Archive for July, 2020

Late July Heat wave on tap as subtropical high sets up over Southern California today….Pattern is Dry through the weekend….Isolated thunderstorms return the following week….

TGIF Everyone….

As we come to the end of July, The Dweebs have come to the realization that its been an A-Typical Summer. The June Gloom season has lasted much longer than usual along the southern coasts of California. LA has not had any significant heat waves so far. The waters off the Southern CA coast are much cooler than normal. The Sierra and Southern Deserts has yet to experience deep SE flow. The AZ Monsoon season has been anemic at best.

Weather Type:

The large scale weather pattern over the West and Southwest has been highlighted by a stronger than normal, persistent upper trough off the coast of the Pacific Northwest. This trough has in the “long range means”, displaced the Subtropical High to the east. It has warped its configuration to where the upper flow along the west coast has been vigorous WSW. In the wintertime, that may be normal. But in the Summer?  By this time of the summer we usually experience much lighter flow aloft or southerly flow.

The results of the enhanced WSW flow over Southern CA has been steeper pressure gradients between the deserts and the coast.  Stronger onshore flow leeds to more persistent June Gloom along the coast. Stronger westerly winds over coastal waters creates up-welling, resulting in colder SSTs and then feeds back to even stronger differences in air pressure and intensifies and deepens the marine layer further.

A positive result that is beneficial from the strong up welling, is that more nutrients are lifted upwards in the seas which can be beneficial to fish population.

Short, Medium and Longer Range:

No sensible change is expected in Sierra Weather through next Tuesday.  Expect an enhanced afternoon and early evening Zephyr in Mammoth. This will suppress high temps by as much as 5 degrees from what we would expect from the current 500mb height structure this time of the year. High temps will range in the very low 80s with night time lows dependent upon the micro climates of Mammoth as they relate to breezes during the night.  Lows may range up to 10 degrees cooler in areas like the Mammoth RV Park verses Snowcreek where it may remain somewhat breezy all night. As an example, In the meadow last night, it was breezy enough to keeps lows limited to 62 degrees, whereby in the more eastern sections of the city limits, lows were in the low 50s.  These spreads are likely to continue the next few days. Our air-mass is bone dry now. So be especially careful with fire. No campfires are allowed in the forest now. Only in approved campsites.

Longer Range:

An extension of the Eastern Pacific Trof develops while the upper ridge weakens over the SW. As the cap comes off and heights fall….instability develops with a pattern similar to what we had some 10 days ago with isolated to scattered thunderstorms. High Temperatures will cool to the 70s later next week. Lows in the 40s and 50s.

Still no sign of the AZ monsoon….

 

Dr Howard and the Dweebs……………………..:-)

 

 

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Tuesday July 28th:

This looks like the Summer without the Monsoon

Latest guidance continues the trend of dry weather in the high country with little if any convection expected this week. A strong subtropical high develops over Southern California today that is east-west oriented. This system builds the heat over the state without any import of SE moisture. In addition, strong subsidence will put a lid on any convection as the freezing level hikes to 17,000 feet, both Wednesday through Friday. High temperature records will be in jeopardy toward the weekend in the high country and over the weekend for the Owens Valley.  Additionally, the Trof over the pacific NW will weaken temporarily, then strengthen again, increasing the gradient for a bit stronger Mono Zephyr during the afternoon and evening hours. Thus you will be able to opened the windows in the evening and let the west wind blow some of the heat out, a little later in the week. This Ridge shifts more east with time into AZ, as the Eastern Pacific Trof strengthens. This allows some cooling next week. However, the trof in the Pacific Northwest keeps the SW flow going, so not much more than isolated TSRWs expected when the heat breaks. Eventually, we get a weak closed low set up again, off the Central CA coast like this past weekend, for the return of high based thunderstorms. However, this is not the AZ monsoon!

 

Dr Howard and the Dweebs………………………:-)

 

Weak Upper level low keeps temps seasonal this week with isolated thunderstorms for Southern Mono County through Monday…..A warm up is expected for the first week of August …..

The weather pattern along the west coast thus far this Summer, affecting Mono County has resulted in drier, more temperate weather. Southern Mono County has had fewer heat spells as compared to many summers and fewer thunderstorm days in Mammoth. Early in the summer there was an enhanced zephyr, as the Pacific NW trof was stronger. This trof, centered off coast of the pacific NW and weak extension south has resulted in mainly high based thunderstorms.  On a synoptic scale, the trof has weakened the AZ monsoon season and has allows almost none of the usual moisture that moves north through the four corner states to reach Mono County. Virtually, no sustained SE flow has developed over Eastern CA, so far this Summer.  That pattern  typically results in the transport of deep moisture from our South East along with upper level forcing around the perimeter of the Continental High. This summer’s upper level forcing has been associated with weak west coast toughing which leads to mainly high based thunderstorms.  Most of this forcing has affected areas of the Sierra well to our north.

 

Highs in Mammoth continue to be in the MId to upper 70s with lows now in the 40s.

 

Looking forward:

The “week two” outlooks  continue to try to develop at least of some periods of southerly flow.  However, the persistence in weather pattern seems to continue for the time being.   It may very well be, that our future heat spells will continue  drier than normal and with mainly high based TSRWs action in Mammoth Lakes. A Stronger Mono Zephyr look possible after the first 10 days of August….

In the meantime, expect mainly isolated high based thunderstorms over Mono County the next two days with most action over the Northern Sierra. This is due to a weak negative tilt trof over Central CA. Dry weather is expected Tuesday through Friday next week. The first week of August looks warmer than normal with dry WSW flow, under the Continental Subtropical High.

 

Long Range Thoughts….

“IF” This persistent trough continues into the Fall…..Expect an early winter…….

 

Dr Howard and the Dweebs………………………….:-)

Warm Sierra Weather to continue with slightly warmer than normal temps….Upper divergence Mid Week to begin Summertime Thunderstorms Tomorrow Wednesday and Thursday…..However the long awaited Summertime Monsoon will begin during the second half of next week…

Our Summer weather thus far has been warm and dry with stronger afternoon Zephyr.  This is about to change as a weak upper low has developed west of the Bay Area this evening. This feature will move further south with time putting the high country of Mono County under at least weak upper divergence. Our air mass continues very dry and so expect mainly dry high based thunderstorms with strong outflow winds next to the rain shafts. The National weather service has issued a fire weather watch Wednesday afternoon and Thursday afternoon, as lightning over a very dry forest will likely create hazardous conditions with strong gusty outflow winds. Most Storms will be over Northern Mono County Wednesday but develop further south over Southern Mono County Thursday.

 

High temperatures moved into the low 80s Today. The bump up from the upper 70s was probably due to a weakened zephyr. Little change in temps are expected with highs in the low 80s. The upper divergence that is currently developing will weaken this weekend. Thus thunderstorms will become more isolated. Note this is not the Summertime Monsoon!! (Seasonal wind)

 

Outlook for next week:

Its been long in coming but the Summertime Monsoon looks to arrive during the second half of next week. Latest guidance shows the subtropical high developing over Texas this weekend then expanding westward next week. The GFS model shows PWAT (low and mid level moisture) really increasing over Southern CA by middle of next week with hot humid weather becoming more likely during the 2nd half over So Cal.. A northerly surge is expected over most of the State by the following weekend. Although it is too soon to tell what type of focusing will highlight the pattern; it looks like we will get into a wet thunderstorms pattern during the last week of July. This pattern change next week completes the transition to our Sierra Summertime Thunderstorm pattern.