the weekend with seasonal temperatures…..
Monday August 18, 2014
Posted at 9:12 am by Howard
A weak upper level low was spinning up along the Northern CA coast this morning well NW of Mammoth and at the same time a weak upper jet was spreading some high cloudiness over our region. New 12Z 250mb Nam 212 shows strong divergence over the sierra from Southern Mono County south over the Northern portion of the Southern Sierra between 2100Z Tuesday and 00Z Wednesday. However the 700MB RH has only between 40% and 50% RH, so there is little moisture to work with tomorrow afternoon instability. This is a case that if we had the kind of moisture that we had a week or two ago, during the monsoon SE flow, we would be looking at heavy rain with a system like this. This time only the slight chance of a few showers or thunder boomer late in the afternoon and early evening.
The over all upper pattern is changing from the peak of the Summer a few weeks ago. There is in process a westward shift in the key anomalies over the northern CONUS with the coldest weather retrograding toward the northern Great Plains instead of the Great Lakes and the upper ridge that has been over the pacific NW back toward 140west. So far the Monsoon is focused over the 4 corner states and should remain well east of the Eastern Sierra.
Looking at the prospect’s for some rainfall from an eastern pacific tropical storm, as long as the Subtropical continental upper high is extended far enough west, the likelihood of significant rain bearing subtropical moisture getting this far north is very remote…..However, with that said, the odds will begin to increase by the very end of the month of August and especially into September as the subtropical continental high begins to weaken climatically.
Interesting article from WSI
The models appear to be flip-flopping a lot with the position of low off Ca coast next 3 days which is to be expected with any weak closed low. However the 12Z GFS is now giving this low the boot ejecting it inland on Tuesday with resulting PVA and deformation in NE quadrant kicking up the thunderstorm potential over the Sierra by Tuesday afternoon. The 00z EC constructively phases CA lo with subtropical low moving n from Baja but retrogrades dumbelling low to nw while stronger trough digs into nrn Rockies. 12Z GFS on the other hand destructively phases with Baja low which helps spin up stronger west to east upper jet which in turns helps to eject Ca low ewd Tuesday. In a majority of cases I’ve seen with tropical or subtropical lows in Ern Pacific there is more of a tendency toward destructive phasing which tracks energy ewd south of our area which usually diminishes the chances of seeing a tropical energy connection this far north. Watch the trend of the 200 mb isotach forecast on the SJSU site as this phasing occurs and the resulting upper level divergence field. You will typically see a rapid spin up of jet speeds and divergence as the tropical low comes closer or merges with the northern lattitude low or trough. The rapid increase in upper divergence will result in a large plume of high and sometimes mid level level moisture that you typically see on the IR and Wv satellite loop eminating from the NE quadrant of the tropical system. The lower level moisture at 700 mb and below will usually stay with the parent low level circulation which often times dissipates over colder waters. The mistake many forecasters make is believing the high level moisture plume seen on WV loop will somehow initiate thunderstorms over the Sierra but more often it cuts off solar radiation and decreases instability, needed for deep convection. What can happen as seen a few weeks ago is the upper jet that is spun up from this subtropical connection will proving a favorable upper divergence pattern over a pre-existing area of unstable air (positive CAPES and lifted indices at zero or less) and if enough low or mid level convergence occurs to trigger this instability then deep convection will occur. So when these tropical moisture surges appear on satellite loop you have to ask if they are high level debris clouds supported by upper divergence or is it the actual low circulation being constructively phased with jet intact moving north which would support a convergence/divergence couplet and a true deep layer tropical connection. Its all in the details best seen on the SJSU and SPC graphics.