Unstable Showery Pattern to continue the Next Several Days…No Major Precipitation but continued mainly afternoon Showery Weather with the Chance of Thunder through Friday…The Weekend Looks Drier and Warmer…..Especially by Sunday……
Monday April 20, 2015
Posted at 9:42 pm by Howard
Nothing to write home about yesterday except for a lot of high based convection. Most of the rain and thunder was on the west side again. Today the atmosphere is a little different. The PWAT is higher up to a 1/2 inch and the upper low over Southern CA will lift north a bit in response to another low dropping down the coast and displacing it. It may end up that over the next two days, there will be more storms on the east side. We are expecting convective snow showers here in Mammoth with snow pellets and possible thunder through tomorrow night. Saturday looks breezy and drier as a NNW slider comes through. Sunday through Tuesday look fair and warmer.
ENSO: The Dweebs are going to give you all some important tools to track EL Nino This Summer. It appears that a good part of the equation that needs to be in place for an El Nino event later this year is colder water north of Australia. Remember, the western pacific has to follow through. It did not last year and so I hope it will this year. In order for a strong El Nino to take place during the Winter of 2015/16 the western pacific has to couple with it. This means that although we can have all the ingredient’s working along the central and eastern equatorial pacific, if there is no follow through from the western pacific, then the warm Sea Surface temperature anomalies that are now developing over the NINO Basin will have occurred in vain as the anomalies will weaken as it did with last winters El Nino.
A link to a blog with graphics from Michelle L’Heureux is linked below. It simply says that the waters around and over Northern Australia needs to be cooler than normal for a major El Nino to sustain itself during the following winter. It is all about the difference in surface air pressure between the city Darwin over Northern Australia and the Nino Basin. Cold water has higher pressure at the surface and warm water has lower pressure at the surface. (The NOI is the Index) A Surface Pressure Gradient moves from higher pressure to lower pressure. Or in this example of a warm ENSO event from West to East. So…..the waters over Northern Australia have to cool down for the higher surface pressure to develop there. Once the waters get really cool, the movement of air along the surface at the Equator will be both pushed and drawn eastward to “perpetuate and the sustain” the anomalous warm sea surface temps over the NINO Basin that is being created initially by the Oceanic Kelvin Wave. (“Bjerknes or positive feedback”) At the moment, we have a very warm strong KV rising to the surface over the eastern EQ pacific like last April 2014. So my fellow Dweebs, it is your job to keep an eye on the SSTA’s over Northern Australia to see if there will be a “coupling of the western pacific” to sustain El Nino for next Winter. (The NOI has to be equal to or greater than +1.5 to be considered a strong El Nino) (The NOI is reflective of an index that measures the difference of air pressure between Darwin and Tahiti)
2. Here is the SSTA loop: http://www.ospo.noaa.gov/Products/ocean/sst/anomaly/anim.html
So far the coupling has not developed…however there are some signs that the waters are beginning to cool off the NE coast of AU.
Dr Howard and the Dweebs……………………..:-)
The details of the pattern discussed last week still involves a split flow over the Eastern Pacific with a Ridge in the northern branch over Western Canada. The southern stream has verified pretty weak. However, with strong daytime heating this time of the year, the weak baggy trof in the mean will continue to produce showers and thunder and some snowfall through Friday or Saturday. The Central and Southern Sierra appeared to be in the divergent quad of the upper low. As another sheer lobe will slide down along the coast to reload the Baggy System with another circulation center developing to keep the action going a bit longer this week… There will be a period of southerly flow that may possibly help some areas get more precip on the east side. Today Monday, there was a lot of lightening over the sierra crest and over the west side. It was rain below 9500 feet. Southern CA also had thunderstorms in some areas. No more than 1/4 to 1/3 of an inch of precip is expected within any 24 hours period over the sierra.
The Split Flow off the OR/CA coast progresses inland next Sunday and into Monday ushering in a ridge which will dry us out and warm us up. Thereafter…. the longer range shows a pretty strong Trof for April pushing into the west coast mid-week next week, with the chance of wind, cooling and precipitation as well. The timing is possibly the last few days of the month.
It was mentioned earlier that this would have been a better pattern had it developed during the winter months. However, in all reality, it would not and did not happen because of the strongest +PDO on record along with a weak Modoki El Nino. This has kept, the ever resilient ridge in place. It is only now during the spring, as the thermal heat source shifts from the oceans to continental, that the eastern pacific can open up. However, unfortunately and climatically, the wet season is just about over……