Archive for August, 2014

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…..

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.

ENSO UPDATE:

Interesting article from WSI

http://www.wsi.com/blog/energy/el-nino-update-rising-from-the-grave/

 

 

Toms Corner:

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.

 

Tom

Dry Southwest flow is the word for the next 5 to 7 days keeping Mammoth dry with near seasonal temps……Expect cooler nights now with the drier air….CFS forecasting more wet weather ahead for CA………

 

Friday/Weekend Update:

An upper level ridge of high pressure will build over the Eastern Sierra while a weak baggy trof remains off shore. This will continue the dry pattern over the eastern sierra while temperatures return to more seasonal levels. High temps in Mammoth will rise to the upper 70s this weekend with lows in the 40s.  Little change is expected over the next 5 to 7 days….

PS. The ECMWF model  (week 2) has a Fetch of Hurricane moisture lurking off the Southern CA Coast by the end of the Month….

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With a combination of weak troughing aloft, an on-shore SW flow and an upper high with an axis that is not conducive for the import of monsoonal moisture, these actions finally turn our air mass dry over the eastern sierra.  This pattern may continue for a week or even longer….

Highs temps in Mammoth will be in the low 70s the next few days then rise to the mid to upper 70s this weekend.

Overnight lows will range in the mid 30s to low 40s depending upon wind. Winds will occasionally gust up to 30MPH here locally with more moderate winds to 50mph over the crest today and tonight.

Overall…..It is Eastern Sierra Weather at its best!

Thoughts about this Summer so Far…

Lots of folks like to try to tie past events to future weather or climate events….  Like a wet summer precedes a wet Winter or a dry and windy summer precedes a wet winter.  Or pinecones clustering at the top of pine trees in Summer precedes a wet winter.

The facts show that all of these observations can be explained by what has already happened. Not a forecast for future events.

Example:   If one goes outside in Mammoth today and looks at the local pine trees. There is difficulty finding pinecones at all!  That is because the trees are in survival mode with the three-year drought. This will have nothing to do with what the upcoming winter will be like precip wise.

Heavy clustering of Pinecones in the Summer is a reaction to past years of normal to above normal snowfall.

Another observation:   This has been one of the wettest Summers for the Eastern Sierra in recent memory.   Does that mean that the winter will be wet?  No…  The wet Summer is directly related to the exceptionally strong Kelvin Wave that traveled from the Indian Ocean last winter to the Western Pacific and finally washed up upon the Central American coast late last Spring. The warm water underneath the surface was forced to rise and then was squeezed north and south by the continent.  The northern portion of the squeeze pushed warm water as far north as over much of the California coastline. SSTA’s in the Sea of Cortez was recorded showing high temps well into the 90s!  SST’s along the Southern CA coast were up to the mid to upper 70s!   All this heat and humidity and the “shorter” June Gloom season over Southern CA was caused to a great extent from that giant Kelvin Wave. A big part of this years California Thunderstorm Equation and was a result to a great degree to the same Kelvin Wave that was actually initiated very early this calendar year.  To my knowledge, no one forecasted a wet Summer for CA in the early to mid spring with record rains in the San Gabriel Mts. However, the CFS (Climate Forecast System) did forecast last June, precipitation departures from normal of over 200% over Mono County for July! The Dweebs here did put that into an interseasonal outlook early this Summer.

Fall type weather is settling into the Arctic now. The upper jet is gaining strength and tropical storm action over the eastern pacific is increasing. This is typical by mid August.   The “Dog Days” of Summer are over…….  From what I see in the extended outlook…The Eastern Sierra Monsoon Season of Anomalous Easterly flow from AZ is over……  However, with that said, in that it is expected to be a bit above normal in temps for the next two weeks, there is always the possibility of high based, isolated air mass type thunderstorms action over the Sierra.

Inter-seasonal:

OK…the Dweebs used the CFS for the Summer Precipitation outlook back last June and it accurately forecasted a wetter than normal July.  Here is what it says for late August thru mid September.  It says that between the last full week of August and the 1st half of September, precipitation will range from +200% to +250% as a departure from normal. However, the clustering is not from AZ, rather from the south-south west. Thus it suggests significant moisture from a tropical storm or two getting entrained ahead of eastern pacific trofs during that time frame.

This is the direction of where the eyes of the Dweebs will be focused over the remaining weeks of Summer.

 

The Dweeber………………………………:-)

 

 

 

North Central CA Coast upper trof to kick out Monday afternoon, leaving drier weather for the rest of the week…..The AZ Monsoon may be coming to an end…..

Monday Night:

Major air mass pattern change for much drier weather coming up as an eastern pacific trof sets up offshore with upper Jet currently bringing Thunderstorms to the Mammoth area shifting east.  Once the Southwest flow develops, we’ll experience dry weather with the usual afternoon and evening Zephyr winds along with chillier early morning lows.  The prind. point here is that WSW flow will continue for at least a week, possibly longer. So back to the weather the eastern sierra is famous for. Lots of sunshine and little rain beginning tomorrow Tuesday. Again and according to the CFS model, it is possible that the dry pattern may last a week to 10 days before moisture starts working back into the eastern sierra the last 10 days of the month.

 

Expect highs in the low to mid 70s then upper 70s by weeks end.

 

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

 

 

Sunday PM Update:

Now cast:  Thunderstorms are training NNW from Alpine County.

Upper central coast trof to kick out late Monday………………..Leaving drier and more stable weather the rest of the week……

However, before it does Monday may be an active day of thunderstorms over Mono County eastward.
Daytime highs in the mid 70s with nighttime lows in the upper 30s and 40s

There will be a few remaining days of Thunder….Namely today and possibly Monday…….

As far as another Monsoon Surge…..None in the cards this week as Hemispheric Pattern begins to change showing more pacific amplification and an adjusted eastern pacific ridge further west.  Week two holds some possibility as again, an expansion of the subtropical ridge extends from the SE to California. This may happen during, early the last week of August.  However, by that time it will be getting a bit late for the AZ Monsoon……

This Summers California Central Sierra active Monsoon Season appears to be on the Wane………

By the End of August and especially September, the Dweebs will be keeping a wary eye to the SSE to see if any tropical storms will come up from Baja and merge with an eastern pacific trof…..thereby pulling subtropical rain bearing moisture up over the Sierra Via Southern CA.

 

Note:

For you Ranchers in Fish Lake Valley, outside of a few thunderstorms Monday afternoon and evening, the weather looks dry Wednesday  through the following Sunday…..

 

The Dweeber…………………………………………………….:-)