Dry Dry As Far As The Eye Can See…PNA Pattern Likely To Rule The Western Hemisphere The Next 1 To 2 Weeks! (Wednesday AM MJO Update)
Tuesday January 18, 2011
Posted at 4:21 pm by Howard
Skiing is fabulous up on Mammoth Mountain. The groomers are out nightly mixing it up on an 11 to 16 foot base! Temperatures to cool the next few days as our upper ridge retrogrades to 140W. Highs will cool to the 30s again. It will be breezy Wednesday and NGT.
The 3 to 5, 6 to 10 and 8 to 14 day forecasts and outlooks are all singing the same tune. It’s called “The PNA”. The Pacific North American circulation pattern. It is one of the most common teleconnection patterns over the northern hemisphere.
The positive phase of the PNA pattern features above-average heights in the vicinity of Hawaii and over the inter-mountain region of North America, and below-average heights located south of the Aleutian Islands and over the southeastern United States (Hudson Bay Low). The PNA pattern is associated with strong fluctuations in the strength and location of the East Asian jet stream. The positive phase is associated with an enhanced East Asian jet stream and with an eastward shift in the jet exit region toward the western United States.
Plain and simple…the positive phase PNA is a dry pattern for California in December, January and February. The West Coast ridge will shift back and forth between 140west and 110W.
When the upper Ridge is between 130 to 140 west, Mammoth is cooler and dryer then normal with windy periods and sometimes snow showers…..(inside sliders) Even a cut off low can develop over Nevada.
With the upper ridge just off shore or over the Great Basin….California is warmer then normal with ocassional Santana winds over Southern Ca Once the upper ridge slips east of 110, the door can open to pacific moisture for Ca.
The Dweebs have said it before and they will say it again……La Nina winters are highlighted by intense stormy periods with long breaks in between. Winter will be back!
Quick MJO UPDATE:
The enhanced portion of MJO is quite strong over phase space 7 of the Wheeler Hedon Phase Space. The numerical guidance of the GFS from the 00z Wednesday Jan 19th is just beginning to reflect the signature of the inter-seasonal oscillation. Although very *incipient…it is encouraging…however, it was not reflected on the 06Z run.
CPC did cite that the pattern over the high latts was not favorable for an west coast wet event. Additionally, the cold waters of La Nina would also diminish MJOs effects.
The Dweebs see some slight evidence of amplification toward the end of January of amplification and then undercutting of the westerlies. The Eastern Pacific Ridge becomes pinched off and bubbles up along the coast of BC, Canada about February 1st. The timing does teleconnect with MJO and its location.
We will have to have many more model runs as well as much more development in this pattern before any serious confidence can be attained for a California wet MJO related event.
Dr Howard and the Dweebs……………………………….:-)
Reference Glossary of Weather Terms
Disclaimer: I have been a hobbyist meteorologist for over 30 years here in the Mammoth area and I do this for my personal enjoyment. The National Weather Service saves lives every day . . . I do not. When making important planning decisions please use information provided by the National Weather Service as they are the most knowledgeable and accurate information source available today.
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